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47
Agricultural Science Series
L. H. BAILEY, Eprror
THE NATURE AND
PROPERTIES OF SOILS
AGRICULTURAL SCIENCE SERIES
UNDER THE EDITORSHIP OF
L. H. BAILEY
THE NATURE AND PROPERTIES OF SOILS,
by T. Lyttleton Lyon and Harry O. Buckman
THE NATURE AND
PROPERTIES OF SOILS
A COLLEGE TEXT OF EDAPHOLOGY
T. LYTTLETON LYON
PROFESSOR OF SOIL TECHNOLOGY, CORNELL UNIVERSITY
HARRY O. BUCKMAN
PROFESSOR OF SOIL TECHNOLOGY, CORNELL UNIVERSITY
jdew Bork
THE MACMILLAN COMPANY
1922
All rights reserved
PRINTED IN THE UNITED STATES OF AMERICA
CopyriGcHT, 1922,
By THE MACMILLAN COMPANY.
Set up and electrotyped. Published April, 1922.
APR 19 1999
Oc aA659657
INnG |
TABLE OF CONTENTS
CHAPTER PAGE
I. Somr CONCEPTIONS OF THE SOIL AND ITS RELATION TO
PLANTS ey ee ats eon O5-\ ae aga ee RE eRe he oe 1
II. Som Forming PROCESSES SE Aly plist Seba! BAT eee eee 16
IIT. THE GEOLOGICAL CLASSIFICATION OF SOILS... . . 38
IV. Tue Som PARTICLE AND CERTAIN IMPORTANT RELATIONS 66
Ve Tam OrGAnic MATTER OF THE Som. 5 1. 9. 2. 99
Vi. THe ContomaL. Matter OF THE Som . . . . . . 27
VII. Som StructuRE AND Its MopIFICATION. . .. . . 139
VIII. THe Forms or Som WATER AND THEIR CHARACTERISTICS 151
IX. THE WATER OF THE Sorin IN Its RELATION TO PLANTS . 184
Xe HE CONTROL OF SOM, MOISTURE 3/2 9s) 4 meee « 202
EXO SOLA ELIOAUD os oe iee | Gok a Reems mel tar meu US Vee 2S
Rallies SOT pATR ey Ose eS Wee Meare em (RE A mi ats Ph Me Ay
XIII. THe ABSORPTIVE PROPERTIES OF SoS... . . . 263
XC REE’ SOM ag OOLULION = sai le. ene ek aren veh apeiron Iecilio
XV. THE REMOVAL OF NUTRIENTS FROM THE SOIL BY CROPPING
AND PUBACHING cyl. 4c) poate ar yes arte gay cn se 289)
ROVE CHEMICAT: -ANATVSIS OR SOILS 9. 5 «4 = |. = 4 toll
PRG SAT CAT TE e SOLES! cnt esay Vs citebe seu, Men en) Veil oe) | Pent oon) Sas B28
QV eC SOM ACIDITY 500 ek) we Wie es oe hel eS oa eee, OSD
XGOXS eH IMINGS THEE SOM! <2) irc, seus ele) 8%, 6 ee) S62
XX. Som ORGANISMS, CARBON, SULFUR AND MINERAL CYCLES 384
XXI. Som OrGANISMS—THE NITROGEN CYCLE . .. . . 409
XX CoMMERcIAL WertmizeR MATERIAES . . . © . « 442
XXIII. THe PRINCIPLES OF FERTILIZER PRACTICE. ... . 471
NOX Ee ARNO NTAN URE cng, s em Uo eM Soa’ Bh eee ale 409
POXQVAUGRERN: IMIANURE so io a fouls te 3 oe el es te) Hen OSD
XXVI. THE MAINTENANCE OF SOIL FERTILITY . . . . . . 502
ENDERGOR PAU THORS ss Wsihyobe | se) 0 feck nae eays ee uae (OGL
INDE OF ISUBUEOT MATINR F) 4) 5c ek ee) eh 86T
Vv
NATURE AND PROPERTIES
OF SOILS
CHAPTER I
SOME CONCEPTIONS OF THE SOIL AND ITS RELA-
TIONS TO PLANTS
Due to the action of climatic agencies the outer solid por-
tions of the earth readily pass into a loose and disintegrated
condition. This layer, although superficial and insignifi-
eant in comparison to the bulk of the earth, has performed
and is still performing a marvelous function. Life on the
earth has been slowly but steadily developing and changing
until we see about us the forms that characterize our age.
This evolution has depended to no small degree on this super-
ficial layer of decomposed rock with its admixture of de-
caying organic matter which together form the soil. In
this medium many and varied organisms have lived and from
it have drawn, wholly or in part, their sustenance, leaving
as a recompense a contribution of organic debris, which in its
turn has given rise to reactions of almost unbelievable com-
plexity.
Like the life which it has sustained and nourished, the
soil has been changing and evolving. The soil of today
is not the soil of yesterday nor will it be the soil of tomorrow.
It is never still. It is continually seeking a mechanical and
chemical adjustment with the forces which surround it or
1
2 NATURE AND PROPERTIES OF SOILS
are active within its precincts. Such an equilibrium it never
attains and thus the evolution goes on and on. It is this
continual change and this endless response to environment
that makes the soil useful to plants. The disintegrating
rock and the decaying organic additions are thus converted
into a mechanical support for plants, while at the same
time they are forced to liberate the nutrients essential to
plant growth.
In the light of its origin and function the soil may be
defined as a mixture of broken and weathered fragments of
rock and decaying organic matter, which covers the earth
in a thin layer and supplies mechanical support and in part
sustenance to plants.
This debris of rock and plant residue, teeming with its
microscopic life and ever restless in its endless efforts at
equilibrium, is the arable soil from which man must obtain
his bread. As the light of investigation is thrown on it,
new changes, new functions and new and unsuspected re-
lationships are brought to view until the story of the soil
may be retold with a clearer insight into those processes
that render it useful to man.
1. Composition of the soil—The soil as defined is com-
posed of two general classes of material, mineral and organic.
The former in most cases makes up from 90 to 99 per
cent. by weight of the dry substance of a soil, the organic
matter, except in the case of peat and muck, being in rela-
tively smaller amounts. In spite of the low proportion of
organic matter its presence is vital, not only because of its
influence physically but because of the nutrients, especially
nitrogen, that it carries. The mineral portion of a soil
functions as a frame-work and as a source of certain chem-
ical elements, which are necessary to proper crop growth and
development.
It must be realized at the very outset that the two main
constituents in a normal soil exist in very intimate relation-
SOME CONCEPTIONS OF THE SOIL 3
ship, reactions occurring not only within each group but
between the groups as well. Unless such interactions take
place it is unlikely that the mixture will ever be in a con-
dition either chemically, physically or biologically to sus-
tain plant growth. These reactions, although very complex,
take place with surprising ease and rapidity. As a con-
sequence the study of this complex, heterogeneous and
highly dynamic mass that
we call the soil is often be-
set with difficulties that
completely baffle our pres-
ent facilities for its study.
2. Soil-forming rocks.'
Ine any study of ‘soil
origin or composition, how-
ever cursory, the geological
phases of the problem im-
mediately force attention.
This is due to the bearing
that certain geological phe-
nomena have on soil condi-
tions and crop growth. In fig, 1,.—Volume composition of a
the soil we find that the loam soil when in good condition
: : : for plant growth. The air and
inorganic materials have water in a soil are variable and
originated from the com- their proportion determines to a
considerable degree the productiv-
mon rocks. The best known ity,
country rocks are of course
involved because they present the greatest outcrop surface and
of necessity must contribute most to the mineral fabrication of
the soil. They are classified under three heads—igneous, sedi-
mentary and metamorphic. The most important types from
the standpoint of soil formation are the following:
1For excellent non-technical discussions of rocks and minerals:—
Pirsson, L. V., Rocks and Rock Minerals; New York, 1915. Merrill,
G. P., Rocks, Rock Weathering and Soils; New York, 1906.
+ NATURE AND PROPERTIES OF SOILS
Igneous Sedimentary Metamorphic
Granite Limestone Marble
Syenite Dolomite Schist
Diorite Shale Slate
Gabbro Sandstone Quartzite
Basalt Conglomerate Gneiss
The mineralogical complexity of rocks has an important
bearing on the question of soil formation and soil composi-
tion. The fragments of any soil are, for the most part, dis-
tinguishable as separate minerals rather than as mineral aggre-
gates. For example, a soil from a granite would be char-
acterized by separate grains of quartz, orthoclase, micro-
cline and perhaps mica rather than by fragments of the orig-
inal granite itself. Again, it is the composition of the easily
decomposable minerals rather than the composition of the
bulk rock that determines what simplifications shall occur,
what new substances shall arise in the soil and what elements
shall be liberated for plant use.
8. Soil minerals Although hundreds of minerals have
been identified, comparatively few are common or important *
in rock formation. As a consequence, the list of im-
portant minerals found in soils will be correspondingly cur-
tailed, although enough are always present, especially in the
finer portions, to make the soil very complex mineralogically.
The minerals as to origin may be divided into two groups:
(1) those that persist from the original rock and (2) those
that are produced by the decomposition of the original min-
erals, during soil formation. For example, the quartz grains
1The following table indicates the approximate proportions of the
common minerals in the earth’s crush to a depth of ten miles:
BlelASPALS citer erate BTS Clay. ccivesnd) te ce ohare 1 eee
Amphibole and Py- Carbonates: i.ctaectect
MOXENE Vee eres Ne eerie UGHO = brie) -oobcadcrc0cc. 3
QUES Sobecosovvence IPAS SN OHS cose teojo06e Cc 8.2
ITT CE pate sshletsiers atts Breve aie 3.6
Recaleulated from Clarke, F. W., Data of Geogr REE U. S. Geol.
Survey, Bul. 695, pp. 32-33. 1920.
SOME CONCEPTIONS OF THE SOIL 5
of soil almost always come directly from the original rock
as do particles of orthoclase, biotite, and apatite. Hematite,
the kaolinite group and the chlorite and epidote groups
generally originate in soils through weathering. The fol-
lowing list of minerals is by no means complete, yet it includes
the more important forms from the soil and plant standpoint.
A LIST OF THE MOST IMPORTANT SOIL MINERALS.
(The elements in bold type are those necessary for plant nutrition.)
1. Quartz Sid,
2. Orthoclase and KAISi,0,
Microcline feldspar
3. Muscovite mica KH,A1,8i,0,,
4, Biotite mica KHMgFeAl,Si,0,,
5. Plagioclase feldspar Ca and Na aluminum silicates
6. Calcite and Dolomite CaCO, and (Ca, Mg) CO,
7. Hornblende and Augite Ca, Mg, Fe aluminum silicates
8
9
. Olivine (Mg, Fe).SiO,
. Apatite Ca, (PO,). (Ch EP)
10. Kaolinite group Typified by kaolinite.
H,Al1,Si,0,
11. Serpentine and Tale Hydrated Mg silicates
12. Chlorite group Hydrated Mg, Fe aluminum
silicates
13. Epidote group Hydrated Ca, Fe aluminum
silicates
14. Hematite FeO,
15. Limonite group Typified by limonite 2 Fe,0.,.
3) HO
1 Below are some of the most important mineralogical investigations of
soil: McCaughey, W. G., and Williams, H. F., The Microscopic De-
termination of Soil-Forming Minerals; U. 8. Dept. Agr., Bur. Soils, Bul.
91. 1913. Plummer, J. K., Petrography of Some North Carolina
Soils and Its Relationship to their Fertilizer Requirements, Jour. Agr.
Res., Vol. V, No. 13, pp. 569-581. 1915. Robinson, W. O., The Inor-
ganic Composition of Some Important American Soils; U. 8. Dept. Agr.,
Bul. 122. Aug., 1914.
6 NATURE AND PROPERTIES OF SOILS
4. Importance of soil minerals.—Quartz is found in al-
most all soils, making up often from 80 to 90 per cent. of
the composition, although a range from 40 to 70 per cent.
is more common. Its universal presence is due to its hard-
ness and insolubility. Quartz is a make-weight material,
however, as it probably contributes but little to plant nutri-
tion. in the form of sand, quartz has a great influence on
the friability of soil, improving and maintaining the phys-
ical condition to a marked degree.
Orthoclase, microcline, muscovite and, to a lesser degree,
biotite are important because of their potash content. They
decompose, often rather readily, into kaolinite and similar
products, thus liberating potassium in soluble form. The
plagioclase feldspars also give rise to kaolinite. They carry,
however, sodium and calcium. The latter element? plays an
important role in soil both as a nutrient and as an amend-
ment. When not sufficiently active it must be applied in
some form. Calcite and dolomite also carry calcium. Horn-
blende and augite bear calcium as well as magnesium and
iron. Olivine is a magnesium and iron silicate. The oxida-
tion of the iron of the above minerals gives rise to hematite,
so common as a red coloring matter of soil.
Practically all of the phosphorus of the soil, either organic
or inorganic, has its origin in apatite, yet this mineral occurs
but sparinely either in rock or soil. It makes up but 6 per
cent. of igneous rocks. This accounts for the small percent-
age of phosphoric acid in most soils and explains why it is
often added in fertilizers.*
1Plummer, J. K., Availability of Potash in Some Common Soil-
forming Minerals, Jour. Agr. Res., Vol. XIV, No. 8, pp. 297-315.
Aug., 1918. de Turk, E., Potassiwm-bearing Minerals as a Source of
Potassium for Plant Growth; Soil Sci., Vol. 8, No. 4, pp. 269-301. 1919.
*Shorey, E. C. et al., Calcitwm Compounds in Soils; Jour. Agr. Res.,
Vol. VII, No. 3, pp. 57-77. Jan., 1917.
’Fry, W. H., Condition of Phosphoric Acid Insoluble in Hydro-
chloric Acid; Jour. Ind. and Eng. Chem., Vol. V, No. 8, pp. 664-
665. 1913.
SOME CONCEPTIONS OF THE SOIL 7
The members of the kaolinite group are decomposition prod-
ucts resulting from the decay of the feldspars and similar
minerals. While kaolinite itself shows no nutrients in its
formula, it often carries considerable calcium, potassium,
magnesium and phosphorus by absorption. Moreover, its
close association with other decomposition products such as
serpentine, tale, chlorite and epidote tends to accentuate its
importance in plant nutrition. The plasticity and cohesion
imparted to a soil by the presence of the kaolinite group
and its associated minerals are of great practical importance
as is also the capacity to hold, either physically or chemically,
the bases already mentioned.
Hematite and limonite are simple iron compounds and
usually occur in the soil as a result of the decomposition of
certain iron-bearing minerals such as biotite, hornblende and
augite. These iron compounds impart the red and yellow
colors so characteristic of certain southern soils. Most of the
soluble iron of the soil has its source in these minerals. Hema-
tite and limonite are produced by the same general processes
as are the kaolinite group and are found in very intimate
contact with the serpentine, epidote, chlorite and kaolinite.
5. Soil organic matter.—One of the essential differences
between a normal fertile soil and a mass of rock fragments
hes in the organic content of the former. The organic matter
practically all comes from plants and animals that have in-
vested the surface of the soil and the soil material. Through
the agency of bacteria and other organisms with which the
soil is liberally supplied, this organic tissue yuickly loses its
original form, and becomes the dark incoherent material so
noticeable in fertile soils. The decay is not one of immediate
simplification, as might be supposed. The split-off compounds
react not only with materials of a similar origin but also
with the decomposing mineral fragments. This tendency pro-
vides the intimate relationship between the organic and in-
organic constituents of the soil already emphasized as an ex-
8 NATURE AND PROPERTIES OF SOILS
ceedingly desirable condition. Incidentally the soil is ren-
dered thereby very much more difficult to study, especially
chemically.
The incorporation of organic matter in any soil, either by
natural or artificial means, tends, if the proper decay occurs,
to make the soil more friable. The water capacity is markedly
increased and the vigor of the bacterial and chemical activ-
ities stimulated to a marked degree. As these two latter
actions progress, some of the organic matter passes into simple
combinations, allowing certain elements to become available
to crops. Nitrogen, which is held in the soil largely in organic
combination, emerges in the form of ammonia, nitrites and
nitrates. It is from a salt of nitric acid that most plants
absorb their nitrogen. Small amounts of sulfur, phosphorus,
potassium and calcium are liberated from the tissue as decay
proceeds. The largest product of organic decay, however, is
carbon dioxide (CO,), which in the soil becomes important
as a solvent for minerals, thus hastening the decomposition
processes.
6. Factors for plant growth.—The growth and develop-
ment of a plant depends on two sets of factors, the internal
and external. The latter may be classified as follows: (1)
mechanical support, (2) heat, (3) light, (4) oxygen, (5)
water, and (6) nutrients.1 With the exception of light, the
soil supplies, either wholly or in part, all of these conditions.
Mechanical support is a function entirely of the soil. The
comparatively loose and friable condition presented by most
soils allows ample foothold to the ramifying roots.
Air and water are easily supplied because of the open
condition of the soil, and its large pore spaces. Temperature
depends almost wholly on climatic relationships. The water
1Nutrients are materials from which food may be elaborated once
they have been absorbed by plants. The energy for this synthetic proc-
ess comes from the sun. A food is any substance from which the plant
may obtain energy for its normal processes. A large proportion of the
materials absorbed by plants are nutrients.
SOME CONCEPTIONS OF THE SOIL 9
of the soil acts as a plant nutrient in itself and functions
also as a solvent for other materials. By its circulation it
not only promotes solution but it continually brings nutrient
elements in contact with the absorbing surfaces of the roots.
The two prime functions of the soil are thus realized through
the factors discussed above—mechanical support and a suffi-
cient supply of certain nutrient elements under favorable
conditions.
7. Nutrient elements.\—Although the physical condition
of the soil exerts a far-reaching influence on plant growth,
the relationships involved are more readily understood than
those which have to do with plant nutrition. Moreover, the
solubility of the necessary nutrients is very closely related
to the complex processes of soil formation. Ten elements ”
are usually considered as necessary for plant growth. If one
is lacking, normal development will not occur. They may
be classified as follows:
From air or water From the soil
Carbon Nitrogen Calcium
Oxygen Phosphorus Magnesium
Hydrogen Potassium Sulfur
Nitrogen Tron
Plants obtain most of their carbon and oxygen directly
from the air by photosynthesis and respiration. The hydro-
gen comes, at least partially, from water. All of the other
elements, except a small amount of nitrogen utilized directly
from the air by certain plants, are obtained from the soil.
It must not be inferred, however, that the bulk of the plant
1For an excellent discussion of the functions of plant nutrients, see
Russell, E. J., Soil Conditions and Plant Growth, Chap. II, pp. 30-46;
New York. 1915.
*It may be possible that manganese and silicon and possibly chlorine
and fluorine function as nutrients. They as well as sodium, aluminum,
titanium, barium, strontium, and certain rarer elements are found in
plant ash.
10 NATURE AND PROPERTIES OF SOILS
tissue is fabricated from the soil. Quite the reverse is true.
Fresh plant tissue generally carries only from .5 to 2.5 per
cent. of mineral material. In spite of this, it is the mineral
elements of nutrition that generally limit crop growth since
a plant can always obtain, except in cases of drought or
disease, unlimited amounts of carbon, hydrogen and oxygen.
8. Primary nutrient elements.—While all of the seven
soil nutrients must be available that plants may grow normally,
only four or five are likely to become limiting factors. The
others are almost always in great sufficiency. These few,
nitrogen, phosphorus, potassium, calcium and_ occasionally
sulfur, receive as a consequence especial attention. They
may limit growth because they are actually lacking or be-
cause their availability is low. These conditions often occur
in the same soil.
Combined nitrogen exists in the soil to a large degree as
a part of the partially decayed organic matter present
therein.t As decay proceeds, small quantities of this nitrogen
appear aS ammonia in combination with some acid radical
such as the chloride or sulfate or with the hydroxal group.
Later, it is changed through further bacterial action to the
nitrate form, united with some bases such as calcium or po-
tassium. It is from this latter combination that most plants
obtain the greater part of their nitrogen. These inorganic
nitrogen compounds, present at any one time in a soil, are
but a small proportion of the total soil nitrogen. The air
both above the soil and that circulating within its pores has
been the original source of all the combined nitrogen. Nat-
ural processes have facilitated the combination which has been
necessary for such a transfer. The encouragement of such
*Certain rocks, particularly those of a sedimentary nature, carry
considerable nitrogen. When such rocks weather, this nitrogen tends
to become available. The organic matter, therefore, does not absolutely
control the amount of nitrogen in a soil, Hall, A. D., and Miller,
N. H. J., The Nitrogen Compounds of the Fundamental Rocks; Jour.
Agri. Sci., Vol. II, Part 4, pp. 343-345. July, 1908.
SOME CONCEPTIONS OF THE SOIL 11
fixation processes, especially those of a biological nature, is
a feature of practical soil improvement.
Phosphorus has its origin in the mineral apatite (Ca,-
(PO,),(Cl,F)) and exists in the soil not only in this form
but as tri-calcium phosphate (Ca,(PO,).), iron and alum-
inum phosphates (FePO, and AIPO,) and in certain other
inorganic complexes. It also exists in organic combinations
of a constantly varying nature. It probably is utilized by the
plant as a simple phosphate such as the mono- or di-caleium
salt (Cal, (PO,), and Ca,H,(PO;),):
Potassium, as already stated, occurs in the soil in orthoclase
and microcline (KAISi,O,), in mica, especially muscovite
(H,KAI,Si,0,,), and in other aluminum silicates, both hy-
drated and non-hydrated. These complex forms supply potash
to the soil solution and thus to the plant at a more or less
rapid rate in the bicarbonate, carbonate, chloride, nitrate, and
sulfate forms.
Calcium, while necessary in the soil as a nutrient, also
functions as an amendment in that it seems to preserve a
proper soil reaction. It is possible that this relationship is as
much nutritive as strictly chemical. Calcium exists in the soil
in many minerals, of which calcite, plagioclase feldspar, horn-
blende and augite are perhaps the most important. It is
carried as an absorbed compound by kaolinite and similar
materials. Calcium becomes available in the soil as the ni-
trate, bicarbonate, chloride, phosphate, and sulfate.
Sulfur is found in the soil in rather small amounts and
generally forms a part of the organic matter. Inorganically
it usually occurs as a sulfate combined with the common
bases. In this form it is available to plants. The original
source’ of most of the soil sulfur has been pyrite (FeS,), the
*Considerable sulfur is brought to the soil in atmospheric precipita-
tion. From 5 to 150 pounds an acre a year have been reported. Wilson,
B. D. Sulfur Supplied to the Soil in Rain Water, Jour. Amer. Soe.
Agron., Vol. 13, No. 5, pp. 226-229. 1921,
12 NATURE AND PROPERTIES OF SOILS
commonest sulfide of this element. Although sulfur is no
more abundant in the average soil than phosphorus, it is
generally not considered as an extremely important fertilizing
constituent.
It is interesting to note at this point the amounts of the
above elements in ordinary mineral soils. Generally the nitro-
Fig. 2.—Chemical composition of a representative productive soil.
gen (N) may range from .1 to .2 per cent., the phosphoric
acid (expressed as P,O,;) from .05 to .380 per cent. and the
potash (expressed as K,O) from 0.5 to 2.0 per cent. Of the
plant nutrients in the soil nitrogen, although usually present
in small quantities, is relatively more available than is
phosphoric acid or even potash. Phosphoric acid may be in
the minimum because of its unavailability as well as because
of the small quantity. Potash is commonly present in rela-
SOME CONCEPTIONS OF THE SOIL 13
tively large amounts. Its occurrence in complex and insoluble
silicates makes its availability of vital consideration. The
presence of abundant organic matter may have much to do
with the liberation of sufficient potash for vigorous plant
growth.
The amount of lime (expressed as CaQ) in soils is difficult
to state with any degree of satisfaction because of a very
wide range in composition. Some soils carry only a fraction
of a per cent., while others, especially those formed under
conditions where an originally high calcium content has been
maintained or where calcium has accumulated, show as much
as 10 or 12 per cent. The variability of the sulfur is much
less. A range from .02 to .30 per cent. of sulfur (expressed
as SO,) will include most soils.
It is interesting at this point to note the average composi-
tion of thirty-five representative American surface soils’,
which were studied by the United States Bureau of Soils dur-
ing a systematic investigation of the arable lands of the United
States east of the Rocky Mountains. A comparison of these
data with those setting forth the composition of the litho-
sphere? may be made with profit. (Table I, page 14.)
It is immediately noticeable that silicon, aluminum, and
iron make up the greater portion of both soil and lithosphere
and that the nitrogen, sulfur and phosphorus are particu-
larly low in both cases. Magnesium, calcium, sodium, and
potassium occur in fair amounts, especially in the earth’s
erust. It is noticeable also that the soil is much higher than
the lithosphere in silicon, nitrogen, organic matter, and ecar-
bon but much lower in all of the other constituents. These
differences have developed as a result of the losses and gains
during soil formation.
*Robinson, W. O. et al., Variations in the Chemical Composition of
Soils; U.S. Dept. Agr., Bul. 551. June, 1917.
? The Lithosphere refers to the solid portion of the earth, in this case
to a depth of ten miles. Clarke, F. W., Data of Geochemistry; U.S.
Geol. Survey Bul. 695, p. 33. 1920.
14 NATURE AND PROPERTIES OF SOILS
TABLE I
COMPARISON OF THE CHEMICAL COMPOSITION OF AMERICAN
SURFACE SOILS WITH THAT OF THE LITHOSPHERE.
GOAT TRe 35 AMERICAN COMPOSITION OF
SURFACE SOILS LITHOSPHERE
Si0, 84.67 DOG
Al,O, 6.73 14.89
TiO, . 66 Ba A
Fe,0, 2203 6.29
MnO 06 .09
Na,O 49 See
K,0 LOS 2.98
CaO 40 4.86
MgO sot 3.74
P.O, .09 28
SO, .09 28
Nitrogen 07 a —
Organic Matter 2.61b _
Carbon tele 03
(a) Average of 22 soils only. (b) Average of 13 soils only.
(ce) Calculated from the organic matter.
9. The soil and the plant.—aAs the soil considered agri-
culturally is essentially a medium for crop production, its
rational study has to do with the consideration and applica-
tion of such scientific principles as have a bearing on prac-
tical soil management. Anything that makes clearer the
relationships between soil and crop has a proper place. Un-
less a scientific phase has a crop relation, either directly or
indirectly, it need receive but scant consideration. The com-
position of the soil, its chemical and biological changes, its
physical peculiarities and its reaction to certain additions
must receive especial attention. More knowledge of the soil
1Soils contain many other elements, although in small amounts, such
as chlorine, barium, cesium, chromium, lithium, molybdium, rubidium,
vanadium, ete. Robinson, W. O., The Inorganic Constituents of Some
Important American Soils; U. S. Dept. Agr., Bul. 122. Aug., 1914.
SOME CONCEPTIONS OF THE SOIL 15
will mean better systems of management and will allow the
farmer to fulfill to a greater degree his duty to himself and
to the State—the production of paying crops and the passing
on to the next generation of a soil depleted as little as possible
in fertility.
CHAPTER II
SOIL-FORMING PROCESSES
Tue forces which have to do with soil formation are largely
climatic in nature. They promote the physical and chemical
breaking down of rock masses, they intermix there with the
decaying organic matter and they shift the products from
place to place. Even after the soil is apparently at rest and
has become an effective agency in plant production, these
same forces are still much in evidence. The physical and
chemical evolutions through which mineral and organic mate-
rials at or near the earth’s surface are passing due to natural
forces are spoken of as weathering.: Erosion and deposition
are terms referring to the natural translocations which soils
and soil materials are frequently forced to undergo.
If a soil represents a condition more stable than the rock,
the rock change is in that direction. If a soil presents con-
stituents or conditions not wholly stable to the forces effective
at that particular time, it in turn seeks a change by an altera-
tion or an elimination. A cycle of development is thus set
up proceeding from youth to adolescence and even into old
age. According to conditions, soils may age rapidly or slowly.
Rejuvenation may even occur, while cases of arrested develop-
ment may exist for short periods.
10. Soil-forming processes classified—While weather-
ing, with the changes in form and composition which inva-
riably accompany it, profoundly affects topography, it is very
1The term weathering is somewhat misleading since it comprehends
forces other than those generally considered as weather. All of the
forces involved, however, depend upon climatic conditions.
16
SOIL-FORMING PROCESSES 17
superficial in comparison to the earth’s bulk. Nevertheless,
the weathered mantle, in spite of its comparative insignifi-
cance, presents an effective medium for plant growth. The
agencies of formation, therefore, demand more than the brief
mention just given. These forces are geologic when the soil
is being evolved, but once the soil materials are in place, the
actions become localized and the influences may be considered
as soil processes rather than more broadly geological.
The soil-forming processes', while diverse both in action
and product, may be classified under two heads, mechanical
and chemical. The former is often designated as disintegra-
tion, the latter as decomposition. ,
SOIL-FORMING PROCESSES
I. Mechanical (disintegration)
A. Erosion and deposition.
Water, ice and wind.?
B. Temperature change.
Differential expansion of minerals, exfoliation
and frost.
C. Biological influences.
Plants and animals.
II. Chemical (decomposition )
A. Oxidation and deoxidation.
B. Carbonation and decarbonation.
C. Hydration and dehydration.
D. Solution.
11. The mechanical action of water.—From the time that
that water as rain beats down upon the solid earth until it
is finally discharged into the ocean, there to pound as waves
upon the bordering lands, it is moving, sorting, and rework-
ing the products of weathering. Water to erode must be
*For a complete and detailed discussion of soil formation, see Merrill,
G. P., Rocks, Rock Weathering and Soils; New York. 1906. Also,
Emerson, H. L., Agricultural Geology; New York. 1920.
*Gravity is generally included in this group. While indirectly of
great significance in soil formation, its direct action is not of great
importance and is adequately disposed of in paragraph 27.
18 NATURE AND PROPERTIES OF SOILS
armed. Its cutting power, therefore, depends on the amount
of sediment that it carries and on its velocity of flow.
Erosion by water deserves particular attention, as its denud-
ing effects are very rapid when geologically viewed. Most
of the changes in topography are due to such activity. The
material swept away is partly in suspension and partly in
solution.1 The Appalachian Mountains, whose uplift was
complete in Carboniferous times, have lost vastly more of their
mass than now remains in view.
While most of the debris from the ancient erosive cycles
has been changed to rock or has become a noticeable charac-
teristic of ocean water, remnants persist. To these remnants
rivers, lakes and oceans are making, year by year, substantial
additions. The cutting, carrying and depositing activity of
streams produce alluvial soils of which the Mississippi flood
plain is a well known example. Deltas built into oceans, lakes
and gulfs represent stream activity under different condi-
tions, while uplifted continental shelves are often bedded with
erosive products. The delta and marine soils of the Atlantic
and Gulf coastal plains afford examples of the latter types
of soil production. Even the pounding, grinding and sorting
activities of waves in ocean and lake are no mean factors in
the mechanics of soil formation.
12. Glacial action.—Ice at the present time, especially
in temperate regions, is of little importance in soil forma-
tion. Nevertheless, at a comparatively recent date geolog-
ically, it had much to do with the preparation and deposition
of soil materials over great areas in central and northern
North America, northern Europe and the British Isles. Dur-
ing the Great Iee Age immense continental glaciers succes-
sively invaded these regions, much as the ice cap is over-
1The chemical denudation by streams is generally spoken of as corro-
sion. Abrasion is applied to the wear of the stream load upon its
channel and of the particules in suspension upon themselves. Erosion
is a broader term including corrosion and abrasion as well as trans-
portation.
SOIL-FORMING PROCESSES 19
riding Greenland to-day. Of great thickness and weight and
impelled southward by tremendous pressure, these ice sheets
swept away the old soil mantle and ground the underlying
rocks with irresistible energy. The heterogeneous debris, im-
bedded in the ice, only served to enhance the cutting power
of the slowly moving mass. Hundreds of square miles were
covered and as the ice was often several thousand feet thick,
mountains as well as hills were over-ridden. (See Fig. 3.)
In the melting back of these tremendous ice sheets, the
accumulated debris was of necessity left behind. When the
ice retreat was rapid, the deposit was comparatively thin and
uniform. When a halt occurred, the material was left in
irregular hummocks. It is hardly necessary to state that the
soil developed from the former deposit is the more important
agriculturally, due to its level topography and wide extent.
The area of the latter is fortunately small. The streams
flowing from the ice fronts were no insignificant feature of
the glacial phenomena. Such streams were heavily laden with
sediment, which was distributed far and wide in regions miles
beyond the ice front.
In whatever manner the glacial debris was laid down it is
necessary to note that such deposits were soil material, not
soil. Chemical action in all its complexity and the interven-
tion of plants and animals, especially the former, were neces-
sary before a true soil could be born, a soil still in its youth
and covering in the United States alone over 500,000 square
miles. (See Fig. 3, page 20.)
13. The influence of wind.—Wind, like water and ice,
has both cutting and earrying power. The fluting of rocks,
the polishing of stones, and the undermining of cliffs are of
such frequent note as to require but brief mention. There
seems no escape from the conclusion that wind is engaged in
rock disintegration. Its geological function in arid regions
seems similar to that of running water in humid lands.
It is, however, as a transporting agency of fine materials
NATURE AND PROPERTIES OF SOILS
20
hon
IW wy
>
LABRABOR
Grr.
SW
BS
c fre
G |
Ns
NG ac
(((rree* ‘Aad 99)))))) i)
Wee AsO
Se
SS S
)
f(
DS
MCE uy
Sees
iu
“
¥y
Wie
FG
sa ae
gil iN A?
CLG OLY <i a)
Gee fi ie
Pa fe = weg 7 1) :
Gs Ke ae Ie Te?
WWE 5 CRAY yh
TWELY, Dy °
WEBEL ogo SS
\S SEZ Ba, GT ™ &
SLE EESTI N
Py»,
oN
Fig. 3.—Sketch map of North America showing the approximate south-
ward extension of the great ice sheets and the three centers of
accumulation.
SOIL-FORMING PROCESSES 21
that the wind is of especial importance in soil formation. The
movement of sand and dust in both humid and arid regions
is almost incessant. In desert storms 200 tons of materials
have been known to float over every acre of land. The finer
particles travel for miles in a very short time. Southern Italy -
has received as much as one inch of dust from Africa during
a single storm. The movement of sand dunes is but another
evidence of the transporting power of air in motion.
Wind as an agency in soil formation would perhaps receive
much less attention were it not for the existence of large
areas of a certain silty soil called loess. This soil exists along
the Rhine both in France and Germany, in southern Russia,
in Roumania, in China and in central United States. This
material, as well as the adobe of our arid Southwest is con-
sidered as largely wind laid. Since the loess is highly fertile
and of great agricultural importance, added attention is thus
directed towards wind as a soil-forming agency. (See Fig. 4.)
14. Change in temperature.—Variations of temperature,
especially if sudden or wide, greatly augment the denuding
actions of water, ice, and wind. Rocks and soil become heated
during the day and at night often cool much below the tem-
perature of the air. This warming and cooling is particularly
effective as a disintegrating agent. Rocks are mineral aggre-
gates, the minerals varying in their coefficients of expansion.
With every temperature change differential stresses are set
up, which eventually must produce cracks and rifts, since the
minerals never assume their original position. Incipient focii
for further physical and chemical change are thus established.
Although the expansion coefficient of rock is low, it must be
remembered that very large surfaces are involved. Moreover,
it is the multiplicity of the rifts rather than their magnitude
that is important.
The influence of temperature change is manifested on rocks
in another way. Due to slow conduction the outer surface
of a rock often maintains a markedly different temperature
22 NATURE AND PROPERTIES OF SOILS
than the inner and more protected portions. This differential
heating tends to set up lateral stresses which may cause the
surface layers to peel away from the parent mass. This phe-
nomena is spoken of as exfoliation. The differential expansion
OKLAHOMA
Fic. 4.—Approximate distribution of loess in central United States.
of the rock minerals of course plays a part in this disintegra-
tion, although exfoliation readily occurs in rocks which are
more or less homogeneous. While this form of weathering
may go on alone, it is much accelerated by chemical action
and the prying of freezing water.
SOIL-FORMING PROCESSES 23
One peculiarity of pure water is that its maximum density
occurs at 39.2 deg. F. From this point the volume increases
as the temperature is lowered. Ice, which forms at 32 deg. F.,
thus occupies a greater space than the water from which it
was derived. The force developed by freezing is equivalent
to about 150 tons to the square foot or a pressure of 141
atmospheres. The cracks and crevices of surface rocks in
humid regions are from time to time filled with moisture.
Rocks below the surface contain water continuously. The
change of this water from a liquid to a solid always produces
marked disintegration. Mountain-top rubble, talus slopes,
alluvial fans, and similar formations are evidences of such
action. The load of sediment carried by streams is often due
to the prying action of temperature change, especially where
crevice water is present.
This action of temperature is by no means ended when a
soil is produced. Freezing and thawing is of tremendous im-
portance in bettering the physical condition, especially of
heavy soils. It is to such forces that the farmer owes the
good tilth of his land. In addition it must be noted that the
rapidity of chemical change is largely a function of temper-
ature. The concentration of the soil solution and the avail-
ability of the nutrient elements thus come under the influence
of this apparently simple force.
15. Plants and animals.— While plants and animals unite
their activities with the processes already mentioned, their
influence is confined largely to the soil and the soil material.
Simple plants such as mosses and lichens grow upon exposed
rock, there to catch dust and dirt until a thin film of highly
organic material accumulates. Higher plants sometimes exert
a prying effect on rock, which results in some distintegration.
Such influences, however, are of but little import in soil for-
mation compared to the drastic activities of water, wind, ice
and temperature change.
In the soil, roots by their ramifications promote aération
24 NATURE AND PROPERTIES OF SOILS
and drainage, as well as an accumulation and distribution of
organic materials. Lichens, mosses, and alge play their parts
in a similar manner. It must be noted, however, that while
plants tend to preserve and improve the soil tilth, their action
in this respect is not wholly physical. Decay due largely to
bacterial action is necessary before the accumulated organic
matter can improve to any marked degree the physical con-
dition of the soil. This is only one of the many examples
illustrating the cooperation of physical and chemical changes
incident to soil formation.
Animals influence the soil physically by their burrowing
propensities. Gophers, squirrels, ants, and the like mix and
open up the soil, thus providing for the circulation both of
air and water. Other soil forces, both physical and chemical,
are markedly encouraged thereby. Earth worms produce
similar effects. They not only pass great quantities of soil
through their bodies, but they carry much to the surface.
This has been estimated as amounting to one or two surface
inches in a decade. Man also is producing important physical
changes on the soil and soil material. The plowing under of
green-manures, crop residues and farm manure, the addition
of lime and fertilizers and the tillage incident to cropping
have much to do with the physical changes, which are con-
tinually occurring in the soil.
16. Oxidation and deoxidation.—Scarcely has the disin-
tegration of rock begun than its decomposition is also appar- .
ent. This is especially noticeable in humid regions where the
chemical and physical processes of soil formation are par-
ticularly active and markedly accelerate each other. Of the
chemical forces, oxidation is usually, especially near the sur-
face, the first to be noticed. It is particularly manifest in
rocks carrying iron in the sulfide, carbonate or silicate forms.
The sulfide, although widespread, is less important in pro-
moting rock decay than the other combinations. The oxida-
tion of iron in any form is indicated by a discoloration of the
SOIL-FORMING PROCESSES 25
affected rock, which from the first is streaked with iron oxide.
The mica, amphibole, pyroxene and garnet groups are par-
ticularly affected, until, as the process continues, these min-
erals waste away into unrecognizable forms so weakening the
rock as to cause it to crumble easily. The way is now open
for vigorous chemical and physical changes of all kinds. Oxi-
dation may be illustrated chemically, using olivine as the
mineral decomposed. It is to be noted that the first step is
the assumption of water and the production of serpentine and
ferrous oxide. The latter quickly changes to the susquioxide.
3MeFeSi0,+2H,O—H,Mg,S8i,0,+S8i0,+3Fe0O
Olivine Water Serpentine Silica Ferrous
Oxide
4FeO + O, = 2Fe,0, (red)
Ferrous Oxygen Ferric Oxide
Oxide
Deoxidation is the reverse of oxidation, being a reduction
of the amount of oxygen present in the compound. With
hematite it might occur as follows:
2Fe,0, — O, = 4FeO
Ferric Oxide Oxygen Ferrous Oxide
In a similar way, other oxides and salts may be reduced by
the withdrawal of oxygen. This action occurs in poorly
drained soils or in soil very rich in organic matter. It is
generally apparent in forest soils just below the organic sur-
face layer. Here the leaching downward of small quantities
of organic acids has been sufficient to develop a definite grey-
ish zone, varying both in color and depth. The bleaching of
sands, shales, sandstones, and clays may often be due to
deoxidation rather than the actual removal of ferric iron.
No great importance need be attached to deoxidation either
in soil formation or in the chemical processes which continue
to affect the soil after it is definitely developed.
26 NATURE AND PROPERTIES OF SOILS
17. Carbonation.—The process of oxidation is almost al-
ways accompanied by the action of carbon dioxide. This gas
is a constituent of the air and is a product of the organic
decay which vigorously progresses in most soils. It occurs
in large amounts in rain water, especially in warm climates.
It increases the solvent action of water by actively engaging
in chemical reactions, producing carbonates and bicarbonates
with the various rock and soil bases. The decomposition of
orthoclase and muscovite mica into kaolinite and carbonates
is as follows:
2K AlSi,0, + 2H,O + CO, = H,Al,Si,0, + K,CO, + 4810,
Orthoclase Water Carbon Kaolinite Potassium Silica
Dioxide Carbonate
2H,KAI,Si,0,, + CO, + 4H,O = 3H,Al1,Si,0, + K,CO,
Muscovite Carbon Water Kaolinite Potassium
Dioxide Carbonate
Under certain conditions decarbonation may occur. When-
ever the processes of weathering produce either mineral or
organic acids carbonates are rapidly decomposed. The
presence of unsaturated aluminum silicates may also rapidly
promote decarbonation by absorbing the base and liberating
the acid radical. This latter reaction is of especial importance
in soil.
18. Hydration.—All the chemical transformations above
discussed depend on the presence of a certain amount of
water, especially if rapid changes are to occur. The illus-
trative reactions already cited indicate this. Oxidation pro-
ceeds but slowly in a dry atmosphere, water being necessary
as a catalytic agent. In the carbonation of the potash of
orthoclase and mica, water enters into the reactions, produc-
ing not only kaolinite but also potassium hydroxide, which is
later changed to the carbonate.
Water functions in the chemical changes of rock and soil
SOIL-FORMING PROCESSES 27
in another way—as water of combination.t The process is
ealled hydration. While hydration usually proceeds or ac-
companies oxidation and carbonation, thus making them pos-
sible, it often, unlike these transformations, occurs at great
depths and may be practically the only change that the rock
minerals have undergone. Many minerals, especially the oliv-
ine, feldspar and mica groups, are so affected. They become
soft and lose their luster and elasticity on the assumption of
this chemically combined water. Considerable increase of
bulk occurs during the transition of the rock to soil. The
latter change has no small physical significance. This hydra-
tion is particularly effective in encouraging other kinds of
chemical decay. In addition to the examples already cited,
the change of hematite to limonite, which occurs to a greater
or less degree in every soil where the sesquioxide is present,
is worthy of note:
2Fe,0, + 3H,O = 2Fe,0, . 3H,O
Hematite Water Limonite (yellow)
When the products of weathering dry out due to varying
weather conditions, dehydration may occur. Thus limonite
may readily reduce to a lower hydrate or to hematite.
19. Solution.—It is quite evident that while weathering
and erosion produce many compounds of a very complex char-
acter, there is a tendency toward simplification and, as water
is universally present, some solution occurs. Such bases as
calcium, magnesium, sodium and potassium are found in the
water that circulates in rocks, soil materials and soils. These
bases, when in solution, are generally combined as chlorides,
phosphates, nitrates, carbonates, and the like. Carbon dioxide
intensifies to a marked degree the solvent action of water and
consequently increases its power as a weathering agent. The
*Note carefully the difference between hydration and the production
of an hydroxide. The former is the more important as a soil phenome-
non.
28 NATURE AND PROPERTIES OF SOILS
atmosphere carries about .03 per cent. of carbon dioxide by
volume, while considerable amounts are brought down on
rocks and soil by rain and snow. ‘Traces of nitric and sul-
furie acid are also found in rain water. The carbon dioxide
produced within the soil by decaying organic matter keeps
the concentration of this gas high at points where it can act
most effectively.
Solution, accelerated both by mechanical and chemical
means, is of particular importance in two directions. In the
first place, it allows a continual loss of plant nutrients not
only as the soil is being formed but after it becomes a proper
medium for plants. This constant drain accounts for the
deficiency of certain elements in the soil and the need in cer-
tain cases of such additions as lime and fertilizers. On the
other hand, this solution, however wasteful, is necessary since
plants absorb nutrients from the soil only in soluble form.
The concentration and composition of the materials in the
soil water is thus a function of solution, which is a culmina-
tion of the activities of the soil processes already discussed.
20. General statement of soil formation.—By a very
complicated coordination the mechanical and chemical forces
of weathering reduce the solid rock to small fragments and
mix therein the necessary organic matter. The process slowly
proceeds until a suitable medium for the growth of higher
plants is produced. As a rule, the chemical processes are in-
complete and all stages of decay are exhibited. This is for-
tunate, as solution may thereby continue to renew the nutrients
in the soil-water for a long period and thus maintain the
continuous productivity of the soil.
The products of disintegration and decomposition are com-
monly classified into two general groups, sedentary and trans-
1 While the formula for water is generally given as H.O the molecule
is not as simple as this, being at low temperature as high as (H,0),.
The remarkable power of water as a solvent may be due to extra oxygen
valences as well as to the high dielectric constant which favors ioniza-
tion, thus hastening chemical reaction.
SOIL-FORMING PROCESSES 29
ported. The former remains in place, being the rock residuum
in which organic matter accumulates. Residual clay is an
example. The second group, on the other hand, in addition
suffers transportation and is represented by the soils arising
from glacial drift, alluvial accumulations, aéolian deposits,
and the like. In the first case, the soil is derived from a single
lithologic unit; in the second place, the assorted and blended
materials are from many sources. A general statement of
the formation of a residual soil! is obviously the easier to
ely
- ve
ai Won é SS
Wor MS
~
2 SOIL. MATERIAL
°
Fie. 5.—The gradual transition of country rock into residual soil by
weathering in situ.
make. Such a statement adequately covers every process in
the production of a transported soil except the disintegra-
tion, assortment, and solution due to translocation. (See
Fig. 5.)
“The changes that a rock undergoes in forming a residual
soil are first a physical breaking down, accompanied by certain
chemical transformations, which consist in the hydration of
a portion of the feldspars, micas and similar minerals; the
1Buckman, H. O., The Formation of Residual Clay; Trans. Amer.
Cer. Soc., Vol. XIII, p. 362. Feb., 1911.
30 NATURE AND PROPERTIES OF SOILS
oxidation and hydration of a part of the combined iron; and
a carbonation and solution of a large proportion of the soluble
bases. These processes are hastened and the whole mass
evolved into a soil by the admixture and decay of certain
amounts of organic matter.’’ +
21. Variation of soil formation with climate—It may
be seen readily that the activity of the various soil-forming
agencies will fluctuate with climate. A comparison of weath-
ering and erosion in an arid and a humid region will illustrate
the point at issue. Under arid conditions, the physical forces
will dominate and the resultant soil will be coarse. Tempera-
ture changes, wind action and the influence of animals will
be almost the sole agents. In a humid region, however, the
forces are more varied and practically the full quota will be
at work. Chemical decay will accompany disintegration and
the result will be shown in the greater fineness of the product.
The separate minerals will also show the change of color and
loss of luster so characteristic of chemical action. A granite,
for example, is a very insoluble rock, compared with a lime-
stone, and in a humid region, where chemical agencies are
dominant, it will be markedly more resistant. If, however,
these rocks are exposed in an arid region, where physical
weathering is potent, the results will be entirely different.
The limestone, being homogeneous, will not be affected mark-
edly by temperature changes, but the stresses set up in granite
must ultimately reduce it to fragments.
Arid soils, besides being rather coarse, are generally rather
uniform, there being little difference between soil and subsoil.
The soils of humid regions are usually of fine texture, par-
ticularly in residual sections, since the chemical agencies have
1Tt is well to remember that synthetic processes as well as forces of
simplification and dissolution are active in soil formation. The soil
features that result are of two kinds, hereditary and acquired. The
former develop through geological forces, the latter through the activity
of true soil processes.
SOIL-FORMING PROCESSES 31
been so active. Various colors may develop because of oxida-
tion, hydration, and the presence of organic matter. Such
soils usually are not excessively deep, and are likely to be
underlaid by subsoils heavier than the surface. The general
physical condition and tilth of arid soil is uniformly better
than that of regions of plentiful rainfall.
Chemically, because of less leaching, the arid soils contain
more of the important mineral elements. The following
analyses bring out the differences in a striking manner:
TABLE II
COMPARATIVE ANALYSES OF ARID AND’ HUMID SOILS?
ARID SoILs Humip SorLs
CONSTITUENTS AVERAGE OF AVERAGE OF
313 SAMPLES 466 SAMPLES
Insoluble dilieoe 88.24
Al,O, 7.89 4.30
Fe,O, 5.75 3.13
CaO 1.36 11
K,0 73 mp)
P.O, S12 11
MgO 1.41 .23
Volatile 4.94 3.64
It is immediately apparent that the arid soil is poorer in
silica than the humid soil, but richer in iron and alumina, in-
dicating a less weathered condition of the feldspars. Due to
a greater amount of leaching, the humid soil is much lower
in phosphoric acid, lime, magnesia, and potash. The humus
in arid soils is somewhat lower than in the soils under better
1Hilgard, E. W., Die Boden arider und humider Linder; Internat.
Mitt. Bodenkunde, Bd. I, pp. 415-529, 1912.
32 NATURE AND PROPERTIES OF SOILS
conditions of rainfall, as one would naturally expect. The
amount of easily soluble material is higher in arid regions,
due to the lack of rain and the tendency for soluble salts to
accumulate. Biologically, organisms are active at greater
depths' in arid than in humid regions, because of the loose
structure of arid soils and because of their good aération.
Such soils are seldom water-logged except from improper ir-
rigation. In humid regions bacterial action is limited very
largely to the surface foot of soil, since only there are the
aération and the food conditions adequate. The intensity of
biological activity in arid soils is very largely governed by
moisture, and when moisture conditions are satisfied, bacterial
changes may be expected to take place rapidly.
22. Special cases of soil formation.—Having compared
the weathering of granite and limestone under different cli-
matic conditions, it is interesting to note the quantitative chem-
ical changes of these rocks as they are reduced residually to
soil under humid conditions. The following analyses? indicate
the elements that are likely to be lost to the greatest extent
during the process. (See Tables III and IV, page 33.)
The soil resulting from the decay of the granite was a deep
red clay, with numerous quartz grains present. The soil
from the limestone was very plastic and high in silicate silica.
Leaching has probably gone on to a very great extent in both
soils. It is noticeable in both cases that the bases, such as
calcium, magnesium, sodium, and potassium, have suffered
severe losses. The carbonate has almost wholly disappeared
from the limestone clay, indicating that a residual soil from
such a rock will probably need an application of lime. (See
Figs 6 and 7, pages 34 and 35.)
1Lipman, C. B., The Distribution and Actwwities of Bacteria in Sotls
of the Arid Region; Univ. Calif., Pub. in Agr. Sci., Vol. I, No. 1, pp.
1-20. 1912.
2 Merrill, G. P., Weathering of Micaceous Gneiss; Bul. Geol. Soc.
Amer.) Viol. 85 p. L605) 1879"
SOIL-FORMING PROCESSES 33
TABLE IIT
FRESH GRANITE AND ITS RESIDUAL CLAY
CONSTITUENTS Rock Soin cane
Si0, 60.69 45.31 52.45
Al,O, 16.89 26.55 .00
Fe,0, 9.06 12.18 14.35
CaO 4.44 .00 100.00
MgO 1.06 .40 74.70
K,O 4.25 1.10 83.52
Na,O 2.82 .22 95.03
PO: 25 AT .00
Ignition 62 13.75 gain
TABLE IV
VIRGINIA LIMESTONE AND ITS RESIDUAL CLAY ?
PERCENTAGE ?
CONSTITUENTS Rock SorL e S
Lost
Si0, 7.41 57.57 27.30
Al,0, 1.91 20.44 00
Fe,0, 98 7.93 24.89
CaO 28.29 ol 99.83
MgO 18.17 1.21 99.38
K,0 1.08 4.91 57.49
Na,O 09 28 76.04
EO; .03 10 68.78
CO; 41.57 38 99.15
H,0 ot 6.69 gain
*The percentage loss of any constituent is calculated as follows:
A x 100
=X 100 — X = % Lost.
C
Bx —
D
A=9% any constituent in residual material.
B= % same constituent in fresh rock.
C=% of the constant constituent in residual soil.
D=4% of the constant constituent in fresh rock.
*Diller, J. S., Educational Series of Rock Specimens; U. S. Geol.
Survey, Bul. 150, p. 385. 1898.
34 NATURE AND PROPERTIES OF SOILS
The analyses indicate that the soil from the granite does
not differ greatly from the original rock, except in the loss of
bases, assumption of water, and increase of organic matter.
The soil from the limestone presents greater differences, due
C——IGRANITE
GHB RESIDUAL SOIL
Fig. 6.— Diagram showing the composition of fresh granite and its
residual soil. Note the marked hydration of the soil.
to the disappearance of the calcium carbonate. The analyses
of the two soils resemble each other rather closely in spite of
their widely different sources. Since weathering, especially
residual weathering, causes a loss of basic materials and
SOIL-FORMING PROCESSES 39
thereby favors the accumulation of silica, alumina and iron,
all soils as they age tend to approach each other in chemical
composition. Yet, owing to a difference in the adjustment
of the forces at work and to the time element, no two soils
Fee03+/ 290-4
AloOs (28, 4 a ay
a os
Mq0 1.7
Cc LIMESTONE,
BR RESIDUAL SOIL
Fig. 7—Diagram showing the composition of limestone and its residual
soil. Note the excessive loss of lime and earbon dioxide in soil
formation.
will ever be exactly alike. Soils will differ from the original
rock and from one another according to the intensity and
character of the weathering and erosive forces and to the
constitution of the parent minerals.
36 NATURE AND PROPERTIES OF SOILS
23. Red and yellow colors of soil..—The presence of
iron, as already noted, is a very important factor in rock
weathering, and the discoloration due to its presence is an
unfailing indication of chemical decay. The iron in minerals
occurs usually as ferrous oxide, which is soluble, especially
if the water circulating among the rock fragments carries
earbon dioxide. When this water comes in contact with the
air its excess of carbon dioxide is discharged and the oxides
and carbonates of iron are deposited. Under this condition
oxidation goes on rapidly, and the iron passes to the ferric
state and becomes insoluble. Thus it may be seen that iron
imparts a fatal weakness to rocks and minerals in which it
exists, due to its solubility; yet from the oxidation that it
undergoes it tends to persist and accumulate in soils. The
more iron a mineral or rock contains the more susceptible it
is to weathering.
The red and yellow soils of the southern states frequently
excite comment, especially as a difference in fertility is popu-
larly recognized, the red surface soil with a red subsoil being
considered more fertile than a similar soil with a yellow sub-
soil. This is probably due to differences in hydration of
the iron oxides.”
The soil temperatures, particularly in tropical and sub-
tropical regions, have first tended fully to oxidize and hydrate
the iron, and then to dehydrate the soil at the surface into
the deep red color, leaving the subsoil yellow and causing
the contrasts so markedly evident. Soils having a yellow
surface soil are generally considered to be older and more
weathered than those where the red is well developed. When
1 Robinson, W. O., and MeCaughey, W. J., The Color of Soils; U.S.
Dept. Agr., Bur. Soils, Bul. 79, p. 21. 1911.
2 Crosby, W. O., Colors of Soils; Proc. Boston Soc. Nat. Hist., Vol. 23,
pp. 219-222. 1875. Merrill, G. P., Rocks, Rock Weathering and Soils;
p. 375. New York, 1906. Van Bemmelen, J. M., Beitrage zur Kenntnis
der Verwitterungsprodukte der Silicate in Ton-, Vulkanischen-, und
Laterite-Boden; Zeit. Anorg. Chem., Bd. 42, Steite 290-298, 1904.
SOIL-FORMING PROCESSES 37
these old residual soils are poorly drained a well defined
mottling develops, especially in the subsoil, due to the ir-
regularities of aération.
The compositions of hematite and of the limonite group
indicate the possibility of a progressive change from red to
yellow by hydration:
UG TALELE schhe cect others one eel 5 Fe,0O, Red
ANUTSIGE)) cba 2Fe,0,. H,O
Limonite Goethite ..... FesO;) HO
Group on: Lamonite) 472: 2Fe,0,.3H,O
Xanthosiderite . Fe,O,.2H,O
aminiher 2s hc Fe,0,.3H,O Yallow
24. Practical relationships of weathering.—Soil-form-
ing processes fortunately remain intensely active after the
soil has been produced. The physical agencies especially
tend to loosen and fine the soil, contributing largely to its
tilth. The farmer encourages such influences by plowing his
land and by other tillage operations. The addition of organic
matter is another means whereby these physical changes may
be influenced. Granulation in a clay soil is due almost en-
tirely to natural agencies. Were it not for such activities
the soil would soon become physically unfit as a foothold for
plants. The continual chemical changes, culminating in solu-
tion, provide the soil-water with plant nutrients not only
in suitable concentration but in correct. proportion. By
slow processes, over geologic periods, Nature has provided
us with soil and by the same slow processes Nature is at-
tempting to maintain the fertility of her creation. The en-
couragement and control of such agencies is of no small
moment in practical soil management.
CHAPTER III
THE GEOLOGICAL CLASSIFICATION OF SOILS
WEATHERING must be considered as affecting soils, whether
they are in motion or at rest. This gives rise to two general
classes of soil materials—those that have not been shifted
far from their original situation and those that have suffered
considerable translocation. These two general groups, desig-
nated as sedentary and transported, are subject to subdivision
as follows: +
_ fsResidual
Sedentary Cumulose
Gravity. ess: Colluvial
Alluvial
5 Water .... ~ Marine
Transported ceueeene
ECA E dete s ie Glacial
Windia Sos: ASolian
25. Residual soils.2—This group of soils covers wide
areas of arable regions, especially in the tropics and sub-
tropics, and comes from many kinds of rock. Residual soils
are, in the main, old soils, usually the oldest with which we
deal in agricultural operations, although some residual soils
are comparatively young. Since they are formed in situ,
A ia G. P., Rocks, Rock Weathering and Soils, p. 288; New York,
1906.
? For a full discussion of the origin and characteristics of the soils
of the United States see Marbut, C. F. et al., Soils of the United States;
U.S. Dept. Agr., Bul. 96. 1913. For the soils of the Southern States,
consult Bennett, H. H., The Soils and Agriculture of the Southern
States; New York, 1921.
38
GEOLOGICAL CLASSIFICATION OF SOILS 39
the rocks that underlie them, if sound, often given some clue
to the character and composition of the parent material.!
Under such conditions the changes that a rock undergoes in
forming a soil may be studied to the best advantage.
Residual soils are usually non-stratified and present a
heterogeneous mass of material, grading from a true soil,
with its normal content of organic matter, downward through
the typical soil material to the unweathered country rock
below. Since such soil has been subject to leaching for long
periods, a very large amount of its soluble materials have
been washed out, tending to leave high percentages. of the
persistent elements, such as silica, iron and aluminum. The
preceding discussion of soii formation has already emphasized
this phase sufficiently.
The great age of residual soils has given opportunity for
very thorough oxidation, so that much of the iron has changed
to hematite or to the hydrated limonite group. The yellow
color of the latter group is indicative of greater age than the
former. Since almost all soil material contains considerable
iron the prevailing colors of residual soils are reds and yel-
lows, depending on the degree of oxidation and hydration.
Grays, browns, and blacks often occur, however, where oxida-
tion has not progressed or where organic matter is present in
amounts sufficient to mask the iron coloration.
As residual soils have been subjected to intense physical
and chemical weathering, the particles have been reduced
to a very fine state of division. Over residual areas the
heavier types, such as silt loams, clay loams and clays pre-
dominate. Sands and sandy loams may occur, however,
when the parent rock carried considerable quartz and a low
percentage of clay-producing minerals, such as feldspar, horn-
blende and augite. Soils from limestones, granites, and
*Residual soils are not always derived from rock similar to that
directly underlying the soil as is often assumed. When the present
bed rock is much different from the stratum which gave rise to the
soil, the soil is said to be ‘‘ inherited.’’
40 NATURE AND PROPERTIES OF SOILS
gneiss’ are generally clayey in nature, although loams and
even stony loams may occur if the limestone was sandy or
cherty and if the igneous rocks carried much quartz. Dolo-
mites weather more slowly than limestone and often give
rise to gravelly and stony types. Sandstone of course pro-
duces sandy soils, although a soil from an argillaceous sand-
—=—_Y7ye en Ro a
ees x fie nie
Fig. 8.—Diagram showing the relationship between the underlying rocks
and the overlying residual soils. Gettysburg, Pa. (After Emerson.)
stone may be rather heavy. Quartzite and slaty soils are
generally shallow, and unfavorable, both in texture and fer-
tility, for crop growth. Soils from basic igneous rocks, such
as diorite and basalt, generally produce sticky reddish or yel-
lowish clays containing little quartz. Rocks that carry con-
siderable mica, such as schists, give rise to highly micaceous
soils.
1 For a complete discussion of the influence of various parent rocks on
the resultant residual soil see Emerson, H. L., Agricultural Geology,
Chap. IV; New York, 1920.
GEOLOGICAL CLASSIFICATION OF SOILS 4]
The following analyses! show the general chemical char-
acter of surface residual soils and the variations that may
be expected:
TABLE V
CONSTITUENTS iL 2 3 4
SiO, 66.49 76.71 74.33 70.99
Al,O, geal 12.85 11.00 11.39
Fe,O, 7.43 2.81 4.64 4.23
TiO, 1.02 Al 1.04 1.28
CaO 36 08 PAS 93
MgO ol 29 69 1.08
K,O .62 3.26 oO Zot
Na,O 16 39 1.53 82
P30: Allyl 05 16 19
é O07 a ly a5) 34
Organic matter 1.26 1.78 1:99 .93
The organic matter of residual soils largely depends, in
amount and condition, on climatic factors. If rainfall and
temperature, for example, are favorable for the rapid and
continued development of a natural vegetation the soil will
be rich in humus, so rich at times as to mask to a certain
extent the red color so characteristic of such soils. If plants
do not grow well on this soil, however, it will be low in organic
matter and probably in poor physical condition. Residual
soils vary greatly in their general characteristics, especially as
to crop productivity.
Residual soils are of wide distribution in the United States,
particularly in the eastern and central parts, although great
1Robinson, W. O., The Inorganic Composition of Some Important
American Soils; U.S. Dept. Agr., Bul. 122, Aug. 1914.
1. Cecil clay, from granite and gneiss. Charlotte, N. C.
2. York silt loam, from schists. Bethany, S. C.
3. Penn silt loam, from sandstone. Morristown, Pa.
4, Hagerstown loam, from limestone. Conshohocken, Pa.
42 NATURE AND PROPERTIES OF SOILS
areas are found in the West as well. A glance at the soil
map of this country shows four great eastern and central
provinces—the Piedmont Plateau, the Appalachian Moun-
tains and Plateaus, the Limestone Valleys and Uplands, and
the Great Plains Region. The first three groups alone oc-
ecupy 10 per cent. of the area of the United States. The age
of these soils varies in the order named, showing that, while
they are very old as compared with other soils yet to be dis-
cussed, there may be vast periods of geologic time between
their beginnings. As a matter of fact, there is probably a
greater difference in age between the soils of the Piedmont
Plateau and those of the Great Plains Region than has elapsed
since the latter were formed. (See Fig. 9.)
26. Cumulose soils.—At relatively recent periods shal-
low lakes, ponds, and basins have been formed, partly by
stream action, partly by marsh conditions along sea or lake
coasts, or by glaciation, a common origin in northern United
States and Canada. The highly favorable moisture rela-
tions along the banks of such standing water has encouraged
the growth of many plants, such as algw, mosses, reeds, flags,
grass, and even larger types of vegetation. These plants
thrive, die and fall down to be covered by the water in which
they grew. The water shuts out the air, prohibits rapid
oxidation, and thus acts as a partial preservative. The decay
that does go on is largely through the agency of fungi and
anaérobic bacteria, that break down the tissue, and liberate
certain gaseous constituents. As the process continues the
organic mass becomes dark or even black in color.
Accumulations of this nature are dotted over the entire
country. Their size may vary from a few acres to several
thousand. Along streams the old abandoned beds offer ready
opportunity for the beginning of such accumulations.
Marshes either salt or fresh often contain such deposits.
Shallow basins produced by the scraping or damming action
of glaciers are frequently occupied by such material. In the
125°
Juan de Fud
C. Flattery
Z
LEGEND
Soil Kegions
a
Pacific Coast Northwest ~—4
Region Intermountain Region
Great Basin Southwest
Region Arid Region 4
Rocky Mountain Great Plains
Region Region
Fic. 9.—Map showing the soil provinces and soil regions of the United States. Thi
Valleys and Uplands are residual. The soil regions of western Un
Delaware Bay
LEGEND
Soil Provinces
Glaciat Lake and
River Terraces
Greenville \ a
alias —— DOE, j = :
Yar sha o f Z 1 f ~ ts as N Glacial and Limestone
hs é \ : Bae Loessial Valleys and Upland
Appalachion Moun Piedmont
al tains and Plateaus Plateau
Canaver
Tampa he}
Bay e
Cane Ld
Kyokechobee River Atlantic and Gulf
r Flood Plains Coastal Plains
Miami
G.Sable »
= WILLIAMS ENGRAVING CO,, NEW YORK
) ° ° 3 ry
93 89 85 z 81 77
ils of the Piedmont Plateau, Appalachian Mountains and Plateaus and the Limestone
States contain soils of many different origins. (Bul. 96, Bur. Soils.)
GEOLOGICAL CLASSIFICATION OF SOILS 43
last named case the beds are more or less independent of
topography, and may be found on hillsides as well as in lower
lands.
Cumulose materials may be grouped under two heads, peat
and muck. The only difference is in their state of decay.
In peat the stem and leaf structure of the original plants
ean still be detected, and identification is quite possible. In
muck, however, the plant tissue has lost its identity as such
and is merged into a complicated and indefinite mass of
organic material.t
The composition of peat and muck may be much altered
by the washing-in of mineral matter. In some cases the beds
may be from 90 to 95 per cent organic, while in other cases,
due to this foreign material, the percentage may drop as low
as 20 per cent giving a black or swamp marsh mud.
The analyses given illustrate the composition of some rep-
resentative cumulose soils. (See table VI, page 44.)
Peat and muck are often of large extent? and become of
extreme value when drained, especially if they are near a
good market. They are of peculiar value in trucking oper-
ations, being adapted to such crops as onions, celery, lettuce,
and the like. Usually they must not only be provided with
drainage, but must also be treated with fertilizers carrying
1The term ‘‘muck’’ is often used interchangeably with peat. Tech-
nically it is best to limit the former term to those peats which are very
thoroughly decomposed or contain a high proportion of mineral matter.
Chemically muck is often used in reference to soils containing from 20
to 50 per cent. of organic matter, while peat is confined to soils in which
the amount of organic constituents is above 50 per cent. According to
such a definition most cumulose soils are peats instead of muck. The
term ‘‘muck’’ is so popular, however, that in the United States its use
will continue in spite of the technical distinctions that have been
established.
? Alway reports the following figures:
Germany .... 5,000,000 acres Wisconsin ... 3,000,000 acres
Sweden ...... 12,000,000 ‘¢ OWIOasic.s ere « illrsy(0X0K0) SC
Minnesota ... 7,000,000 ‘‘ Canada ......22,000,000 ‘*
Alway, F. J., Agricultural Value and Reclamation of Minnesota Peat
Soils; Minn, Agr. Exp. Sta., Bul. 188, 1920.
44 NATURE AND PROPERTIES OF SOILS
TABLE VI
COMPARATIVE CHEMICAL COMPOSITION OF A PRODUCTIVE MIN-
ERAL SOIL AND CERTAIN REPRESENTATIVE PEAT
AND MUCK SOILS.
ORGANIC | MINERAL
SoILs Meare | Nicene N OF ee © CaO
Representative
mineral soil 5-003) 95:
Minnesota peat? | 94.00 6
Minnesota peat’ | 59.00 | 40
Minnesota Muck*| 50.6 49 ;
Minnesota Muck?!}| 41.4 58.6 TS sem — =
Florida peat? . | 68.4 31.6 2.63 | .20 li on
Canadian peat * 74.3 2550 | 21Sh 20 16 i
German peat *
(Low lime) 97.0 3.0 207) eG 05 3D
German peat *
(High lime) 90.0 10.0 2.50 | .25 10 | 4.00
phosphorous and, especially, potash. It is also a good prac-
tice to start vigorous decay by the applicaton of barnyard
manure, as the nitrogen carried by muck soils is usually not
very readily available to plants.°
* Alway, F. J., Agricultural Value and Reclamation of Minnesota Peat
Soils; Minn. Agr. Exp. Sta., Bul. 188, Mar., 1920.
? Pickel, G. M., Muck: Composition and Utilization; Fla. Agr. Exp.
Sta., Bul. 13, 1891.
* Rept. Can. Exp. Farms, 1910. Rept. of chemist, p. 160.
“Fleischer, M., Die Anlage und die Bewirtschaftung von Moorwiesen
und Moorweiden; Berlin, 1913.
5 Publications regarding the practical utilization of peat and muck
lands: Robinson, C. 8., Utilization of Muck Lands; Mich. Agr, Exp.
Sta., Bul. 273. 1914. Whitson, A. R., et al., The Improvement of Marsh
Soils; Wis. Agr. Exp. Sta., Bul. 205. 1914. Stevenson, W. H., and
Brown, P. E., Improving Iowa’s Peat and Alkali Soils; la. Agr. Exp.
Sta., Bul. 157, 1915. Smalley, H. R., Management of Muck Land
Farms in Northern Indiana and Southern Michigan; U. S. Dept. Agr.,
Farmers’ Bul. 761. 1916. Thompson, H. C., Truck Growing on Peat
Soils; Jour. Amer. Peat Soc., Vol. Il, No. 3, pp. 113-125. 1918.
Alway, F. J., Agricultural Value and Reclamation of Minnesota Peat
Soils; Minn. Agr. Exp. Sta., Bul. 188. Mar., 1920.
GEOLOGICAL CLASSIFICATION OF SOILS 45
In many cases muck and peat are underlaid at varying
depths by a soft impure calcium carbonate, called bog-lime.'
Such a deposit may come from the shells of certain of the
Mollusca, which have inhabited the basin, or from aquatic
plants, such as mosses, alge and species of Chara. In ear-
bonated water these plants become incrusted with calcium
carbonate, possibly because of their ability to absorb carbon
dioxide,” thus precipitating the carbonate. In most cases
this carbonate accumulation is due to a combination of the
two agencies. Such material, because of its richness in cal-
cium, is valuable as a soil amendment, and often, where it is
found pure enough in quality and in sufficiently large quan-
tities, it is handled commercially.
27. Colluvial soils—This soil is formed in regions of
precipitous topography, and is made up of fragments of rocks
detached from the heights above and carried down the slopes
by gravity. Talus slopes, cliff debris, and other heterogeneous
rock detritus are examples of colluvial soil. Avalanches are
made up largely of such material.
As the physical forces of weathering are most active in the
formation of these soils the amount of solution and oxidation
is usually small. The upper part of the accumulation ex-
hibits physical action to the greatest extent, the particles being
angular, coarse, and comparatively fresh; farther down the
slope the material may merge by degrees into ordinary soil.*
Such soils are usually shallow and stony, and approach the
original rock in color unless large amounts of organic matter
have accumulated. Colluvial soils are not of great importance
1 Bog-lime is often spoken of as marl. Marl, as used by the geologist,
refers to a caleareous clay of variable composition. Bog-lime, when it
contains numerous shells, is often termed shell-marl. See Stewart, C. F.,
The Definition of Marl; Eeon. Geol., Vol. 4, No. 5, pp. 485-489, 1909.
7 CaH,(CO;), == CO, + H,O + CaCoO,.
*Colluvial soils generally merge so gradually into alluvial fans that
the line of separation is difficult to establish. When the area of col-
luvial material is small, as it usually is, it is best included in the fan
soils,
46 NATURE AND PROPERTIES OF SOILS
agriculturally because of their small area, their inaccessibility,
and their unfavorable physical and chemical characteristics.
28. Alluvial soils.\—In considering water as a soil-form-
ing agency, it was found to have both cutting and transporting
powers. Alluvial soils are the direct result of these activities,
especially the latter. The carrying power of water varies di-
rectly as the sixth power of the velocity; so that doubling the
velocity increases the transportive ability sixty-four times.
Obviously any checking of a stream’s velocity will force it to
deposit its load, the larger particles first and the finer as the
current becomes more sluggish. With changes of velocity dif-
ferent grades of material are laid down, giving rise to strati-
fication, one of the important characteristics of an alluvial
soil. Streams never deposit, either along their course or at
their delta, all of their sediment. Many tons of material both
in suspension and in solution are discharged yearly into the
ocean.”
There are three general classes of alluvial soils: (1) flood
plain deposits, (2) deltas, and (3) alluvial fans. As the
outlet of a stream is approached, its gradient generally be-
comes less inclined and its current is slackened. In a large
stream this often means an aggrading of the channel due to
the deposited material. A stream on a gently inclined bed
usually begins to swing from side to side in long, gentle
curves, depositing alluvial material on the inside of the curves
and cutting on the opposite banks. This results in oxbows and
*If a detailed discussion regarding alluvial, marine, and glacial activi-
ties is desired, the following books will be helpful: Tarr, R. S., and
Martin, L. M., College Physiography; New York, 1918. Pirsson, L. V.,
A Text Book of Geology, Part I; New York, 1915. Emerson, H. L.,
Agricultural Geology; New York, 1920. The considerations of river
and stream action by Russell and Davis are classical: Russell, I. C.,
Rivers of North America; New York, 1898. Davis, W. M., The Rivers
and Valleys of Pennsylvania; Geological Essays, Boston, 1909.
?Streams each year discharge into the ocean, on the average, 100 tons
of soluble matter for every square mile of drainage area. The Mississippi
River pours into the Gulf of Mexico each year 406,250,000 tons of sedi-
ment, not to mention a vast amount of soluble salts.
GEOLOGICAL CLASSIFICATION OF SOILS 47
lagoons, which are ideal not only for the further deposition
of alluvial matter but also for the formation of cumulose soils.
This state of meander naturally increases the probability of
overflow in high water, a time when the stream is carrying
much suspended matter. This suspended material is deposited
over the flooded areas; the coarser near the channel, building
up natural levees; the finer sediment farther away in the
lagoons and slack water.
Due to a change in grade, a stream may cut down through
its already well-formed alluvial deposits, leaving terraces on
one or both sides. Often two, or even three, terraces may be
detected along a valley, marking a time when the stream-bed
was at these elevations. On the lower slopes of hills bordering
valleys the colluvial deposits may touch or even mingle with
the alluvial, furnishing the stream with some detritus. Flood
plain soils are variable in character, ranging from sandy loams
to heavy clays.
A great deal of the sediment carried by streams is not de-
posited in the flood plain but is discharged into the body of
water to which the stream is tributary. Unless there is suffi-
cient current and wave action the suspended material ac-
cumulates, forming a delta. Such deposits are by no means
universal, being found at the mouths of but a small propor-
tion of the rivers of the world. A delta is generally a con-
tinuation of the flood plain and as it is built farther and far-
ther out the stream is forced to aggrade its bed and both
flood plain and delta are raised. Near the front of the delta
the land is swampy; farther back it is higher and may assume
considerable agricultural importance.
Where streams descend from mountains or plateaus, sudden
changes in gradient often occur as the stream emerges in the
lower lands. <A deposition of sediment is thereby forced, giv-
ing rise to alluvial fans.t They differ from deltas in their
1 As already noted, alluvial fans and colluvial material are very closely
related. Soil survey classifications usually do not recognize the latter
separation.
48 NATURE AND PROPERTIES OF SOILS
location and in the character of their material. The material
of the latter is generally sandy, more or less porous and well
drained. Deltas, on the other hand, are characterized by poor
drainage and by heavy
soils, silt loams, clay
loams and clays predom-
inating.
Alluvial soils, espe-
clally those of flood
plain origin, are com-
paratively young. Delta
and first bottom soils are
usually in need of drain-
age. Alluvial fans and
terrace soils are often
loose and open to the
point of droughtiness.
The latter group is usu-
ally not so well sup-
pled with organic mat-
ter as are the delta and
flood plain soils, which
exist under conditions
where organic accumu-
lation is rapid. All allu-
vial soils are greatly in-
fluenced by the source
Fic, 10.—The flood-plain and delta of the Of the detritus. For ex-
lower Mississippi River. ample, a red upland soil
will give a reddish allu-
vial, while a soil or rock poor in lime will certainly not be
parent to one rich in that constituent. Alluvial soils are gen-
erally richer in the essential constituents than the soils from
which they are a wash, as is shown by the following data
from North Carolina.
i"
|
|
GEOLOGICAL CLASSIFICATION OF SOILS 49
TaBLE VII
CHEMICAL ANALYSES OF TWO ALLUVIAL SURFACE SOILS AND THE
RESPECTIVE SURFACE SOILS FROM WHICH
THEY WERE DERIVED.*
- re 1 2 3 4
CoNSTITUENTS ALLUVIAL UPLAND ALLUVIAL UPLAND
Jf serpy i aie .073 .048 iS .038
BBO Os ek Ban .076 041 118 .027
ECA OSE ae aie ana 1.697 1.330 433 .286
CEO) Aaa dea eee | 1.103 .200 AIT PA |
Delta soils, where they occur in any acreage, are very im-
portant. The deltas of the Mississippi, Ganges, Po, Tigris,
and Euphrates rivers are striking examples. Egypt, for
centuries the granary of Rome, bespeaks the fertility of such
land. Flood plain soils are found to a certain extent along
every stream, the greatest development in the United States
occurring along the Mississippi. This area varies from forty
to sixty miles in width and has a length from Cairo to the
Gulf of over 600 miles. Such soils are very rich but, if
they are first bottoms, they require drainage and protection
from overflow. Alluvial fan soils are found over wide areas
in arid and semi-arid regions and when irrigated and prop-
erly handled have proven very productive. They often occur
in large enough areas in humid regions to be of considerable
1 Williams, C. B., et al., Report on the Piedmont Soils; Bul. N. C.
Dept. Agr., Vol. 36, No. 2, Feb., 1915.
1. Average of 8 analyses of Piedmont alluvial soils, Congaree
series, to a large extent a wash from the Cecil.
2. Average of 71 analyses of Cecil series soils, the typical upland
soil of the North Carolina Piedmont.
Williams, C. B., et al., Report on the Coastal Plain Soils; Bul. N. C.
Dept. Agr., Vol. 39, No. 5, May, 1918.
3. Average of 8 analyses of coastal plain alluvial soils, Johnston
and Kalmia series.
4, Average of 165 analyses of Norfolk series soils, the typical
upland coastal plain soil of North Carolina,
50 NATURE AND PROPERTIES OF SOILS
importance. The type of farming and the crops grown on any
area of alluvial soil will vary with climate, soil conditions,
and markets.
29. Marine soils.\.—A great deal of the sediment carried
away by stream action is eventually deposited in the sea,
the coarser fragments near the shore, the finer particles at
a distance. Such material is largely clastic and if there have
Fie. 11.—Block diagram showing how marine soils are formed and their
relation to the uplands. The emerged coastal plain has already
suffered some dissection from stream action. (After Emerson.)
been many changes in shorelines, the alternating beds will
show no regular sequence. Such material, when raised above
the sea by diatrophism and subjected to sufficient weathering
and denudation, is classed as marine soil. (See Fig. 11.)
Such material has been worn and triturated by a number
of agencies. First, the forces necessary to throw it into
stream suspension were active, and next it was swept into
1For an excellent discussion of the marine soils of the Atlantic and
Gulf coasts of the United States see Bennett, H. H., Soils and Agri-
culture of the Southern States; New York, 1921.
GEOLOGICAL CLASSIFICATION OF SOILS 51
the ocean to be deposited and stratified, possibly after being
pounded and eroded by the waves for years. At last came
the emergence above the sea and the action of the forces
of weathering in situ. The latter effects are of great moment
since they determine not only the topography but the fertility
of the new soil as well. The availability of the nutritive ele-
ments, and especially the amounts of organic matter, are de-
termined by recent and still active forces.
The marine soils of the United States, while younger than
most of our residual soils, are usually more worn and gener-
ally carry less of the nutrient elements. Their silica con-
tent is very high and they are often sandy, especially along
the Atlantic seaboard. Sands, sandy loams, and loams pre-
dominate, although silt loams and clays are by no means un-
usual, especially in the Atlantic and Gulf coastal flatwoods
and the black prairies and interior flatwoods of Alabama and
Mississippi. The organic content of the sandy soils is geu-
erally low, but on the heavier types it may almost equal delta
and flood plain soils.
A direct comparison’ between typical coastal plain and
residual soils usually shows the former to be considerably
higher in silica but lower in iron and aluminium. The marine
soil is, on the other hand, lower in phosphorie acid and
potash. The nitrogen, organic matter, and lime are so vari-
able in both soils that no reliable deductions can be drawn.
_ The following data from Eastern United States substantiate
the above generalizations.?, (Tables VIII and IX, page 52.)
The soils of the Atlantic and Gulf coastal provinces, formed
as vast outwash plains and occupying 11 per cent. of the area
of the United States, are very diversified, due to source of
* When soils are compared on the strictly chemical basis great caution
should be observed in drawing conclusions as to relative productivity.
The amount of a nutrient present is by no means a measure of its
availability. A chemical analysis usually throws but little light on the
fertilizer needs of a soil.
?See also Walker, 8. S., Chemical Composition of Some Louisiana
Soils as to Series and Texture; La. Agr. Exp. Sta., Bul. 177, Aug., 1920.
52 NATURE AND PROPERTIES OF SOILS
TABLE VIII
COMPARATIVE COMPOSITIONS OF COASTAL PLAIN AND RESIDUAL
SOILS OF EASTERN UNITED STATES."
_ i 2
DO STSIRIATOISINS CosTAL PLAIN RESIDUAL
POU Cetin a Ral IR sivas Stee tet dara 93.44 TTAS
MT 58 cena a ote ey et ea 5 .69 90
iO aR ere emteniah a 1.96 9.13
SRO) 3 Lips, al ON tigen ey ati deta nea Ee 3.75
TABLE IX
COMPARATIVE COMPOSITIONS OF NORTH CAROLINA COASTAL PLAIN
AND RESIDUAL SOILS.”
= : 1 2 3
CONSTITUENTS CosTAL PLAIN |COASTAL PLAIN RESIDUAL
ING GB eae ue ae .038 188 .048
| Ege Ot aoe ey sae ne ere O20 .033 041
1 CL @ eee deaede 286 346 1.330
CaO apes sme 22k 94 .200
Robinson, W. O., et al., Variation in the Chemical Composition of
Soils; U. S. Dept. Agr., Bul. 551, June, 1917. .
1 and 2. Average analyses of 15 coastal plain and 8 residual soils,
respectively, taken from various places in eastern United States.
* Williams, C. B., et al., Report on the Coastal Plain Svils; Bul.
N. C. Dept. of Agr., Vol. 39, No. 50, May, 1918.
1. Average of 165 analyses of Norfolk series soils. This is
the typical soil of the Atlantic coastal plain.
2. Average of 84 analyses of Portsmouth series soils. This
series is above the average coastal plain soil in organic
matter and fertility.
Williams, C. B., et al., Report on the Piedmont Soils; Bul. N. C.
Dept. of Agr., Vol. 36, No. 2, Feb., 1915.
3. Average of 71 analyses of Cecil series soils. This series is
the typical residual scil of the Piedmont plateau,
GEOLOGICAL CLASSIFICATION OF SOILS 53
material, age, and climatic conditions. There are great
tracts of general farming land, besides wide areas of special-
purpose soils adapted to highly specialized industries. The
latter soils require refined and intensive methods of culti-
vation. Except for certain areas the coastal plain soils are
well aérated and easy to cultivate. Except in the lower
coastal plain belt they are well drained. Severe leaching as
well as serious erosion occurs in times of heavy rainfall.
When sufficiently supplied with organic matter, carefully
fertilized, and cultivated properly, these soils support a great
variety of crops such as cotton, maize, oats, forage crops,
and peanuts, besides vegetables and fruits of many varieties.
30. The ice age and the American ice sheet.'—If in any
region the temperature and snowfall stand in such rela-
tionship that the heat of summer does not offset the winter’s
accumulation of snow, great snowfields form. If this con-
dition persists year after year the temperature is reduced
to such an extent as to increase the proportion of the snowfall,
which escapes the summer heat. The pressure of overlying
snow and the influence of the summer melting soon change
the snow into ice with a complicated recrystallization. As the
depth of the accumulation increases outward movement is
inaugurated due to the strong lateral pressure. As the ice
moves slowly forward under this tremendous pressure, with
an almost incredible thickness and a plasticity which ordi-
nary ice does not possess, it conforms itself to the uneven-
ness of the areas invaded. It rises over hills and shapes
itself to valleys with surprising ease. Not only is the exist-
ing soil mantle swept away by such an invasion but the
underlying rocks are ground and gouged. When the ice
melts back and the region is again free a mantle of soil ma-
terial remains.
For a complete discussion of glaciers and glaciation, see Salis-
bury, R. D., The Glacial Geology of New Jersey; Geol. Survey of
New Jersey, Vol. 5, 1902.
54 NATURE AND PROPERTIES OF SOILS
This drift is often merely ground-up rock, at other times
the original soil is mixed with foreign detritus, while again
the variable mixtures may be wholly reworked and consid-
erably stratified. Besides this the streams of water, which
issue from under the ice, may be instrumental in distribut-
ing sediments for miles beyond the ice front. Glacial lakes,
when in existence for sufficiently long periods, furnish basins
for the deposition of materials derived from the erosive and
grinding influence of the ice. The ice may also provide a
large amount of detritus so fine as to be susceptible to wind
movement, and thus eolian influences as well as alluvial and
lacustrine may be concomitant to a great ice invasion.
During the Pleistocene northern North America, as well
as part of Europe, was successively invaded by ice sheets,
which exerted the influences above described and, while the
central ice caps in Canada probably never wholly disap-
peared, the regions to the southward certainly experienced
alternate glaciation and interglaciation. At least five in-
vasions are evident in central United States. Debris from the
last, called the Wisconsin, now covers wide areas. The in-
terglacial periods are shown by forest beds, accumulations
of organic matter, and evidences of erosion between the drift
deposited by the successive ice sheets. Some of the inter-
glacial periods evidently were times of warm, and even semi-
tropical, climate. Just what was the exact cause of the ice
age is still under dispute: That it was due to a change in
the carbon dioxide content of the air seems as probable as
any of the numerous hypotheses that have been advanced.
The area covered by glaciers in North America is estimated
as 4,000,000 square miles, while at least 20 per cent. of the
United States is either directly or indirectly influenced by the
debris. The greatest southward extension of the ice is marked
1 Humphreys, W. J., Factors of Climatic Control, Jour. Franklin Inst.,
Vol. 189, No. 1, pp. 63-98, Jan., 1920.
GEOLOGICAL CLASSIFICATION OF SOILS 59
by a terminal moraine wherever the ice margin was station-
ary long enough to permit such an accumulation. Many
other moraines are found to the northward, marking points
where the ice became stationary for a time as it retreated
by melting." While the moraines are generally outstand-
ing topographic features, they are commonly unimportant
agriculturally due to their small area and unfavorable physi-
ography. The ground moraine is the material which fur-
nishes the bulk of the soils which have directly resulted from
glaciation. This ground moraine is of wide extent and pos-
sesses a favorable agricultural topography. The weathering
in situ of this great area of soil material has evolved one of
the most productive soil provinces of the world.
31. Glacial soils—The soils which have been developed
from the glacial till are usually rather heavy, loams, silt
loams, and clay loams predominating. The subsoil is gen-
erally finer than the surface and may induce poor drainage.
The individual particles of such soils are less weathered than
those of residual soils. The feldspars have retained their
normal luster and the iron staining so common in the Pied-
mont Plateau is almost absent. The color is usually sub-
dued, grays and browns prevailing. Red glacial soil may
occur, however, where red sandstones have been ground up
or where considerable residual soil has been incorporated
in the till. The subsoils usually present colors ranging from
light gray and yellows to brown. Mottling is common, es-
pecially in the subsoil, due to lack of aération.
The chemical composition of glacial soils approaches that
of the parent rock more nearly than does any other, since
*The position of the ice front of a glacier is determined by the
relationship between the forward movement of the ice and the rate
of melting. When the former is dominant, the ice front advances.
When melting in dominant, the ice front recedes. When these two
forces are balanced, conditions are favorable for a stand of the
ice and the building of a moraine.
56 NATURE AND PROPERTIES OF SOILS
the forces of weathering, while they have had time to pro-
duce a soil from the material left by the ice, have not as yet
seriously depleted the essential constituents. The mineral
elements in such soils are governed to a considerable degree
by the composition of the original rock. Calcium content,
STi
(aL a
opr by
Fig. 12.—Block diagram showing the relationship which sometimes exists
between glacial soils and the underlying rocks. Glacial movement
left to right. (After Emerson.)
for example, is controlled largely by such a relationship.
The hill soils of southern New York (Volusia and Lords-
town) come from shales low in lime and their productive-
ness is seriously affected thereby. On the other hand, cer-
tain glacial soils of central New York and of the Mississippi
Valley (Ontario and Miami) have been formed from eal-
eareous till and owe their productivity partly thereto. Gla-
GEOLOGICAL CLASSIFICATION OF SOILS 57
cial soils from limestones generally contain plenty of lime,
a condition that is far from true with residual soils.*
The organie content of glacial soils depends to a large
extent on the climatic conditions under which the soil has
existed since its formation. If environmental factors have
been such as to encourage the accumulation of organic mat-
ter, these soils will exhibit the deep black color that arises
from the presence of such material. If, however, conditions
do not encourage the natural growth of a heavy vegetation,
the amount of organic matter in such virgin soil will be low.
Lime and other nutritive elements may also be a great factor
in the development of vegetation on these soils. Glacial till
soils are distributed over all the area north of the great
terminal moraine, and stretch, roughly, from New Eng-
land to the Pacific coast. They comprise a great variety of
soils, differing not only in their physical characters, but also
as to fertility. They are adapted to many crops, but general
farming is practiced on them to the greatest degree. This
means extensive, rather than intensive, operations. In some
1 PARTIAL ANALYSES OF SOILS FROM THE LIMESTONE DRIFTLESS AND
GLACIAL REGION OF WISCONSIN? ARE OF INTEREST IN THIS REGARD:
RESIDUAL GLACIAL
CONSTITUENTS
1 2 3 4
ISikO}s ag oS Secs EEO Re Eee leds 49.13 40.22 48.81
INNO M5 INO) oa wingan cease 18.02 Sled, 11.30 10.07
I Ooi coven ttateue fois o eue 8 ye .38 1.92 7.80 7.95
CAO ee eee ce ee 85 122, 15.65 11.83
LEC LO Et, ee ee Me ee rt 1.61 1.61 2.36 2.60
121 OER 9m Bsr S CAG IEEE .02 .04 .05 ail}
COMA ohc. Satie sch a ders mi nG 43 .39 18.76 15.47
? Chamberlain, T. C. and Salisbury, R. D., The Driftless Area of the
Upper Mississippi; Sixth Ann. Rep. U.S. Geol. Survey, pp. 249-250, 1885.
These analyses illustrate to very good advantage the beliefs entertained
by Chamberlain and Salisbury regarding the differences between residual
and glacial clays. Residual clay is designated by them as ‘‘rock rot,’’
and glacial clay as ‘‘rock flour.’’ The latter, being less weathered, re-
tains a larger proportion of its easily soluble materials.
58 NATURE AND PROPERTIES OF SOILS
regions dairying has been developed to a large extent, while
in certain localities, where climate, soil, and market are fa-
vorable, trucking is of great importance.
32. Effect of glaciation on agriculture.—In comparing
glaciated soils with corresponding residual areas, certain
differences are usually apparent. The agricultural condition
within the zone of glaciation is usually consistently higher
than that beyond the regions of drift accumulation. The
extensive leveling due to glacial erosion and deposition has
almost always resulted favorably for agricultural operations.
Even the thickness of the drift is found to conserve the
ground water supply. While it is difficult to show any con-
sistent difference between residual and glacial soils as to total
constituents, it is generally admitted that glaciation has been
a benefit to agriculture, in that the soils have been rejuven-
ated and their crop-producing power raised.
The dominant textural quality of glacial soils seems adapted
to certain staple food crops, and, due to their interming-
ling, a considerable opportunity for diversified and intensi-
fied farming is offered. It is, therefore, evident that in any
study of soils, particularly those of the United States, a
eareful consideration of the effects of glaciation is neces-
sary. Even the alterations in topography are factors not
to be ignored. In a comparison of the driftless area of Wis-
consin with the glaciated parts only 43 per cent. of the
former is improved as against 61 per cent. of the latter, while
the value of the farms on the glaciated soil averages 50 per
cent higher. The same general differences appear between
the glacial and residual soils of Indiana and Ohio.
33. Lacustrine soils—glacial lake—Great torrents of
water were constantly gushing from the front of the great
1 Whitbeck, R. H., The Glaciated and Driftless Portions of Wisconsin ;
Bul. Geog. Soc. Phil., Vol. IX, No. 3, pp. 10-20, 1911. Von Englen,
O. D., Effects of Continental Glaciation on Agriculture; Bul. Amer.
Geog. Soc., Vol. XLVI, pp. 353-355, 1914. Ames, J. W., and Gaither,
E. W., Sotl Investigations; Ohio Agr. Exp. Sta., Bul. 261, 1913.
GEOLOGICAL CLASSIFICATION OF SOILS 59
ice sheets as they advanced and retreated in response to their
environment. The great loads of sediment carried by such
streams were either dumped down immediately or carried to
other areas for deposition. As long as the water had ready
egress it flowed rapidly away to deposit its load as gravelly
Fie. 13.—Diagram showing how glacial lakes were formed in New York
State. The lighter shading represents the Ontarian ice lobe; the
darker shading indicates the position of the glacial lake waters in
the Ontario and Hudson river basins. (After Fairchild.)
outwash, river terraces, valley trains and alluvial fans. In
many cases, however, the ice front came to a stand where
there was no such ready egress and ponding occurred. Often
very large lakes were formed which existed for many years.
(See Fig. 13.)
With the ice melting rapidly on the hill tops these lakes
were constantly fed by torrents from above, which were
laden with sediment derived not only from under the ice,
60 NATURE AND PROPERTIES OF SOILS
but also from the unconsolidated till sheet over which it
flowed. As a consequence there were in the glacial lakes
deposits ranging from coarse delta materials near the shore to
fine silts and clay in the deeper and stiller waters. Such
materials now cover large areas, not only in New York state
and along the Great Lakes, but also in the Red River Valley
and in the valleys of the Rocky Mountains and the Cascades
and Sierra Nevadas. They make up by far the most im-
portant of the lacustrine soils. Glacial lake soils probably
present as wide a variation in physical characteristics as any
of the great soil provinces. Being deposited by water they
have been subject to much sorting and stratification, and
range from coarse gravels on the one hand to fine clays
on the other. They are generally found as the lowland soils
in any region, although they may occur well up on the
hillsides if the shores of the old lakes encroached thus far.
The color of such soils varies from gray to black, according
to the degree of organic matter present. The organic con-
tent of such soils, as with the glacial till, varies with climate,
and may be high, low, or medium according to conditions.
The thickness of glacial lake deposits is variable, ranging
from a few to many feet. In chemical composition they
closely approximate the soil material from which they were
derived. This is particularly true as regards the presence
of lime. The distribution of glacial lake deposits is not
only wide but the areas are large enough to be of great
agricultural influence. Extending westward from New
England along the Great Lakes until the broad expanse
of the Red River Valley is reached these deposits have pro-
duced some of the most important soils of the northern
states. They are valuable not only for extensive cropping
with grain and hay, but also for fruit and trucking.
34. Lacustrine soils—recent lake—While the glacial
lake deposits were formed many thousands of years ago the
lake soils of the second group are still in process of construc-
GEOLOGICAL CLASSIFICATION OF SOILS 61
tion. It is a well-known fact that lakes are only enlarged
stream beds, and are doomed ultimately to be filled by river
sediments. Such soils have been reclaimed to a certain ex-
tent, but their acreage is not large enough to give them the
importance of the glacial lake soils. The lake soil is usually
of a fine character, rich in organic matter and of good tilth.
If properly drained, it is almost invariably highly produc-
tive, and is adapted to a variety of crops depending on c¢li-
matic conditions.
35. Afolian soils —Loess.—During glaciation much fine
material was carried miles below the front of the ice sheets
by streams that found their source within the glaciers. This
fine sediment was deposited over wide areas by the over-
loaded rivers. The accumulations occurred below the ice
front at all points, but seem to have reached their greatest
development in what is now the Missouri Valley and the
Great Plains. Much of the sediment in the latter area prob-
ably came from local glaciers, which debouched from the
Rockies.
It is generally agreed by glacialists, that a period of aridity,
at least as far as this particular region is concerned, im-
mediately followed the retreat of the ice. The low rain-
fall of this period was accompanied by strong westerly winds.
These winds, active perhaps through centuries, were instru-
mental in the picking-up and distributing of this fine ma-
terial over wide areas of the Mississippi, Ohio, and Missouri
valleys. One strong argument for this wolian origin is that
the soil is in its deepest and most characteristic development
along the eastern banks of the large streams. Especially
noticeable is the extension down the eastern side of the Missis-
sippi River almost to the Gulf of Mexico. This wind-blown
material, called loess, is found over wide areas in the United
States, in most cases covering the original till mantle. It
covers eastern Nebraska and Kansas, southern and central
Iowa and Illinois, northern Missouri and parts of Ohio and
62 NATURE AND PROPERTIES OF SOILS
Indiana, besides a wide band, as already noted, extending
southward along the eastern border of the Mississippi River.
Due to its mode of origin, its depth is always greatest near
the streams and gradually becomes less farther inland. In
places, notably along the Missouri and Mississippi rivers, its
accumulation has given rise to great bluffs, which bestow a
characteristic topography to the region.
Not only is loess found over thousands of square miles in
the central part of the United States but it occurs else-
where in large areas. It is greatly developed in northern
France and Belgium, and along the Rhine in Germany, where
it is an important soil in all the valleys that are tributary
to that river. Silesia, Poland, southern Russia, Bohemia,
Hungary and Roumania have deposits of this highly fertile
material. Some of the most important moves of the World
War had as their aim the possession of these fertile areas.
In China loess is found over a very large part of the valley
of the Hwangho, a region probably larger in area than France
and Germany combined. The thickness of the deposit is
variable, ranging from a few feet to several thousand in
places. The depth is practically always sufficient for any
form of agricultural operations.
Loess is usually a fine calcareous silt or clay loam, of a
yellowish or yellowishy buff color. While it may be readily
pulverized when subjected to cultivation, it possesses remark-
able tenacity in resisting ordinary weathering. The vertical
walls and escarpments formed by this soil show one of its
striking physical characteristics. In China caves that house
thousands of persons are dug in the defiles and canons ex-
isting in this deposit. Another feature of loess is the pres-
ence, especially in the subsoil, of minute vertical canals lined
with a deposit of calcium carbonate. These canals are sup-
posed to give the soil its vertical cleavage and its tenacity.
The particles of loess are usually unweathered and angular.
Quartz seems to predominate, but large quantities of feld-
GEOLOGICAL CLASSIFICATION OF SOILS 63
spar, mica, hornblende, augite, calcite and other minerals
are found.
A few typical analyses are given below which show the
variability that may be expected, especially in the nitrogen,
phosphorie acid, potash, and lime.
TABLE X
ANALYSES OF AMERICAN LOESS SURFACE SOILS!
CONSTITUENTS 1 2 3 4
LO ga ae TASO 81.13 86.96 69.66
TO ane She 60 is .69 le 72
S215 0 ieee 11.47 8.52 4.69 12.71
EN ee eee 4.05 2292) 2.86 4.89
Ores vies 1.10 39 .43 1-28
ara 1.38 St Sift 1.09
INGE ORG. 1.95 52 OT ety
RE Oley ites wes 2.40 1 ETA) a Oil 2.42
ROB 2's ms a) .08 07 15
et ooo cine Pips sal pall 23
Whenever moisture relations are favorable, loess is an
exceedingly fertile soil. Under heavy cropping, especially
when little in the way of organic or mineral matter is re-
turned, this soil shows a need of phosphoric acid and hme,
the application of which is becoming part of good farm prac-
tice in the Central West. Considering the wide extension of
*1. Marshall silt loam, Pottawattamie Co., Ia.
Bennett, H. H., Soils and Agriculture of the Southern States,
p. 332; New York, 1921.
2. Memphis silt loam, Grenada Co., Miss.
Robinson, W. O., et al., Variation in the Chemical Composition
of Soils; U.S. Dept. Agr., Bul. 551, June, 1917.
3. Cherokee silt loam, Cherokee Co., Kan.
Bennett, H. H., Soils and Agriculture of the Southern States,
p. 332; New York, 1921.
4, Silt loam, Weeping Water, Neb.
Alway, F. J., and Rost, C. O., The Loess Soils of the Nebraska
Portion of the Transition Region, Part IV; Soil Sci., Vol. I,
No. 5, p. 431, May 1916.
64 NATURE AND PROPERTIES OF SOILS
the loess and the great variety of climate and cropping to
which it is subject, it may be classed as one of the world’s
most important soils. In the United States it is the great
maize-producing soil of the upper Mississippi Valley.
36. Other xolian soils.—The term ‘‘adobe’’ is applied to a
fine calcareous clay or silt formed in a manner somewhat
like loess. It is supposed that, while part of the deposit came
from the waste of talus slopes as mountains were weathered
under conditions of aridity, the remainder had eolian origin.
Certain characteristics also seem to indicate that the valley
adobe might have been deposited almost entirely by water.
It appears, therefore, that, while the physical characteristics
of all adobe are somewhat similar, its mode of origin and
chemical composition may be variable.
Like the loess, the adobe is an exceedingly rich soil, but
it occurs in an arid or a semi-arid region. When irrigated
its fertility seems inexhaustible. It is found in Colorado,
Utah, southern California, Arizona, New Mexico, and Texas.
It has an especially wide distribution in New Mexico. Like
loess, its elevation is variable, ranging from sea level in Cali-
fornia and Arizona to 6000 feet along the eastern border of
the Rocky Mountains. Its maximum thickness cannot be esti-
mated, as it is very little eroded and is supposed to be still
accumulating. Some valleys are known to be filled to a depth
of 3000 feet with this material. Its characteristics are its
fine texture, its great depth, its wide distribution, and its
great fertility when moisture conditions are suitable for crop
growth.
Sand dunes are the outgrowth of two conditions—a large
quantity of sand and a wind that blows in a more or less
prevailing direction. Under such conditions the sand and
other fine materials are not only blown into heaps, but also
tend to move in the direction of the prevailing wind. Sand
dunes may often assume gigantic proportions, sometimes be-
ing several hundred feet high and twenty or thirty miles
GEOLOGICAL CLASSIFICATION OF SOILS 65
long. In such proportions they become a grave menace to
agriculture, not only because they are an absolutely valueless
medium for plant growth, but also because they cover fertile
lands and entirely blot out all vegetation.
From early geologic times deposits of the very fine material,
that is continually being ejected from volcanoes, have been
distributed over the earth’s surface. These deposits are
usually flour-like, and while at one time they probably cov-
ered many square miles of territory, they have succumbed
very largely to erosion and denudation, and only remnants
are found at the present time. Such material may be found
in Montana, Nebraska, and Kansas. AXolian deposits of this
character are usually rather porous and light, and are likely
to be highly siliceous. They are not of great agricultural
importance, except in certain localities.
37. Resume.—The geological classification of soils pro-
vides a logical basis for the discussion of the formation, char-
acter, and agricultural value of soils in general. A detailed
consideration on any other basis would lead to endless con-
fusion and repetition. In classifying soils a study must be
made not only of the past effects but of the present influences
of the soil-forming processes, and while the conclusions and
observations are apparently purely agricultural in nature,
they really spring from a geochemical foundation.
With such a classification at hand one cannot fail to under-
stand the occurrence of so many distinct and different types
of soil. It is really difficult to see why soils do not present
greater differences and why transition types do not utterly
prevent clean-cut field distinctions. In such soil study the
all-important character of climatic control must always be
remembered. Weathering is strictly a climatic influence and
crop adaptation is usually dominated by climate rather than
by soil.
CHAPTER IV
THE SOIL PARTICLE AND CERTAIN IMPORTANT
RELATIONS
AN examination of a soil, however cursory, immediately
reveals that it is made up of irregular fragments of mineral
material mixed and more or less coated with organic matter.
These fragments, varying in size from particles easily discern-
ible by the naked eye to particles so fine as to be invisible
under the ultra-microscope, determine to a very large degree
the complex relationships of soil to plant. The movement of
air in the soil, the circulation of the water, chemical reactions
resulting in solution, and the presence and virility of the
various organisms are determined largely by the size of par-
ticles making up a soil and by the proportion and condition
of the organic material present. In expressing the size or
sizes of particles making up a soil, the term textwre is used.
Thus a soil texture may be coarse, medium, or fine, indicating
that the particles making up the soil conform in general to
such description.
Texture is a condition which can . but little modified in
a normal soil. We have seen how a rock ean be disintegrated,
decomposed and gradually built into a soil. A change in
texture has been wrought, but such a process demands geo-
logic ages for its fulfillment. In the time covered by the life
of man, the necessary forces are not active enough to have
this effect; consequently, as far as the farmer is concerned,
the texture of the soil in his field is subject to but slight
alteration. A sand remains a sand and a clay remains a clay,
as far as practical considerations are concerned. Changes
66
THE SOIL PARTICLE 67
in texture may be made on a small scale by mixing two soils,
but this is not practicable in the field.
38. Separation and classification of soil particles—In
order that the particles of soil, varying so tremendously in
size as they do, may be studied successfully, they must be
separated into groups according to their diameters. The va-
rious groups are spoken of as soil separates. Such a grouping
is of course arbitrary, and must meet certain theoretical as
well as practical requirements. It must be simple, short, and
eapable of expressing in a practical way the physical char-
acter of the soil. Moreover, it must lend itself to the actual
separation and percentage evaluation of each group. This
analytical procedure is called a mechamcal analysis.
With the large number of different methods of mechanical
soil analyses, there has arisen considerable variation in tex-
tural groupings expressed in diameter of particles. This
would naturally occur because of the differences in degree of
refinement, which the various methods of separation allow,
and also because of the uses which the investigators wished to
TABLE XI
THE NAMES AND RANGES IN SIZE OF SOIL PARTICLES AS ESTAB-
LISHED BY THE BUREAU OF SOILS CLASSIFICATION!
SIzE IN FINE SANDY
SEPARATE MILLIMETERS LOAM CLAY
m.m. % %
1. Fine Gravel.... a af i
2. Coarse Sand... 5 2 2
3. Medium Sand..)~ .5—.25 3 2
Aeinipe mand...) oe 25 10 Up 6
5. Very Fine Sand} .10—.05 35 7
RASpSaM eT) cle Soka tes 05 —— 2005 27 39
Legh CLEh eee nse .005 and below 10 43
* Briggs, L. J., et al., The Centrifugai Method of Soil Analysis; U. 8S.
Dept. Agr., Bur. Soils, Bul. 24, 1904.
68 NATURE AND PROPERTIES OF SOILS
make of such analyses. The grouping established by the
United States Bureau of Soils is met with in all soil literature
and is really the standard classification for this country.
Table XI sets forth the essential points of the Bureau of Soils
classification. In the first column are given the names of the
various separates, and in the second the range in size of each
group. Columns three and four show the percentages of each
separate in two very different specimen soils, a sandy loam
and a clay. In order to obtain such figures, a sample of the
dry soil must actually be separated into the arbitrary groups
and the percentage of each group to the whole soil calculated
from the dry weights obtained. This operation is the mechan-
ical analysis already mentioned.
This classification establishes seven distinct groups' rang-
1VARIOUS TEXTURAL CLASSIFICATIONS OTHER THAN THAT OF THE
BurREAU OF Sorts USED IN THE MECHANICAL ANALYSES
oF SoIts. EXPRESSED IN DIAMETER OF PAR-
TICLES IN MILLIMETERS
SEPARATE OSBORNE? HILGARD? ENGLISH? ATTERBERG*
1 3.00-1.00 3.00-1.00 1.00 - .200 20.00 -2.00
2 1.00- .50 1.00- .50 .20 - .040 2.00 - .20
3 .00- .25 .50- .30 .04 - .010 .20 - .02
4. .20- .05 .00- .16 01 - .002 .02 - .002
5 .05- .01 .16- 12 .002- — .002- —
6 .01- — 12-07
and six
other divisions
1QOsborne, T. B., Methods of Mechanical Soil Analysis; Ann. Rep.
Conn. Agr. Exp. Sta., 1886, pp. 141-158; 1887, pp. 144-162; 1888, pp.
154-157.
*Tlilgard, E. W., Methods of Physical and Chemical Sotl Analysis ;
Ann. Rep. Cal. Agr. Exp. Sta., 1891-1892, pp. 241-257.
Hall, A. D. and Russell, E. J., Soil Surveys and Soil Analysts; Jour.
Agr. Science, Vol. IV, part 2, pp. 182-223, 1911.
* Atterberg, A., Die Mechanische Bodenanalyse und die Klasstfikation
der Mineralboden Schwedens. Internat. Mitt. f. Bodenkunde, Band II,
Heft 4, Seite 312-342, 1912. Schucht, F., Uber die Sitzwng der Inter-
nationalen Kommission fiir die Mechanische und Physikalische Boden-
untersuchung in Berlin am 31, October 1913; Internat. Mitt. f. Boden-
kunde, Band IV, Heft I, Seite 1-31, 1914.
THE SOIL PARTICLE 69
ing from fine gravel, readily visible to the naked eye, to the
clay separate, the largest particle of which is .005 of a milli-
meter or .0002 of an inch in diameter. The stone and large
eravel, while they figure in a practical examination and de-
scription of a soil in the field, obviously need not be considered
in such a elassification as this.
The seven separates may be thrown into two groups for
a preliminary examination on the basis of visibility to the
naked eye. The gravel and sand particles are readily seen,
while the silt and especially the clay particles are invisible
as individuals, although some of the larger silt particles may
be seen with the naked eye when suspended in water. The
gravel and sand, when dominant in a soil, give properties
known to every one as sandy, while if the soil is made up
largely of silt and clay, its plasticity and stickiness proclaim it
as clayey in nature. The characteristics of the two soils of the
above table may be read easily from their mechanical analyses.
The classification, therefore, meets the criteria already estab-
lished. It is simple, easy to remember, and is capable of
expressing, to a certain extent at least, the dominant physical
characters of soils. As will be shown below, it lends itself
to the quantitative separation of a soil, the so-called mechan-
ical analysis.
39. The beaker method of mechanical analysis— When
fragments of rock or soil are suspended in water they tend
to sink slowly, and it is a well recognized fact that, other
things being equal, the rate of settling depends on the size
of the particle. As the particle is decreased in size its weight
decreases faster than the surface exposed to the buoyant force
of the water. As a consequence the rapidity with which the
soil particles settle is more or less proportional to their size.
The suspension of a sample of soil would, therefore, be the
first step in mechanical separation by water; the second step
would be subsidence and the withdrawal of each successive
grade of particles as it slowly settled; the third step would
70 NATURE AND PROPERTIES OF SOILS
be the determination of the percentage of each grade, or group,
of particles as based on the original sample. This is precisely
what every method of mechanical analysis in which water is
utilized aims to do, although the irregularity in the shape of
the particles prevents to a certain extent a perfect separa-
tion. The apparatus and technique of the various methods
employed are generally rather complicated.
One of the earliest and most useful methods to be perfected
was the separation of the various grades of soil by simple
subsidence in a column of still water. This is commonly
spoken of as the Osborne beaker method.t The determination
is very simple. The soil sample is first fully deflocculated and
thrown into suspension, each particle functioning separately.
Beakers are commonly used as containers, but any vessel that
is relatively deep will do for the determination. The larger
particles, gravel and sand, will of course settle first, and the
finer silts and clays may be decanted off. As the sands carry
finer particles down with them, the suspension and subsidence
must be repeated a number of times. The sands are later
dried and sieved into their respective groups. The silt and
clay particles, thus decanted, may be separated from each
other by subsidence as above described. The time necessary
for such decantation as will leave in suspension only particles
below a given size is determined by the examination of a drop
of the suspension under a microscope fitted with an eyepiece
micrometer. In this way the size of the particles decanted
may be measured accurately. (See Fig. 14.)
The four steps in this method of separation are: defloccula-
tion of the sample; separation by successive subsidence and
decantation ; evaporation to dryness of the separates and the
sieving of the sands; and the weighing of the separates and
the calculation of percentages based on the original dry sam-
*Osborne, T. B., Methods of Mechanical Soil Analysis; Ann. Rep.
Conn. Agr. Exp. Sta., 1886, pp. 141-158; 1887, pp. 144-162; 1888, pp.
154-157.
THE SOIL PARTICLE 71
ple. The method, however, is slow, as the time necessary for
each subsidence of the finer particles is very great and the
number of individual subsidences is large. As a consequence,
it has been superseded by methods that utilize centrifugal
force for the finer separations, while retaining gravity for
removing the various grades of sand.
Fig. 14.—Diagram showing the relative sizes of soil particles as they
appear under a microscope with eye-piece micrometer. Particles
one space or less in diameter are clay; from one space to ten, silt
and above ten spaces, very fine sand.
40. Bureau of Soils centrifugal analysis—Of the cen-
trifugal methods used in mechanical analysis that employed
by the United States Bureau of Soils' is the most successful.
A five-gram sample of well-pulverized soil is put into a shaker
bottle of about 250 cubic centimeters capacity. This bottle
is filled about two-thirds full of water so that in shaking the
disintegrating force of the liquid may be utilized. A few
1 Fletcher, C. C. and Bryan, H., Modifications of the Method of Soil
Analysis; U.S. Dept. Agr., Bur. Soils, Bul. 84, 1912.
72 NATURE AND PROPERTIES OF SOILS
drops of ammonia are added to dissolve the organic matter
and to make deflocculation easier. The sample is then agi-
tated in the bottle until disintegration is complete. This
period ranges from five to twenty hours, depending on the
sample. (See Fig. 15.)
The separation of the silt and the clay from the sands is
made in the shaker bottle by simple subsidence, the time for
decantation being determined by a microscopic examination
of a drop of the suspension. The silt and the clay are de-
canted directly into a test-tube fitted into a centrifuge. Whirl-
ing at the rate of 800 to 1000 revolutions a minute will cause
the subsidence of the silt to the bottom of the test-tube in a
few minutes. The clay is then decanted. The microscope is
necessary here in order to determine when the settling of the
silt is complete. As small particles tend to cling to the larger
particles the entire operation must be repeated several times;
therefore the processes of gravity subsidence and centrifugal
subsidence are carried on side by side, material being con-
stantly poured from the shaker bottle into the centrifuge tubes
and from the test-tubes into the receptacles for the clay.
The centrifuge is usually large enough to allow the separa-
tion of several duplicate samples at once. The various sep-
arates made by this method are dried and weighed. The
sands, which are obtained in bulk, are further separated by
Sieves into the grades desired. When a large quantity of
organic matter is present it must be determined and included
in the final report on the sample.
This method of mechanical analysis as perfected by the
Bureau of Soils has been very commonly adopted by soil work-
ers. It has many advantages over other methods.‘ In the
first place, it is rapid, often requiring only hours where other
* Classification of the Various Methods of Mechanical Analysis:
{ Wet
ts Steve < or
Dry
’ Used to separate sands in practically all
methods.
THE SOIL PARTICLE 73
methods take days for completion; secondly, it is simple, and
the technique of the separation is easily acquired; thirdly, in
the decantations no very large amount of water is accumulated
with the separates, except for the clay, and thus the time and
cost of evaporation is reduced. The clay, moreover, may be
as accurately determined by difference as by direct methods,
thus allowing a further saving of time. While the method
is accurate only within one per cent., it is sufficiently precise
for all practical purposes.
41. Physical characters of the soil separates.—It is im-
mediately apparent that as these groups vary in size they
must exhibit properties, especially physical ones, which are
widely different. These properties should in turn be imparted
to the soil of which the separates form a part. If a person is
2. Air —— (Cushman’s? air elutriator).
{ Gravity (Schéne’s? elutriator
] and Hilgard’s* churn elutria-
In motion } tor).
! Centrifugal (Yoder’s * Centrifu-
gal elutriator).
Se ctr erases (Osborne’s beaker
method and Atterberg’s® modi-
At rest fied silt cylinder).
Centrifugal (Bureau of Soils
method).
For a detailed discussion of all methods of mechanical analysis see
Wiley, H. W., Agricultural Analysis, Vol. I, pp. 195-276; Easton, Pa.,
1906.
*Cushman, A. S. and Hubbard, P., Air Elutriation of Fine Powders;
Jour. Amer. Chem. Soc., Vol. 29, No. 4, pp. 589-597, 1907.
?Schone, E., Uber Schlimmansalyse; Bul. Soc. Imperiale des Natural-
istes de Moscow, 40, Part 1, p. 324, 1867. Uber Schlimmanalyse und
einen neuen Schlémmapparat; Berlin, 1867. Also see Wiley, H. W.,
Agricultural Analysis, Vol. I, pp. 231-241; Easton, Pa., 1906.
*Hilgard, E. W., Methods of Physical and Chemical Soil Analysis;
Ann. Rep. Calif. Agr. Exp. Sta., pp. 241-257, 1891-1892.
“Yoder, P. A., 4 New Centrifugal Soil Elutriator; Utah Agr. Exp.
Sta., Bul. 89, 1904.
° Appiani, G., Uber einen Schlimmapparat fur die Analyse der Boden-
und Thonarten; Forsch. a.d. Gebiete d. Agri-Physik, Band 17, Seite 291-
297, 1894. Atterberg, A., Die Mechanische Bodenanalyse und die Klassi-
fikation der Mineralboden Schwedens; Internat. Mitt. f. Bodenkunde,
Band II, Heft 4, Seite 312-342, 1912.
74 NATURE AND PROPERTIES OF SOILS
conversant with these various values, a mechanical analysis
should reveal at a glance certain soil conditions, which may
or may not be conductive to the best plant growth.
The sands and the gravel, because of their sizes, function
as separate particles. They are irregular and rounded, the
continual rubbing that they have received being sufficient in
many cases to have ef-
faced their angular char-
acter. They exhibit very
low plasticity and cohe-
sion, and as a consequence
are little influenced by
changes in water content.
Their water-holding ea-
pacity is low, and because
of the large size of the
spaces between each sep-
arate particle the passage
of percolating water is
rapid. They, therefore,
facilitate drainage and
encourage good air move-
Fic. 15.— Apparatus for making a ment. In all the grades
mechanical analysis of soils. of sand, the separate par-
Shaker-bottle (4), shaking-rack (B), ticles are visible to the
sieves (C), centrifuge (D) and c¢en- Pies
trifuge-tube (F). naked eye, a condition
impossible with the silt
and clay groups. Soil containing much sand or gravel, there-
fore, is of open character, possessing good drainage and
aération, and is usually in a loose friable condition.
The clay and silt particles are very minute, many of the
former being so small as to be invisible under the ultra-micro-
scope. Both groups are really shreds and fragments of min-
erals often rather gelatinous in nature. The clay particles
are highly plastic and when kneaded with just the correct
THE SOIL PARTICLE 75
amount of water they become sticky and impervious. On dry-
ing, they shrink with the absorption of considerable heat. On
wetting, again swelling occurs. The absorptive capacity of
clay material for water, gases, and soluble salts is very high,
due to the presence of colloidal material. As material in a
colloidal condition is very finely divided, it is found largely
in the heavier types of soil. Some clays carry very large
amounts of material in a colloidal state. Silt possesses the
same properties of plasticity, cohesion, and absorption as does
clay, but to a less extent, because the particles of the former
are larger than those of the latter. The presence of silt and
especially clay in soil imparts to it a heavy texture, with a
tendency to slow water and air movement. Such a soil is
highly plastic, but becomes sticky when too wet, and hard
and cloddy when too dry. The expansion and the contraction
on wetting and drying are very great. The water-holding
capacity of a clayey or silty soil is high. Such soils are spoken
of as heavy because of their working qualities in the field in
contrast to the easily tilled sandy soils.
42. The mineralogical and chemical characteristics of
soil separates—From the mineralogical standpoint there
are often considerable differences between the soil separates,
especially when the sands and clays are compared. Quartz
would naturally be expected to persist and because of its low
solubility would very soon be dominant not only in the coarser
separates but in the silt and clay as well. Other minerals,
such as the feldspars, hornblende, mica, and augite being less
resistant would concentrate in the finer separates. This tend-
1 The colloidal state—when material is in a very fine state of division,
approaching but not attaining a molecular condition (true solution), it
assumes certain characteristic properties, such as high absorption for
water, gases, and salts in.solution. It may also, under certain conditions,
cause a marked increase in plasticity and cohesion. The colloidal con-
dition is purely physical and depends -on fineness of division, the
particles being molecular complexes. Material in a colloid state is
heterogeneous and is dispersed through a second material called the
dispersive medium.
76 NATURE AND PROPERTIES OF SOILS
eney together with the formation, as weathering proceeds,
of the fine coloidal-like epidote, chlorite and similar groups,
should in general keep the percentage of minerals other than
quartz higher in the finer portions of a soil.t_ The following
data sustain this assumption :
TABLE XII
MINERALS OTHER THAN QUARTZ IN THE SANDS AND SILTS OF
VARIOUS SOILS ”
MINERALS OTHER THAN QUARTZ IN
SOILS
SANDS SILTS
IP IRESTOMI Ae eee etelate 15% 21%
6 Glacial and Loessial 12 15
4A Marines2 040. eit were 5 18
PENG Wig 3 We ae RR AVE ee onl 42
It is to be seen immediately that in every case the silt car-
ries a large quantity of the important soil-forming minerals
and a smaller amount of quartz than does the sand. This re-
veals at least one of the reasons for the greater fertility and
lasting qualities of fine-textured soils as far as agricultural
operations are concerned. It is important to note, however,
1A petrographic analysis as now developed is very unsatisfactory as it
throws practically no light on the character of the clay group because
of the extreme fineness of this material. Even for silt the results are
unsatisfactory and difficult to express quantitatively. The correlation
of a petrographic analysis and productivity is vague.
*McCaughey, W. G., and Fry, W. H., The Microscopic Determina-
tion of Soil-forming Minerals; U. 8. Dept. Agr., Bur. of Soils, Bul. 91,
1913. See also, Plummer, J. K., Relation of the Mineralogical and
Chemical Composition to the Fertility Requirements of North Carolina
Soils; N.C. ‘Agr:, Exp. Sta., Tech.’ Bull 9, 1914. Plummerte ss
Petrography of Some North Carolina Soils and its Relationship to their
Fertilizer Requirements; Jour. Agr. Res., Vol. V, No. 13, pp. 569-581,
1915. Robinson, W. O., The Inorganic Composition of Some Important
American Soils; U. S. Dept. Agr., Bul. 122, Aug., 1914. Shorey, F. C.,
et al., Calcium Compounds in Soils; Jour. Agr. Res., Vol. VII, No. 3,
pp. 57-77. Jan., 1917.
THE SOIL PARTICLE 77
that, although quartz is the predominating mineral in sands,
all the common soil-forming minerals are usually accessory.'
It is interesting in passing to observe the differences ex-
hibited by the various soil provinces although the number of
samples shown by Table XII are far too small for definite
conclusions. The marine soils are particularly low compared
with the residual and glacial, due to the hard usage which
the soil material of the former has received. No significant
differences exist between the glacial and residual soils. The
arid soils, however, are markedly higher in the important min-
erals due to the suppression of chemical weathering and the
activity of the physical agents. The silica in such soils is
held as complex silicates, which carry the elements that are
so important in plant development. Although these data are
based on but a few samples, they are so concordant with what
would naturally be expected that these general conclusions
eannot be avoided.
The mineralogical examination has revealed a larger per-
centage of such minerals as feldspars, mica, hornblende, and
the like, in the finer separates. A larger percentage of the
important nutrient elements would, therefore, be expected in
those groups. The following data,? compiled from work per-
formed by the United States Bureau of Soils, substantiate this
assumption. (See Table XIII, page 78.)
It is evident that the finer portions of soil are in general
1 Below is given the mineralogical description of a loessial silt loam of
the Marshall Series from Missouri: Robinson, W. O., The Inorganic
Composition of Some Important American Soils; U. 8. Dept. Agr., Bul.
122, Aug., 1914.
Very fine sand—minerals other than quartz, 20 per cent. Orthoclase,
10 per cent. Muscovite, 2 per cent. Biotite, magnetite, epidote, albite,
labradorite, oligoclase, tourmaline, zircon, garnet, and augite are also
present.
Silt—Minerals other than quartz, 34 per cent. Orthoclase, 4 per cent.
Muscovite, 4 per cent. Biotite, magnetite, epidote, albite, labradorite,
oligoclase, tourmaline, rutile, glaucophane, hornblende, and augite are
also present.
2 Failyer, G. H., and Others, The Mineral Composition of Soil Particles ;
U.S. Dept. Agr., Bur. Soils, Bul. 54, 1908,
78 NATURE AND PROPERTIES OF SOILS
TaBLE XIIT
CHEMICAL COMPOSITION OF VARIOUS SOIL SEPARATES
NuM-|PERCENTAGE OF ||PERCENTAGE OF|| PERCENTAGE OF
BER OF P.O, IN K,0 IN CaO IN
Sorts are ; phigh eh
PLES. |Sanp|Siut |CLAy||SAND|SILT |CLay Sanp | SILT |CLAY
Crystalline
Residual ... 30% |) 2227) 370") 1602.37 12:86 50 82) 94
Limestone
Residual ... 3 | .28 | .23 | .387 ||1.46/1.83 | 2.62 || 12.26] 10.96 | 9.92
Coastal Plain. | OS¥ MOw oa: S| Migs || IL; .O7 19} .55
Glacial and
Loessial ... LOM alae 2ome Sond arenas OrenOit 1.28) 1.30 | 2.69
sANT CL) Us icone aes 2 | 19 | .24 | .45 || 3.05 |4.15 | 5,06 4.09 | 9.22 |8.03
richer in phosphoric acid, potash and lime than the coarser.
As would be expected the sands, silts, and clays of arid soils
show less difference than those of the other provinces. Under
arid conditions the sands have not as yet become depleted of
their store of essential elements. Average figures compiled
from Hall’s analyses* of soils from southeastern England ecor-
roborate the data already noted. In addition, Hall shows that
the magnesia, iron, and alumina are higher in the finer sep-
arates while there is considerably more silica in the sand
groups.’
1Hall, A. D., and Russell, E. J., Soil Surveys and Soil Analyses;
Jour. Agr. Sci., Vol. LV, Part 2, p. 199, 1911. Also A Keport of the
Agriculture and Soils of Kent, Surrey, and Sussex; Board of Agriculture
and Fisheries, 1911. See also: Loughridge, R. H., On the Distribution
of Soil Ingredients among Sediments Obtained in Silt Analyses; Amer.
Jour. Sci., Vol. VII, p. 17, 1874. Puehner, H., Uber die Vertielung von
Ndhrstoffen in den Verschieden Feinen Bestandteilen des Boden; Landw.
Ver. Stat., Band 66, Seite 463-470, 1907. Hendrick, J., and Ogg, W. J.,
Studies of Scottish Drift Soil, Part I. The Composition of the Sotl and
of the Mineral Particles Which Compose It; Jour. Agr. Sci., Vol. VII,
Part 4, pp. 458-469, Apr. 1916. McGeorge, W. T., Composition of Ha-
watian Soil Particles; Haw. Agr. Exp. Sta., U. S. Dept. Agr., Bul. 42,
Jan., 1917. Robinson, G. W., Studies of the Palezoic Soils of North
Wales; Jour. Agr. Res., Vol. VIII, Part 3, pp. 380-381, June, 1917.
*McGeorge’s investigation of the residual voleanie soils of Hawaii
shows some noteworthy exceptions to the work of Failyer and Hall in
THE SOIL PARTICLE 79
TABLE XIV
COMPOSITION OF SOIL SEPARATES (HALL)
SEPARATE
SiO, | Al,O, | Fe,O,}CaO |MgO| K,0O |P,0,
Coarse Sand (1—-2 mm.) | 93:9) 1.6) 1.2) 4) .5) .8| .05
Binersand (2—04 mm.) | 94.0): 2:0) 1.2) | .2)1.5) 1
Silt (.04—.01 mm.) SNe! be 285) 9.38'|-2.3))) 1
Fine Silt (.01—.002 mm.)| 74.2) 13.2; 5.1/1.6) 3) 4.2) 2
Clay (Below .002 mm.) Forene2do Ls.2 1.6) 104.9 | 4
43. Value of a mechanical analysis.—It is evident that a
proper interpretation of a mechanical analysis will throw con-
siderable light on the probable condition of a soil, especially
physically. To the trained observer the preponderance of
sand, clay, or silt signifies the probable presence of certain
physical properties, which may affect the plant not only me-
chanically but physiologically as well, through air, water, and
nutrient movement.
The chemical and mineralogical phases of such interpreta-
tion are also worthy of consideration, as the proportion of the
various separates determines whether the essential nutrient
will be present in sufficient quantities to permit normal crop
growth. Thus a mechanical analysis not only enlightens as
to the general properties of a given soil, but when correlated
with other factors is to some extent a criterion of agricultural
value and crop adaptation. Some authors maintain that in
the investigation of any soil a mechanical analysis should first
be made, as it throws much light on many properties of a soil.
44. Soil class—how soils are named.—aAs a soil is not
eomposed of particles of uniform size and shape, a blanket
term is needed, which will not only give some idea of the
textural character of the mixture, for every soil is a mixture,
that he found the lime and magnesia higher in the coarser particles and
the silica higher in the finer separates. McGeorge, W. T., Composition
of Hawaiian Soil Particles; Haw. Agr. Exp. Sta., Bul. 42, Jan. 1917.
80 NATURE AND PROPERTIES OF SOILS
but at the same time will name it in such a manner as to reveal
its general physical peculiarities and proportions. For this
class names, such as sandy loam, loam, silt loam, and the
like, are used. Class differs from texture, however, in that it
has reference to the properties exhibited by a soil rather than
GRAVEL SAND LOAM CLAY
Fic. 16.—Diagram showing in a general way the mechanical compo-
sition of gravel, sand, loam and clay soils and indicating in addi-
tion how some of the more common field names arise.
to any absolute grain size. Consequently, there may be a
number of class names depending on the proportionate mix-
tures of different sized particles that occur in the field.
Class names have originated through long centuries of agri-
cultural observations, but of late they have been more or less
standardized because of the necessity of a definite nomen-
clature. In general, the names used for the soil classes are the
THE SOIL PARTICLE 81
same as those employed in mechanical analyses to designate
the soil separates. This is rather unfortunate, but it obviates
the increase of technical terms and a Little care will prevent
confusion in this regard. Four fundamental groups of soil
are recognized: gravel, sand, loam, and clay (See Fig. 16).
Gravel is a soil constituent that does not often occur alone
and is not of great importance agriculturally because of its
low fertility. The other three, however, either alone or in
combination make up most of the arable soil. Their average
mechanical analyses are set forth in Table XV.
TABLE XV
MECHANICAL ANALYSES OF SANDY, LOAMY AND CLAYEY SOILS!
SANDY LOAMY CLAYEY
SEPARATES Soin Soin Soin
To To Jo
ie Nine Gravel... ../3::. 2 2 1
DeeCoarse Sand) aw. ic: 15 5 3
SovMedinm Sand: 3.5.5: 23 5 2
APO IBE SANG. hove. icc cs > 30 15 8
5. Very Fine Sand.... il 17 8
Genter ea’ wrk eereislees ee fi 40 36
Of (CHE a ae es Sea ee 5 16 42
The sand group includes all soils of which the silt and clay
separates make up less than 20 per cent of the material by
weight. Its properties are, therefore, characteristically sandy
in contrast to the more open character of gravel and the
stickier and more clayey nature of the heavier groups of soil.
A soil to be clay must carry at least 30 per cent. of the clay
separate. It may even have more silt than clay but, since
the silt particles impart clayey characters, as long as the per-
centage of clay is 30 or above, the class name must remain
elay.
*Whitney, M., The Use of Soils East of the Great Plains Region;
U.S. Dept. Agr., Bur. Soils, Bul. 78, p. 12, 1911.
82 NATURE AND PROPERTIES OF SOILS
The loam class is rather difficult to explain. In mechan-
ical composition it is more or less midway between sand and
clay. A loam may be defined as such a mixture of sand, silt,
and clay particles as to exhibit sandy and clayey properties
in about equal proportions. It is a half and half mixture
on the basis of properties, although the sum of the sands and
the sum of the silt and clay are generally near 50 per cent.,
respectively. (See Fig. 16.) Because of the marked inter-
mixture of coarse, medium, and fine particles, loams are
usually soils of good physical character. They generally pos-
sess the desirable qualities both of sand and clay without
exhibiting those undesirable properties, such as extreme loose-
ness and low water capacity on the one hand and stickiness,
compactness, and slow air and water drainage on the other.
Most of the better soils are some type of loam.
It is obvious that in the field not only various kinds of
gravelly, sandy, loamy, and clayey soils must occur, but the
groups must grade into each other, thus giving rise to a con-
siderable number of field names. (See Fig. 16.) These field
names are listed below:
Common Class Names
1. Gravel 9. Very fine sandy loam
2. Coarse sand 10. Loam
3. Medium sand. 11. Silt loam
_4, Fine sand 12. Silty clay loam
5. Very fine sand 18. Clay loam
6. Coarse sandy loam 14. Clay
7. Sandy loam 15. Heavy clay
8. Ine sandy loam 16. Sandy clay
The meaning of these names should be clear except possibly
those into which the loam group is divided. Loam, as already
explained, refers to a soil possessing in about equal amounts
the properties imparted by the various separates. If, how-
ever, we have practically the same condition but with one
THE SOIL PARTICLE 83
size of particle predominating, the name of that particular
separate is prefixed, giving still more data regarding the soil
in question. Thus, a loam in which clay is dominant will be
classified as a clay loam. In the same way, we may have a
sandy loam, silt loan, and so on. It is to be noted that the
loams make up half of the class names. In fact, the greater
proportion of the soils so far classified in the United States
are loams, which is fortunate as the loams in general are more
favorable for crop production than any of the other class
groups.
The mechanical analyses of some of the more common
classes! are listed in Table XVI:
TABLE XVI
Fine |Coarse |MeEpIuM | FINE — s
Gravet | SAND SAND SAND Syn ILT Cay
Coarse Sands....| 12 31 19 20 6 cf 5
SH ats (an 2 5 23 37 al ff i
Fine Sands...... iI 4. 10 Sirf 17 {( 4
Sandy Loams....| 4 | 13 12 25 13 21 12
FineSandy Loams| 1 3 4 | 32 | 24 24 | 12
Gamishsct. sien 2 5 5 15 i Ly 40 16
Silt Leams ss: .. 1 2 1 5 11 65 15
Sandy Clays..... 2 8 8 30 12 Se ae
Clay Loams...... 1 4 4 14 13 38 26
Silty Clay Loams} 0 2 a 4 i 61 | 25
LOLS Slee a como i a 2 8 8 36 42
It is evident that a mechanical analysis of a soil is nothing
more or less than an expression of class, and the inferences
that may be derived from either are in general the same. This
leads to a consideration of class determination.
45. Determination of soil classes——The common method
of class determination is that employed in the field. It con-
* Whitney, M., The Use of Soils East of the Great Plains Region;
U.S. Dept. Agr., Bur. Soils, Bul. 78, p. 12, 1911.
84 NATURE AND PROPERTIES OF SOILS
sists in an examination of the soil as to color, an estimation of
its organic content, and, especially, a testing of the ‘‘feel’’ of
the soil in order to decide as to the class name. Probably as
much can be judged as to the texture and class of a soil merely
by rubbing it between the thumb and the fingers or in the
palm of the hand as by any other superficial means. This
method is used in all field operations, especially in soil survey
work. It really consists in sufficiently recognizing the textural
composition of a soil that the class name may be determined.*
The accuracy of such a determination depends largely on
experience. Inaccuracies are likely to occur in distinguishing
between the various finer grades of soil; for this reason, more
nearly exact methods are necessary at times, especially in
checking soil survey work or in carrying out investigations in
which absolute accuracy is required.
As a mechanical analysis of a soil is really a percentage
expression of texture, it presents an exact method for class
determination. For detailed work, somewhat complicated
tables? have been arranged; but the following diagram
1 Key for the practical classification of mineral soils:
I. Soils possessing the properties of one size of
particle largely.
iS sParticlestvenyalarcesseprsmiseioceceieiettets Gravel
2. Particles apparent to eye; feel gritty and
Non=plastles).v2s/ch.)- noes een tes ete Sands
3. Particles very small; soil very plastic when
Wet marduwihe nn cinyaraletersrdtaiet risers itelene Clay or
Sandy Clay
Il. Soils possessing the properties of a number of
sizes of particles—a mixture.
1. A fairly equal exhibit of sandy and
clayey, Properties... cm aes -)-calye let eee Loam
2. A mixture but with sand predominating. ..Sandy Loam
3. A mixture but with silty character dom-
inant. The soil has a floury or tale feel
and is quite plastic when wet ............ Silt Loam
4, A mixture but with clayey characters very
apparent. Soil is very plastic and ap-
proaches a clay in character ............ Clay Loam
2 Bur. of Soils, Soils Survey Field Book, p. 17; U. S. Dept. Agr., Bur.
Soils, 1906. Also, Bur. Soils, Bul. 78, p. 12, 1911.
THE SOIL PARTICLE 85
(Fig. 17), devised by Whitney,’ presents a simple method for
the identification of a soil from a mechanical analysis. The
convenience of such a triangular representation is obvious.
CLAY
100
90
80|
0 10 20 30 40 50 60 70 60 99 100°”
PER CENT
Fig. 17—Diagram for the determination of class from a mechanical
analysis. In using the diagram the points corresponding to the
percentages of silt and clay are located on the silt line (abscissa)
and clay line (ordinate) respectively. Perpendiculars at these
points are then projected inward until they intersect. The name
of the compartment in which the intersection occurs gives the class
name of the soil in question.
46. Soil survey classification—soil type—The function
of the soil survey is to investigate the nature and occurrence
1Whitney, M., The Use of Soils East of the Creat Plains Region;
U. S. Dept. Agr., Bur. Soils, Bul. 78, p. 13, 1911.
86 NATURE AND PROPERTIES OF SOILS
of soils in the field. The soils thus studied are classified into
areas having approximately the same crop relations and tillage
properties. The location of the areas of each kind of soil is
represented on an adequate base map, and their character and
chief economic and agricultural relations are described in a
printed report accompanying the soil map.t (See Fig. 18).
In classifying soils six primary factors are considered.
These, beginning with the broadest, are as follows: (1) tem-
perature, (2) precipitation, (3) agency of formation, (4) kind
of material, (5) special properties other than texture, and
(6) texture. It is obvious that certain soils may be of different
texture but alike in all other ways. Their climatic environ-
ments, mode of formation, rock materials, and specific prop-
erties, such as color, drainage, organic condition, and lime
content may be approximately the same. Such soils are
grouped together as series and the series are named, generally
from some town, county, or river of the near vicinity. Thus
we have the Norfolk series of the Atlantic coastal plain; the
Cecil soils of the Piedmont Plateau; the Ontario series arising
from the calcareous till of central New York state and the
Marshall soils of the loessial region of the Middle West. The
soils within each series are approximately the same except for
class distinction.
The soil type is the unit of classification and may be defined
as an area of soil alike in all characteristics, including crop
productiveness. Obviously any soil class of any particular
series would be a soil type. Norfolk sandy loam, Ontario loam,
and Cecil clay are examples of how soil types are designated.
The type designation is especially valuable in soil description
since the series name expresses in one word a great number of
conditions, which otherwise would require detailed explana-
tion. The class name establishes in addition the textural con-
dition.
1For further information consult one of the numerous soil survey
reports as published by the U. 8S. Dept. Agr., Bur. of Soils.
PLATE 1
Bul. 60, Bureau of Soils, U. S. Dept. of Agriculture.
——- 7 . \ :
] SI :
Volusia Volusia Dunkirk Huntington Dunkirk Muck
silt loam loam gravelly doam loam clay
Fic. 18.—Part of the Madison County, New York, soil map showing the
topography and drainage and the relation of the various soil types
to one another. The Volusia series arises from the ground moraine,
the Dunkirk from glacial lake sediments while the Huntington is
alluvial. Note the varying elevation of the muck.
THE SOIL PARTICLE 87
While the principles of series identification are too com-
plicated to be expanded farther at this time, enough has been
said to establish the importance of accurate soil classification.
Unless soils are accurately named in soil survey work, the map
and its accompanying report are useless.
Soil texture and class are thus the basis for practical soil
study, whether regarding some particular property or a gen-
eral condition, such as crop adaptation. No matter what the
phase of soil study may be, texture and class are sure to have
some important influence and must be considered in the in-
vestigation.
47. Soil structure.— While texture is of great importance
in determining the general characteristics of a soil, it is evi-
dent that the arrangement as well as the size of the particles
must exert some influence. The term structure is used to refer
to this arrangement or grouping. It is at once apparent that
soil conditions—such, for example, as air and water move-
ment, heat transference, and the like—will be as much affected
by structure as by texture. As a matter of fact, the great
changes wrought by the farmer in making his soil better
suited as a foothold for plants are structural rather than
changes in texture. The compacting of a light soil or the
loosening of a heavy one is merely a change in the arrange-
ment of the soil grains and in the condition and nature of the
colloidal complexes! thereof.
From the standpoint of size and arrangement of particles
there are really two classes of soils, those of single grain struc-
ture and those which are complex, the particles both large
and small being bound together by indefinite colloidal com-
plexes. The former condition is of course best exemplified
by a sand. Such a soil is loose and open with large individual
pore spaces and ready circulation of air and water. The com-
*Material in a colloidal state has a great deal to do with all soil
phenomena. Its characteristics and influence must be kept constantly in
mind in soil study.
88 NATURE AND PROPERTIES OF SOILS
plex structure is best developed in clay. Here the soil gran-
ules are made up of many particles, the colloidal material act-
ing as a binding agent. Such a soil may be loose, open and
friable, if granules of the proper size and nature are developed.
On the other hand, improper handling may run the complexes
together and an impervious and puddled condition may result.
The sand will obviously permit of no very great structural
change, while the clay can be modified very materially by
certain field manipulations.
The ideal structural condition is most likely to occur in a
loam soil. In such a soil some of the particles are large and
function separately ; others are medium in size and tend to
form the nuclei around which smaller particles, both colloidal
and non-colloidal, may cluster to form granules, or aggregates.
There are thus a few large pore spaces which facilitate drain-
age, and numberless small openings in which water is retained.
Air, therefore, finds easy movement and sanitation is pro-
moted. In promoting such a condition the organic matter
plays an important part. It usually exists as a dark, partially
decayed material, often colloidal in nature. It pushes apart
the grains and lightens the soil, and contributes much in bring-
ing about the loamy condition so favorable to plant develop-
ment. It is a valuable addition also on account of its water-
holding capacity and its nitrogen content.
48. Specific gravity of soils—The texture, as well as the
structure of a soil, has considerable influence on certain phys-
ical conditions other than those already mentioned. One of
these is weight. The weight of a soil is determined by two
factors: the weight of the individual particles and the amount
of the space occupied by the soil material. The former is
determined by the chemical and mineralogical character of
the particles, the latter by their structural arrangement. Thus,
if the soil particles are heavy and the soil is compact, the
weight of any given volume, a cubic foot for example, will be
high.
THE SOIL PARTICLE 89
The specific gravity’ of a soil is obviously the average spe-
cific gravity of the particles. It is unaffected by the structure,
remaining the same whether the soil is loose and open or com-
pact and unaérated. Although a great range is observed in
the specific gravities of the common soil minerals’, the spe-
cific gravity of a purely mineral soil varies between the nar-
row limits of 2.6 and 2.7. This occurs because quartz and
feldspar, whose specific gravities are about 2.65 and 2.57,
respectively, usually make up the bulk of the mineral portion
of most soils. The fineness of the particles seems to have no
appreciable effect on specific gravity as shown by the follow-
ing data from Whitney and Smith*:
TABLE XVII
SPECIFIC GRAVITY OF SOIL SEPARATES
SEPARATES WHITNEY SMITH
CRAVEN, 24 S/.uie daa ewias< 4 2.64 2.67
@oarseusands 26 ues caaele ites ads 2.65 2.64
PASTS ATG 5. rua, gaan ioserele: =-aNeds 2.64 2.64
TEMAS) FSET 10 DA a eee 2.65 2.69
Were He SANG e265 «3 sevee en! 2.68 2.66
Se ee SER ear ad alee duets. 2 2.69 2.65
Bree ie Sen ak eS ne De8a 2.66
1Specific gravity is expressed as a ratio of the weight of any volume
of a substance to the weight of an equal volume of some other substance
taken as a standard unit. Liquids and solids are usually compared with
water at its maximum density (4° C.).
2The specific gravities of some of the common soil minerals are as
follows:
(QUIET nl encaie aeckemeeeponaee PAG OE 2 OM weAeutben eer sbsteesi 3.20
Orthoclase A PET Kaolinite yas sean 2.60-2.63
Plogtoclase™.. 2 .....-2.62-2.76 Serpentine... ... 6. . 2.50-2.65
Marscomiteme sae i eaO-oLO00es “Ohloriben se ctekic as sieicc 2.65-2.92
IBTObIe mE creer. be SDs) VM OGKOIEY Good a eo oc 3.25-3.50
Hiornblendes = a.sn. Rbesay lelanteynire: Gooaaudaos 4,.90-5.30
ANI, OS Series Se SSCA SOO) Winrar Soa onocndoc 3.60-4.00
> Whitney, M., Some Physical Properties of Soils; U. S. Dept. Agr.,
Weather Bur., Bul. 4, 1892. Smith, Alfred, Relation of the Mechanical
Analysis to the Moisture Equivalent of Soils; Soil Sei., Vol. IV, No. 6,
p- 472, Dec., 1917.
90 NATURE AND PROPERTIES OF SOILS
The only marked variation here observed is in the clay
separates of the first column. This may be due to the concen-
tration of the iron-bearing silicates in this grade and would
thus be an apparent rather than a real variation.
Only one condition may vary the specific gravity of any
soil. This is the quantity of organic matter present. As the
specific gravity of organic matter usually ranges from 1.2 to
1.7, the more that is present the lower will be the figure for
any given soil. A purely organie soil, such
as muck, presents a variable specific grav-
ity ranging from 1.5 to 2.0, according to
the amount of inorganic wash it has re-
ceived from external sources. Some highly
organic mineral soils may drop as low as
2.3. Nevertheless, for general calculations,
the average arable soil may be considered
to have a specific gravity of about 2.65.
The specific gravity of a soil is generally
Fic. 19.—Drawing determined by means of a picnometer, a
showing the type ‘
of picnometer bottle fitted with a perforated ground-glass
generally used in stopper and accurately calibrated (Fig.
determining the : 2
specific gravity of 19). By comparing the weight of the total
soil. The ground- water held by the bottle, usually 50 cubic
glass stopper 1s c é 3
perforated. centimeters, with the weight of the water
when any given amount of dry soil, say 5
grams, is present in the bottle, the weight of the water dis-
placed by the soil can be determined and the specific gravity
calculated therefrom.*
1 Below will be found a sample calculation:
Weight of picnometer ..........-.-2---seeeeeeees 23.257 grs.
Volume of picnometer ......0.2..ees-seeeeseccces 50 ce
Wt. of picnometer + 5 grs. soil + X grs. water... .76.347 grs
Wt. of picnometer + 5 grs. soil...........----2---- 28.257 grs.
Ne OM. fate WEN Ao oe oonouddooncueodoWuuoonouC 48.090 grs,
Water displaced (50 —48.09) ..........-0-----e- 1.910 grs.
0
Specific gravity =
5.0
eG)
pay
THE SOIL PARTICLE 91
49. Volume weight of soils—The actual weight of dry
soil in any given volume is generally expressed by volume
weight, a figure indicating the number of times heavier the
dry soil is than the water that will occupy the same soil vol-
ume. Thus, if the dry soil in a cubic foot of space weighs
99.8 pounds, the volume weight would be 99 .8+62.42 or 1.6.
The volume weight differs from specific gravity in that it
compares the weight of the dry soil to the weight of water
that will occupy the total soil volume—that is, the space
usually filled by soil particles, soil air, and soil water. Specific
gravity, however, compares the weight of the dry soil to that
of water that will occupy only the volume of the particles
alone, taking no consideration of the normal pore space. It
is consequently always the higher figure."
This volume weight figure depends on the texture of the
soil, the structure and the amount and condition of the organic
matter. The particles of sandy soils always tend to le in
close contact, thus increasing the weight of soil to a given
volume. The particles of the finer soils, such as silt loams,
clay loams, and clays, on the other hand, being smaller and
lighter, do not lie so closely together. A greater total pore
space is, therefore, usually present in the finer soils and the
volume weight is correspondingly lowered. Mineral soils may
range in volume weight from 1.10 to 1.35 for clay to 1.55 to
1.70 for sand.2 The influence of texture on the volume weight
is thus evident.
The structural and organic condition of soils often pro-
duces wide variation in volume weight. When a soil is loos-
1 As a soil is compacted, its volume weight increases due to the increase
volume occupied by the soil particles and the corresponding decrease in
pore space. If it were possible to compact a soil to a completely solid
condition, its volume weight would approach its specific gravity as a
limit. Specific gravity represents, therefore, 100 per cent. soil particles.
Volume weight in comparison indicates the proportion of space occupied
by the soil particles.
*Sandy soils are commonly spoken of as light soils, while clays are
called heavy. Such usage refers to working properties and has no
reference to actual weights.
92 NATURE AND PROPERTIES OF SOILS
ened through tillage, it becomes lighter for any given volume.
The addition of organic matter has the same effect, since the
particles are spread wider apart and the air and water spaces
increased. The specific gravity figure of a sandy loam of 1.55
may readily be lowered to 1.45 by an increase of organic
material. Some loams high in organic matter may drop as
low as 1.1 in specific gravity while muck often reaches the
low figure of .40.
In the field the volume weight of a soil may be estimated by
driving a cylinder of known volume into the ground and ob-
taining thereby a core of natural soil. By weighing the soil
and then determining the amount of water that it holds, the
amount of absolutely dry soil may be ascertained. Dividing
this by the weight of an equal volume of water gives the figure
for volume weight."
A laboratory determination may be made by putting the
soil into a receptacle of known volume and weighing it. From
the weight of the absolutely dry soil and the weight of an
The rubber tube method has proven very convenient for the field de-
termination of volume weight. A hole is bored in the soil to the required
depth by a specially constructed auger, the soil being carefully removed
and later oven dried. A very thin-walled tubular rubber bag of the size
of the auger hole is carefully inserted in the hole previously bored. The
tubular bag is then filled with water flush with the surface of the soil.
The water is measured and the volume of the soil removed is thus de-
termined. Knowing the weight of dry soil and its original volume, the
volume weight may be calculated. The experimental error of the method
is rather low.
Israelsen, O. W., A New Method of Determining Volume Weight;
Jour. Agr. Res., Vol. XIII, No. 1, pp. 28-35, April, 1918.
The paraffin-immersion is valuable with heavy soils. Small pieces of
soil are dried, weighed and then coated very thinly with paraffin, just
sufficiently to prevent the entrance of water, yet not enough to intro-
duce serious experimental error. The weight of the water displaced by
a number of such pieces may be determined easily by the use of a
graduated cylinder.
Shaw, C. F., A Method for Determining the Volume Weight of Soil
in Field Condition; Jour. Amer. Soc. Agron., Vol. IX, No. 1, pp. 38-42,
1917. See also, Trnka, R., Hine Studie tiber einige physikalishchen
Higenschaften des Bodens; Internat. Mitt. of Bodenkunde, Bd. IV, Heft
4-5, S. 363-380, 1914.
THE SOIL PARTICLE 93
equal volume of water, the volume weight may be calculated.
This method will give only approximate results, however, as
the structural relationships are more or less artificial.
50. Actual weight of soil—When the volume weight of
a soil is known, its weight in pounds to the cubic foot may be
found by multiplying by 62.42. Soils may vary in weight
from 68 to 80 pounds for clays and silts to 100 to 110 pounds
for sands. The greater the organic content, the less is this
weight to the cubie foot. A muck soil often weighs as little
as 25 or 30 pounds. This weight, of course, is for absolutely
dry soil and does not include the water present, which may be
much or little, according to circumstances.
The actual weight of soil may also be expressed in acre-feet.
An acre-foot of soil refers to a volume of soil one acre in
extent and one foot deep. In the same way we may have
an acre-eight-inches or an acre-six-inches. The weight of an
acre-foot of soil usually varies from 3,500,000 to 4,000,000
pounds. The standard usually adopted is 2,000,000 pounds,
being the weight of average soil to a depth of 6°/, inches.
The value of knowing the actual weight of a soil hes in the
possibility of calculating thereby the amount of water, the
amount of organic matter, or the actual number of pounds of
the mineral constituents present in the soil. Such informa-
tion affords another means of comparing two soils.
51. Pore space of soil—The pore space of soil is oceu-
pied by air and water in constantly varying proportions. The
amount of this pore space is determined by the texture and
the structure of the soil. As already emphasized, the coarser
+A comparison of the four methods is given by Israelsen, O. W., A
New Method for Determining Volume Weight; Jour. Agr. Res., Vol.
FEE No. 1, sp. 32,1918.
Average Volume Weight of Tehama Clay to a Depth of 60 Inches.
Laboratory method on disturbed soil.......... 1.35 + .008
Rubber<tubesmethodcs . aera. cree = oe alee wees 1.74 + .010
lina Cyahinelere iMedia oasaogoeecgedoseed oD 1.73
Parafiin-immersion method ...............ee- io == 035
94 NATURE AND PROPERTIES OF SOILS
soils are heavy due to the close contact of the particles, while
the finer soils are much lighter due to the tendency of the
small particles to resist compaction.t This means that soils
such as sands and sandy loams contain less pore space than
silt loams, clay loams, and clays. While the heavier soils have
more combined air and water space, the individual spaces are
much smaller than in the sands, which accounts for the slow
air and water drainage in the former and the ease with which
such phenomena take place in the lighter soils.
A very simple formula may be used to calculate pore space,
providing the specific gravity and volume weight are known.
It is subject to considerable inaccuracy, however, because
of the presence of colloidal matter, the exact influence of which
cannot be determined.
vol. wt. 100
% Pore Space = 100 — (oe a x
A soil having a volume weight of 1.6 and a specific gravity
of 2.6 has, according to this formula, 38.5 per cent. of pore
space. A soil in which the above figures are 1.1 and 2.5,
respectively, possesses 56 per cent. of air and water space.
The following figures taken from King * illustrate the rela-
tion that texture and, to a certain extent, structure also occu-
pies in relation to soil pore space:
1Sandy soils are generally spoken of as loose, while clays are called
compact. The term compact is thus used in the sense of hard, unyielding,
stiff, or impenetrable, and does not indicate that the pore space of clay
is less than that of a sandy soil.
?Tt has already been explained in a previous footnote (see under
volume weight) that the specific gravity of a soil represents 100 per
cent. soil material or the weight of absolutely solid soil. Volume weight
indicates in comparison thereto, the soil material actually present. The
ration of the specifie gravity to the volume weight when multiplied by
100 becomes the percentage of the soil volume occupied by the soil
particles.
* King, F. H., Physics of Agriculture; published by the author, Madi-
son, Wisconsin, 1910.
THE SOIL PARTICLE 95
TasBLE XVIII
PERCENTAGE PORE SPACE IN SOILS OF DIFFERENT TEXTURE
“SH TTLNGY SEUCTl noes Sa tee sear cee ey ae ne een er 32.5
ite Mnte erm asttige ie ss eek 2h eM Sse teva gasses 34.5
INE FIV VEO CUENL Macy ropo re Stas Hea) hc sass nrwlern de sain sates 8% 44.1
Een Ys CLAVE waavcseebecrds taut ertte saueigr casts) ak seue wieteue tees 45.3
MBO OSM eis shraie isc ce ee esata atti. Satelay ce 47.1
(CHISS* Ske ze | at kk a oe a Sea Ae en 48.0
TS ICHAT CGT EA 2s es Aer ta eae EP ea ea Oras)
The pore space in a normal soil is occupied by water and
air. If the water content is low, the air space is large, and
vice versa. Thus the relationships of the total pore space
and the size of the individual spaces to the amount of air and
water contained, to their movement through the soil, to soil
sanitation, to root extension, to bacterial action, and to erop-
ping conditions in general, become apparent. It is the regu-
lation of this pore space that is really important in any struc-
tural consideration. The effect on plant growth of a change
of pore space is the only test of its advisability.
52. Soil particles—their number and surface exposed.
—Since soil particles run to extremely small diameters, the
number in any given volume is very large, especially when
fine-textured soils are considered. However, any calculation
of the number of particles present in a soil is open to great
inaccuracy ; first, because it is impossible to get a correct fig-
ure for the average diameter of the particles of any soil or of
the various groups of separates that go to make it up; and,
secondly, because it must be assumed in the calculation that
the particles are spherical. The presence of colloidal matter,
especially in the heavier soil types, introduces an error the
magnitude of which must be very great. Nevertheless, such
a calculation, even if very inaccurate, gives some idea as to
the immense number of grains that are present even in the
96 NATURE AND PROPERTIES OF SOILS
coarser soils. A few figures are given in Table XIX for some
of the average soil classes‘ established by the Bureau of Soils:
TABLE XIX
APPROXIMATE NUMBER OF PARTICLES TO A GRAM OF VARIOUS SOIL
CLASSES ?
NUMBER OF PARTICLES
Som CLass See Gn
SINS alee eee tere nis sr er ee 2,287,000,000
Samy sloamiseponcaavgae a's sti ais Siareus eee 5,483,000,000
irenmigtaae eters tent), bee S 00 ee 7,332,000,000
Wiaiyaloamis sree 2 6 cu tee eee aie 11,877,000,000
CHILE TAT UE aa A mS ee PS 19,177,000,000
An important property of the surface of the grains is the
tendency toward the retention of soluble material in a par-
tially or wholly available condition for plant use. This power,
designated as absorption, is exhibited to a high degree by
fine soils, in which the individual pore spaces are small and
the amount of surface exposed is large, due to the presence
of considerable colloidal matter. This capacity is an especially
important factor in the economical use of fertilizer salts. Ab-
sorption may also, by bringing materials into closer contact,
hasten or retard certain chemical actions. Changes may thus
*The mechanical analyses of these particular classes are given on
page 83.
*The number of particles in any soil sample may be arrived at from
a mechanical analysis and the diameters that limit each group. Using
the average diameter of each group together with the percentage of
the groups in a given sample, the number of particles may be calculated
by the following formula:
Weight of sample in grams
1/6 x, D® X 2.65
The formula 1/6 z D* is that used for determining the volume of a
sphere, the diameter in this case being expressed in centimeters. When
multiphed by the average specific gravity of soil particles the weight of
an average particle is obtained in grams. In the above calculations,
2.7 was used instead of 2.65.
Number of particles in a sample of soil=
THE SOIL PARTICLE o7
be expected to go on in the soil that would not take place in
the laboratory beaker. The relation of this absorption to bac-
terial activity also cannot be overlooked.
The minerals of the soil are all very resistant to solution;
if they were not, they would long ago have been leached away.
Such materials, while almost insoluble under ordinary cir-
cumstances, allow appreciable amounts of nutrients to appear
in the soil solution, because of the immense amount of surface
exposed, although the specific solubility remains the same.
In order to present some idea of the internal surface of
ordinary soils, a few figures are given on the same soil classes
for which the number of particles have already been calcu-
lated:
TaBLE XX
APPROXIMATE INTERNAL AREA OF SEVERAL AVERAGE SOIL
CLASSES 1
SQUARE SQUARE ACRES PER
SorL CLAss INCHES FEET PER AcRE-F'00T OF
PER GRAM POUND 3,000,000 LBS.
SIGUA [se Oe 89 280 22,549
Sandy loams...... . 213 671 53,965
lvenend Shetaea ge ihe cova. 294 926 74,410
(lays. loams:.;...+.. 430 1354 108,830
BIAS SG sabe ate bse e's 653 2057 165,270
While these figures are as grossly inaccurate as those re-
garding the number of particles, they tend to emphasize the
tremendous internal surface possessed by even the coarser
soils. The data presented for an acre-foot of soil, while al-
most too large for adequate comprehension, are probably
much too low. It is not to be wondered at that the slowly
soluble minerals are able to supply sufficient nutrients to the
1When the approximate number of particles and their sizes in any
given weight of soil are known, the internal surface may be calculated
by the following formula:
Surface = x D* x number of particles.
98 NATURE AND PROPERTIES OF SOILS
erop growing on the soil, when such a large amount of sur-
face is continually available for chemical action.
53. Resume.—The discussion of the soil particle as to its
size, its classification, its chemical characteristics, and its
mineralogical peculiarities is undoubtedly important. Im-
portant also are the specific physical properties which arise
because of textural and structural make-up, such as specific
gravity, volume weight, pore space, and immense internal
surface. These phases, however interesting in themselves,
must not be studied so closely as to prevent their broad and
vital plant correlations from becoming evident. None of the
transformations concomitant with normal crop production
takes place in the soil without definite and widespread co-
operation. The study of the soil particle is, therefore, more
than a consideration of a few interesting physical and chem-
ical phenomena. From such investigations have been devel-
oped and perfected the broad principles which govern suc-
cessful soil management and economical food production.
CHAPTER V
THE ORGANIC MATTER OF THE SOIL
ONE oF the essential differences between a soil and a mass
of rock fragments lies in the organic content of the former.
Organic matter is necessary in order that mineral material
may become a soil and that it may grow crops successfully.
The physical condition of soils depends largely on the pres-
ence of organic matter and chemical reaction is greatly ac-
celerated by its decay.
In the process of soil formation the addition of organic
materials is more or less a secondary step. In residual debris
the amount of organic matter held by the growing soil in-
creases as the process of weathering goes on; in glacial soils,
however, the matrix or skeleton of the soil is already formed
before there is an opportunity for organic matter to become
incorporated in it. The final result from the mixing of min-
erals and their weathered and altered products with the
decayed or partially decayed organic matter that is sure to
accumulate, is a mass much more complicated than either
of the original constituents. The complexity of the average
soil has already been sufficiently stressed.
54. The source of soil organic matter’ and the char-
acter of plant tissue——The source of practically all soil
*The soil organic matter includes not only all compounds contained
in the original vegetable and animal tissues but also those existing in
the partially decayed portions of such material. Carbon dioxide, methane
and like compounds are usually not considered as a part of the soil
organic matter. In this respect, the above definition is narrower than
that for organic chemistry, which is the chemistry of carbon compounds.
For a very good review of literature on soil organic matter, see Morrow,
C. A., The Organic Matter of the Soil: A Study of the Nitrogen Distri-
bution in Different Soil Types; Dissertation, Univ. Minn., 1918.
99
100 NATURE AND PROPERTIES OF SOILS
organic matter is plant issue.t Some of this matter ac-
cumulates from the above-ground parts of plants that have
died and fallen down to become mixed with the surface soil;
the remainder is a result of root extension and subsequent
decay. The organic matter of the surface soil is derived from
the tops and the roots of plants growing on it, while that of
the subsoil is very largely a result of root extension and sub-
sequent decomposition.
Since soil organic matter has its origin very largely from
the higher plants, it is advisable to consider the general chem-
ical nature of such material.2, About 75 per cent. of average
green plant tissue is water. The dry matter is made up of
carbon, oxygen, hydrogen, and mineral material in the ap-
proximate ratio of 6, 5, 1 and 1 respectively. The preponder-
ant elements of normal plant tissue are evidently carbon,
oxygen, and hydrogen. (See Fig. 20.)
It is usual in classifying the compounds in plants to group
them under the following heads: (1) carbohydrates, (2)
fixed oils and waxes, (3) volatile oils and resins, (4) organic
acids and their salts, and (5) nitrogenous compounds.* The
1It must not be inferred that higher plants are the only source of soil
organic matter. Assuming that the weight of one bacterial cell is
.000,000,002 of a milligram and that in each gram of a normal fertile
soil, weighing 2,000,000 pounds to an acre-seven inches, there are
100,000,000 of such organisms, the weight of bacteria alone would be
400 pounds to the surface acre. This is a very conservative estimate,
800 pounds probably being more nearly correct. Considering the molds,
fungi, alge, actinomycetes, insects, and earthworms, there are probably
2000 pounds of living material in every acre of normal soil exclusive
of plant roots. These organisms in their functioning supply no insig-
nificant portion of the soil organic matter.
2For a fuller discussion see: Ingle, Herbert, Manual of Agricultural
Chemistry, Chap. X, London, 1913. Also, Stoddard, C. W., The Chem-
istry of Agriculture, Chap. III, Philadelphia and New York, 1915.
Also, Thatcher, R. W., The Chemistry of Plant Life, New York, 1921.
37, Carbohydrates—Sugars, starch, cellulose, legnin, inulin, gums,
pectins, and pentosans.
II. Fixed oils and waxes—Castor oil, corn oil, cottonseed oil, linseed
oil, and the like.
III. Volatile oils and resins—Oil of mustard, of cloves, of pepper-
mint, etc. Rosin, myrrh, balsam, ete.
THE ORGANIC MATTER OF THE SOIL 101
mineral matter or so-called ash exists as a part of the com-
pounds listed under these headings. The carbohydrates, hav-
ing the general formula of C,(H,O), include such compounds
as starch, cellulose, dextrose, glucose, cane sugar, and the like.
The fats and oils may be represented in plants by such glycer-
ides as butyrin, stearin, olein, palmitin, while many acids of
an organic nature exist especially in fruits and vegetables.
H-2%
ASH-2%
WATER-T5 %
Fig. 20.—Diagram showing the general composition of green plant tissue.
The nitrogen which is generally less than .5 per cent. is included
with the ash in the above diagram. (After Stoddard.)
Of the five groups, however, the nitrogenous compounds are
probably the most complicated as they carry not only carbon,
hydrogen, oxygen, and nitrogen, but also mineral elements
such as sulfur, phosphorus, calcium and iron. They are com-
pounds of high molecular weight and many are of unknown
IV. Organic acids and their salts—Citrie acid, malice acid, tannic acid,
tartarie acid, and the like.
V. Nitrogenous compounds—Nitrates, ammonia, amides, amino-acids,
alkaloids, and proteins.
102 NATURE AND PROPERTIES OF SOILS
constitution. Simple proteins, such as albumin, globulin, pro-
tamins, and others, are found in plants, besides certain de-
rived proteins such as proteosis and peptones. In addition
to all these, there is a host of other nitrogenous compounds
that have no small influence on the composition of the soil
organic matter.’
It is also necessary to consider that certain portions of the
cell contents and cell walls are in a collodial state. Such a
condition is important as the translocation of dissolved sub-
stances from soil to plant and rrom cell to cell depend largely
on their diffusibility through colloidal membranes.
It is evident even from this brief discussion that the chem-
ical character of plant tissue is far from simple. The degra-
dation of such material, especially in the presence of com-
plex mineral products, generally gives rise at first to com-
pounds no simpler; in fact, the chances are that the result-
ing compounds will be much more complicated. It is only
later in the processes of decomposition that simple products
result.
1Crops are usually analyzed for six constituents—water, ash, crude
protein, crude fiber, nitrogen free extract, and crude fat. Water is
determined by drying the sample at the temperature of boiling water.
By burning a sample of the plant tissue until all of the organic matter
has been driven off, the percentage of mineral matter may be found.
Crude protein is obtained by mulptiplying the figure for total nitrogen
by 6.25. Crude fat is found by extracting the dry plant tissue with
ether, while the crude fiber is that which remains of the fat-free material
after treatinent with both dilute sulfuric acid and dilute sodium hydrox-
ide solutions. Nitrogen-free extract is the difference between the sum
of the above constituents and 100 per cent. Below are four typical
analyses:
NITROGEN
CRUDE | CRUDE CRUDE
CROP Water | ASH PROTEIN| FIBER FREE Fat
% % EXTRACT
Jo Jo ‘ Jo
Alfalfa (green) ...| 71.8 2.7 4.8 7.4 12.3 1.0
Lettuce (fresh) ...| 94.7 2 1.2 sil 2.2 m3)
Wheat (grain) ....| 10.5 1.8 11.9 1.8 71.9 Dall
Timothy (hay) ....| 13.2 4.4 5.9 29.0 45.0 2.5
THE ORGANIC MATTER OF THE SOIL 103
55. Decomposition’ of organic matter in soils—While
the general trend of organic degradation in soils is towards
simplification, the process is by no means a progressive one.
Many products are built up that are much more complex
than the original tissue. Most of the fermentation and putre-
faction is due to that great group of organisms called bacteria,
although molds, fungi, and the like also are important. The
action of these organisms may be direct, but is more likely
to be enzymic. A cycle is therefore set up, in which the
higher plants and animals are occupied in building up, while
bacteria are tearing down and reducing the residue of plant
action to simple forms, such as can be ultimately utilized again
in plant nutrition. The importance of soil organisms is thus
evident, and the encouragement of their growth and function
is clearly a part of good soil management. (See Fig. 21.)
When the complex molecules that make up plant tissue
break down, they split along definite lines of cleavage, de-
pending on the structure of the original molecule. These
bodies, which are usually simpler in nature than those from
which they have sprung, are called cleavage products, and
without a doubt their appearance is the first step in organic
decomposition. These compounds are subject to still further
change, and because of the great number of agencies at work
the secondary products that result may be simpler or more
complex, according to conditions. Some bacteria have a tend-
ency, while tearing down organic matter, to produce syn-
thetic compounds, which present a very complicated molecule
until they are in turn degraded. The tendency for the sec-
ondary products to react both among themselves and with the
*Decomposition and decay are general terms referring to all of the
degradation processes through which the original tissue passes in the
soil. Fermentation refers to the decomposition of carbohydrates while
putrefaction has to do usually with nitrogenous materials.
*A catalytic agent is a material capable of hastening or retarding a
chemical reaction, the catalyst emerging unchanged from the transforma-
tion. Enzymes are catalysts produced by living organisms and may be
active within or without the cell. They are generally colloidal in nature.
104 NATURE AND PROPERTIES OF SOILS
mineral constituents is by no means an unimportant factor
in accounting for the complexity of the decaying organic mat-
ter.
As the processes of fermentation and putrefaction go on
the complex intermediate compounds are gradually broken
down and certain simple products result. Such materials may
result from a progressive simplification of the partially de-
HIGHER
PLANTS
NUTRIENTS
PLANT
TISSUE
LOST FROM
THE
SOIL
Fig. 21.—Diagram showing the transformations through which the con-
stituents of the plant tissue pass from the time the organic matter
enters the soii until it is in a condition to be used by succeeding
crops. The cycle is very largely biological.
cayed matter or may be by-products or split-off compounds
from the more complex reactions. These simple materials are
partially solid and partially gaseous. Carbon dioxide is a
universal product of bacterial activity of all kinds and is
constantly being evolved. Other simple constituents arising
from organic decay are water, ammonia, nitrites, nitrates, free
nitrogen, and sulfur dioxide. Some of these are lost from
the soil, some lose their identity by reacting with the soil con-
stituents, while others may function as plant nutrients. When
THE ORGANIC MATTER OF THE SOIL 105
they are absorbed again by a crop, the organic cycle is com-
pleted.
56. The partially decomposed organic matter..—The
most complicated parts of the organic matter in the soil are
the primary and secondary products of decomposition, the
materials between the original tissue and the simple products.
These compounds are not only complex but they are contin-
ually changing. <A certain compound present in the soil one
week may be altered the next. Again, at least a part of the
decomposing organic matter is colloidal, thus possessing spe-
cial absorptive and catalytic properties. When the soil
organic matter is treated with the various extractive agents,
reactions may be induced which would not take place in a
normal soil. Compounds are then formed which would prob-
ably not exist under natural conditions.
Many chemists have worked on the problems of the con-
stitution of the organic matter of the soil and have published
their results. The early conceptions were rather simple.
Mulder,’ for example, considered the soil organic matter to
consist almost entirely of carbon, hydrogen, and oxygen. Such
a concept ignores the presence of nitrogen, sulfur, and the
mineral elements of the original plant tissue, and is much
too simple to explain organic transformations.
Even the investigators * of Mulder’s time obtained discor-
See Morrow, C. A., The Organic Matter of the Soil; A Study of the
Nitrogen Distribution in Different Soil Types; Dissertation, Univ.
Minn., 1918.
4Mulder, T. J., Die Organischen Bestandtheile im Boden; Chemie der
Ackerkrume, I, pp. 308-360, Berlin, 1863. Also, Wiley, H. W., Agricul-
tural Analysis; Vol. I, p. 53, Easton, Pa., 1906.
Mulder contended that the organic matter consisted of seven distinct
compounds, as follows: 1 & 2, Ulmie acid and ulmin; 3 & 4, Humie acid
and humin; 5, Geie acid; 6, Apocrenic acid; 7, Crenic acid. These
bodies he considered as arising from one another by oxidation; thus
ulmi¢ acid (C,H,,0,.) gave humie acid (CyH,,0,,), which in turn yielded
geic acid (C,H,,0,,), followed by apoerenic acid (C,,H,.0,,), and finally
by erenic acid (C,,H,,0,,).
§See Schreiner, O., and Shorey, E. C., The Isolation of Harmful Or-
ganic Substances from Soils; U. 8. Dept. Agr., Bur. Soils, Bul. 53, pp.
15-16, 1909.
106 NATURE AND PROPERTIES OF SOILS
dant results, but these were explained for the time being by
assuming that the discrepancies occurred because of added
molecules of water.
Later investigators, while progressing rather slowly toward
definite results, did accomplish one thing of importance. They
threw considerable doubt on the old ideas of the Mulder
school of chemists.
One of the men, whose work established beyond a doubt the
fact that organic matter was a mixture of very complicated
compounds, was Van Bemmelen.' His investigations still
further showed that the soil organic matter was largely in a
colloidal condition, and, therefore, exhibited properties quite
distinct from those shown by true solutions or matter in a
coarse state of division.
In recent years, Baumann? by his researches has shown
freshly precipitated organic matter to possess properties which
are largely colloidal in nature. Among these characteristics
are high water capacity, great absorptive power for certain
salts, ready mixture with other colloids, power to decompose
salts, great shrinkage on drying, and coagulation in the pres-
ence of electrolytes. Jodidi* has studied the composition of
the acid-soluble organic nitrogen in peat and mineral soils.
The nitrogenous compounds thus obtained can be divided into
the following groups: (1) ammoniacal nitrogen, (2) nitric
nitrogen, (3) acids amides, (4) mon- and diamino-acids. The
two: latter groups* carry the bulk of the organic nitrogen,
1Van Bemmelen, J. M., Die Absorptions Verbindungen und das Ab-
sorptionsvermogen der Ackererde; Landw. Versuch. Stat., Band 35,
Seite 67-136, 1888.
Baumann, A., Untersuchungen Uber die Hummussduren; Mitt. d. K.
bayr. Moorkulturanstalt, Heft 3, Seite 53-123, 1909.
§ Jodidi, S. L., Organic Nitrogenous Compounds in Peat Soils I; Mich.
Agr. Exp. Sta., Tech. Bul. 4, Nov., 1909. Also, The Chemical Nature of
the Organic Nitrogen in Soil; Ia. Agr. Exp. Sta., Res. Bul. I, June 1911.
4 Amides or acid amides are formed from organic acids by replacing
the hydroxyl of the carboxyl group with NH, Acetic acid (CH,COOH)
THE ORGANIC MATTER OF THE SOIL 107
but quantitative determinations are uncertain. These com-
pounds produce ammonia readily, the rate depending on their
chemical structure.
The present knowledge of the chemical constitution of the
soil organic matter is due largely to investigations prosecuted
by the United States Bureau of Soils.t. As a result of several
years work a large number of compounds were isolated. Some
are original constituents of the plant tissue but the bulk has
arisen through the process of organic decomposition.
The compounds isolated were classified from the chemical
standpoint under four heads, those containing: (1) carbon
and hydrogen; (2) carbon, hydrogen, and oxygen; (3) ear-
bon, hydrogen, and nitrogen, or carbon, hydrogen, oxygen,
and nitrogen; (4) sulfur in combination with any or all of
the elements listed above. With the possible presence in
soils of compounds containing so many elements, it is little
wonder that the subject is a complicated one. It is evident,
moreover, that any list now available will be only partial, and
that many other compounds of even more intricate composi-
tion will be isolated later.
A list of some of the compounds isolated from soil organic
matter by the Bureau of Soils follows:
thus becomes acet-amide (CH.CONH,). Amino-acids are produced by
replacing one of the alkyl/hydrogens with NH,. Acetic acid thereby
becomes amino-acetic acid or glycocoll (CH,(NH,)COOH). Protein/hy-
drolysis is probably as follows:
pee amides
Proteins — Proteoses — Peptones — Peptides <
Amino-acids
1Sehreiner, O. and Shorey, E. C., The Isolation of Harmful Substances
from Soils; U.S. Dept. Agr., Bur. Soils, Bul. 53, 1909; also Buls. 47, 70,
74, 77, 80, 83, 87, 88, and 90. See also, Sullivan,eM. X., Origin of
Vanillin in Soil; Jour. Ind. & Eng. Chem., Vol. 6, No. 11, pp. 919-921,
1914. Kelley, W. P., The Organic Nitrogen of Hawaiian Soils; Jour.
Amer. Chem. Soe., Vol. XXXVI, No. 2, pp. 429-444, Feb., 1914. Walters,
E. H., Proteoses and Peptones in Soils; Jour. Ind. & Eng. Chem., Vol.
7, No. 10, pp. 860-863, 1915. Lathrop, E. C., Protein Decomposition
in Soils; Soil Sci., Vol. I, No. 6, pp. 509-532, June, 1916.
108 NATURE AND PROPERTIES OF SOILS
Hentriacontane—C,,, H,, Histidine—C,H,O.N,
Dihydroxystearie acid— Trithiolbenzaldehyde—
OFS! 5 OY (C, HZCSH):.
Suecinie acid—C,H,O, Creatinine—C,H,ON,
Picoline carboxylic acid— Salicylic Aldehyde—
C,H,O,N C,H,OHCOH
57. Relation of organic compounds to plants.—So far as
the plant is concerned, organic compounds may be divided
into three groups: those that are beneficial, those that are
neutral, and those that are toxic or harmful in their effects.
As an example of the first group, histidine and creatinine '
may be mentioned. Here is a case in which the compounds
in the soil organic matter may exert a stimulating effect on
plant growth, supplementing the nitrates? to a certain extent.
That the nitrogen of the soil organic matter may be utilized
by plants is well summarized by the publications of Hutchin-
son and Miller.2 As an example of a harmful compound aris-
ing from the decomposition of the organic matter, dihydroxy-
stearic acid may be mentioned as one of the best known. This
compound was the first to be isolated and identified by the
Bureau of Soils and is very toxic. |
The discovery of such compounds in the soil has revived the
old theory of toxicity,t by which the infertility of certain
soils was accounted for. Root excretions were also held to be
detrimental to succeeding crops of the same kind. The toxic
materials of the soil organic matter largely originate under
1Skinner, J. J., Effect of Histidine and Arginine as Soil Constituents;
Eighth Internat. Cong. App. Chem., Vol. XV, pp. 253-264, 1912. Also,
Beneficial Effects of Creatinine and Creatine on Growth; Bot. Gaz.,
Vol. 54, No. 2, pp. 152-163, 1912.
?Schreiner, O., and Skinner, J. J., Nitrogenous Soil Constituents and
Their Bearing upon Soil Fertility; U. 8. Dept. Agr., Bur. Soils, Bul. 87,
p. 68, 1912. Also, Schreiner, O., and Others, A Beneficial Organic Con-
stituent of Soils; Creatinine; U. S. Dept. Agr., Bur. Soils, Bul. 83, p. 44,
1911.
3 Hutchinson, H. B., and Miller, N. H. J., The Direct Assimilation
of Inorganic and Organic Forms of Nitrogen by Higher Plants; Jour.
Agr. Sci., Vol. 4, Part 3, pp. 282-302, 1912.
*See Schreiner, O., and Reed, H. S., Some Factors Influencing Soil
Fertility; U. 8. Dept. Agr., Bur. Soils, Bul. 40, pp. 36-40, 1907.
THE ORGANIC MATTER OF THE SOIL 109
conditions of poor drainage and aération. The toxicity of
sueh compounds as dihydroxystearic acid, picoline carboxylic
acid and aldehydes may, therefore, be overcome by oxidation.!
Good soil aération is a factor in dealing with such conditions.
Fertilizers, according to Schreiner and Skinner,? seem to
decrease the harmful effects of such compounds; nitrogenous
fertilizers overcoming some toxic materials, and phosphoric
acid or potash neutralizing others. Robbins * has shown that
soil organisms have the power of causing the disappearance
of certain toxic materials in the soil, such as cumarin, vanillin,
pyridine, and quinoline.
While. Schreiner found twenty soils, out of a group of sixty
taken in eleven states of this country, to contain dihydroxy-
stearic acid, this does not necessarily mean that this or sim-
ilar compounds are serious detrimental factors. It is very
likely that such compounds are merely products of improper
soil conditions, and are to be considered as concomitant with
depressed crop yield. When such conditions are righted, the
so-called toxic matter will disappear, as has been shown by
the researches of Davidson.t Good drainage, lime, tillage,
aération, and oxidation, are so efficacious in this regard that
permanent organic soil toxicity need never be a factor in soils
rationally managed.
1Schreiner, O., and Others, Certain Organic Constituents of Soils in
Relation to Soil Fertility; U. S. Dept. Agr., Bur. Soils, Bul. 47, p. 52,
1907. Also, Schreiner, O., and Reed, H. 8., The Role of Oxidation in
Soil Fertility; U.S. Dept. Agr., Bur. Soils, Bul. 56, p. 52, 1906.
2Schreiner, O., and Skinner, J. J., Organic Compounds and Fertilizer
Action; U. S. Dept. Agr., Bur. Soils, Bul. 77, 1911. Also, Hapert-
mental Study of the Effect of Some of the Nitrogenous Soil Constituents
on Growth; Plant World, Vol. 16, No. 2, pp. 45-60, Feb., 1913.
5 Robbins, W. J., The Cause of the Disappearance of Cumarin, Vanillin,
Pyridine and Quinoline in the Soil; Ala. Agr. Exp. Sta., Bul. 195, June,
1917. Also, The Destruction of Vanillin in the Soil by the Action of
Soil Bacteria; Ala. Agr. Exp. Sta., Bul. 204, June, 1918. Robbins, W. J.,
and Massey, A. B., The Effect of Certain Environmental Conditions on
the Rate of Destruction of Vanillin by a Soil Bacterium; Soil Sci.,
Vol. X, No. 3, pp. 237-246, Sept., 1920.
‘Davidson, J., 4 Comparative Study of the Effects of Cumarin and
Vanillin on Wheat Grown in Soil, Sand and Water Culture; Jour.
Amer. Soc. Agron., Vol. 7, No. 4, pp. 145-158, 1915.
110 NATURE AND PROPERTIES OF SOILS
58. Simple products of organic decomposition—dAs the
processes of chemical and biological change of the soil organic
matter proceed, the simple compounds already noted begin
to appear. This change is of course codrdinate with a certain
amount of synthetic action, but compounds thus built up
must ultimately succumb to the agencies at work and suffer a
splitting-up and reduction to simple bodies. Carbon dioxide
is one of the most important of these compounds, always being
a product of bacterial activity. Its importance has already
been noted in the discussion of weathering. Here it heightens
the solvent power of water and tends to increase the amount of
nutrient material carried in the soil solution. Carbonation
is a direct result of its presence.
With increased organic matter in any soil, greater bacterial
action and an increase in the carbon dioxide evolved may well
be expected. In fact, the carbon dioxide production of a
soil is considered by some authors! to be a measure of bacterial
activity. With this increase in carbon dioxide, the soil air
is markedly reduced in its free oxygen and an alteration in
bacterial and plant relationships may thereby be induced.
The following figures by Wollny? show the composition of
the soil atmosphere and the effects of additional organic ma-
terial on the carbon dioxide content :
TABLE X XI
PERCENTAGE BY VOLUME OF
SoILs
co, O
AG IMOSPRETIC(AUrs con citeee dees eee 04 20.96
Soil air (average 19 analyses)..... 2.54 18.33
PMESANGY siSOUL 5 tacnce cree ae eae en 1.06 19.72
Sandy soil plus manure... 5.07.2. 9.74 10.35
1Stoklasa, J.. and Ernest, A., Uber den Ursprung, die Menge, und die
Bedeutung des Kohlendioxyds im Boden; Centrlb. Bakt., II, 14, Seite
723-736, 1905.
?Wollny, E., Die Zersetzung der Organischen Stoffe; Seite 2, Heidel-
berg, 1897.
THE ORGANIC MATTER OF THE SOIL 111
While carbon dioxide may be evolved by the splitting-up
of both carbohydrate and nitrogenous bodies, ammonia re-
sults only from the latter. It is really the first extremely
simple nitrogenous body produced. It can be utilized by
some plants as a source of nitrogen, as is also true of certain
products of partial decomposition such as urea, but ordinarily
it must undergo oxidation. This oxidation results in nitrites
(NO,) and ultimately in nitrates (NO,), the latter usually
being considered as the chief source of the nitrogen utilized
by plants.
Other simple products, such as methane (CH,), hydrogen
disulphide (H,S), carbon disulphide (CS,), and the like, may
also result. They are relatively unimportant, however, as
regards the plant, in comparison with the role played by ear-
bon dioxide, ammonia, the nitrites, and the nitrates. The
production of the nitrates from ammonia is very closely cor-
related with good soil conditions, especially optimum moisture
and adequate aération. The proper handling of the soil, then,
will not only tend to eliminate toxic matter and prevent its
further formation but will encourage the proper decay of the
soil organic matter and the production of simple compounds
which will function directly or indirectly as nutrients.
59. Carbonized materials of soil.—After the extraction
of the soil for the study of the ordinary organic compounds,
a considerable mass of material remains, which is insoluble
in water, alkali, and other ordinary solvents. By the extrac-
tion of a large amount of soil, Schreiner and Brown?! were
able to study this material. They found it susceptible to di-
vision into six groups, as follows: (1) plant tissue, (2) insect
and other organized material, (8) charcoal particles, (4) lig-
nite, (5) coal particles, and (6) materials resembling natural
hydrocarbons, as bitumen, asphalt, and the like. Such ma-
1Schreiner, O., and Brown, B. E., Occurrence and Nature of Carbon-
ized Material in Sotls; U.S. Dept. Agr., Bur. Soils, Bul. 90, 1912.
112 NATURE AND PROPERTIES OF SOILS
terial was found not only near the surface of the soil but at
depths of fifteen or twenty feet.
The exact origin of this material is problematical. Forest
and prairie fires, infiltration, mild oxidation, and lgnifica-
tion might be mentioned. Of a certainty the agencies of dis-
tribution are the natural forces engaged in physical weather-
ing. Such material can be divided into two general groups,
organized and unorganized; in the former, the normal strue-
ture remains intact, while in the latter the original features
have been obliterated. Part of it belongs, therefore, in the
original plant tissue group; a part of it with the partially de-
cayed material; while some must be included with the simple
products of decomposition. This carbonized material is im-
portant, as it makes up no inconsiderable part of the soil
organic matter. It is very resistant, and consequently lends
stability to the organic constituents.
60. The determination of soil organic matter..—A num-
ber of methods have been proposed for the direct or indirect
determination of the organic matter in soils, but none has
proved entirely satisfactory, since the composition of this ma-
terial is so indefinite and complicated and so likely to change
while under investigation. Other soil constituents also tend
to interfere with the determination. Three general methods
seem worthy of mention, as they have been used very widely
in soil analyses and at least give comparative, if not absolutely
accurate, results. They will be discussed in the inverse order
of their value.
Loss of ignition.2—This is a simple method which designs
to burn off the organic matter and determine its loss by dif-
ference. Five grams of dry soil are placed in a crucible and
ignited at a low red heat until the organic matter is all oxi-
1Soil organic matter as here used refers only to the original and
partially decayed organic constituents. Carbon dioxide, methane, nitrites,
nitrates and similar compounds are, therefore, not included in this term.
2 Wiley, H. W., Official and Provisional Methods of Analysis; U. 8S.
Dept. Agr., Bur. Chem., Bul. 107, p. 19, 1908.
THE ORGANIC MATTER OF THE SOIL 113
dized. The cold mass is moistened with ammonium carbonate
and heated to a temperature of 150°C. in order to expel the
excess of ammonia and replace the carbon dioxide. The
change in weight is rated as loss on ignition.
This method is open to the objection that, besides the loss
of organic matter, a certain amount of water of combina-
tion, and all ammoniacal compounds, nitrates, carbon dioxide,
and some alkali chlorides, if the temperature is carried too
high, are driven off. The method, therefore, gives high results,
especially in the presence of large amounts of hydrated sili-
cates such as are likely to occur in residual soils. Notwith-
standing these objections, this method has been used to a very
great extent in soil analysis.
Chromic acid method.—This method, proposed by Wolff,
has been modified and improved by various chemists. War-
ington and Peake’ have perhaps done more with the method
than any other investigators. In the United States the modi-
fication by Cameron and Breazeale * has been very generally
aecepted.* It consists in the treatment of the soil sample with
sulfuric acid, and chromic acid, or potassium bichromate.
The organic matter, in the presence of the sulfuric acid and
an oxidizing agent, evolves carbon dioxide until, if the mix-
*Rather offers a modification to this method which seems to obviate
some of its difficulties. The soil is first extracted with dilute HCl and
HF to remove the hydrated aluminum silicates, the organic matter being
little influenced thereby. The sample is then ignited in the usual
manner. Rather, J. B., An Accurate Loss-on-Ignition Method for the
Determination of Organic Matter in Soils; Jour. Ind. and Eng. Chem.,
Vol. X, No. 6, pp. 439-442, June, 1918.
* Warington, R., and Peake, W. A., On the Determination of Carbon in
Soils; Jour. Chem. Soc. (London), Trans., Vol. 37, pp. 617-625, 1880.
* Briggs, L. J., and others, The Centrifugal Methods of Mechanical
Soil Analysis; U. S. Dept. Agr., Bur. Soils, Bul. 24, pp. 33-38, 1904.
Also, Cameron, F. K., and Breazeale, J. F., The Organic Matter in Soils
and Subsoils; Jour. Amer. Chem. Soe., Vol. 26, pp. 29-45, 1904.
*Waynick offers a simplification of this method: Waynick, D. D., A
Simplified Wet Combustion Method for the Determination of Carbon in,
Soils; Jour. Ind. and Eng. Chem., Vol. XI, No. 7, pp. 634-637, 1919.
114 NATURE AND PROPERTIES OF SOILS
ture is boiled, practically all of the carbon is thus driven off.
This gas is drawn through a train of absorption bulbs, caught
in a solution of potassium hydroxide, and thus weighed.
A second determination is now made on a new sample of
soil, leaving out the chromic acid. The carbon dioxide given
off under such conditions is that of an inorganic nature. The
weight of this gas substracted from the total carbon dioxide
leaves the organic carbon dioxide.
The data from the use of the chromic acid method may be
expressed as organic carbon or as organie matter. Multiply-
ing the carbon dioxide by .471 or the carbon by 1.724 is con-
sidered as giving an approximate figure for the organic mat-
ter.
The results obtained with the chromic acid method are usu-
ally lower than those from ignition or combustion, due par-
tially to the oxidation resistance of the carbonized matter,
already discussed. This material, while it succumbs to igni-
tion, resists the action of the sulfuric and chromic acids ‘to
a very large degree. The water of hydration is, of course, not
a factor in the chromic acid method.
Bomb Combustion.'—Two grams of soil, .75 gram of mag-
nesium powder, and 10 grams of sodium peroxide (Na,O,)
are thoroughly mixed in a closed dry calorimeter bomb. The
mixture is then exploded by heating, all of the carbon of the
soil being changed to the carbonate form by the reaction.
The fused charge is now removed to a flask and by treating
with acid, the carbon in the form of carbon dioxide may be
driven off into a Parr apparatus and measured under stand-
ard conditions of temperature and pressure.
The amount of inorganic carbonate carbon in the soil must
1Wiley, H. W., Official and Provisional Methods of Analysis; U. 8S.
Dept. Agr., Bur. Chem., Bul. 107, p. 234, 1908.
There are a number of other methods of complete combustion. Very
often the combustion is carried on in a current of oxygen over hot
cuprous oxide. The organic carbon may thus be very accurately
determined.
THE ORGANIC MATTER OF THE SOIL 115
be determined on a separate sample and deducted from the
figure obtained by the combustion above described. This will
give the organic carbon of the soil in terms of carbon dioxide.
The percentage of organic carbon may now be calculated as
well as the approximate amount of organic matter (C Xx 1.724
= organic matter or CO, X .471 = organic matter.)
61. Determination of soil humus.—Humus? is a term ap-
plied to that portion of the organic matter which can be re-
moved with ammonium hydroxide after the soil has been
treated with hydrochloric acid and washed free thereof. The
common method of humus estimation is that proposed by
Grandeau.* The sample of soil is first washed with acid in
order to remove the bases in combination with the organic mat-
ter. It is next treated with ammonia, which will then dissolve
out the humous materials. The method is based on the fact
that when a soil is lacking in active basic material, certain
parts of the organic matter are soluble in an alkali. The dark
humous extract obtained with the ammonia is called Matiére
Noire and is supposed to be the most active part of the soil
organic matter.
This method has undergone several modifications * of which
Wiley presents the following comparisons of the three methods dis-
cussed above:
COMBUSTION | CHROMIC ACID
Som TENEBION (e X 1.724) (e x 1.724)
Midipasture .....0.. 5. 9.27 6.12 4.84
New pasture ......... 7.07 4.16 3.32
PATA Le SOR lars'S evi esore eile 5.95 2.44 2.03
Wiley, H. W., Principles and Practices of Agricultural Analysis, Vol.
1, pp. 352-354, Easton, Pa., 1906.
*The term ‘‘humus’’ is used in a number of different ways. Conti-
nental Europeans make it synonymous with organic matter. In some cases
it is used to indicate all of the partially decayed material of the soil. The
restricted meaning employed in this text is less confusing as it coincides
with the chemical interpretation. Grandeau believed the organic matter
thus dissolved was a determining factor in soil fertility.
*Grandeau, L., Traiti d’ Analyse de Matiéres Agricoles; I, p. 151, 1897.
*A comparison of the various methods is found as follows: Alway,
116 NATURE AND PROPERTIES OF SOILS
that of Hilgard? and that of Houston and McBride? seem
most important.
In the procedure an attempt is made to keep the concen-
tration of the ammonia in contact with the soil constant dur-
ing the extraction. Consequently the sample, after treatment
with the acid, is washed into a 500 cubic centimeter flask,
which is filled to the mark with 4 per cent. ammonia. Diges-
tion is allowed to proceed for twenty-four hours, with fre-
quent shakings. The solution is then filtered and evaporated
to dryness. The residue is weighed, after drying thoroughly
at 100° C, and then ignited, the loss being considered as
humus.
This method is open to serious criticism in that it is wholly
arbitrary and subject to considerable inaccuracy through
manipulation and the ignition of the humic residue. There
is also some doubt whether the figures obtained have any
direct relation to the fertility of the soil.*
62. The organic matter and nitrogen of representative
soils.—The amount of organic matter in soils varies so widely
according to the nature of the soil and climate conditions that
it is difficult to present representative figures. Excluding
peat and muck, which are 20 to 80 per cent. organic, the aver-
age mineral surface soil is found to contain from .50 per cent.
to 18 or 20 per cent. of organic matter. Some surface soils
of West Virginia,* averaging 2.88 per cent. organic matter,
F. J., and others, The Determination of Humus; Neb. Agr. Exp. Sta.,
Bul..115, June, 1910.
1Hilgard, E. W., Humus Determination in Soils; U. 8. Dept. Agr.,
Diy. Chem., Bul. 38 (edited by H. W. Wiley), p. 80, 1893.
? Houston, H. A., and McBride, F. W., A Modification of Grandeau’s
Method for the Determination of Humus; U. 8. Dept. Agr., Div. Chem.,
Bul. 38 (edited by H. W. Wiley), pp. 84-92, 1893. See also, Smith, O. C.,
A Proposed Modification of the Official Method of Determining Humus ;
Jour. Ind. and Eng. Chem., Vol. 5, No. 1, pp. 35-37, Jan., 1913.
’Gortner, R. A., The Organic Matter of the Soil; III. On the Pro-
duction of Humus from Manures ; Soil Sci., Vol. III, No. 1, pp. 1-8, Jan.,
1917. Carr, R. H., Is the Humus Content of the Soil a Guide to Fer-
tility; Soil Sci., Vol. III, No. 6, pp. 515-524, June, 1917.
‘Salter, R. M., and Wells, C. F., Analyses of West Virginia Soils;
W. Va. Agr. Exp. Sta., Bul. 168, Dec., 1918.
THE ORGANIC MATTER OF THE SOIL 117
range from .73 per cent. to 15.14 per cent., while similar fig-
ures on the Russian Tschernozen? vary from 3.45 to 16.72
with an average of 8.07 per cent. The subsoil of course runs
lower in every case. The following figures, while far from
representative, are suggestive :
TABLE XXII
PERCENTAGE OF ORGANIC MATTER (C X 1.724) IN CERTAIN
REPRESENTATIVE SOILS OF THE UNITED STATES.
DESCRIPTION SURFACE SUBSOIL
8 Residual soils—Robinson ?......... 1.76 64
3 Glacial and loessial soils—Robin-
FSCO Sah ARG pte AG NPN act AR 4.59 1.44
Piwansas Gill sols—Oall 2.2.52) 2.86 1.98
6 Nebraska loess soils—Alway?...... 3.83 1.96
30 Minnesota till soils—Rost and
DUIS RT RTC eT ard gee RE a AU 7.46 1.88
As the soil nitrogen is carried almost wholly by the organic
matter, and is a true organic constituent of the soil, its con-
sideration at this point is opportune. The nitrogen ° of soils
varies with the organic matter and may range in surface
mineral soils from .01 to .60 per cent. West Virginia“ soils,
* Kossowitsch, P., Die Schwarzerde; Internat. Mitt. f. Bodenkunde,
Band I, Heft 3-4, S. 316, 1912.
Robinson, W. O., The Inorganic Composition of Some Important
American Soils; U.S. Dept. Agr., Bul. 122, 1914.
Call, L. E., e€ al4 Soil Survey of Shawnee County, Kansas; Kans.
Agr. Exp. Sta., Bul. 200, 1914.
*Alway, F. J., and McDole, G. R., The Loess Soils of the Nebraska
Portion of the Transition Region: I. Hygroscopicity, Nitrogen and
Organie Carbon; Soil Sci., Vol. I, No. 3, pp. 197-238, Mar., 1916.
°Rost., C. O., and Alway, F. J., Minnesota Glacial Soil Studies; I. A
Comparison of the Soils of the Late Wisconsin and Iowan Drifts;
Soil Sci., Vol. XI, No. 3, pp. 161-200, Mar., 1921.
‘Soil nitrogen is determined by either the Kjeldahl or the Gunning
method. These will be described later. See paragraph 165.
"Salter, R. M., and Wells, C. F., Analyses of West Virginia Soils;
W. Va. Agr. Exp. Sta., Bul. 168, Dec., 1918.
118 NATURE AND PROPERTIES OF SOILS
for example, while averaging .147 per cent. nitrogen, range
from .043 to .539. Louisiana * soils average .049 per cent. with
a range from .001 to .109. In muck and peat the amount of
nitrogen is much higher, attaining in some eases 3 per cent.
The following figures indicate the nitrogen contents that
may be expected in average soils:
TABLE XXIII
PERCENTAGE OF NITROGEN IN CERTAIN REPRESENTATIVE SOILS
OF THE UNITED STATES
DESCRIPTION Soi SUBSOIL
71 Cecil soils of North Carolina?.... .048 .024
165 Norfolk soils of North Carolina ?. . .039 .020
16 Loess soils of Central U. S.*...... 154 .083
Sod Sentucky Soilsic 2 ecclesia 120 .070
50) Minnesota till sorls| osc. 46 a nae 308 .092
While the ratio between the respective amounts of soil
nitrogen and organic matter is no more constant than that
between the organic carbon and the organic matter
(C X 1.724 = organic matter), it is of some general value. If
* Walker, S. 8., Chemical Composition of Some Louisiana Soils as to
Series and Texture; La. Agr. Exp. Sta., Bul. 177, Aug., 1920.
*Williams, C. B., et al., Report on the Piedmont Soils, Particularly
with Reference to their Nature, Plant-food Requirements and Adapta-
bility to Different Crops; Bul. N. C. Dept. Agr., Vol. 36, No. 2, Feb.,
1915.
Williams, C. B., et al., Report on Coastal Plain Soils, Particularly
with Reference to their Nature, Plant-food Requirements and Suitability
for Different Crops; Bul. N. C. Dept. Agr., Vol. 39, No. 5, May, 1918.
*Robinson, W. O., et al., Variation in the Chemical Composition of
Soils; U.S. Dept. Agr., Bul. 551, June, 1917. Alway, F. J., and MeDole,
G. R., The Loess Soils of the Nebraska Portion of the Transition Re-
gion: I. Hygroscopicity, Nitrogen and Organic Carbon; Soil Sci.,
Vol. I, No. 3, pp. 197-238, Mar., 1916. Also, Bennett, H. H., Soils and
Agriculture of the Southern States, pp. 332-353; New York, 1921.
° Averitt, S. D., The Soils of Kentucky; Ky. Agr. Exp. Sta., Bul. 193,
July, 1915.
* Rost, C. O., and Alway, F. J., Minnesota Glacial Soil Studies: I. A
Comparison of the Soils of the Late Wisconsin and the Iowan Drifts;
Soil Sci., Vol. XI, No. 3, pp. 161-200, Mar., 1921.
THE ORGANIC MATTER OF THE SOIL 1)
the percentage of nitrogen in the soil is multiplied by 20, a
rough idea of the amount of organic matter may be obtained
(N X 20 = organic matter). The following data from Rost
and Alway? illustrate not only the variations in organic
matter and nitrogen that may be expected in the surface and
subsurface of different soils, but the correlation between the
organic matter and nitrogen just mentioned:
TABLE XXIV
AVERAGE PERCENTAGE OF ORGANIC MATTER (C X 1.724) ANpb
NITROGEN IN THIRTY REPRESENTATIVE MINNESOTA TILL SOILS
FROM THREE SERIES. THE FIGURES FOR EACH OF THE
THREE SOIL TYPES ARE AVERAGES OF TEN ANALYSES.
FOREST UPLAND PRAIRIE LOWLAND
CARRINGTON |CARRINGTON SILT PRAIRIE
LOAM LOAM FarcGo SItt LoAM
DEPTH
ORGANIC] NitrRo- JORGANIC|} NiTRO- | ORGANIC | NITRO-
MatTrEeR| GEN | MarTreR| GEN | MATTER GEN
1— 6 inches...| 5.384 | .253 | 7.96 | .873 | 13.08 | .616
(17 ae Ona 2.41 | .119 | 6.00 | .285 8.00 | .385
13—24 “...... Pas ONS: oll) 2165 3.24 | .150
20308 “Fees coon) 20415) 131 | 2062 1.39 | 054
The following tentative classification of mineral soils on the
basis of their percentages of organic matter and nitrogen is
offered for generalized field use:
TABLE X XV aoe
PERCENTAGE OF PERCENTAGE OF
DESCRIPTION ORGANIC MATTER NITROGEN
LSI 2, CR ee .0O— 3.0 00-— .10
IRC MIMER IAN 8 2) ons hcsavahs ee. 5 3.0— 6.0 1025
Lalas fh. eae ee 6.0—10.0 .20— .40
Wheel i rr above 10.0 | above .40
*Rost, C. O., and Alway, F. J., Minnesota Glacial Soil Studies: I. A
Comparison of the Soils of the Late Wisconsin and the Iowan Drifts ;
Soil Sci., Vol. XI, No. 3, pp. 161-200, Mar., 1921.
120 NATURE AND PROPERTIES OF SOILS
63. The humus content of soils is of course lower than
the organic matter contained in them. It likewise varies
according to climate and region, not only in amount, but also
in composition. The following data from Hilgard! and
Alway ” illustrate these points:
TABLE X XVI
THE COMPOSITION OF CALIFORNIA ARID AND HUMID SOILS.
(HILGARD )
HuMUS IN | NITROGEN IN| NITROGEN IN
DESCRIPTION Sorin Humus Sorn
(Percentage)|(Percentage)| (Percentage)
41 Arid uplands soils..... 91 15.23 S35
15 Subirrigated arid soils. . 1.06 8.38 .099
DA» mig: SONS {hse ee 4.58 4.23 .166
TABLE X XVII
COMPARATIVE COMPOSITION OF SEMI-ARID (WAUNETA) AND HUMID
(WEEPING WATER) LOESS SOILS OF NEBRASKA. (ALWAY)
ORGANIC MATTER Humus NITROGEN
(Percentage) (Percentage) _ (Percentage)
DEPTH
WEEPING WEEPING WEEPING
WAUNETA Thien WAUNETA Wig naae WAUNETA WATER
let foot. | 297 |. 458) || toe | aaa set) sean
Amd nce leae 3.02 65 1.29 082 154
BEG utes) 1209 1.38 .48 may) 065 .083
AGE ys) P 19 83 4 27 .046 059
Deny (ak OO 45 .26 23 .038 043
Gthe 45 36 .26 ag .030 .038
1 Hilgard, E. W., Soils, pp. 136-137; New York, 1911. For further
data regarding Hilgard’s conclusions see: Alway, F. J., and Bishop,
E. S., Nitrogen Content of the Humus of Arid Soils; Jour. Agr. Res.,
Vol. 5, No. 20, pp. 909-916, Feb., 1916.
2 Alway, FP. J., et al., The Loess Soils of the Nebraska Portion of the
Transition Region: I. Hygroscopicity, Nitrogen and Organic Carbon;
Soil Sci., Vol. I, No. 3, pp. 197-238, Mar., 1916. IJ. Humus, Humus-Nt-
trogen and Color; Soil Sci., Vol. I, No. 3, pp. 239-258, Mar., 1916.
THE ORGANIC MATTER OF THE SOIL 121
It is evident that humid soils not only contain the greater
amounts of organic matter, but also excel in humus. The
humus of the arid regions, however, is richer in nitrogen, due
to the character of the decomposition going on. As a conse-
quence the nitrogen in the soil of humid regions is not greatly
in excess of that in the soils of drier climates. The percentage
of humus not only decreases in the lower depths of the soil,
but also changes in composition, becoming poorer in nitrogen
the deeper the soil.
64. The influence of organic matter on the soil_—The
effects of organic matter on soil and plant conditions are as
numerous as they are complex. Some of the influences are
direct, others are indirect. As the specific gravity of organic
matter is low, the first effect of its addition would be to lower
the specific gravity of the soil. The organic matter tends also
to spread the individual particles of soil farther apart, especi-
ally in a clay.. Such action will markedly influence the volume
weight.
The loosening effects of organic matter are especially ap-
parent in such soil as clay. On the other hand, because or-
ganic matter has a higher cohesive and adhesive power than
sand, it performs the function of a binding material with the
latter soil, a condition much to be desired in a material pos-
sessing such loose structure.
As the water capacity of organic matter is very high, a soil
rich in organic constituents usually possesses a high water-
holding power. This makes possible greater volume changes
both on drying and in the presence of excessive moisture. The
eranulating effects of wetting and drying and freezing and
thawing are, therefore, accelerated. The increased water ca-
pacity of the soil, resulting from the presence of organic ma-
terials, is of great importance in drought resistance, while
the black color imparted by the humus tends to raise the
heat absorptive. power of the soil.
The better tilth induced by the presence of organic matter
122 NATURE AND PROPERTIES OF SOILS
in any soil tends to facilitate ease in drainage and to encour-
age good aération. These two conditions are of course neces-
sary for the promotion of soil sanitation. Root extension and
bacterial activity are thus increased. It is of especial impor-
tance that the splitting-up of the organic matter shall take
place in the presence of plenty of oxygen, in order that toxic
compounds may not be generated and that products highly
favorable to plant growth should be formed.
The soil organic matter, however, functions in other ways
than those strictly physical and chemical. Its degradation
products may serve as nutrients for higher plants. Bacteria
and other soil organisms are also furnished a source of energy
thereby and the production of carbon dioxide is much in-
creased. This carbon dioxide, as well as the organic acids
generated, tends to raise the capacity of the soil-water as
a solvent, and thus the amount of mineral material available
to the crop is greatly increased. The general effect of organic
matter, then, is to better the soil as a foothold for plants, and
to increase either directly or indirectly the available nutri-
ent supply for the crop.
65. Maintenance of soil organic matter..—The mainte-
nance of a proper supply of organic matter in a soil is a ques-
tion of great practical importance, as productivity is gov-
erned very largely by the organic content of the soil. This
maintenance of the soil organic matter depends on two factors:
(1) the source of supply and methods of addition; and (2)
the promotion of proper soil conditions in order that the
1Snyder, H., Effect of the Rotation of Crops upon the Humus Content
and the Fertility of Soils; Minn. Agr. Exp. Sta. Bul, 53, June,
1897. The Production of Humus in Soils; Minn. Agr. Exp. Sta., Bul.
89, Jan., 1905. Morse, F. W., Humus in New Hampshire Soils; N. H.
Agr. Exp. Sta., Bul. 138, June, 1908. Hopkins, C. G., Phosphorus and
Humus in Relation to Illinois Soils; Il. Agr. Exp. Sta., Cire. 116, Feb.,
1908. Thatcher, R. W., The Nitrogen and Humus Problem of Dry
Farming; Wash. Agr. Exp. Sta., Bul. 105, June, 1912. Fippin, E. O.,
Nature, Effects and Maintenance of Humus in the Soil; Cornell Reading
Course for the Farm, Vol. III, No. 50, Oct., 1913. Loughridge, R. H.,
Humus of California Soils; Calif. Agr. Exp. Sta., Bul. 242, Jan., 1914.
THE ORGANIC MATTER OF THE SOIL 123
organic matter may perform its legitimate functions. The
source of supply will be considered first.
The organic matter of the soil may be increased in a nat-
ural way by the plowing under of green crops. This is
called green-manuring and is a very satisfactory practice.
Such crops as rye, buckwheat, clover, peas, beans, and vetch
lend themselves to this method of soil improvement. Not
only do these crops increase the actual organic content of
a soil, but in the case of legumes the nitrogen may also be in-
creased in amount, if the nodule bacteria are present and
active.
Green-manures to be effective must be hardy, rapid in
growth, succulent, and should produce abundant foliage. Rye
and oats are particularly valuable from this standpoint. Such
legumes as cowpeas, vetch, field peas, soybeans, and velvet
beans are adapted to summer growth. Red clover or sweet
clover, being a biennial, may be seeded one year and turned
under the next spring. Oats and peas or rye and peas make
a very good combination for fall green-manuring. Hairy or
winter vetch may be seeded with rye in the autumn and used
as a green-manure in the spring. In the South green-manur-
ing crops may be ucilized to much better advantage than in the
northern states as the longer growing season permits the use
of a green-manure following the normal harvest.
Due to the tendency of bare soil to lose nutrients by leach-
ing, especially in the summer and fall, it is always best to
keep the land covered with vegetation of some kind. Cover- or
catch-crops are used for this purpose, especially on sandy land,
although they are profitable on heavier soils as well. Wheat
on sandy land may be followed by cowpeas, which not only
conserve nitrates but fix nitrogen from the air in addition.
Rape, cowpeas, vetch, and soybeans are sometimes seeded in
corn at the last cultivation. When a soil receives clean culti-
vation a part of the year, as is practiced very frequently in
orchards, it is very desirable that a crop be plowed under oc-
124 NATURE AND PROPERTIES OF SOILS
easionally to replace the organic matter lost by oxidation.
Whether such catch-crops are pastured or turned under, they
tend to increase the soil organic matter. Weeds, which spring
up after the crop is harvested, are often valuable as cover-
and catch-crops and when turned under aid in maintaining
the organic content of the land.
Crop residues form no inconsiderable portion of the organic
matter produced on the land. If such materials as straw,
stubble, cornstalks, and the like are incorporated in the soil,
much will be accomplished towards the upkeep of the organic
matter. The burning of straw and cornstalks, especially in
the Middle West, entails an enormous waste of carbon as well
as of nitrogen. The value of crop residues has been demon-
strated very conclusively by the Illinois Experiment Station *
on their outlying experimental farms. At Bloomington, for
instance, the turning under of crop residues for five years
increased the wheat yields 4.4, 7.9 and 5.9 bushels in 1911,
1912 and 1913 respectively.
Farm manure is one of the most important by-products on
the farm and is especially valuable because of its organic mat-
ter. Although only about one-fourth of the organic materials
of the original food given the animal ever reaches the land,
the use of such a by-product is worth while, since the carbon
it contains comes from the air and not from the soil. The main
losses that the carbon of the crop undergoes when thus util-
ized are due to the digestive influences of the animal and to
the leaching and fermentation which goes on in the manure.
While sufficient manure ordinarily can not be produced from
the crops grown on the farm to maintain the organic matter
of its soil, the use of farm manure with green-manure and crop
residues in a proper rotation is fundamental in good soil man-
agement.
66. Organic matter and soil conditions—Improper soil
*Mosier, J. G., and Gustafson, A. F., Soil Physics and Management,
p. 171; Philadelphia and London, 1917.
THE ORGANIC MATTER OF THE SOIL 125
conditions not only prevent the proper decay of organic mat-
, but also tend to encourage the production of products in-
imical to plant growth. Therefore, in order that organic ma-
terials added to any soil may produce the proper decomposi-
tion products and perform their normal functions, soil con-
ditions in general must be of the best. Tile drainage should
be installed, if necessary, in order to promote aération and
y:
50 [ere
ANIMAL [ere
oO a _ 36
y RGANIC
“ ercanie
GN ma aM ase ae
A2SAQ IWAN
GREEN MANURES
CROP RESINVES
Fig. 22.—Diagram showing the practical sources of the soil organic
matter and the cycle through which its constituents pass. Note
that the carbon, oxygen and hydrogen come very largely from air
and water and that fixation of nitrogen may occur if the crop is
a legume. Only about 25 per cent. of the organic matter fed to
animals ever reaches the soil in farm manure under average con-
ditions.
granulation. Lime should be added if basic materials are
lacking, for it promotes bacterial activity as well as plant
growth. The addition of fertilizers will often be a benefit,
as will also the establishment of a suitable rotation. The
rotation of crops not only prevents the accumulation of toxic
materials, but also, by increasing crop growth, makes pos-
sible a larger addition of organic matter by green-manuring.
126 NATURE AND PROPERTIES OF SOILS
67. Resume.—An understanding of the complex organic
relationships within the soil is of great practical value, as
it determines to a large degree the yield of crops, their rota-
tion order and their fertilization. Moreover, tillage operations
must be varied according to the organic nature of the soil.
Unless a system of soil management is adopted which will at
least partially keep up the organic matter of the soil, crop
yields may be expected to decrease materially in a few years.
Good soil management seeks to adjust the addition of or-
ganic matter, the physical and chemical condition of the soil,
and the losses through cropping and leaching, in such a way
that paying crops may be harvested while impairing the or-
ganic supply of the soil as little as possible. Any system of
agriculture that tends permanently to lower the organic mat-
ter of the land is impractical and improvident, as well as un-
scientific.
CHAPTER VI
THE COLLOIDAL MATTER OF THE SOIL?
RESEARCH in physics and physical chemistry is each day
making it clearer that the properties of matter are by no
means entirely determined by chemical composition. Matter
varies in its physical character and its chemical activities with
its fineness of division. Coarsely divided substances function
much differently when they become molecular complexes and
still more diversely when their aggregates are divided into
their molecular and ionic components. Because of the par-
ticular properties exhibited by material in a fine state of di-
vision, approaching but not attaining a molecular simpiifica-
tion, a special name is utilized. A substance in such a con-
dition is said to be colloidal or in the colloidal state.
68. The colloidal state? arises when one form of matter
(either a gas, liquid, or solid) in a very fine state of division
1 Colloidal chemistry is now so well understood that it will be necessary
to develop only those phases which have a direct bearing on soil
phenomena.
*Some of the following general references may prove helpful:
Ramann, E., Kolloidstudien bei Bodenkundlichen Arbeiten; Kolloid-
chemische Beihefte; Band II, Heft 8/9, Seite 285-303, 1911.
Niklas, H., Die Kolloidchemie und ihre Bedeutung fiir Bodenkunde,
Geologie, und Mineralogie; Internat. Mitt. fiir Bodenkunde, Band II,
Heft 5, Seite 383-403, 1913.
Bancroft, W. D., The Theory of Colloid Chemistry ; Jour. Phys. Chem.,
Vol. 18, No. 7, pp. 549-558, 1914.
Taylor, W. W., The Chemistry of Colloids; New York, 1915.
Hoa E. F., The Physical Properties of Colloidal Solutions; London,
1916.
Zsigmondy, R., The Chemistry of Colloids, Part I; trans. by E. B.
Spear, New York, 1917.
Wiegner, G., Boden und Bodenbildung ; Dresden and Leipzig, 1918.
Bancroft, W. D., Applied Colloidal Chemistry ; New York, 1921.
Thatcher, R. W., Chemistry of Plant Life; Chap. XV, New York, 1921.
127
128 NATURE AND PROPERTIES OF SOILS
is distributed through a second, which may also be a gas, a
liquid, or a solid. The material in the finely divided state
is called the dispersed phase, while the matter containing it
is designated as the continuous or dispersive medium. A
very good example of a colloidal system occurs when very
fine clay particles (solids) are suspended in water (liquid)
or when an emulsion of oil and water is formed, the oil under
certain conditions becoming the dispersed material, hetero-
geneously disposed. The particles of material in a colloidal
state in these cases are so small that they will not sink as long
as conditions are stable. Moreover, they exhibit the Brownian
movement,’ the oscillations increasing very rapidly as the
size decreases. Such particles are molecular complexes and
the solution is heterogeneous. In this respect a colloidal solu-
tion differs from a true solution, which is homogeneous, the
particles being molecules and often ions.
69. Size of colloidal particles——The size of the particles
of matter in a colloidal state vary with the material and with
the conditions of formation. The diameters of material in a
colloidal state are considered to range from 100 uw uw? (.0001
m.m.) to 1 uw uw (.000001 m.m.). Above 100 uw uw suspended
material is usually sinkable, while below 1 wu u the particles
generally become single molecules and a true solution is at-
tained. Theoretically it would seem possible to pass from
a suspension to a true solution without a break by a progres-
sive subdivision of particles. There seems to be a discontinu-
ity, however, between the colloidal state and a true solution.
As the molecular complexes subdivide, they at last go into
solution and may reprecipitate as coarser complexes, thus
1Small particles, even those well within the range of ordinary micro-
scopic vision, exhibit, when suspended in a liquid, an oscillating motion
around a central position. This movement, which is called the Brownian,
is inversely proportional to the size of the particle. It is probably due
to the bombardment of the molecules and ions of the liquid in which
the particle is suspended. The Brownian movement is very slow for
particles of a diameter of .001 mm.
2A micron (#) =.001 mm. or 10-? mm. A millimicron (144) =
.000001 mm. or 10-°mm.
THE COLLOIDAL MATTER OF THE SOIL 129
maintaining a considerable gap between the two states of
matter.*
70. The phases of a colloidal state——As already empha-
sized, two phases are necessary for a colloidal state—a dis-
persive medium and a material that will heterogeneously
disperse therein. Threee materials may function as a dis-
persive medium—a liquid, a solid, or a gas. In the same way,
with each dispersed material there are three possibilities—
a liquid, a solid, or a gas. This gives eight general phases
to be considered in colloidal chemistry.”
The liquid-solid and the liquid-liquid phases are by far
the most important as far as soil materials are concerned.
The dispersed materials of soil colloids are the minerals either
in a hydrous or non-hydrous condition and the organic mat-
ter in various stages of decay. The dispersive medium is of
course the soil solution.
71. Colloids vs. crystalloids—It must not be inferred,
because the colloidal state is often wrongly contrasted with
the crystalloidal, that material in a colloidal condition is al-
ways amorphous. It is often crystalline. Moreover, it may be
animate, as some bacteria are minute enough to function col-
loidally. It is obvious also that the same chemical material
may exist either in the colloidal or non-colloidal state. For
example, silicic acid, hydrated ferric oxide, gold, carbon black,
* Bancroft, W. D., Applied Colloidal Chemistry, p. 183; New York
1921.
? The eight phases with examples are:
ES{aIITiG lar cl=(0) Io Has Rare ree te eee Carbon in steel.
quid imsolid 520.5. ..26.-5 water of crystallization
Grasmime sOlid@ sven cra todas hee gases in minerals
Sle thay Wels Bers ode . colloidal solution of metals
rgpidian WqQuid: 2\ a... es ope whe emulsions of oil in water
(GiT S10) CGT Cs lye ee een ee air in water, foam
(= CIS Pn ET: ae ee eee ee smoke in air
AAU QUNG UNAS! ychdta «slam a sie clouds
\CiGTS TED) 7077) en a noncolloidal, merely a mixture of
molecules.
After Burton, E. F., The Physical Properties of Colloidal Solutions,
p. 10; London, 1916.
130 NATURE AND PROPERTIES OF SOILS
and other materials, may or may not be colloidal, according
to circumstances. The fineness of division is the explanation
of colloidal properties. In order to place such a discussion on
a more understandable basis, a few additional illustrations
may not be amiss. The following materials, which may exist
in a colloidal condition, are for convenience grouped under
two general heads, organic and inorganic:
Orgamc: Gelatin, agar, caramel, albumin, starch jelly,
humus, some bacteria, carbon black, and tannic acid.
Inorgamc: Gold, silver, hydrated ferric oxide, arsenious
sulphide, zine oxide, silver icdide, Prussian blue, and the like.
72. The properties of colloidal materials——In general,
there are certain properties which materials in a colloidal
state exhibit and by which they are distinguished from true
solutions. In the first place, since they are not in true solu-
tion, they exert little or no effect on the freezing point and
the vapor pressure of liquids. Some colloids have absolutely
no effect on these properties, while others, as they allow a
certain small amount of true solution to take place, do possess
such influences to a slight degree. Secondly, colloids do not
pass readily through semi-permeable membranes, such as
parchment paper or pig’s bladder. Their diffusive powers
are low. This serves as an easy way of separating colloidal
and non-colloidal material. Thirdly, heat and the addition
of electrolytes will serve to coagulate certain colloids, a prop-
erty which again serves to distinguish them sharply from a
true solution. Fourthly, colloidal material has great ab-
sorptive power, not only for water, but also for gases and
materials in solution, a quality of extreme importance in soil
phenomena.
Many colloids are coagulated by the addition of an elec-
trolyte,t the phenomenon often being spoken of as floccula-
* An electrolyte is any substance which has the ability when in solution
to carry an electric current, the substance suffering decomposition there-
by. The current is carried by the liberated ions. Hydrochloric acid,
for example, dissociates into ionic hydrogen and ionic chlorine, the
THE COLLOIDAL MATTER OF THE SOIL 181
tion.1 A very good example is afforded by treating a colloidal
clay suspension with a little calcium hydroxide. The tiny
particles almost immediately coalesce into floccules, and be-
eause of their combined weight, sink to the bottom of the
containing vessel, leaving the supernatant liquid clear. The
same action will take place in the soil itself, but of course with
less rapidity and under conditions less noticeable to the eye.
Some dispersed materials, when thus separated from their
dispersive medium, will reassume the colloidal state with
ease when an opportunity is offered. In other cases, the col-
loidal condition is difficult to restore. Gelatin is an example
of the first group and is called a reversible colloid. Ferric
hydrate is an example of the more or less irreversible type.
Just why this phenomenon of flocculation or agglutination
takes place is rather difficult to state. It is found that cer-
tain colloids, when subjected to the proper electric current,
will migrate to either the positive (anode) or the negative
(cathode) pole. These particles evidently carry a charge of
electricity. Hydrated ferric oxide, aluminium hydrate, and
basic dyes, for example, move toward the cathode and carry
a positive charge; while arsenious sulphide, silicic acid, gold,
silver, humus and acid dyes move toward the anode and are
negative. It is assumed that as long as the colloidal particles
remain charged, they repel each other and the colloidal state
persists. When an electrolyte is added, which develops by
ionization a dominant opposite charge, it is supposed to cause
a neutralization of the repellent electricity carried by the
colloidal particles, and flocculation occurs.
Certain colloids may flocculate certain others, as the gela-
tinization of silic acid by hydrated ferric oxide. At times
one colloid may protect another, probably by surrounding it
former carrying a positive and the latter a negative charge of electricity
(H++C-). KNO, gives K*+ NO,. The ionization varies with the
substance, the dilution and certain other conditions.
1See Wolkoff, M. I., Flocculation of Soil Coiloidal Solutions; Soil
Sei., Vol. I, No. 6, pp. 585-601, June, 1916. A good bibliography is
appended.
132 NATURE AND PROPERTIES OF SOILS
with a protective film. Such a case may be shown by adding
gelatin to a clay suspension. When a colloid such as hy-
drated ferric oxide is flocculated, it loses to a certain extent
its colloidal properties, and assumes the characteristics of
non-colloidal materials.
73. Soil colloids and their generation.1—In soils there
seem to exist two very general and indefinite groups of col-
loidal materials, besides all gradations and variations: (1) vis-
cous, gelatinizing and reversible colloids, and (2) non-viscous,
non-gelatinizing, easily coagulable and irreversible colloidal
matter. The decaying organic materials in the soil and the
mineral matter contribute liberally to both groups. Both
of these groups, with their bewildering variations and grada-
tions, play important parts in the physical and chemical phe-
nomena of the normal soil.
The organic colloidal matter in a soil rich in decomposing
tissue is obviously of great importance. Such material is very
heterogeneous, very complex, and constantly changing. As
yet very little study of the organic soil colloids has been made
because of the difficulties presented by the problem. Humus
colloids may be viscous or non-viscous, as the case may be,
and may or may not be thrown down by calcium hy-
droxide. The absorptive power of these colloids for water,
gases, and such materials as calcium, magnesium, and potas-
sium is very highly developed—as much so, probably, as that
of the inorganic colloids. These organic colloids are not only
added as a part of the original plant tissue but are also
formed during the tearing-down and splitting-off processes
1Van Bemmelen, J. M., Dis Absorption; Seite 114-115, Dresden, 1910.
Also, Die Absorptionsverbindungen und das Absorptsvermogen der
Ackererde; Landw. Ver. Stat., Band. 35, Seite 69-136, 1888; Way, J. T.,
On Deposits of Soluble or Gelatinous Silica in the Lower Beds of the
Chalk Formation; Jour. Chem. Soe., Vol. 6, pp. 102-106, 1854. War-
ington, R., On the Part Taken by Oxide of Iron and Alumina in the
Adsorptive Action of Soils; Jour. Chem. Soe., 2d ser., Vol. 6, pp. 1-19,
1868. Cushman, A. 8., The Colloid Theory of Plasticity; Trans. Amer.
Cer. Scc., Vol. 6, pp. 65-78, 1904. Ashley, H. E., The Colloid Matter
of Clay and its Measurements; U. S. Geol. Survey, Bul. 388, 1909.
THE COLLOIDAL MATTER OF THE SOIL 1383
incident to bacterial activity, during which, compounds are
thrown off in such a state of division as to assume the condi-
tion that has been designated as colloidal. Of course the chem-
ical forces of weathering are also operative in this process of
organic colloidal production.
While some inorganic soil colloids, as silicic acid and hy-
drated ferric oxide, are rather simple chemically, most of
the mineral colloidal material is extremely complex. The soil,
especially when of a clayey nature, always contains large
amounts of compheated hydrated aluminum silicates of con-
stantly varying constitution. Such material, whether simple
or complex, arises from ordinary weathering reactions and
develops in the soil as the latter is built up. <A simple ex-
ample may be cited. When a feldspar undergoes decomposi-
tion the following reaction may be used to illustrate the pos-
sible change that takes place:
2K Al1Si,0, + 2H,O + CO, = H,Al1,Si,0, + 4810, + K,CO,
Orthoclase Water Carbon Kaolinite Silica Potassium
Dioxide Carbonate
Kaolin almost always originates in this way, an alkali car-
bonate and silica being formed at the same time. The proc-
ess is essentially one of hydration and carbonation; the ear-
bon dioxide by reacting with the alkali permits the process to
go on. The silica may go to one or more of three possible
destinations, according to conditions,—to free quartz, to col-
loidal silica or to make up complex colloidal hydrated alu-
minum silicates. The last mentioned condition seems the most
*The Bureau of Soils have prepared a colloidal solution from soil
by passing a well shaken mixture of soil and water through a Sharples
centrifuge. The colloidal matter was separated from its dispersive
medium by means of a porcelain filter. This ultra-clay seemed to be
a mixture of various colloids and consisted mainly of hydrated alu-
minum silicates with varying amounts of ferric hydroxide, silicic acid,
organic matter and possibly aluminum hydroxide.
Moore, C. J., Fry, W. H., and Middleton, H. E., Methods for Deter-
mining the Amounts of Colloidal Material in Soils; Jour. Ind. and
Eng. Chem., Vol. 13, No. 6, pp. 527-530, June, 1921.
134 NATURE AND PROPERTIES OF SOILS
probable fate of the silica as the process is strongly one of
hydration.
74. Influence of colloidal material’ on soil properties.—
1The amount of matter in a colloidal state in soils is extremely
variable, ranging from almost nothing in sand to a very large percentage
in heavy plastic clays. There is no satisfactory means of finding the
amount of colloidal material in soil. All of the available methods depend
for their expression on the intensity of certain qualities, supposed to
be developed by colloid content. This indicates that the methods are
largely comparative rather than exact or strictly analytical in nature.
Ashley ’s method depends on the absorption of certain dyes to indicate
the relative amount of material in a colloidal state. The difficulty in this
method, however, lies in choosing the most effective dye and regulating
its concentration. Moreover, different colloids vary so much in absorp-
tive capacity for the same ‘dye, that only roughly comparative results
have thus far been possible.
Mitscherlich uses the absorptive capacity of the soil for water vapor
as a colloidal index. In this method the air-dry soil in a thin layer is
brought to absolute dryness over phosphorus pentoxide. It is then
placed in a desiccator over a 10 per cent. solution of sulfuric acid and
the condensation is hastened by a partial vacuum. The sulfuric acid
is used in order to prevent the deposition of dew on the soil. After
exposure for about twenty-four hours, the soils are found to have taken
up their maximum moisture of condensation, which is called the hygro-
scopic water. The soil is then weighed, and the increase, figured to a
percentage based on dry soil, is taken as a measure of colloidal content.
The reverse process may also be followed, by exposing air-dry soil in a
saturated atmosphere and afterwards drying over phosphorus pentoxide.
The hygroscopicity of the soil, or its hygroscopic coefficient, is thus the
basis for colloidal comparison.
Ashley, H. E., The Colloid Matter of Clay and Its Measurement;
U.S: Geol. Survey, Bul. 388, 1909.
Rodewald, H., und Mitscherlich, A. E., Die Bestimmung der Hygro-
skopizitat; Landw. Ver. Stat., Band 59, Seite 433-441, 1903. Also,
Mitscherlich, E. A., und Floess, R., Hin Beitrage cur Bestimmung der
Hygroskopizitét und zur Bewertung der physikolischen Bodenanalyse ;
Internat. Mitt. f. Bodenkunde, Band 1, Heft 5, Seite 463-480, 1912.
Ehrenberg, P., und Pick, H., Beitrage zur Physikalischen Bodenunter-
suchung; Zeit. f. Forst- und Jagdwesen, Band 43, Seite 35-47, 1911.
Also, Vageler, P., Die Rodewald-Mitscherlichsche Theorie der Hygro-
skopizitat vom Standpunkte der Colloidchemie und ihr Wert zur Beur-
teitung der Boden; Fuhling’s Landw. Zeit., Band 61, Heft 3, Seite 73-83,
1912.
Stremme, H., and Aarnio, B., Die Bestimmung des Gehaltes anorgan-
ischer Kolloide in Zersetzten Gesteinen und deren tonigen Unlagerungs-
produkten; Zeitsch. f. Prak. Geol., Band 19, Seite 329-349, 1911. ;
Tempany, H. A., Shrinkage in Soils; Jour. Agr. Sci., Vol. VIII,
Pio, apps ol2-530)) June, 19.
Beaumont, A. B,, Studies in the Reversibility of the Colloidal Condi-
tion of Soils ; Cornell Agr. Exp. Sta., Memoir 21, Apr., 1919.
THE COLLOIDAL MATTER OF THE SOIL 135
As may naturally be inferred the influence of the colloidal
matter on soil conditions, especially as related to plants, is
extremely important. This influence is exerted in a number
of ways, modifying the physical and chemical as well as the
biological activities within the soil.
One important attribute imparted to soil by colloid develop-
ment is high absorptive power. This power extends not only
to condensation of gases, but also to water and to materials
in solution. The water of condensation on dry soil particles
when exposed to a saturated atmosphere is largely determined
by the colloidal content. The absorptive capacity for mate-
rials in solution affects both bases and acid radicals, although
the former is usually more strongly influenced. This has a
very important bearing on the economic use of fertilizers and
on the loss of plant nutrients from the soil. Colloidal mate-
rial may also function as a catalyst’ in that it may force
certain reactions that otherwise might proceed but slowly.
Since an adjustment is always taking place between the
soil colloidal material and the soil solution as far as soluble
constituents are concerned, it is readily seen that not only
the concentration but also the composition of the latter is at
least partially a function of the colloidal matter of the soil.
Colloidal matter, moreover, does not exert the same absorptive
power for all material but is capable of a certain amount of
selection. For example, if ammonium sulfate is added to a
soil, the ammonia is strongly taken up, which tends to release
the sulfate ion. The continuous use of such a fertilizer on a
soil low in active bases will ultimately result in an acid con-
dition. This is another example of the practical importance
of the soil colloidal matter.
The movement of air and water in the soil is strongly in-
fluenced by colloidal materials. In a fine soil in which the
individual pore spaces are normally very minute the develop-
* A catalyst is a material capable of hastening or retarding a chemical
reaction, the catalytic agent itself not entering into the reaction.
136 NATURE AND PROPERTIES OF SOILS
ment of colloidal matter may seriously interfere with aération
and capillary movement of water. The loosening of a clay
soil tends to ameliorate such conditions and to counteract
0 1000 2000 5000 4000 5000 c.c.
Fig. 23.—Curves showing the absorption of PO, in parts per million by
various soils from a solution of mono-calcium phosphate containing
200 parts to the million of PO, The volume of the percolate is
used as the abscissas. Such absorption is a rough measure of the
colloidal content of a soil.
the unfavorable influence of the colloidal condition of the
soul. Such a structural condition is largely ascribed to the
plasticity and cohesion’ of the soil, which are in turn, of
+ Any material which allows a change of form without rupture and
which will retain this form when the pressure is removed, is said to be
plastic. Putty with a proper admixture of oil is a very good example
of a plastic body. As is well known, various materials differ in
plasticity.
Very closely correlated with plasticity, but not in exact similarity, is
cohesion. By the cohesion of a soil is meant the tendency that its
particles exhibit in sticking together and in conserving the mass intact.
THE COLLOIDAL MATTER OF THE SOIL 137
course, governed by the amount and the quality of colloidal
matter present.'
In general it is found that, other conditions being equal,
an increase of certain types of colloidal matter increases plas-
ticity; in other words, the ease with which a soil may be
worked into a puddled condition becomes greater. This is a
rather undesirable quality when too pronounced, and in clays,
in which it is most likely to be developed because of the pres-
ence of large amounts of mineral colloids, some means of
decreasing the colloidal influence is advisable. This great
plasticity is developed because the colloids, especially those
of a gelatinous and viscous nature, facilitate the ease with
which the particles may move over one another and yet cohere
sufficiently to prevent disruption of the mass. In general,
also, the greater the plasticity of a soil, the greater is the
cohesion when dry. In soils, then, in which certain kinds of
colloidal materials are very high, clodding may occur if the
soil is tilled too dry because of the great tendency of the par-
ticles to cohere. Cohesion and plasticity, as factors in soil
structure, soil granulation, and tilth will receive further atten-
tion later.
Tt must not be inferred from the preceding discussion that
the generation of colloidal matter is always detrimental to
soil conditions. In sandy soils the presence of such material
is extremely beneficial as it tends to bind the soil together,
promotes granulation, and prevents loss of plant nutrients by
leaching. It is only in heavy soils in which excessive amounts
of mineral colloids may develop that a detrimental condition
is likely to exist. This occurs because of a high cohesion and
plasticity, because of the absorption of plant nutrients and
because of tendencies toward acidity. The addition of organic
*Davis, N. B., The Plasticity of Clay; Trans. Amer. Cer. Soc., Vol.
16, pp. 65-79, 1914. Cushman, A. S., The Colloid Theory of Plasticity ;
Trans. Amer. Cer. Soc., Vol. 6, pp. 65-78, 1904. Also, Ashley, H. E,,
The Colloid Matter of Clay and Its Measurement; U. S. Geol. Survey,
Bul. 388, 1909.
138 NATURE AND PROPERTIES OF SOILS
matter and the development of non-plastie organic colloids
will do much to alleviate such conditions.
75. Resume.—The attempt to explain natural phe-
nomena from the standpoint of crystalloidal chemistry alone
is a failure. Nature has chosen to reveal herself, largely in
colloidal form. Such a condition of matter is the rule and
not the exception. Whether the sky, the ocean, or the land
is dealt with, the larger part of the natural phenomena are
plausibly explained only through knowledge of colloidal chem-
istry.
In general, the more complex the material and the more
intricate the reactions to which it is subjected, the more likely
it is that the colloidal state will result. Proteid materials, for
example, whether in plants or animals, are almost always col-
loidal. It is to be expected, therefore, that the soil with its
complicated organic and inorganic components and its rapid
and complex reactions should generate colloidal matter and
that material in such a state should play a prominent part
in soil and plant activities.
CHAPTER VII
SOIL STRUCTURE AND ITS MODIFICATION
THE structural condition of the soil is very important to
plant growth, since the circulation of air and water so nec-
essary to normal development is controlled thereby. The struc-
tural condition may be loose or compact, hard or friable, gran-
ulated or non-granulated, as the case may be. Of these con-
ditions granulation, especially in heavy soils, is of vital im-
portance, since it is really a summation of all favorable struc-
tural conditions. By granulation is meant the drawing to-
gether of the small particles around suitable nucleii, so that
a crumb structure is produced. The grains thus cease to
function singly. The importance of such a structural condi-
tion on a heavy soil is obvious. The soil becomes loose because
of the larger units, air moves more freely, and water not only
drains away readily when in excess, but responds with celerity
to the osmotic pull of the plant.
76. Soil structure types.—The Sencar condition of
a soil can generally be attributed directly to its textural nature
as can readily be seen by comparing sandy and clayey soils.
For convenience of discussion two general structural groups
may be established: (1) single-grained, and (2) compound-
grained. In the former the particles function more or less
separately and the soil is, as a consequence, rather open and
friable. In the latter group the particles, being small, tend
to stick together and the units instead of being solid are aggre-
gates, their size and character as well as their relations to each
other being a determining factor in the physical condition of
the soil. As most soils are mixtures of large, medium, and
139
140 NATURE AND PROPERTIES OF SOILS
small particles, it is only the coarse sandy soils on the one
hand and very fine clayey soils on the other that ideally repre-
sent these two groups. Most soils, especially loams, present
combinations of the single and compound grain structures.
Single-grain structure as found in sandy soils has certain
obvious advantages, such as looseness, friability, good aéra-
tion, and drainage and easy tillage. On the other hand, such
soils are often too loose and open and lack the capacity to
absorb and hold sufficient moisture and nutrient materials.
They are, as a consequence, likely to be droughty and lacking
in fertility. There is only one method of improving in a prac-
tical field way? the structure of such a soil—the addition of
organic matter. Organic material, if it undergoes favorable
decomposition when incorporated with the soil, will not only
act as a binding material for the particles but will also in-
crease the water capacity. Nitrogen also is added and if the
organie matter is properly supplemented with fertilizers and
lime, the soil fertility will usually be markedly improved. A
sandy soil high in organic matter is almost ideal from a struc-
tural standpoint.
The modification of the structural condition of a heavy soil
is not such a simple problem as in the case of a sandy one.
In the latter the plasticity and cohesion is never high even
after the addition of large amounts of organic materials that
rapidly develop into a colloidal state. In clays and similar
soils the potential plasticity and cohesion? are always high
1In the greenhouse or garden, structure may be modified by mixing
different soils. This is not practicable in the field.
There are no satisfactory methods of determining either the plasticity
or the cohesion of soils. For plasticity determination, see: Atterberg,
A., Dis Plastizitdt der Ton; Internat. Mitt. f. Bodenkunde, Band I,
Heft 1, Seite 10-43, 1911. Kinnison, C. 8., A Study of the Atterberg
Plasticity Method; Trans. Amer. Cer. Soc., Vol. 16, pp. 472-484, 1914.
For methods of estimating cohesion:
A good description of Schiibler’s apparatus is found on page 104 of
Bodenkunde, by E. A. Mitscherlich, published by Paul Parey, Berlin,
in 1905. MHaberlandt, H., Uber die Kohdreszenz, Verhaltnisse ver-
schiedener Bodenarten; Forsch. a. d. Gebeite d. Agri.-Physik., Band I,
Seite 148-157, 1878. Also, Wissenschaftlich praktische Untersuchungen
SOIL STRUCTURE AND ITS MODIFICATION 141
due to the presence of large amounts of complex hydrated
aluminum silicates in a colloidal condition. The more plastic
a soil becomes, the more likely it is to puddle,’ especially if
worked when wet. Moreover, a soil of high plasticity is prone
to become hard and cloddy when dry, due to the cohesive ten-
dencies of the small particles. Heavy soils must, therefore,
be treated very carefully, especially in tillage operations. If
plowed too wet, puddling occurs, the aggregation of particles
is broken down, and an unfavorable structure is sure to re-
sult. If plowed too dry, great lumps are turned up which
are difficult to work down into a good seed-bed. In a sandy
soil, no such difficulties are encountered.’
Granulation or the production of a compound-grain struc-
ture is the only means of correcting the physical condition of
a heavy fine-grained soil. In this process the small particles
are drawn towards innumerable suitable nucleii and a porous
structure is developed. The size of the individual pore spaces
is thereby increased and air and water drainage is facilitated.
The structural condition in reality simulates a single-grain
state with this important difference, however: the particles
are porous and not solid. Unless a heavy soil possesses at least
some granulation, it is more or less unfit for agricultural
operations. (See Fig. 24.)
77. Granulation—While it is possible to list the factors
auf dem Gebeite des Pflanzenbaues; Band I, Seite 22, 1875. Puchner,
H., Untersuchungen iiber die Kohdreszenz der Bodenarten; Forsch. a. d.
Gebiete d. Agri.-Physik., Band 12, Seite 195-241, 1889. Atterberg, A.,
Die Konsistenz und die Bindigkeit der Boden; Internat. Mitt. f. Boden-
kunde, Band II, Heft 2-3, Seite 149-189, 1912. Cameron, F. K., and
Gallagher, F. E., Moisture Content and Physical Condition of Soils;
U.S. Dept. Agr., Bur. Soils, Bul. 50, 1908.
1When a soil in a plastic condition has been kneaded until its pore
space is much reduced and it has become practically impervious to air
and water, it is said to be puddled. The development of gelatinous
and viscous colloidal materials seems to be the controlling factor in
such a condition, the pore space of a puddled soil being largely filled
with such material. When a soil in this condition dries, it becomes hard
and dense.
7Sandy soils are often plowed rather wet in order to render them
more compact than they normally would be.
142 NATURE AND PROPERTIES OF SOILS
that bring about granulation in a soil, it is difficult to state
specifically just why this phenomenon takes place. It has been
suggested that much of the granule formation in the soil is
due to the contraction of the moisture around the particles
when, for any reason, the moisture content is reduced. It
is known that the soil particles tend to be drawn together
by this reduction in the soil-moisture, due to the pulling power
of the thinned films.
If to this condition is added a material which tends to exert
not only a drawing power on loss of moisture, but also a bind-
Fig. 24.—A well granulated soil and a puddled soil. Organic matter
plays an important réle in structural condition.
ing and cementing power when dry, all the essentials for suc-
cessful granulation are present. This second force is found
in the colloidal material existing in considerable quantities in
heavy soils. Such materials have already been shown to deter-
mine the cohesion of the soil. The influence of the colloidal
material is considered by many authorities as the more im-
portant in the structural adjustments of the soil.
It is evident that if cohesion and plasticity are to function
in granulation—or, in other words, locally in the soil instead
of generally and uniformly as when clodding or puddling
oceurs—a certain moisture content must be maintained. In
a soil subject to such a condition, the cohesive forces being
SOIL STRUCTURE AND ITS MODIFICATION 148
localized, the internal strains and pressures are unequal and
a tendency arises for the mass to divide along lines of weak-
ness into groups of particles. The binding capacity of col-
loidal material, as well as of salts deposited from the soil
solution, tends to make such a crumb structure more or less
permanent. The moisture content most favorable for granu-
lation seems to be that which is optimum for plant growth.
78.—Forces facilitating granulation.” — Granulation is
nothing more or less than a favorable condition brought
about by the force exerted by a variable water film and the
pulling and binding capacities of colloidal material, operating
at numberless localized foci. It is evident that any influence
or change in the soil which will cause a greater localization
of these operative forces will promote the aggregation of the
particles. The addition of materials from extraneous sources
is also a practice that may tend to develop lines of weakness
and thus cause a more intense activity of the forces at work.
The conditions, additions, and practices tending to develop
or facilitate a granular structure in soils may be listed under
six heads: (1) wetting and drying of the soil, (2) freezing
and thrawing, (3) addition of organic matter, (4) action of
roots and animals, (5) addition of lime and (6) tillage. Only
the last two need additional consideration.
79. Granulating influence of lime.*—One of the effects
of lime in the soil, especially of the oxide and hydroxide forms,
*Cameron, F. K., and Gallagher, F. E., Moistwre Content and Physical
Condition of Soils; U. S. Dept. Agr., Bur. Soils, Bul. 50, p. 8, 1908.
*Fippin, E. O., Some Causes of Soil Granulation; Trans. Amer. Soe.
Agron., Vol. 2, pp. 106-121, 1910. Czermak, W., Hin Beitrag zur Erkent-
uis der Verdnderungen der Sog physikalischen Bodeneigenshaften durch
Frost, Hitze, und die Beigabe einiger Salze; Landw. Ver. Stat., Band
76, Heft 1-2, Seite 73-116, 1912. Also, Ehrenberg, P., und Romberg,
G. F. von, Zur Frostwirkung auf den Erdboden; Jour. f. Landw.
Band 61, Heft 1, Seite 73-86, 1913.
* Lime in a strictly chemical sense refers only to calcium oxide (CaO).
The term is used here with an agricultural meaning, including all cal-
cium and magnesium compounds which are ordinarily added to the soil
to correct acidity, thus including not only calcium oxide but calcium
hydroxide and calcium carbonate [Ca(OH), and CaCO,] as well.
144 NATURE AND PROPERTIES OF SOILS
is a flocculating action. This agglomeration, as already ex-
plained, is the drawing together of the finer particles of a
soil mass into granules. When calcium hydroxide is mixed
with water containing fine particles in suspension there is
almost immediately a change in the arrangement of the par-
ticles. They first draw together in light, fluffy groups, or floc-
cules, which then rapidly settle so that the supernatant
liquid is left clear or nearly so. This phenomenon is termed
flocculation, because of the peculiar appearance of the
aggregates. This floecculating tendency when lime is added
goes on in the soil as well as with suspensions, although more
slowly. In general, the lime tends to satisfy the absorptive
capacity of the colloidal material and by throwing down these
colloids develops lines of weakness. The cohesive power of
the soil is thus localized and agglomeration must necessarily
occur. The various forms of lime differ in their flocculating
capacities, calcium oxide and hydroxide being very active,
while calcium carbonate is relatively inactive in this regard.
It must not be inferred that lime is generally added for its
flocculating influence. It is used primarily for other reasons,
the amounts applied being in general too small to have very
much influence on the structural condition of the soil. War-
ington,! however, reports a statement of an English farmer
to the effect that by the use of large quantities of lime on
heavy clay soil, he was enabled to plow with two horses instead
of three. It is generally true that soils rich in lime are well
granulated, and maintain a much better physical condition
than soils of the same texture that are low in lime.
80. Tillage.—Tillage aims to accomplish three primary
1 Warington, R., Physical Properties of Soils, p. 33, Oxford, 1900.
2For a very complete review of the theory and practice of plowing
and cultivation, with a complete bibliography: Sewell, M. C., Tillage:
A Review of the Literature; Jour. Amer. Soc. Agron., Vol. II, No. 7,
pp. 269-290, Oct., 1919.
The following books upon the mechanies of tillage may prove helpful:
Davidson, J. B., and Chase, L. W., Farm Machinery and Farm Motors;
New York, 1908.
The Oliver Plow Book; South Bend, Ind., 1920.
SOIL STRUCTURE AND ITS MODIFICATION 145
purposes: (1) modification of the structure of the soil; (2)
disposal of rubbish or other coarse material on the surface, and
the incorporation of manures and fertilizers into the soil; and
(3) the deposition of seeds and plants in the soil in position for
growth.
The most prominent of these purposes is the modification
of the soil structure. This affects the retention and movement
of moisture and air, the absorption and retention of heat,
and either promotes or retards the growth of organisms. The
ereation of a soil-mulch is merely a change in the structure
of the soil at such times and in such a manner as may prevent
the evaporation of moisture. In fine-textured soils, in which
Fic. 25.—Three types of plow bottoms; 1, stubble; 2, sod; 3, general
purpose.
the granular structure is most desired, tillage may have an
important influence on the formation or destruction of gran-
ules. As has been pointed out, any treatment that increases
the number of lines of weakness in the soil structure facili-
tates the activities of the moisture films and the colloidal mate-
rials in producing soil granules. Tillage shatters the soil and
breaks it into many small aggregates, which may be drawn
together and loosely cemented as a result of the evaporation
of moisture. The more numerous the lines of weakness pro-
duced, the more pronounced is the granulation; and, con-
versely, the fewer the lines of weakness produced, the more
coarse and cloddy is the structure.
According to their mode of action, tillage implements may
Ramsower, H. C., Equipment for the Farm and Farmstead; Boston,
1917.
King, F. H., Physics of Agriculture; Chap. XI, Madison, Wis., 1910.
146 NATURE AND PROPERTIES OF SOILS
be grouped as follows: plows, cultivators, packers and
crushers.
81. The action of the plow.—The moldboard plow
brings about its effects because of the differential stresses set
up in the furrow slice as it passes over the share and the
moldboard. The soil in immediate contact with the plow sur-
face is retarded by friction, and the layers above tend to
slide over one another much as the leaves of a book when they
are bent. If the soil is in just the proper condition, maximum
granulation results; but if the moisture is too high or too low,
puddling or clodding may follow, especially on a heavy soil.
Not only does a shearing occur, but this shearing is differ-
ential, due to the slope of the share and especially to the curve
of the moldboard. When the soil is to be turned over with
the least expenditure of energy, the share is sloping and is
set to deliver a slanting cut, and the moldboard is long and
gently inclined. This allows the furrow slice to be turned with
little granulation and with a minimum effort. When maxi-
mum granulation and pulverization are desired, the mold-
board is short and sharply turned, and the share is less slop-
ing and the cutting edge less slanting. Such conditions make
for the development of more friction and the generation of
those internal twisting and shearing stresses necessary for
good granulation. The sharper the bending of the furrow
slice, the greater are the internal stresses set up. Various
types of moldboards and shares designated for special soils
and particular operations are on the market. (See Fig. 25.)
The disc plow is a sharp rolling dise set at such an angle
that it slices off and turns over the soil, pulverizing it fairly
effectively somewhat after the manner of the moldboard plow.
One advantage of the dise plow is its lighter draft, due to
a rolling rather than a sliding friction in the soil. In prac-
tice it is especially effective on very dry, hard soil.
While the plow is the very best pulverizing agent when
optimum soil-moisture conditions prevail, it is also a most
SOIL STRUCTURE AND ITS MODIFICATION 147
effective puddling agent when the soil is wet. Therefore, care
in the judging of optimum conditions for plowing is a most
important feature in the maintenance and encouragement
of soil granulation. A careful study of the moisture con-
ditions in a elay soil is especially necessary in order to de-
termine just what is the correct moisture content for good
plowing. That this condition must be gauged carefully and
immediate use made of the advantages it offers is shown by
its narrow limits. A few days may suffice for the moisture to
pass through and beyond such a condition. A clay soil is so
Fig. 26.—A_ six-shovel cultivator.
difficult to handle at best that no opportunities such as are
offered by optimum moisture conditions should be lost. More-
over, a heavy soil plowed too dry or too wet does not regain
its normal granular condition for several seasons. Such care
is unnecessary with a sandy soil.
82. Cultivators, packers and crushers.——The many
types of cultivators may be grouped under three heads: (1)
cultivators proper, (2) levelers and harrows, and (3) seeder
cultivators. The action of all these implements is the same
in that they stir the soil, at the same time loosening the struc-
ture and cutting off weeds. While the action is much shal-
lower than with the plow, the same attention should be paid
to moisture conditions. Particularly is this true in pulveriza-
148 NATURE AND PROPERTIES OF SOILS
tion immediately after plowing. When the moisture condi-
tions are optimum, the clods are more easily shattered and
the formation of a suitable seed-bed is speedily accomplished.
The cultivators proper are well represented by the ordinary
corn cultivator whether equipped with shovels, knives or discs.
Under the leveler and harrow type may be placed the spike
and spring-tooth harrow, the various kinds of weeders, the
acme harrow and the disc harrow. The latter may be equip-
ped with solid, cut-away, or spading discs. The grain drill,
either of the press or disc type, is a representative of the
seeder cultivators, which considerably influence the structural
condition of the soil although such action is not their primary
purpose. (See Fig. 26.)
Packing and crushing are ordinarily performed by the same
implement, since any tool that compacts does a certain amount
of crushing; and, conversely, any implement that crushes the
soil does some compacting. Such an implement as the culti-
packer cultivates, packs and promotes granulation in one
operation. The difficulty of establishing a rigid classification
is evident.
Rollers may be of the solid or barrel type, the corrugated
type, or the bar type. The subsurface packer is also included
in this group. Rollers tend to force the soil particles nearer
together and smooth the surface. If at the same time they
establish a soil-mulch so much the better. The rolling of the
land after seeding is an attempt to stimulate the capillary
movement of the water and to hasten germination by bring-
ing the seed in closer contact with the soil.
The planker, drag, or float is a common type of single
erusher. It is generally broad and heavy, without teeth and
is dragged over the soil. The lumps are rolled under its edges
and ground together in such a manner as effectively to reduce
their size. The soil is leveled and smoothed at the same time.
This implement may be used instead of a roller in many eases.
(See Fig. 27.)
SOIL STRUCTURE AND ITS MODIFICATION 149
83. Soil tilth—The previous data and discussion have
clearly shown the very great importance of structure in the
successful handling of the soil in the field. Since good phy-
sical condition will reflect itself on crop yield it is evident
that structure must ultimately be considered in ,relation to
all plant growth. This relationship is usually expressed by
the term tilth. While structure refers to the arrangement of
the particles in general, and granulation to a particular aggre-
gate condition, tilth goes one step farther and includes the
plant. Tilth, then, refers to the physical condition of the soil
Fig. 27.—A planker or drag, useful in the crushing of clods.
as related to crop growth. It may be poor, medium, good, or
excellent, according to circumstances. Good tilth may de-
mand in many soils maximum granulation, in others only a
medium development. Tillage operations by influencing the
structure of the soil aim to develop optimum tilth. Optimum
tilth always implies the presence of water since the best phys-
ical relationships cannot be developed without such moisture
conditions.
84. Summary.—The factors which control the struc-
tural condition of the soil to the greatest extent are plasticity
and cohesion, their influence intensity being due directly to
the presence of certain kinds of materials, especially hydrated
aluminum silicates, in a colloidal state. As plasticity and
cohesion increase the tendencies of a soil to puddle when wet
150 NATURE AND PROPERTIES OF SOILS
and to clod when dry are augmented. Therefore in heavy
soils a modification in these factors is advisable, through a
eareful control of moisture and a bettering of the granular
structure of the soil. Granulation, while due to some extent
to the influence of the water film, is traceable largely to col-
loidal matter both mineral and organic. It is really a con-
centration of the forces of cohesion and plasticity around num-
berless localized foci. Granulation takes place under the in-
fluence of wetting and drying, freezing, plants and animals,
addition of lime and organic matter, and tillage operations,
especially plowing. The farmer exerts a modifying influence
on structure most efficiently by increasing the organic content
of the soil and by plowing. He is, of course, aided and abetted
by natural forces.
Efficient tillage requires good judgment in the selection of
proper implements and mechanical skill in their operation.
It demands besides an understanding of the properties of soils
and a knowledge of their plant relationships. Sandy soils are
easily handled provided sufficient organic matter is main-
tained. Such cannot be said of clayey soils. Due to the high
cohesion and plasticity of heavy soils the moisture zone for
successful tillage is particularly narrow. The ability to detect
when this zone has been reached in a clay soil is one of the
essentials of its successful management. Another essential
is the effective widening of such a zone by granulation oper-
ations.
The optimum moisture condition for tillage is generally near
the optimum condition for plant growth—a happy coinci-
dence, since by regulating the moisture content for plant devel-
opment conditions are rendered most favorable for all soil ac-
tivities. It is thus possible to produce in one operation that
desideratum in all soil physical operations, an optimum tilth.
CHAPTER VIII
THE FORMS OF SOIL-WATER AND THEIR
CHARACTERISTICS *
A som, in order to function as a medium for plant growth,
must contain a certain amount of water. This moisture pro-
motes the innumerable chemical and biological activities of the
soil, it acts as a solvent and carrier of nutrients, and in addi-
tion it functions as a nutrient itself. The amount, character,
and control of the soil-moisture must evidently be reckoned
with in any study of soil and plant relationships, whether they
are of a practical or a theoretical nature. The productivity
of a soil is often a direct function of its moisture condition.
85. Forms of soil-water—As has already been demon-
strated, a soil of a given volume weight has a definite pore
space which may be occupied largely by air or by water, or
shared by both, as the case may be. Of course, an ideal soil
for growth is one in which there is both air and water, the
proportions depending on the texture and the structure of
the soil and the character of the crop. Assuming for the time
being, however, that the pore space is almost entirely filled
with water, or, in other words, that the soil is saturated, three
forms of water are found to be present—hygroscopic, capillary
and gravitational. These forms differ not only in the amount
and proportion of the solutes which they carry but also in the
positions that they oceupy in their relation to the larger soil
particles and the accompanying colloidal complexes.
*Keen, B. A., Relations Existing Between the Soil and Its Water
Content; Jour. Agr. Sci., Vol. X, Part 1, pp. 44-71, Jan., 1920. A
good review of the subject.
151
152 NATURE AND PROPERTIES OF SOILS
If an absolutely dry soil is exposed to a moist atmosphere,
it will absorb moisture rather rapidly until the colloidal sur-
faces are in equilibrium with the air as far as water vapor is
coneerned. Other conditions being equal, maximum water
will be taken up from an atmosphere which is saturated with
moisture. The moisture thus taken up is called hygroscopic
water, its amount being determined quite largely by the mag-
nitude of the colloidal material present in the soil.
On adding more water, it will be found that the absorptive
power of the soil has been by no means satisfied by the hygro-
scopic water. Moisture will still be taken up by the colloidal
complexes and it will also collect in the interstices between
the soil particles. This water which is above and beyond the
hygroscopic is generally called the capillary. That part held
by the colloidal complexes is very similar in characteristics to
the hygroscopic water in that it is tightly held and is more
or less immovable. That portion in the interstices, especially
the larger spaces, is in the form of a film, is loosely held, and
responds to capillary action. While typical capillary water
is much different from hygroscopic moisture, it grades into
the latter with no sharp line of demarcation.
Once the capillary capacity of the soil is satisfied, a third
form of water may appear. This water is but slightly in-
fluenced either by the colloidal complexes or the larger soil
particles and consequently is free to respond to the pull of
gravity. It is called the free or gravitational moisture and
is the water which passes through the soil and appears in
streams and rivers bearing in solution the tremendous amounts
of soluble salts which are every year lost from the land.
86. Hygroscopic water.—The hygroscopic water in a
soil has been spoken of as the water of condensation, or ab-
sorption. It is, however, quite distinct from water condensed
on a surface colder than the moist atmosphere in which it is
placed. All bodies possess the power, to a greater or less de-
gree, of absorbing water even when at the same temperature
THE FORMS OF SOIL-WATER 153
as the air with which they are in contact, provided, of course,
that the air contains water-vapor. Such condensation is
largely a function of the surface exposed.
One of the characteristics peculiar to colloidal materials is
a high absorptive power for water, whether it is presented in
the form of a liquid or vapor. This capacity is due to the
tremendous surface exposed by matter in a colloidal state,
which not only may hold the moisture physically but may
even force it into loose chemical combination. The hygro-
scopic water is probably not in the form of a film around
the particles but in a much more intimate relationship. That
which is held physically is probably, in part at least, in a con-
dition of solid solution. If any of the hygroscopic water is
held chemically, the bond is probably a rather loose one.
A large proportion of the hygroscopic moisture is obviously
not in a lquid state and consequently is immovable as such.
When a hygroscopically saturated soil is exposed to a partially
saturated air, a portion of the hygroscopic moisture will be
lost through vaporization. In order to expel the remainder
of the hygroscopic water, the soil must be heated. For con-
venience of determination, it is generally assumed that all of
the hygroscopic moisture will be driven from an air-dry soil
by heating it for four or five hours at a temperature of 100°
or 110° C. This is only an assumption, however, as some of
the moisture in intimate relationship with the colloidal com-
plexes probably still remains.
The amount of energy necessary to expel the hygroscopic
moisture from the soil is very great, since its only movement
is thermal and because it is held so closely. As so much
energy is expended in removing this water, it is reasonable to
*See, Bouyoucos, G. J., Classification and Measurement of the Dif-
ferent Forms of Water in the Soil by Means of the Dilatometer Method ;
Mich. Agr. Exp. Sta., Tech. Bul. 36, Sept., 1917. Relationship between
the Unfree Water and the Heat of Wetting of Soils and its Significance ;
Mich. Agr. Exp. Sta., Tech. Bul. 42, Mar., 1918. A New Classification
of the Soil Moisture; Soil Sci., Vol. XI, No. 1, pp. 33-47, Jan., 1921.
154 NATURE AND PROPERTIES OF SOILS
expect that a certain amount of heat of condensation will be
apparent when it is resumed.‘ Patten * and Bouyoucos ? offer
the following quantitative data concerning this point:
TABLE XX VIII
HEAT EVOLVED BY WETTING SOILS DRIED AT 110° c.
CALORIES TO A
Sor KiLo or Dry Soi
Quartz SawGieye Mein 8 ia Wy crate aun eames 000
INomiolkisanidieeamege ti a oie. c's nates cae 347
lagerstowmeloarigeers 0 o°.0. occa ees ae eiew see 1108
Mira mix sult A@armntierste.cces ses 481s oer ecg 1742
Cecil clanyeaeceeieiiars <'s/> sa. age skeen 3376
SU PeriOruelavane ame te.s 34.5 4 wpa aieayeneere cea ere 5158
Muck (25% organic matter) 6413
Gay (on Mareen ek: acd 6 PL Rac eAnes ea renee 22185
87. Determination of the hygroscopic coefficient.—
The methods for the determination of the maximum hygro-
scopicity of a soil, or, in other words, the hygroscopic coeffi-
cient, are simple in outline. The soil, in a thin layer, is ex-
posed to an atmosphere of definite humidity under conditions
of constant temperature and pressure. Complications arise
from the necessity of using a very thin layer of soil, from the
difficulty of controlling humidity, and from the tendency of
capillary water to form in the soil interstices before the hygro-
scopic capacity is satisfied. The question of how long the
exposure should take place has not been definitely settled. It
1The tremendous heat of wetting is probably due to the latent heat
of water, to the attraction that soils have for water and to the condition
into which the water is transformed. The heat of condensation is so
large as to suggest the probability of a change in the aggregation of
the moisture thus absorbed.
*Patten, H. E., Heat Transference in Soils; U. S. Dept. Agr., Bur.
Soils, Bul. 59, p. 34, 1909.
®Bouyoucos, G. J., Relationship between the Unfree Water and the
Heat of Wetting of Soils and its Significance; Mich. Agr. Exp. Sta.,
Tech. Bul. 42, Mar. 1918.
THE FORMS OF SOIL-WATER 155
is evident, therefore, that not only must any method be more
or less arbitrary but that its value can only be comparative.
In the actual procedure,’ the sample of soil may be air-
dried or dried at 100° or 110°C. If the former method is
followed, the sample after exposure is heated for four or five
hours at 100° or 110° C., the loss being considered as hygro-
scopic water. If oven-dried soil is utilized, the gain in weight
due to the exposure to the moist air is the hygroscopic mois-
ture. If a saturated air is made use of, the gain is maximum
hygroscopicity, from which can be calculated the percentage
of hygroscopic water based on dry soil, called the hygroscopic
coefficient. If a partially saturated air is utilized, a sample
of stock soil, the hygroscopic coefficient of which is known, is
exposed at the same time. The determination on the known
sample shows what proportion of possible hygroscopic water
has been taken up. From this the hygroscopic coefficient of
the unknown soil sample ean be ealeculated.’
88. Hygroscopic capacity of soils—Since hygroscopic-
ity depends almost directly on the colloidal nature of the soil,
it is evident that texture, external factors being under con-
trol, will be an important factor in determining the hygro-
scopic coefficient. When the organic matter of soils is more
or less the same in amount, the inorganie colloids seem to con-
1Hilgard, E. W., Soils; pp. 196-201, New York, 1911. This method
is practically the same as that used for the comparative estimation of
the colloidal content of the soil, the hygroscopic coefficient being the
comparative figure obtained. See note to paragraph 74 of this text.
Bouyoucos determines the hygroscopic coefficient in an approximate
way by means of the dilatometer method. The dilatometer is an
apparatus which measures the expansion of water on freezing. If a given
amount of soil and water is reduced below zero, the expansion attained
will reveal the amount of water remaining unfrozen, due to its soil
relationships. Bouyoucos finds that the amount of moisture unfrozen
after supercooling to —4° C. (slightly more freezes at -78° C.) correlates
fairly well with the hygroscopic coefficient. Bouyoucos, G. J., A New
Classification of Soil Moisture; Soil Sci., Vol. XI, No. 1, pp. 33-47,
Jan., 1921.
?Alway, F. J., and Clarke, V. L., Use of Two Indirect Methods for
the Determination of the Hygroscopic Coefficients of Soils; Jour. Agr.
Res., Vol. VII, No. 8, pp. 345-351, Nov., 1916.
156 NATURE AND PROPERTIES OF SOILS
trol the hygroscopicity. The following figures from Briggs
and Sehantz,' by whom the hygroscopic coefficient was deter-
mined by exposing air-dry soil at 20° C. to a saturated atmo-
sphere and then drying at 110° C., illustrate this point. The
organic matter was not a serious disturbing factor.
TABLE X XIX
HYGROSCOPIC CAPACITY OF VARIOUS SOILS EXPRESSED IN PER-
CENTAGE BASED ON DRY SOIL?
PERCENTAGE HYGROSCOPIC
SOILS OF CLAY COEFFICIENT
Coarse'sand: 225ee re i 2 eee 16 55)
ane: Sadi ook ie ie ote 3.9 Li
Satidiys loamy scene. oe. «Sects 7.9 3.0
Mine: sandy loames 280... 4)see 12109 6.6
TES Hira Ware pe ee NG, A ee ec Tce 14.4 9.6
Clay loamy oo. 2 teens thes rege ree 22.0 11.4
Cai sitibtoin Ha eee, Se. ce os Nici es BYARD 132
1 Briggs, L. J., and Schantz, H. L., The Wilting Coefficient for Dif-
ferent Plants and Its Indirect Determination; U. 8. Dept. Agr., Bur.
Plant Ind., Bul. 230, p. 65, Feb., 1912. See also, Loughridge, R. H.,
Investigations in Soils Physics; Calif. Agr. Exp. Sta., Rep. of Work of
the Agr. Exp. Stations of Calif. for 1892-3-4, pp. 76-77. Ammon, Georg.,
Untersuchungen tiber das Condensationsvermogen der Bodenconstituenten
fur Gase; Forsch. a. d. Gebiete d. Agri.-Physik., Band II, Seite 1-46, 1879.
Dobeneck, A. F., von, Untersuchungen tiber das Absorptionsvermogen
und die Hygroskopizitdt der Bodenkonstituenten; Forsch, a. d. Gebiete
d. Agri.-Physik., Band XV, Seite 163-228, 1892.
? During the many years of soil investigation, especially where the
problems had to deal either directly or indirectly with moisture, five
methods of water expression have been evolved, their use depending on
the nature of the work and on the points to be expressed. They may be
listed under two general heads:
A. Percentage expression
1. Percentage on a dry basis
2. Percentage on a wet basis
B. Volume expression
1. Cubic inches to the cubic foot of soil
2. Percentage by volume
3. Surface inches
A soil carrying 25 per cent. of water on the dry soil basis contains 20
per cent. on the moist basis (soil plus water). The former method is
THE FORMS OF SOIL-WATER 157
Apparently, the finer the soil, the higher the hygroscopic
coefficient. This is due to the fact that most of the inorganic
colloidal matter is carried by the finer separates. In consid-
ering the hygroscopicity, however, the influence of the organic
matter must not be forgotten. Organic colloidal matter has
a very marked influence on absorption, and as the organic
matter of the soil increases, the hygroscopicity rises rapidly.
The following data from Beaumont! is interesting in this
respect :
TABLE XXX
THE HYGROSCOPIC COEFFICIENT? COMPARED TO CERTAIN OTHER
SOIL FACTORS
HyGro-
IGni- SCOPIG
1s
Som ae tion | HUMUS| Copper.
? % fe CIENT
%
Dunkirk silty clay loam, surface} 12.9 | 5.08 | 1.26 3.80
Dunkirk silty clay loam, subsoil] 20.0 | 3.05 20) ly soem
Clyde clay loam, surface....... 20.1 |14.54 | 4.34 | 18.90
Vergennes clay, subsoil........ 74.5 | 5.79 AQ | 17.40
In comparing the two Dunkirk soils it is apparent that the
colloidal clay is the dominant factor in determining the mag-
preferable in that the basis for calculation is not a changeable one as is
the weight of moist soil. The dry basis is practically always used in
soil work.
Where two soils of different volume weight are compared, the per-
centage relationship does not give a true idea of the relative amounts
of water present. A volume expression should then be used. If a cubic
foot of soil, weighing 100 pounds, contains 10 pounds of water it would
be carrying (10 x 27.6) or 276 cubic inches of water. This would
equal (276 — 1728) x 100 or 15.9 per cent. by volume or (10 + 5.2) =
1.92 surface inches.
* Beaumont, A. B., Studies in the Reversibility of the Colloidal Condi-
tion of Soils; Cornell Agr. Exp. Sta., Memoir 21, pp. 501-504, April,
1919,
* Moisture content in this text unless otherwise indicated will always
be expressed on the dry soil basis.
158 NATURE AND PROPERTIES OF SOILS
nitude of the hygroscopic coefficient. With the Clyde and
Vergennes, however, the organic colloidal matter is dominant,
since the Clyde with only 20 per cent. of clay has a higher
hygroscopic figure than the Vergennes which carries 74.5 per
cent. of that separate. The Clyde clay loam and the Dunkirk
subsoil have the same amount of clay, yet the former pos-
sesses a hygroscopic coefficient over three times larger.
Two external conditions seem to be important in determin-
ing the amount of hygroscopic water in soils—(1) humidity
and (2) temperature. It has been definitely established that
the higher the humidity the higher the content of hygro-
scopic moisture. An air-dry soil will, therefore, contain less
moisture in a dry atmosphere than in one carrying large
amounts of water-vapor. When the soil is in contact with a
saturated air it will take up hygroscopic water to its full
capacity and be at the point spoken of as the hygroscopic
coefficient. As the soil air is generally considered to be satu-
rated or almost saturated with water-vapor,' except in the
surface layers or during periods of protracted drought, a soil
in normal condition may be considered, for all practical pur-
poses, to be at its maximum hygroscopicity. An increase of
the temperature of the saturated atmosphere seems to increase
hygroscopicity. With a partially saturated air the influence
seems to be in the opposite direction.? This, however, is not
an important practical point.
The hygroscopic coefficient, defined as the maximum hygro-
scopic water that a soil will hold, is controlled largely by the
texture and organic content of the soil. It may vary from a
very low figure in a sandy soil to as high as 15 per cent. for
a clay high in organic matter. With a muck or peat, the per-
1 Russell, E. J., and Applyard, A., The Atmosphere of the Soil: Its
Composition and Causes of Variation; Jour. Agr. Sci., Vol. VII, Part 1,
p. 5, 1915.
?For a full discussion of this point, see Lipman, C. B., and Sharp,
L. T., A Contribution to the Subject of the Hygroscopic Moisture of
Soils; Jour. Phys. Chem., Vol. 15, No. 8, pp. 709-722, Nov., 1911.
THE FORMS OF SOIL-WATER 159
centage would be considerably higher, in some cases reaching
50 or 60 per cent. It must always be kept in mind, however,
that the point designated as the hygroscopic coefficient is more
or less arbitrary and that there is no sharp line of demarca-
tion between the moisture designated as hygroscopic and that
which lies near it, but is called capillary.
89. The capillary water..—The moisture above the
hygroscopic coefficient but not free to respond to gravity is
generally spoken of as the capillary water. The portion of
this moisture lying in contact or in the immediate neighbor-
hood of the hygroscopic water is probably capable of only
sluggish diffusion movement if any.” This part of the capillary
moisture is held largely by the colloidal matter and may be
considered as transitional between the true hygroscopic and
the more active capillary portion. Although so closely related
to the hygroscopic water in general properties and character-
istics, the soil does not assume it by absorption from vapor-
laden air. This separates it at least analytically from the
hygroscopic form of moisture. Moreover, it is probably
largely in the liquid state, which is hardly true of all of the
hygroscopic water.
The more active capillary water exists in the large inter-
stices and as a film over the particles and the colloidal com-
plexes. It is held rather loosely by the soil, yet strongly
enough to counteract gravitation. This part of the capillary
moisture, being more or less beyond colloidal influence, is
free to respond to the forces active in true solutions and, there-
fore, may move from place to place as equilibrium stresses
may demand. While the inner portion of the capillary water
is held by the absorptive power of the colloidal surfaces, the
outer and freer portion is maintained by the surface tension
+The colloidal conceptions regarding soil-moisture has made it advis-
able to give the term capillary a broader significance than its root
meaning justifies.
* Bouyoucos, G. J.. 4 New Classification of the Soil Moisture; Soil
Sci., Vol. XI, No. 1, pp. 33-47, Jan., 1921.
5
160 NATURE AND PROPERTIES OF SOILS
of the water film. The distinctive characteristics of these two
portions of the capillary water are due to their controls—
colloidal in one case, surface tensional in the other.'
While the outer portion of the capillary water is undoubt-
edly in the form of a more or less continuous film from par-
ticle to particle, the bulk of such moisture probably exists
normally in the interstices between the soil grains. Such a
condition arises because of the pressure developed by the
force of surface tension. The pressure due to surface tension,
however it may be expressed, varies with the curvature of
the film and is proportional to twice the surface tension di-
vided by the radius. The less the radius the greater the cur-
vature and, therefore, the greater the stress developed by sur-
face tension.”
The situation so far as the soil is concerned may be ex-
plained in an empirical way as follows: Suppose that two par-
ticles, each carrying a capillary water film, be brought into
such contact that the films coalesce. There are now two
distinct surfaces, that at A, A’ (see Fig. 28), with the curva-
1 Bouyoucos classifies these two types of capillary water as free (the
more active) and ecapillary-absorbed (the inner group). The distinction
is made on the basis of his dilatometer results, the portion which freezes
at about O°C being considered as the more active or free.
Bouyoucos, G. J., A New Classification of the Soil Moisture; Soil
Sci., Vol. XI, No. 1, pp. 33-47, Jan., 1921.
2 Surface tension is the tension of a liquid surface by virtue of which
it acts like an elastic enveloping membrane, tending always to contract
to the minimum area. While molecules in the interior portion of the
liquid are attracted in all directions and are thus at equilibrium, those
on the surface are attracted by an overbalancing force toward the
interior. In measurement, surface tension is considered as the force with
which the surface on one side of a line, one centimeter long, pulls against
that on the other side of the line. It is generally expressed in dynes.
The pressure due to surface tension varies with the curvature of the film.
It is usually expressed as:
2T
P— —
ron
where P is the pressure; T, surface tension; and r, the radius of the
drop. As the radius becomes less, the curvature increases and the pres-
sure due to surface tension increases. An increase of T will increase
the pressure, P,
THE FORMS OF SOIL-WATER 161
ture of the original film, and that at B, which is very acute
and which naturally must exert a very great outward pull.
Under the stress of this pull developed by the surface tension
acting in this film of very great curvature, the water is drawn
into the space between the particles, where it becomes thicker
than the capillary film about the particles. The readjustment
continues until the forces developed by the two films become
equal. An equilibrium is now established. In the soil the
tendency towards adjustment is somewhat similar in so far
A ae
B
Fic. 28.—A conventional diagram showing the coalescence and read-
justment of the outer capillary water film of two particles when
brought in contact. At the left is shown the condition before the
adjustment with a sharp angle at B; on the right, the films are at
equilibrium with a thickening at B due to movement from A and A’.
as the outer capillary water is concerned. Complete equilib-
rium is probably never reached, however, due to constantly
disturbing factors.
90. The determination of the amount of capillary
water in the soil—The capillary water in a sample of
field soil may be determined by making a moisture test in the
ordinary way for the total water contained,’ after the gravi-
1A moisture determination on a sample of field soil is generally carried
out as follows:—100 grams of the sample, after thorough mixing, is
weighed into a suitable weighing dish and air-dried. The sample is then
placed in an oven and heated at 100°C or 110°C for four or five hours.
It is then cooled in a disiceator and weighed. The loss in weight is
water. The moisture is calculated as percentage based on the dry mat-
ter of the soil. If the weight of the water lost was 20 grams, the
percentage of moisture would be (20 ~ 80) xX 100 or 25 per cent based
on dry soil,
162 NATURE AND PROPERTIES OF SOILS
tational water has had time to drain away. This represents
the hygroscopic plus the capillary water. A determination
of the hygroscopic coefficient on another sample yields a figure
which, when subtracted from the total water, will give the
capillary water present in the soil. The capillary water at
various points in a soil column may be obtained by subtracting
the hygroscopic coefficient from the various percentages of
moisture present, since the hygroscopic moisture is little in-
fluenced by height of column or ordinary structural condi-
tions.
The determination cited above may or may not give the
maximum water-holding capacity of a soil. To fill such a need
a laboratory method has been devised by Hilgard,t which
attempts to show the maximum retentive power of a soil for
water.
A small perforated brass cup is used, having a diameter
of about 5 centimeters and capable of containing a soil column
1 centimeter in height. A short column is used, since it is
only under such conditions that a soil may retain against
gravity the greatest amount of water. Also the soil is able
to expand or contract, as the case may be, on the assumption
of water until an equilibrium is reached. A filter-paper disc
is often placed in the metal cup, and the soil is poured in,
gently jarred down, and stroked off level with the top of the
eup. The cup is then set in water and the soil is allowed to
take up its maximum moisture. After draining, the weight
of the wet soil plus the cup, together with the weights pre-
viously obtained, will allow a calculation of the total water
retained based on the absolutely dry soil. If the maximum
capillary water is desired, the hygroscopic coefficient may be
subtracted from the maximum water retained.
Since this method is a laboratory procedure and the soil
used is not in its normal structural state, the results cannot
be accurately applied to field conditions. While the figures
1 Hilgard, E. H., Soils, p. 209, New York, 1911.
THE FORMS OF SOIL-WATER 163
obtained may be fairly accurate for a sand, they are certainly
much too high for heavy soils. Comparisons with field soils
have shown the data obtained by the above method to be from
30 to 1380 per cent. too high.'
91. The capillary capacity of soils—As might nat-
urally be expected, the factors that tend to vary the amount
of capillary water in a soil are several and their study is
rather complex due to the secondary influences that they may
ewenerate and to the variable nature of the capillary moisture.
These factors may be discussed under four heads: (1) surface
tension, (2) texture, (3) structure and (4) organic matter.
Any condition that will influence surface tension will ob-
viously influence the forces active in the outer portion of the
capillary water. A rise in temperature, for example, if the
soil is eapillarily saturated, will allow some of the water to
become gravitational. A lowering of temperature would cause
an opposite change. This theory has been verified by certain
experiments by King,’ in which he found, other conditions
being constant, a very decided influence on capillary water
through change of temperature. Wollny* has shown that a
depression of .65 per cent. in sand to as high as 3.7 per cent.
in kaolin may occur from a rise in temperature of twenty
degrees. While surface tension may be greatly varied by the
presence of salts in solution, the soil-water is generally so
dilute that the condition is not very important * in determining
1Alway, F. J., and MeDole, G. R., The Relation of Movement of
Water in a Soil to its Hygroscopicity and Initial Moistness; Jour. Agr.
Res., Vol. X, No. 8, pp. 391-428, 1917.
Israelson, O. W., Studies on Capacities of Soils for Irrigation
Water; Jour. Agr. Res., Vol. XIII, No. 1, pp. 1-36, 1918.
* King, F. H., Fluctuations in the Level and Rate of Movement of
Ground Water; U. S. Dept. Agr., Weather Bur., Bul. 5, pp. 59-61,
1892.
*Wollny, E., Untersuchungen tiber die Wasserkapacitat der Bodenarten;
Forsch. a. d. Gebiete der Agri.-Physik, Band 9, Seite 361-378, 1886.
‘Karraker, P. E., Effect on Soil Moisture of Changes in the Surface
Tension of the Soil Solution Brought About By Addition of Soluble
Salts; Jour. Agr. Res., Vol. 4, No. 2, pp. 187-192, May, 1915.
164 NATURE AND PROPERTIES OF SOILS
capillary capacity except in arid or semi-arid regions. In
fact, changes in surface tension through any cause are of little
practical importance.
The finer the texture of a soil the higher is its capillary
eapacity. This is due to the presence of colloidal material
and to the greater number of angles in which capillary water
may be held. The amount of internal surface exposed by a
fine-textured soil is immensety larger than in one of a sandy
character. While texture influences both the inner and outer
capillary water the structure of the soil has more to do with
the active film-like portion. As a clayey soil is granulated
the interstitial spaces are enlarged and an increased capillary
capacity results. At the same time, compacting a sand will
cause a rise in the capillary capacity of, that} soil by increasing
not only the actual effective surface, but also the number of
angles possible for capillary concentration. Further compact-
ing will then cause a decrease.
Organic matter, especially when well decayed, is commonly
recognized as having great capillary capacity, far excelling
the mineral portion of the soil in this respect. Its porosity
affords an enormous internal surface, while its colloids exert
an affinity for moisture which raises its water capacity to a
very high degree. Its tendency to swell on wetting is but a
change in condition incident to an approach to its maximum
moisture content, and has a very marked influence on the
structure of the soil. The water-holding capacity of muck
and peat may range as high as 300 or 400 per cent. based on
the dry matter present. Assuming a hygroscopic coefficient
of 50 per cent., the capillary figure is still very high. Besides
this direct effect, organic matter exerts a stimulus toward
better granulation, a condition in itself favorable to increased
water-holding power.
The capillary water in any soil, other conditions being equal,
tends to vary with the height of the column. This comes about
from the effect of gravity on the outer portion of the capillary
THE FORMS OF SOIL-WATER 165
film, tending to give more water at the
base of the column.
The condition may be explained em-
pirically as follows: If a number of par-
ticles carrying maximum capillary films
are brought together vertically, the weight
of a large portion of the conducting film
is thrown momentarily on the surfaces at
the top. The capillary spaces at this point
immediately lose water downward, so that
they may assume a greater curvature and
thus support this extra weight thrown on
them. This curvature must be sufficient to
balance the curvature pressure of the par-
ticles below plus the weight of the water
in the connecting films. The particles be-
neath are at the same time undergoing a
similar adjustment with a set of particles
farther below, losing water in order to
allow a change of curvature. The action
continues in this manner in an attempt to
establish equilibrium, thus giving more
water at the bottom of the column. If the
amount of capillary water is too great to be
supported, enough is lost by gravity to
bring about an equilibrium (see Fig. 29).
The above illustration, however, does not
apply strictly to soil conditions, since only
part of the capillary water is in a true film
form and free to move with extreme ease.
Moreover, rain water is applied from
above, where also occurs rapid evaporation.
Thus at any particular time the moisture
content of a field soil might be higher near
the surface than farther down in the soil
Fig. 29.—Diagram
showing in a con-
ventional way
the adjustment
tendency of the
outer capillary
water in a long
column and the
appearance of
free water if the
weight is too
great.
166 NATURE AND PROPERTIES OF SOILS
or vice versa as the case may be. As the capillary water in a
soil is reduced there is a tendency for the soil column to be
more nearly uniform, providing, of course, that the equi-
librium forces have had time to act and are not too much
influenced by other factors.
While representative data regarding the moisture-holding
capacity of soils are difficult to give, the following figures
from Alway' indicate the general effect of texture and organic
matter. The maximum water capacity was determined in the
laboratory and the maximum field capacity was obtained by
sampling the soils very shortly after irrigation.
TABLE XX XI
THE MAXIMUM WATER CAPACITY OF VARIOUS SURFACE SOILS AS
DETERMINED IN THE LABORATORY AND UNDER FIELD
CONDITIONS, RESPECTIVELY 7
i is ey
eee eager - Waste Ghskers
Sols eres TaHcaNe CAPACITY Lange ange
: % % METHOD
%
MPEUIN GL 29% bytes Nich ace enki - = es: UG 37.0
aHG Pa een tect ye —- ay 12.8 20g
Sandy soil, residual.| 1.22 3.3 19.6 34.2
Red loam, residual. . 107 10.0 31.5 49.0
Silt loam, loess..... 1.55 10.1 31.3 56.8
Silt loam, loess..... 4.93 10.2 39.2 60.9
Blackadobe!.2.355.. 2.22 12.9 47.6 60.3
The effect of texture on water capacity is very apparent, a
rough correlation existing also between the water retained and
the hygroscopic coefficient. The influence of organic matter
+ Alway, F. J., and MeDole, G. R., The Relation of Movement of
Water im a Soil to its Hygroscopicity and Initial Moistness; Jour.
Agr. Res., Vol. X, No. 8, pp. 391-428, 1917.
*, Note again that moisture percentages are always expressed on dry-
soil weight.
THE FORMS OF SOIL-WATER 167
is clearly shown by the two loess silt loams. Perhaps most
important of all is the marked discrepancy between the actual
field capacity and the arbitrary and artificial laboratory
method. The normal water-holding capacity of a mineral soil,
varying with texture and organic matter, seems to range from
INCHES FROM WATER TABLE
0 5 10 15 20 25 30 “WATER
Fig. 30.—Diagram showing the distribution of moisture in capillary
columns of soil of different textures. The end of each column
rests in free water. (Buckingham, E., Bur. Soils, Bul. 38, 1907.)
about 10 to 50 per cent. based on dry soil. Muck and peat of
course run much higher, 400 per cent. being not uncommon.’
1 Briggs and McLane have perfected a method of comparing soils on
the basis of their capacity to hold water against a definite and constant
centrifugal force of one to three thousand times the force of gravity.
The soils, in thin layer, are placed in perforated brass cups which fit
into a centrifugal machine capable of developing the above force, and
are whirled until equilibrium is reached. The resultant moisture per-
centage is designated as the moisture equivalent. It really represents
the capillary capacity of a soil of minimum column length when subject
to a constant and known force or pull. The finer the soil, the greater
of course is the moisture equivalent. The authors found that 1 per cent.
of clay or organic matter represented a retentive power of about .62
168 NATURE AND PROPERTIES OF SOILS
92. Capillary movement of water.—It has already been
shown that different thicknesses of capillary films tend to
equalize in the soil due to the pulling forces developed by the
angle of curvature between the particles.’ It is evident that
differences in curvatures must be the motive force in the capil-
lary movement of soil-water. Let it be supposed, for conveni-
ence, that three equal spheres when brought in contact contain
unequal amounts of water in the angles of curvature (see
Fig. 31). In this case the greater pull would exist at A, since
the angle here is more acute. Consequently water must move
per cent., while 1 per cent. of silt corresponded to a retention of only
.13 per cent. of water. Representative data is as follows:
ORGANIC MOISTURE
SoILs MATTER Sanps| Smut CLay EQUIVALENT
% To %o To %
Norfolk coarse sand... 9 87.9 7.3 4.8 4.6
Norfolk fine sandy loam. iL 73.4 18.1 8.5 6.8
Wav IGEN Goonenoacs 13) 25.8 64.1 10.1 18.9
Waverly silt loam...... 2.0 14.9 62.9 22.2 24.4
Houston clay loam.... 3.7 30.9 42.5 26.6 32.4
HAO US tomy Claivencrtetsuerateters 1.4 10.0 56.6 33.4 38.2
Briggs, L. J., and McLane, J. W., The Moisture Equivalent of Soils;
U. S. Dept. Agr. Bur. Soils, Bul. 45, 1907.
1An ingenious method for measuring quantitatively the capillary pull
exerted by a moist soil has been devised by Lynde and Dupré. The
apparatus consists of a glass funnel joined to a thick-walled capillary
tube by means of a piece of rubber tubing, a water seal being used at
this point. The lower end dips into mercury. The soil to be studied is
placed in the funnel, and after being saturated is connected by means
of a wick of cheesecloth or filter paper to the water column previously
established in the capillary tube. If no break occurs between the soil
and the capillary water column, the apparatus is ready for use.
The excess water having drained away, there is a thinning of the films
on the soil surface due to evaporation. Equilibrium adjustments now
take place, which result in the drawing upward of the water column.
The mercury follows, and the strength of the pull may be measured by
the length of the mereury column. The old method of measuring capil-
lary power by the water movement through a dry soil is vitiated by two
conditions—the length of time necessary, and the fact that the maximum
lift cannot be obtained due to excessive friction. This new method
uses a wet soil, requires only a short time, and gives a more nearly
accurate idea of the power of the capillary pull. It does not, however,
THE FORMS OF SOIL-WATER 169
through the connecting film until the pull at A and that at B
become the same. Such an adjustment might go on over a
large number of films, and if one end of the column was ex-
posed to an evaporation of just the correct rate and the other
end was in contact with plenty of moisture, large quantities
of water would be moved by ecapillarity.
This capillary movement may go on in any direction in the
soil, since it is largely independent of gravity; yet under
natural field conditions the adjustment tends to take place
very largely in a vertical direction, due to evaporation and
absorption by plants. When a soil is exposed to evaporation,
the surface films are thinned and water moves upward to
adjust the tension. This explains why such large quantities
of soil-water may be lost so rapidly from an exposed soil.
Capillary adjustment may go on downward, also, as is the
ease after a shower. Here the rapidity of the adjustment is
aided by gravity and movement of the water of percolation.
The capillary adjustment in a soil tends to take place
whether or not the soil column is in contact with free water.
If no gravity water is present, the adjustment is merely from
a moist soil to a drier one. In studying the rate and height
of capillary movement of water in any soil, especially in the
yield data regarding rate of movement,—a factor of vital importance
to plant growth.
Lynde and Dupré, in their results, confirm the statements already made
regarding the relation of texture to capillary power:
DIAMETER
oe LIFT OF WATER
IL GRAINS IN
Ee Re COLUMN, IN FEET
Mil@shipin weMvle es se eos ob aenian o 00 - .25 98
LIN OVSAN Cees eer dee sis enters Seis le 25 - 10 1.78
AV mye fie SATE oie Jo SEF co cle ave w evar 10 - .05 4.05
Slt om mepscorsmasie es aie tae ats .05 - .005 9.99
(CHER nga En cc ee at ey, A ee gee .005- — 26.80
Lynde, C. J., and Dupré, H. A., On a New Method of Measuring
the Capillary Lift in Soils; Jour. Amer. Soe. Agron., Vol. 5, No. 2,
pp. 107-116, 1913.
170 NATURE AND PROPERTIES OF SOILS
laboratory, the maintenance of a supply of free water is
usually provided for, since this allows a nearer approach to
the maximum eapillary capacity for any point in the column
and also gives the most rapid capillary adjustment.
To persons familiar with the habits of growing plants, it is
evident that eapillary movement must play an important
part in their nutrition, since the rootlets are unable to bring
their absorptive surfaces in contact with all the interstitial
spaces in which the bulk of the available water is held. Con-
sequently a consideration of the movement of capillary mois-
Fie, 31.—Conventional diagram showing the mechanics of the movement
of the film portion of the capillary water. The readjustment takes
place in the direction of (A) due to the tension developed by the
greater film curvature at that point.
ture is necessary, not only as to its mechanics, but also in
respect to the factors influencing its rate and height of move-
ment. These factors are as follows: (1) surface tension and
viscosity ; (2) thickness of capillary film; (3) texture; and
(4) structure.
Surface tension and viscosity.—As the force developed by
surface tension is the activating factor in capillary adjust-
ment, any change in the former will influence this movement.
Theoretically, a rise in temperature or the presence of soluble
salts would decrease the rapidity of the capillary activity of
soil-water. In a normal soil, however, the change of surface
tension is generally not sufficient to have any very great prac-
tical influence. Viscosity, on the other hand, is much more
important. If the viscosity of water at 0° C. is taken as 100,
THE FORMS OF SOIL-WATER 17]
its viscosity at 25° is 50 and at 30°, 45. This explains to a
large degree the increased rate of capillary movement due to
temperature rise.’ The distance of such adjustment would,
however, be lessened somewhat. Salts in solution would tend
to check the rate of capillary movement both through in-
creased viscosity and the influence on surface tension.2 It
would only be in alkali soils, where the concentration of soluble
salts is very great, that any considerable retardation would
occur.
Thickness of capillary film.—It has been repeatedly noticed,
in the study of the capillary adjustment between two soils
that the lower the percentage of water, the slower is the move-
ment. This indicates that the thickness of the outer capillary
film, which connects the interstices in which lies the bulk of
the movable soil-water, is an important factor in the rate of
movement.
The above phenomena may be empirically explained as fol-
lows: Let it be supposed that a withdrawal of water occurs at
A (see Fig. 32), the interstitial space between two of the
particles, the water surface being represented by the line aa’.
There is an immediate increase in the curvature of this sur-
face, and water tends to flow through the capillary film chan-
nel (cce’c”) toward this area of greater tension. If water
* Bouyoucos has shown that the movement in a soil column of uniform
moisture is from the warmer portion toward the colder. The movement
from a moist layer to a dryer one goes on more rapidly than when the
moist soil is cool and the dry soil warm. Bouyoucos, G. J., Effect of
Temperature on Movement of Water Vapor and Capillary Moisture in
Soils; Jour. Agr. Res., Vol. V, No. 4, pp. 141-172, Oct., 1915.
*Wollny, E., Untersuchungen iiber die Kapillare Leitung des Wassers
in Boden. Forsch. a. d. Gebiete d. Agr.-Physik, Band 7, Seite 269-308,
1884, Also, Forsch. a. d. Gebiete d. Agri.-Physik, Band 8, Seite 206-220.
1885.
Briggs, L. J., and Lapham, M. H., Capillary Studies; U. S. Dept.
Agr. Bur. Soils, Bul. 19, pp, 5-18, 1902.
Karraker, P. E., Effect on Soil Moisture of Changes in the Surface
Tension of the Soil Solution brought about by the Addition of Soluble
Salts; Jour. Agr. Res., Vol. IV, No. 2, pp. 187-192, May, 1915.
Davis, R. O. E., The Effect of Soluble Salts on the Physical Proper-
ties of Soils; U. S. Dept. Agr. Bur. Soils, Bul. 82, pp. 23-31, 1911.
172 NATURE AND PROPERTIES OF SOILS
continues to be withdrawn at A, this adjustment goes on with
considerable ease until the film channel (ce’c’”) becomes so
thin as to cause its surface now (bb’b’”) to approach very
closely to the surface of the soil particle and the inner capil-
lary water. The sluggishness of the water movement becomes
a factor at this point, impeding the capillary adjustment to-
ward A. This point of sluggish capillary movement has been
designated by Widtsoe! as the point of lento-capillarity, and
Fig. 32.—Conventional diagram for the explanation of the effect of the
thickness of water film about the soil particles and their colloidal
complexes on the ease of capillary adjustment.
is expressed in percentage based on the dry weight of the
soil. It lies near the transition zone between the inner and
outer capillary water.
The amount of capillary water delivered at any one point,
therefore, will obviously be influenced by the thickness of the
film and may consequently be taken as a measure of rate of
adjustment. A short soil column should deliver more water
than a longer one, due to the thicker films at the surface of
the former. King,” in studying the evaporation from the sur-
faces of sand columns of different lengths, their bases being
in contact with free water, obtained some significant data.
* Widtsoe, J. A., and McLaughlin, W. W., The Movement of Water in
Irrigated Soils; Utah Agr. Exp. Sta., Bul. 115, pp. 223-231, 1912.
* King, F. H., Principles and Conditions of the Movements of Ground
Water; U. S. Geol. Survey, 19th Ann. Rept., Part II, p. 92, 1897-
1898.
Also Briggs, L. J., and Lapham, M. H., Capillary Studies; U. 8.
Dept. Agr. Bur. Soils, Bul. 19, pp. 24-25, 1902.
THE FORMS OF SOIL-WATER 173
He found, for example, that a six-inch column would deliver
six times more water to its surface in a given time than a
thirty-inch column operating under the same conditions.
In air-dry soil it is obvious that, before capillarity may
function, a continuous film must be present. Such a condi-
tion is impossible unless some of the more active capillary
moisture is in the soil. The water content in a soil must often
be rather high before capillarity is a noticeable phenomenon.
This condition is taken advantage of in the use of soil-mulches,
where a loose dry layer of soil on the surface may check
evaporation by impeding capillary rise. The presence of oily
substances on the soil grains may also be of some importance
in this respect.
Texture.—In soils of fine texture not only is the amount
of film surface exposed greater than in coarse soils but the
curvature of the films is also greater, due to the shorter radii.
The effective pressure exerted by the films is consequently
much higher in fine-grained soil. Both the greater exposure
of surface and the increased pressure serve to raise the fric-
tion coefficient and retard the rate of flow. The finer the
texture of the soil, other factors being equal, the slower is
the movement of capillary water. Water should, therefore,
rise less rapidly from a water-table through a column of clay
than through a sand or a sandy loam.
The distance to which water may be drawn by the effective
eapillary power of a soil, equilibrium being established, de-
pends on the number of interstitial angles. The greater the
number of angles, the greater is the total pulling power of
the films. As a silt soil contains a larger number of such
angles, its capillary pull is greater than that of sand, and con-
sequently the ultimate movement would be of greater scope.
The finer the texture, then, the slower is the rate of capillary
movement but the greater is the distance.
The relation of texture to rate and height of capillary move-
ment in air-dry soil is shown by the following unpublished
174 NATURE AND PROPERTIES OF SOILS
data, obtained in the laboratory of the Department of Soil
Technology, Cornell University :
TABLE XX XII
EFFECT OF MOISTURE ON RATE AND HEIGHT OF CAPILLARY RISE
FROM A WATER-TABLE THROUGH AIR-DRY SOIL
il 1 2 3 4 5
SOIL Hour Day Days | Days | Days | Days
a ies i IncHEs |INcHEs | INCHES INCHES INCHES | INCHES
SANG y SOL cee 3.9 5.0 5.9 6.8 6.8 6.9
Clayey soil....... 3) 5.7 8:9). 10:9")) S22 ase
Silt. loam. a2 95° 145) 20:6") 24-2) | 26 ele
It is seen that the movement in sand is rapid, one-half of
the total rise being attained in one hour. The maximum
height is reached in about three days. The silt loam in this
ease seems to be of just about the proper textural condition
for a fairly rapid rise, yet it exerts enough capillary pull to
attain a good distance above the water-table. The friction
in the clay is greater, however, and this results in a slower
rate.
Structure has already been shown to affect capillary capac-
ity by its influence on the angle interstices and the closeness
of the contacts. Evidently, therefore, it may alter both the
rate and the height of capillary rise. The loosening of a clay
soil or the compacting of a sandy soil will lessen the effective
film friction, while at the same time it may strengthen the
capillary pull resulting in a faster and a higher capillary flow
of water. What may be the best structural condition of any
soil in which this result is realized to its highest degree can
not be predicted exactly. In general, however, this point is
approached when the soil is in the best physical condition for
crop growth. Tillage operations, tile drainage, and the addi-
tion of lime and organic matter operate toward this result by
their granulating tendencies; while rolling, by compacting a
THE FORMS OF SOIL-WATER 175
too loose surface, may accomplish the same effect but by an
opposite process.
At certain seasons of the year ecapillarity should be im-
peded near the surface, as it continually carries valuable
water upward to be lost by evaporation. This movement may
be checked somewhat by producing on the soil surface, by
appropriate tillage, a layer of dry, loose soil. This layer, called
a soil-mulch, resists wetting because of its dryness, while at
the same time it affords but little surface and few angle inter-
stices for effective capillary pull. Moisture also moves very
slowly from a moist, cool soil to a dry, warm one.’ Thus it is
that a farmer, in order to meet immediate or future plant
needs, may alter and control capillary movement by careful
attention to physical conditions, especially those at the sur-
face where evaporation is always active.
93. Gravitational water and its movement.—As soon
as the capillary capacity of a soil column is satisfied, further
addition of moisture will cause the appearance of free water
in the air spaces. By the attraction of gravity, this water
moves forward through the soil at a rate varying with con-
ditions. In general, the flow is governed by four factors—
pressure, temperature, texture, and structure. An under-
standing of the operation of these forces is important, since
the rapid elimination of free water from the soil is necessary
for normal plant growth.
It is very evident that any pressure exerted on a water
column will alter the rate of flow. Under normal conditions
pressure may arise from two sources, atmospheric pressure
and the weight of the water column. Changes in barometric
pressure are communicated to gravitational water through a
movement of the soil-air. As the mercury column rises more
air is forced into the soil and the pressure on the soil-water
*Bouyoucos, G. J., Effect of Temperature on Movement Water
Vapor and Capillary Moisture in Soils; Jour. Agr. Res., Vol. V, No. 4,
pp. 141-172, Oct., 1915.
176 NATURE AND PROPERTIES OF SOILS
increases. The weight of the free water column may also
have some influence. Although King’? and Welitschkowsky?
have shown that definite relationships exist between the move-
ment of gravity water and both atmospheric pressure and
weight of water column, the practical field importance of these
factors are rather slight.
A rise in temperature of the soil not only varies the relative
amounts of capillary and free water present, but at the same
time it increases the fluidity and thus facilitates percolation.
The expansion of the soil-air also tends to inerease such
movement. On the other hand the swelling of hydrogels
which may be present tends to impede percolation to such an
extent that the movement of free water through a heavy soil
is often markedly checked by temperature rise.
Of much more practical importance than either pressure
or temperature in the flow of gravity water is the texture and
the structure of the soil. In working with sands of varying
grades, Welitschkowsky,* Wollny,* and others have shown that
the flow of water varies with the size of particle, or texture.
King °® has demonstrated that in general the rate of flow
through such is directly proportional to the square of the
diameter of the particles. By the use of the effective mean
1King, F. H., Principles and Conditions of the Movements of Ground
Water; U. 8. Geol. Survey, 19th Ann. Dep., Part II, pp. 67-206; 1897-
1898.
King, F. H., The Soil, p. 180, New York, 1906.
SWelitschkowsky, D. von., Experimentelle untersuchungen uber die
Permeabilitit des Bodens fiir Wasser; Archiv. f. Hygiene, Band II,
Seite 499-512. 1884.
Wollny, E., Untersuchungen iiber die Permeabilitat des Bodens fir
Wasser ; Forsch. a. d. Gebiete d. Agy.-Physik, Band 14, Seite 1-28, 1891.
® Welitschkowsky, D. von., Experimentelle untersuchungen liber die
Permeabilitat des Bodens fiir Wasser; Archiv. f. Hygiene, Band II,
Seite 499-512, 1884.
*Wollny, E., Untersuchunger iiber den Einfluss der Struktur des
Bodens auf dessen Feuchtigketis—und Temperaturverhaltnisse ; Forsch.
a. d. Gebiete d. Agr.-Physik, Band 5, Seite 167, 1882.
’ King, F. H., Principles and Conditions of the Movements of Ground
Water; U. S. Geol. Survey, 19th Ann. Rep., Part II, pp. 222-224, 1897-
1898,
THE FORMS OF SOIL-WATER 177
diameter of a sand sample he was able to calculate a theo-
retical flow which compared very closely to observed percola-
tions. In sandy soils low in organic matter this law holds
in a very general way, but in clays it fails entirely. For
example, if such a law was in force a sand having a diameter
of .5 millimeter would exhibit a flow 10,000 times greater
than that through a clay loam with a diameter, say, of .005
millimeter; whereas the actual ratio, as observed experimen-
tally by King, was less than 200. Such a discrepancy is to be
expected as it is impossible accurately to apply mathematics
to soils carrying any appreciable amount of colloidal matter.
Evidently, therefore, while it can be stated as a general
thesis that the flow of gravity water varies with the texture,
being much more rapid through a coarse than through a fine
soil, no law can be deduced for soils, since structure
exerts such a modifying influence. The percolation in a
heavy soil takes place largely through lines of seepage, which
are really large channels developed by various agencies.
If in the drainage of average soil, the farmer depended on the
movement of water through the individual pore spaces, the
soil would never be in condition for crop growth. These lines
of seepage are developed by the ordinary forces that function
in the production of soil granulation, as freezing and thawing,
wetting and drying, lime, organic matter, roots, and tillage
operations.
94. Determination of the quantity of free water that
a soil will hold— While there is no particular advantage
in finding the quantity of gravitational water that a soil will
hold, since a normal soil should never remain saturated for
any length of time, it is nevertheless of interest to know by
what means such data may be obtained. One method is to
saturate a soil column of known weight, and then, by exposing
it to percolation, measure the amount of water that is lost.
The gravitational water can then be expressed in terms of dry
soil.
178 NATURE AND PROPERTIES OF SOILS
As valuable a figure may be obtained by ealculation, pro-
viding the specific gravity and volume weight of the soil is
known together with its percentage of moisture based on dry
weight when it is capillarily satisfied. The following formu-
lea + may be used:
vol. wt. 100
1. Percentage pore space = 100 — [= x T|
2. Percentage free water = Zone Saco % water at
(based on dry weight Vol. Wt. maximum
of soil) eapillarity
Suppose, for example, that a sand with a specific gravity of
2.6 and a volume weight of 1.56 contains 20 per cent. of water
when at its maximum retentive power. Its pore space would
be 40 per cent. If this pore space were filled with water, the
soil would contain 25.6 per cent. based on the dry weight of
the soil (per cent. pore space ~ vol. wt.). If the total capac-
ity of the soil for water is 25.6 per cent. and the hygroscopic
plus the capillary capacity is 20 per cent., the free water must
be 5.6 per cent.?
95. Importance of the study of the flow and composi-
tion of drainage water—A clear understanding of the
factors governing the flow of gravitational water is of special
importance in tile drainage operations, particularly regarding
the depth of and interval between tile drains. Since percola-
tion is so slow in a heavy soil it is evident that the tile must
be near the surface in order to secure efficient drainage. In
a sand the depth may be increased, because of the slight re-
*Percentage of pore space represents the percentage of water by
volume that would occupy such a space. Percentage of water by volume
divided by volume weight gives percentage of water based on dry weight
of soil. Conversely, multiplying percentage of moisture calculated on
dry weight of soil by volume weight will give percentage of water by
volume.
The air space in a soil at any particular moisture content may be ecal-
culated as follows:
Percentage of air space = % pore space — (%H,0 X Vol. Wt.)
? Below will be found some generalized moisture data on two distinct
THE FORMS OF SOIL-WATER 179
sistance offered to water movement. The depths for laying tile
in a heavy soil range from one and a half to two and a half
feet, while in a sand the tile may often be placed as deep as
four feet below the surface. It is evident also that the less
deep a tile drain is laid the less distance on either side it will
be effective in removing the water; consequently on a clay
soil the laterals must be relatively close as compared to the
interval generally recommended for a sandy soil. A rational
understanding of the movements of gravitation water is
clearly necessary in the installation of tile drains not only
that the system may be efficient, but also that a minimum
effective cost may be realized.*
The water lost from the soil by drainage is of especial in-
terest in plant production because of the large amounts of
nutrient elements carried away each year. Such loss is par-
ticularly important in regard to the lime and nitrogen.? The
equivalent of approximately 500 pounds of sodium nitrate
and 1000 pounds of calcium carbonate have been known to
leach from an acre of bare soil every year under humid con-
ditions.
elasses of soils. As usual, all of the moisture data is expressed as per-
centage based on absolutely dry soil.
SANDY CLAYEY
Soin Som
I PRCING COTAVELY (soi 0 sel ceistes, s10.5 aysverat'es 2.67 2.65
Wrolumeswel cht sy). cra sversee ote eters reece 1.60 1.20
OUG a SCO pga ss Se ayotel «occ vanslinte is lors 6-46 3h 40.0% 54.8%
lshfaOs Coeuiteenhy gegcooss assoansac 1.0% 10.0%
Optimum moisture (average)....... 10.0% 30.0%
Maxamnimin tel duicapacity-nmrciaccan ae 17.0% 44.0%
Air space at hygro. coefficient....... 38.4% 42.8%
Air space at opt. moisture.......... 24.0% 18.7%
Air space at max. field capacity..... 12.8% 19%
Possible streemwateraceeettacoe nace or 8.0% 1.6%
See Kopecky, J., Die physikalischen Eigenschaften des Boden;
Internat. Mitt f. Bodenkunde, Bd. IV, Heft 2-3, Seite 138-180. 1914.
*For a more complete discussion of tile drains, see Chap. X, para-
graph 110.
*Lyon, T. L., and Bizzell, J. A., Lysimeter Experiments; Cornell
Univ. Agr. Exp. Sta., Memoir 12, June, 1918.
180 NATURE AND PROPERTIES OF SOILS
Two methods of procedure are available for the study of
drainage problems—the use of an efficient system of tile
drains, and the construction of lysimeters. For the first
method an area should be chosen where the tile drain receives
only the water from the area in question and where the drain-
age is efficient. A study of the amounts of flow throughout
a term of years will yield much valuable data concerning the
factors already discussed. An analysis of the drainage water
will throw light on the ordinary losses of plant nutrients from
a normal soil under a known cropping system. The advantage
of such a method of attack lies not only in the fact that a
large area of undisturbed soil is considered, but also in the
opportunity to study practical field treatments in relation to
the movement and composition of drainage water.
The lysimeter method, however, has been the usual mode of
approaching such problems. In this method a small block of
soil is used, being entirely isolated by appropriate means from
the soil surrounding it. Effective and thorough drainage is
provided. The advantages of this method are that the varia-
tions in a large field are avoided, the work of carrying on the
study is not so great as in a large field, and the experiment
is more easily controlled. One of the best-known sets of lysi-
meters is that at the Rothamsted Experiment Station’ in Eng-
land. Here blocks of soil one one-thousandth of an acre in
surface area were isolated by means of trenches and tunnels,
and, supported in the meantime by perforated iron plates,
were permanently separated from the surrounding soil by
masonry. The blocks of soil were twenty, forty, and sixty
inches in depth, respectively. Facilities for catching the drain-
age were provided under each lysimeter. The advantages of
such a method of construction les in the fact that the struc-
tural condition of the soil is undisturbed and consequently the
data are immediately trustworthy.
*Lawes, J. B., Gilbert, J. H., and Warington, R., On the Amount
and Composition of the Rain and Drainage Waters Collected at Rothai-
sted; Jour. Roy. Agr. Soc., Ser. II, Vol. 17, pp. 269-271, 1881.
THE FORMS OF SOIL-WATER 181
At Cornell University’ a series of cement tanks sunk in
the ground have been constructed. Each tank is about four
feet and two inches square and about four feet deep. A slop-
ing bottom is provided, with a drainage channel opening into
Et:
SESS
_ 5 alk
»>
Z
=
3in. tile >
: A <A
clr7clers
SD
well fainped
Oin. sewer File: ll
‘il
a |
Fig. 33.—Cross section of the lysimeter tanks at Cornell University,
Ithaca, New York. Each tank is one of a series, one tunnel serving
the two rows. Dimensions are given in feet and inches. Soils under
investigation (a), outlet (p), can for catching drainage water (c)
and sky-light (w).
a tunnel beneath and at one side. As the tanks are arranged
in two parallel rows, one tunnel suffices for both. (See Fig.
33.) The sides of the tanks are treated with asphaltum in
*Lyon, T. L., Tanks for Soil Investigation at Cornell University ;
Science, N. Ser., Vol. 29, No. 746, pp. 621-623, 1909.
There are other types of lysimeters. See, for example, Mooers, C. A.,
and MacIntire, W. H., Two Equipments for Investigation of Soil Leach-
ings: I. A Pit Equipment. II, A Hillside Equipment; Tenn. Agr. Exp.
Sta sulee lle TOM.
MacIntire, W. H., and Mooers, C. A., A Pitless Lysimeter Equip-
ment; Soil Sci., Vol. XI, No. 3, pp. 207-209, Mar., 1921.
182 NATURE AND PROPERTIES OF SOILS
order to prevent solution. The soil must of course be placed
in the tanks, this causing a disturbance of its structural con-
dition. As a consequence, data as to rate of flow and com-
position of the drainage water are rather unreliable for the
first few years. Such an experiment must necessarily be of
considerable duration.
96. Thermal movement of water.—Little has been said,
as yet regarding this mode of water movement, the vapor
flow, which is not peculiar to one form of soil-water but affects
them all. It is at once apparent that the movement of water-
vapor can be of little importance within the soil itself, since
it depends so largely on the diffusion and convection of the
soil-air. While the soil-air is no doubt practically always
saturated with water-vapor, the loss of moisture by this means
is slight. Buckingham? has shown that, while sand allows
such a movement to the greatest degree, the loss through any
appreciable depth of layer is almost negligible. The question
of the thermal movement of water at the soil surface, however,
is vital in farming operations. At this point the moisture is
exposed to sun and wind, and drying goes on rapidly, the free,
capillary, and a part of the hygroscopic water vaporizing in
the order named. If the loss of the moisture in the surface
layer of soil was the only consideration, the problem would
not be serious; but the movable water of the whole soil sec-
tion must be considered also. As the films at the surface be-
come thin, a capillary movement begins, and if the evapora-
tion is not too rapid a considerable loss of water may occur in
a short time. The moisture thus lost is that of most value
to plants. The evaporation from the bare soil in the Rotham-
sted lysimeters? averaged about seventeen inches a year, with
1 Buckingham, E., Studies on the Movement of Soil Moisture; U. S.
Dept. Agr. Bur. Soils, Bul. 38, pp. 9-18, 1907.
See also Bouyoucos, G. J., Effect of Temperature on Movement of
Water Vapor and Capillary Moisture in Soils; Jour. Agr. Res., Vol. V,
No. 4, pp. 141-172, Oct., 1915.
*Warington, R., Physical Properties of the Soil, p. 109; Clarendon
Press, Oxford, 1900.
THE FORMS OF SOIL-WATER 183
a rainfall ranging from twenty-two to forty-two inches. This
means that from one-third to one-half of the effective
rainfall was entirely lost as thermal water. The necessity of
checking such a loss becomes apparent, especially in regions
where rainfall is sight or drought periods are likely to occur.
As no country is free from one or the other of such econ-
tingencies, the great prominence that methods of moisture
conservation hold in systems of soil management is under-
standable. While means of checking losses by leaching and
run-off are advocated, effective retardation of surface evapora-
tion is always emphasized.
CHAPTER IX
THE WATER OF THE SOIL IN ITS RELATION TO
PLANTS
WATER begins its service to plants by promoting the proc-
esses of soil weathering, which results in the simplification of
compounds for plant utilization. It also functions more di-
rectly in plant development in maintaining the turgidity of
the cells, in carrying materials, regulating temperature and
in furnishing a supply of hydrogen and oxygen for the plant.
These direct and indirect functions of water in relation to
plant growth may be considered from a number of different
viewpoints.
97. Functions of water to plants.——Water acts as a
solvent and as a medium for the transfer of nutrients from
the soil to the plant. This transfer relationship is rather
complex, since most nutrient materials penetrate the cell-walls
of the absorbing surfaces of the roots in an ionic condition.
As a nutrient water becomes a part of the cell contents with-
out change or is broken down into its elements and utilized in
the production of new compounds. In addition, water by
maintaining turgidity, in equalizing the temperature by evap-
oration from the leaves, and in facilitating quick shifts of
nutrients and food from one part of the plant to another,
acts as a carrier during assimilation and while synthetic and
metabolic processes are going on.
Soil-moisture, therefore, in proper amounts, becomes one
of the controlling factors in crop growth and must be looked
to before the maximum utilization of the nutrient elements
can be expected. The amount of water held within the plant
184
WATER OF SOIL IN ITS RELATION TO PLANTS 185
is not large, however, in comparison with the amount lost
by transpiration, although green plants contain from 60 to
90 per cent. of moisture.
Because of the readiness with which moisture passes from
plants into the atmosphere, large quantities must be taken
30 6 } GOIN. AZO.
1° 20 °
Fig. 34.—The effect of increasing water supply on the production of dry
matter in various crops. The water is expressed in acre-inches.
ORY MATTER IN THOUSANDS OF POUNDS.
®
°
from the soil in order that the plant may maintain its proper
turgor. That the crop may be properly supplied with water,
optimum moisture conditions should prevail in the soil at
all times during the growing season. It must not be inferred
that loss through the plant is the only means by which mois-
ture leaves the soil, since drainage and evaporation are by
no means insignificant factors.
186 NATURE AND PROPERTIES OF SOILS
98. Influence of water on the plant..—As the amount
of water available to a crop is increased up to a certain point,
the vegetative growth also is usually increased, the plant be-
coming more succulent. The percentage of moisture in the
crop, even at harvest time, is usually high. Shipping qualities
are depressed with increased moisture, especially if the water
available is excessive. With an enlargement of the plant
eell a change probably occurs in the cell contents, tending
toward a greater susceptibility to disease.
Ripening especially is delayed by large amounts of mois-
ture, tillering is diminished, and the percentage of protein
content of the crop is decreased. It is a curious fact that
many of the general and morphological effects of large quan-
tities of available water on plant growth are the same as those
caused by the presence of too much soluble nitrogen. In
cereals the stimulation from a large supply of water is
shown especially in the ratio of grain to straw. Widt-
soe’s® findings in this regard are representative of the data *
available on this point:
TaBLE XX XITT
DISTRIBUTION OF DRY MATTER BETWEEN GRAIN AND STRAW WITH
VARYING AMOUNTS OF WATER.
Inches of water ap-
plied pean; fetes 5 716) 10 | 15 1) 25) 1935" eae
Grain in percentage
of dry matter of
entire crop...... 44 | 43 AS | 41" '38 |) 837 Wise
1 Mitscherlich, E. A., Das Wasser als Vegetationsfaktor ; Landw. Jahr.,
Band 42, Seite 701-717, 1912.
2 Widtsoe, J. A., The Production of Dry Matter with Different Quan-
tities of Irrigation Water; Utah Agr. Exp. Sta., Bul. 116, p. 49, 1912.
*Bunger, H., Uber den Einfluss Verschieden Hohen Wassergehalts des
Bodens in den Einzelhen Vegetationsstadien bei Verschiedenem Nahr-
stoffreichtum auf die Entwicklung des Haferpflanzen; Landw. Jahrb.,
Band 35, Seite 941-1051, 1906.
Also, Seelhorst, C., von, und Freckmann, W., Der Einfluss des Was-
sergehaltes des Bodens auf die Ernten und die Ausbilding V erschiedener
Getriedevarietéten; Jour. f. Landw., Band 51, Seite 253-269, 1903.
WATER OF SOIL IN ITS RELATION TO PLANTS 187
As a rule, this depression of the ratio of grain to straw is
not due to an actual decrease in the grain, but to a corre-
spondingly greater production of dry matter in the vege-
tative parts. As available water is augmented, the dry mat-
ter of plants increases until a maximum is reached. The gen-
eral relationships are well exemplified by data from Widtsoe *
(Fig. 34), although other equally valuable figures may be
obtained from von Seelhorst * and Atterberg,* who have done
much work on the subject.
99. The water requirements of plants—As might be
expected, the pounds of water transpired for every pound of
dry matter produced in the crop is very large. This figure,
called the transpiration ratio, or water requirement, ranges
from 200 to 500 for crops in humid regions, and almost twice
as much for crops in arid climates. An accurate determina-
tion of the transpiration ratio of a crop is somewhat difficult,
due to the methods of procedure necessary and also to the
difficulty of controlling the numerous factors that influence
the transpiration. For really reliable figures the plants must
be grown in cans or pots in order that the water lost may
be determined accurately by weighing. If there is no percola-
tion the water ordinarily lost from a cropped soil includes
both that evaporated from the soil surface and that tran-
spired from the leaves. The former loss may be controlled
largely in one of two ways: (1) by covering the soil so that
evaporation is absolutely checked and the only loss is by
transpiration; or (2) by determining the evaporation from a
bare pot and, by substracting this from the total water loss
1Widtsoe, J. A., The Production of Dry Matter with Different Quan-
tities of Irrigation Water; Utah Agr. Exp. Sta., Bul. 116, pp. 19-25,
1912.
2 Seelhorst, C., von, und Krzymowski, R., Versuch tiber den Einfluss,
welchen das Wasser in dem Verschiedenem Vegetationsstadien des Hafers
auf sein Wachstum ausiibt; Jour. f. Landw., Band 53, Seite 357-370,
1905.
° Atterberg, A., Die Variationem der Ndhrstoffgehalte bei dem Hafer ;
Jour. f. Landw., Band 49, Seite 97-113, 1901.
188 NATURE AND PROPERTIES OF SOILS
from a cropped soil, finding the loss due to transpiration
alone.
An objection to the former method is that any covering
which interferes with evaporation interferes with proper soil
aération also and may render soil conditions abnormal. In
the second method, however, an even more serious error en-
ters, since the evaporation from the bare soil is not the same
as that from a soil covered by vegetation because of the effect
of shading. Moreover, due to the action of the roots, less
water is likely to move to the surface by capillary attraction
in the cropped soil. Therefore any data that may be quoted
can be only general in its application, not only because of the
errors of determination but also because of the great num-
ber of factors that under normal conditions may vary the
transpiration ratio. The following data drawn from various
investigators working by the general methods?’ already out-
lined, give some idea of the water transpired by different
crops, due allowance being made for various disturbing fac-
tors. (See Table XXXIV, page 189.)
100. Factors affecting transportation.2—It is obvious
from the figures quoted that the transpiration ratio of a crop
is the resultant of a number of influences.* The factors may
be listed under three heads, as follows:
1. Crop—Difference due to different crops and to vari-
ations of the same crop.
1A brief discussion of the various methods is found as follows:
Montgomery, E. G., Methods of Determining the Water Require-
ments of Crops; Proc. Amer. Soc. Agron., Vol. 3, pp. 261-283, 1911.
Also Briggs, L. J., and Schantz, H. L., The Water Requirement of
Plants; U. S. Dept. Agr., Bur. Plant Ind., Bul, 285, 1913.
*Kiesselbach, T. A., Transpiration as a Factor in Crop Production;
Nebr. Agr. Exp. Sta., Res. Bul. 6, June, 1916.
*A complete review of the literature concerning the climatic and
soil factors in their effect on transpiration may be found as follows:
Briggs, L. J., and Shantz, H. L., The Water Requirement of Plants;
U. S. Dept. Agr., Bur. Plant Ind., Bul. 285, 1913.
See also, Briggs, L. J., and Shantz, H. L., Daily Transpiration dur-
ing the Normal Growth Period and its Correlation with the Weather;
Jour. Agr. Res., Vol. VII, No. 4, pp. 155, 212, Oct., 1916.
WATER OF SOIL IN ITS RELATION TO PLANTS 189
TABLE XXXIV
WATER REQUIREMENTS OF PLANTS AS DETERMINED BY DIFFER-
ENT INVESTIGATORS.
LAWES * 2} HELL- _ \LeaTHER®| AND
C EE PERE Tresibe rege? | Kinet [ DURA, SHANTZ®
ROP DEN, EaenGES DAHME, MADISON, Tra eArcn on
ENGLAND, | ~ 1876 GERMANY|Wis., 1895 1911 Gorn.
1850 hie 1911-1913
Barley ...| 258 774 310 464 468 534
pediien see's) 209 —- 282 = — 736
Buckwheat) —— 646 363 — — 578
Clover” <...|: 269 -- = 310 576 saa 190
Maize ....)| —— 230 — Dat. Boil 368
Millet ....) —— 447 —— = a 310
Oats eet. . s ee 665 376 503 469 597
[Pease 259 416 273 477 563 788
Potatoes — oa a 385 636
Rape — 912 — — — 44]
UR VOr aka es —— —— 353 = —— 685
Wheat ...| 247 a 338 —— 544 513
1 Lawes, J. B., Experimental Investigation into the Amount of Water
Given off by Plants during their Growth; Jour. Hort. Soe., London,
Vol. 5, pp. 38-63, 1850. Pots holding 42 pounds of field soil were used.
Evaporation from soil was reduced to a very low degree by perforated
glass covers cemented on the pots. The figures quoted are from un-
fertilized soil.
7 Wollny, E., Der Einfluss der Pflanzendecke und Beschattung auf die
Physikalischen Eigenschaften und die Fruchtbarkeit des Bodens, Seite
125; Berlin, 1877. Wollny grew plants in sand in amounts ranging
from 5 to 12 kilograms. Evaporation was reduced to a very low
degree by perforated covers. Actual evaporation from uncropped cans
was observed, however.
* Hellriegel, H., Beitradge zur den Naturwissenschaftlichen Grundlagen
des Ackerbaus, Seite 663; Braunschweig, 1883. Hellriegel grew plants
in 4 kilograms of clean quartz sand and supplied them with nutrient
solutions. The loss by evaporation from uncropped pots was used in
determining losses by transpiration. In later experiments covers were
used in order to cut down evaporation.
“King, F. H., Physics of Agriculture, p. 139; published by author,
Madison, Wis., 1910. Also, The Number of Inches of Water Required
for a Ton of Dry Matter in Wisconsin; Wis. Agr. Exp. Sta., 11th Ann.
Rep., pp. 240-248, 1894; and The Importance of the Right Amount and
Right Distribution of Water in Crop Production; Wis. Agr. Exp. Sta.,
190 NATURE AND PROPERTIES OF SOILS
2. Climate—Rain, humidity, sunshine, temperature, and
wind.
3. Moisture and fertility.?
Not only do different plants * show a variation of transpira-
tion the same season, but the same plant may give a totally
different transpiration in separate years. This is due in part
to inherent differences in the plant itself. For example, the
extent of leaf surface or root zone would materially influence
the transpiration relationship under any given condition.
However, a great deal of the variation observed in the ratios
already quoted arises from differences in climatic conditions.
As a general thing, the greater the rainfall the higher is
the humidity and the lower is the relative transpiration.
This accounts for the high figures obtained by Widtsoe* in
Utah. Montgomery‘ found, in studying the water require-
1 Fertility is used here in the sense of potential productivity. It
refers especially to the ultimately available nutrients of the soil.
2Miller, E. C., and Coffman, W. B., Comparative Transpiration of
Corn and the Sorghums; Jour. Agr. Res., Vol. XIII, No. 11, pp. 579-
604, June, 1918.
? Widtsoe, J. A., The Production of Dry Matter with Different Quan-
tities of Irrigation Water; Utah Agr. Exp. Sta., Bul. 116, 1912. Also,
Irrigation Investigations. Factors Influencing Evaporation and Trans-
piration; Utah Agr. Exp. Sta., Bul. 105, 1909.
“Montgomery, E. G., and Kiesselbach, T. A., Studies in Water Re-
quirements of Corn; Nebr. Agr. Exp. Sta., Bul. 128, p. 4, 1912.
14th Ann. Rep., pp. 217-231, 1897. King used cans holding about 400
pounds of soil. Some were set down into the earth while others were
not. Part of the work was carried on in the field; the remainder was
run in vegetative houses. Normal soils were used. Evaporation from
soil was very low, water being added from beneath. The data quoted
are the average of a large number of tests.
5Leather, J. W., Water Requirements of Crops in India; Memoirs,
Dept. Agr., India, Chem. Series, Vol. I, No. 8, pp. 133-184, 1910, and
No. 10, pp. 205-281, 1911. Jars containing from 12 to 48 kilograms
of soil were used. Loss by evaporation was determined on bare pots.
The plants were grown in culture houses or in screened inclosures.
* Briggs, L. J., and Schantz, H. L., Relative Water Requirement of
Plants; Jour. Agr. Research, Vol. III, No. 1, pp. 1-63, 1914. Also,
The Water Requirements of Plants; U. S. Dept. Agr., Bur. Plant Ind.,
Bul. 284, 1913. Plants were grown in cans holding 250 pounds of soil.
Evaporation from soil was prevented by means of a paraffin covering.
Work was conducted in screened inclosures. The data are the average
of several years’ work.
WATER OF SOIL IN ITS RELATION TO PLANTS 191
ments of corn under greenhouse conditions, that an increase
in the percentage humidity from 42 to 65 lowered the
transpiration ratio from 340 to 191. In general, temperature,
sunshine, and wind vary together in their effect on transpira-
tion. That is, the more intense the sunshine, the higher is
the temperature, the lower is the humidity, and the greater
is likely to be the wind velocity. All this would tend to raise ,
the transpiration ratio.
From the soil standpoint, however, the factors inherent
in the soil itself are of more vital importance as regards tran-
spiration, since they can be controlled to a certain extent un-
der field conditions. An increase in the moisture content of a
soil usually results in an increased transpiration ratio. The
work of Hellriegel + with barley grown in quartz sand con-
taining a nutrient solution may be cited in this regard, to-
gether with the data obtained by Montgomery? at Lincoln,
Nebraska, with maize grown in a loam soil:
TABLE XX XV
EFFECT OF SOIL-MOISTURE ON TRANSPIRATION.
BAaRLEY—HELLRIEGEL MaizE—MontTGOMERY
-MOISTURE
Soo MOTStU SOIL-MOISTURE
PERCENTAGE | TRANSPIRATION Secon || | THANSPIBATION
eis eae TOTAL CAPACITY Bs
80 277 100 290
60 240 80 262
40 216 60 239
30 223 45 229
20 168 35 252
10 180
* Hellriegel, H., Beitrige zu den Naturwissenschaftlichen Grundlage
des Ackerbaus, Seite 629, Braunschweig, 1883.
7 Montgomery, EH. G., Methods of Determining, the Water Require-
ments of Crops; Proc. Amer. Soc. Agron., Vol. 3, p. 276, 1911.
192 NATURE AND PROPERTIES OF SOILS
These data show clearly that an excessive amount of mois-
ture in the soil is not a favorable condition for the economical
use of water.
The amount of available nutrients is also concerned in the
economic utilization of water. In general the data along
these lines show that the more productive the soil the lower
is the transpiration ratio. Therefore, a farmer, in raising
the productivity of his soil by drainage, lime, good tillage,
green-manures, barnyard manures, and fertilizers, provides
at the same time for a greater amount of plant production
for every unit of water utilized. The total quantity of water
taken from the soil, however, will probably be larger.
The following figures from Montgomery * are representative
of data available on this phase:
TABLE XXXVI
RELATIVE WATER REQUIREMENT OF MAIZE ON DIFFERENT TYPES
OF NEBRASKA SOILS, 1911.
Dry WEIGHTOF PLANTS
TRANSPI
Ga Cn Dan RANSPIRATION RATIO
Soin
MANURED | UNMANURED | MANURED | UNMANURED
Poor (15 bushels)...| 376 113 350 549
Medium (30 bushels)} 413 184 341 479
Fertile (50 bushels).| 472 270 346 392
The effects of texture have been investigated by a number
of men, the work of von Seelhorst? and of Widtsoe* being
Montgomery, E. G., Water Requirements of Corn; Nebr. Agr. Exp.
Sta., 25th Ann. Rep., p. x, 1912.
See also, Hellriegel, H., Beitrége zu den Naturwissenschafitlichen
Grundlage des Ackerbaus, Seite 629, Braunschweig, 1883.
2Seelhorst, C., von., Uber den Wasserverbrauch von Roggen, Gerste,
Weizen, und Kartoffeln; Jour. f. Landwirtschaft, Band 54, Heft 4,
Seite 316-342, 1906.
8’ Widtsoe, J. A., Irrigation Investigations. Factors Influencing Evapo-
ration and Transportation; Utah Agr. Exp. Sta., Bul. 105, 1909.
WATER OF SOIL IN ITS RELATION TO PLANTS 193
perhaps the most reliable. While these investigators found
in general that plants on heavy soils exhibited a low transpira-
tion ratio, hasty conclusions must not be drawn. Since the
fine-textured soils contain more nutrient materials, it is prob-
able that this is also a factor.
101. Amounts of water necessary to mature a crop.—
Although it may be seen from the transpiration ratios cited
that the amount of water necessary to mature the average
erop 1s very large, a concrete example under humid condi-
tions may be cited to advantage. A fair estimate of the dry
matter produced in the above-ground parts of a forty-bushel
erop of wheat would be about two tons. Assuming the tran-
spiration ratio to be 300, the amount of water actually used
by the plant would amount to 600 tons to the acre, or about
5.2 inches of rainfall. This does not include the evaporation
that is continually going on from the soil surface, which might
very easily amount to as much more. The demand in total,
to say nothing of run-off and drainage, is at least equal to
10 inches of rainfall.
102. Role of capillarity in supplying the plant with
water—A query arises at this point regarding the mode
by which this immense quantity of water is supplied to the
plant. The rootlets, especially their absorbing surfaces, are
few in number as compared with the interstitial angles that
contain most of the water retained in the soil. How, then,
does the plant avail itself of water not in immediate contact
with its rootlets? This question has been anticipated in the
discussion concerning the capillary equilibrium which tends
to oceur in all soils. As soon as the rootlet begins to absorb
at one point the film in that interstitial angle is thinned.
A considerable convexity of the water surface occurs at that
point, resulting in an inward pull, which causes the water to
move in all directions toward that point. Thus a feeding
rootlet by absorbing some of the moisture with which it is in
contact, creates a condition of instability which results in
194 NATURE AND PROPERTIES OF SOILS
considerable film movement. It can, therefore, be said that
eapillarity is an important factor in any soil in supplying
the plant with proper quantities of moisture.
Many of the early investigators have over-estimated the
distances through which this adjustment may be effective in
properly supplying the plant. It must always be kept clearly
in mind that it is the rate of water supply that is the con-
trolling factor. Therefore, capillarity, although it may act
through a distance of eight or ten feet if time enough be al-
lowed, may actually be of immediate practical importance
through only a few inches as far as the crop is concerned. No
extended data are available as to this particular phase, but the
knowledge of capillary movement indicates that capillarity of
the soil is of greatest importance in a restricted zone immedi-
ately around the surface of each absorbing root.*
103. Why plants wilt—As has already been indicated,
water may be of little use to a plant because of distance, since
capillary action may not move the water rapidly enough
for normal needs. Water near at hand may be unavailable
through the obstruction of capillarity, friction in this case
being the cause. As the rootlet thins the interstitial film at
any point, the surface tension equilibrium is disturbed and
water moves toward the absorbing surface. This movement is
rapid enough for plant needs until the film channels on the
particles become thin. As such a condition approaches, fric-
tion inereases rapidly, cutting down the capillary movement
to such an extent as to interfere with the normal functions
of the plant.
Wilting occurs, therefore, merely because the soil is unable
to move the water rapidly enough for crop needs. As the
friction increases very rapidly after the point of lento-capil-
larity is reached, the wilting coefficient is a figure somewhat
1 Burr, W. W., The Storage and Use of Soil Moisture; Nebr. Agr. Exp.
Sta., Res. Bul. 5, 1914.
Miller, E. C., Comparative Study of the Root System and Leaf
Areas of Corn and Sorghums; Jour. Agr. Res., Vol. VI, No. 9, pp. 311-
331, 1916.
WATER OF SOIL IN ITS RELATION TO PLANTS 195
less than the percentage representing the lento-capillarity.
Since the inner capillary water moves very sluggishly if at
all, wilting must occur before the plant has drawn to any great
extent on this part of the capillary moisture. The hygroscopic
water is, therefore, wholly unavailable to plants and generally
some of the capillary as well, although Alway * has shown that
under certain conditions the plant may reduce the moisture
down to the hygroscopic coefficient. The wilting coefficient ex-
pressed in soil-moisture terms may be located somewhere be-
tween the hygroscopic coefficient and the point of lento-
eapillarity.
104. The wilting coefficient and its determination.—It
has been known for many years that the common plants pos-
sess different capacities for resisting drought. This has usu-
ally been ascribed to one or more of three causes: (1) differ-
ences in root extension; (2) differences in ability to become
adjusted to a slow intake of water; and (3) differences in the
osmotic pull that plants exert on the soil-water. The last two
factors argue for different wilting coefficients for crops on the
same soil.
The extended work of Briggs and Shantz,? however, indi-
cate that the permanent wilting point, expressed as a soil-
moisture percentage, is practically the same for all plants.
Later Caldwell * demonstrated that this relationship of the
physical constants of the soil to the wilting point depends on
the rate at which the plant loses water, showing that the soil
factors are not entirely dominant in this respect.
The conclusions of Briggs and Shantz, nevertheless, seem
* Alway, F. J., Studies on the Relation of the Non-available Water of
the Soil to the Hygroscopic Coefficient; Nebr. Agr. Exp. Sta., Res. Bul. 3,
1913.
* Briggs, L. J., and Schantz, H. L. The Wilting Coefficient for Dif-
ferent Plants and its Indirect Determination, U. S. Dept. Agr., Bur.
Plant Ind., Bul. 230, 1912.
*Caldwell, J. S., The Relation of Environmental Conditions to the
Phenomena of Permanent Wilting in Plants; Physiological Researches,
Station N, Baltimore; U. 8S. Dept. Agr., Vol. 1, No. 1, July, 1913.
196 NATURE AND PROPERTIES OF SOILS
more or less accurate for plants growing under humid condi-
tions. If such is the case, it can be accounted for only by the
fact that the soil forces in their effect on the wilting point
are so powerful as to over-ride any distinguishing character-
isties that the plant itself may possess, or at least reduce such
influences within the error of actual experimentation. Crops
wilt because they cannot get water fast enough, the wilting
coefficient in a humid climate being the same for most plants
growing on the same soil.
Briggs and Shantz,’ in their investigations, devised a very
satisfactory method for making determinations of the wilting
point. Glass tumblers holding about 250 cubic centimeters
of soil in an optimum condition were used. The seeds were
placed in this soil after which soft paraffin was poured over
the surface in order to stop evaporation, thus removing this
disturbing factor in the capillary equilibrium of the moisture.
The seedlings on germination were able to push through this
paraffin. While the plants were developing, the tumblers
were kept standing in a constant-temperature vat of water
in order to prevent condensation of moisture on the inside
of the glass. The vegetative room was under temperature
control. When definite wilting occurred, as determined in
a saturated atmosphere, a moisture determination was made
on the soil. The resulting figure, expressed as percentage
of moisture based on dry soil, represents the wilting coefficient
for the soil used.?
It is evident that the wilting coefficient will be influenced
1 Briggs, L. J., and Schantz, H. L., The Wilting Coefficient for Differ-
ent Plants and its Indirect Determination; U.S. Dept. Agr., Bur. Plant
Ind., Bul. 230, pp. 26-33, 1912.
2 Bouyoucos classifies the capillary water into two groups, Free (the
more active), and Capillary-absorbed (inner capillary). The distinction
is made on the basis of his dilatometer (see foot-note, page 155) results,
the portion which freezes at about 0°C being considered the more
active. The point so established by his dilatometer gives in a general
way the wilting coefficient as defined by Briggs and Shantz.
Bouyoucos, G. J., 4 New Classification of the Soil Moisture ; Soil Sci.,
Vol. XI, No. 1, pp. 33-47, Jan., 1921.
WATER OF SOIL IN ITS RELATION TO PLANTS 197
by a number of soil conditions. Important among these is
texture, which in itself really represents a group of soil con-
ditions. In general the wilting point is much higher on a
fine soil than one of a coarse nature. The following data from
Briggs and Shantz? is interesting in this regard. The wilt-
ing coefficient is shown to lie much nearer the hygroscopic
coefficient than to the figure representing the maximum ab-
sorption capacity as determined by the Hilgard method.
TABLE XXXVII
RELATION OF THE WILTING COEFFICIENT TO THE TEXTURE OF THE
SOIL, THE HYGROSCOPIC COEFFICIENT AND THE CALCULATED
MAXIMUM ABSORPTIVE CAPACITY OF THE SOIL
FOR WATER.
a eee
: IMU
Sor Garant WILTING PoINT Teast
CAPACITY
@oarse sands)... 5 9 20.0
BNET SAMCle ve. 5 shes 1) 2.6 28.5
IME SAMO 4) sq 65 ns 1 2.3 3.3 30.5
mandy, loam... . 3.) 4.8 34.9
Bandy loam...) .... 4.4 6.3 39.2
Fine sandy loam .. 6.5 9.7 49.1
Mga Meter! se a he 7.8 10.3 50.8
LLP To Sere hee eae 9.8 13.9 61.3
@layc loam: : 42.0... 11.4 16.3 68.2
In studying the correlation of this wilting coefficient to
soil conditions Briggs and Shantz? advanced the following
relationships. Expressed as formule, they represent methods
1Briggs, L. J., and Schantz, H. L., The Wilting Coefficient for Dif-
ferent Plants and its Indirect Determination; U. S. Dept. Agr., Bur.
Plant Ind., Bul 230, p. 65, 1912.
See also Heinrich, R., Uber das Verméogen der Pflanzen den Bodenen
Wasser zu erschépfen; Jahresbericht der Agr.-chem., Band 18, Seite 368-
372, 1875.
* Briggs, L. J., and Shantz, H. L., The Wilting Coefficient for Dif-
198 NATURE AND PROPERTIES OF SOILS
of at least approximating the wilting point from other soil
factors. These formule ' are arranged in the order of their re-
liability, based on the data obtained by the authors:
Moisture equivalent
1.84
Hygroscopic coefficient
.68
Water-holding capacity—21
( Hilgard Method)
2.9
1. Wilting coefficient =
2. Wilting coefficient =
3. Wilting coefficient =
While such formule are only approximate in their applica-
tion, they are valuable for rough calculations. They also show
in a general way the correlations between the various moisture
conditions established by experimental methods.
105. The availability of the soil-water—From the dis-
cussions already presented regarding the forms of water in
the soil, the ways in which they are held, and their movements,
it is evident that all moisture present in a soil is not available
for plant growth. Three divisions of the soil-water may be
made on this basis: wnavailable, available, and superfluous.
It is obvious that all of the moisture below the wilting point
is out of reach of the plant and may be classified as unavail-
able. It includes all of the hygroscopic and that part of the
capillary which is tightly held, the so-called inner capillary
water. The amount of the capillary moisture unavailable to
plants is much greater with clayey than with sandy soils. For
example, a sand with a hygroscopic coefficient of 1.5 per cent.
ferent Plants and its Indirect Determination; U. 8. Dept. Agr., Bur.
Plant Ind., Bul. 230, pp. 56-77, 1912.
See also, Loughridge, R. H., Investigations in Soil Physics; Calif. Agr.
Exp. Sta., Rep. 1892-3-4, pp. 70-100, 1894. Alway, F. J., and Clarke,
V. L., Use of Two Indirect Methods for the Determination of the
Hygroscopic Coefficient of Soils; Jour. Agr. Res., Vol. VII, No. 8, pp.
345-359, Nov., 1916.
1Note that the wilting coefficient, moisture equivalent, water-holding
capacity and hygroscopic coefficient are expressed in percentage of
water based on dry soil.
WATER OF SOIL IN ITS RELATION TO PLANTS 199
and a wilting coefficient of 2.6 per cent. has 1.1 per cent. of
water of a capillary nature unavailable. A clay loam having
a hygroscopic coefficient of 11.4 per cent. and a wilting coeffi-
cient of 16.3 per cent. would contain 4.9 per cent. of capillary
water unavailable to crops. It must be remembered, however,
that under certain conditions plants may reduce the capillary
moisture almost to the hygroscopic coefficient.1_ The moisture
so obtained is probably not utilized for growth activities.
Advancing from the wilting, or critical, moisture content of
a soil, all the remaining capillary water is found to be avail-
HYGRO. WILTING MAX. FIELD
aS a Seen CAPACITY
OPTIMUM WATER ZONE PUA
UNAVAILABLE AVAILABLE ‘ SUPERFLUOUS
AVAILABLE UNDER
CERTAIN CONDITIONS |
Fig. 35.—Diagram showing the various forms of water that may be
present in the soil and their relations to higher plants.
able for normal plant use. However, when free water begins
to appear, a condition detrimental to growth is established,
conditions becoming more adverse as the saturation point is
approached. This free water is designated as the superfluous
water and its presence generates conditions unfavorable to
plants. The bad effects of free water on the plant arise
largely from the poor aération that results from its presence.’
Not only are the roots deprived of their oxygen, but toxic
materials tend to accumulate. Favorable bacterial activities,
such as the production of ammonia and nitrates, are much re-
1 Alway, F. J., Studies on the Relation of the Non-available Water
etl eae the Hygroscopic Coefficient; Nebr. Agr. Exp. Sta., Res.
*It must be kept in mind that in a clayey soil the superfluous water
may include some of the upper capillary moisture.
200 NATURE AND PROPERTIES OF SOILS
tarded also. The various forms of water in the soil and their
availability to the plant are illustrated diagrammatically in
Fig. 35, page 199.
This diagram may be evaluated in a general way as below,
using the sandy and clayey soils for which full physical data
have already been given in Chapter VIII. (See footnote on
page 179.)
TABLE XX XVIII
THE EVALUATION OF FIG. 35 FOR A SANDY AND CLAYEY SOIL,
RESPECTIVELY.
SANDY SoIL CLAYEY Sorb
Hygroscopic coefficient....... 1.00 10.00
Wirliting? “pOLnt a. Meee aero aed. 1.47 14.70
Maximum field capacity....... 17.00 44.00
Unavailable water ssn... : 3, 1.47 14.70
Available wateriess o)iis lee 15.53 29.30
Superfiuous water............ 8.00 1.60
106. Optimum moisture for plant growth.—It is very
evident that there must be some moisture condition of a soil
which is best for plant development. This is usually desig-
nated as the optimum content. It is not to be assumed, how-
ever, that the total range of the available soil-water repre-
sents this condition. Nor is this optimum water content in
any particular soil to be designated by a definite percentage.
In reality the moisture in a soil may undergo considerable
fluctuation and yet allow the plant to develop normally.t This
is because the physical condition of the soil changes with
varying water content and the plant is able to accommodate
*Wollny, E., Untersuchung iiber den Einfluss der Wachsthumsfaktoren
auf des Produktionsverméogen der Kulturpflanzen; Forsch. a. d. Gebiete
d. Agri.-Physik., Band 20, Seite 53-109, 1897.
Mayer, A., Uber den Einfluss kleinerer oder grosserer Mangen von.
Wasser auf die Entwickelung einiger Kulturpflanzen; Jour. f. Landw.,
Band 46, Seite 167-184, 1898.
WATER OF SOIL IN ITS RELATION TO PLANTS 201
itself to such a fluctuation without a disturbance in its normal
development. Granulation has considerable influence on the
range of optimum moisture conditions, since the better the
granulation, the better able is the soil to accommodate itself
to changes in water content without a disturbance of normal
growth. In moisture conservation~and control, a granular
soil is one of the first improvements to be aimed at. Drainage,
liming, addition of organic matter, and tillage, by leading up
to such a condition, increase the effectiveness and economy of
soil moisture utilization.
Many of the ordinary farming operations have to do with
the maintenance of an optimum moisture condition in the soil.
During periods of excessive rainfall, especially during the
growing season, conditions should be such as to allow the pres-
ence of free water in the soil for the briefest time possible.
This means adequate under-drainage and satisfactory arrange-
ments whereby the run-off may be removed with but little
damage. Moisture control also demands conservation meth-
ods of more or less intensity in arid and semi-arid regions sup-
plemented by irrigation, whereby the soil-moisture may never
drop much below the point of lento-capillarity. By such ar-
rangments the optimum moisture conditions, so essential to
normal and uninterrupted crop growth, are maintained.
CHAPTER X
THE CONTROL OF SOIL-MOISTURE
IN THE discussion of the water requirements of plants it
was apparent that for a normal yield of any crop, the amount
used by the plant alone was very great, varying from five to
ten acre-inches according to conditions. Were this the only
loss of water, the question of raising crops with given amounts
of rainfall would be a simple one. Three further sources of
water loss, however, are usually operating in the soil and tend-
ing to lower the water that would go toward transpiration, a
loss absolutely necessary for proper growth. The various
ways by which water finds an exit from a soil are: (1) tran-
spiration, (2) run-off over the surface, (3) percolation, and
(4) evaporation. The diagram (Fig. 36) makes clear their
relationships.
It is immediately obvious that, as the losses by run-off,
leaching, and evaporation increase, the amount of water left
for crop utilization decreases. Some control of soil-water
is, therefore, necessary both in an arid and a humid region.
Under arid and semi-arid conditions, where run-off and per-
colation are not of such great importance except where irriga-
tion is practiced, loss by evaporation is of especial consequence,
as it competes directly with the plant. Under humid condi-
tions, losses by percolation and run-off seem to merit the
greater attention, because of the loss of nutrients with the
former and the erosion damage from the latter. The influence
of evaporation, however, is not to be under-estimated or ne-
elected. Control of moisture is, therefore, necessary in all
regions. This control consists in so adjusting run-off, leach-
202
THE CONTROL OF SOIL-MOISTURE 208
ing, and evaporation as to maintain optimum moisture condi-
tions in the soil at all times. Such control should result in
a proper and economical utilization of soil-water by the plant.
107. Run-off losses—In regions of heavy rainfall or
in areas where the land is sloping or rather impervious to
water, a considerable amount of moisture received as rain is
likely to be lost by running away over the surface. Under
' TRAN SPIRATION.
AM
Fig. 36.—Diagram illustrating the various ways by which water may be
lost from a soil.
such conditions two considerations are important: (1) the loss
of water that might otherwise be of use to plants; and (2) the
erosion that usually occurs when much water escapes in this
manner. Of the two, the latter is generally the more impor-
tant. The amount of run-off varies with the rainfall and its
distribution, the slope, the character of the soil, and the vege-
tative covering. In some regions loss by run-off may rise as
high as 50 per cent. of the rainfall, while in arid sections it
is of course very low, unless the rainfall is of the torrential
type as in the arid Southwest.
204 NATURE AND PROPERTIES OF SOILS
The quantity of water entering a soil is determined almost
entirely by the physical condition of the soil. If it is loose
and open, the water enters readily and little is lost over the
surface as run-off. If, on the other hand, the soil is com-
pact, impervious and hard, most of the rainfall runs away,
and not only is there a serious loss of water, but considerable
erosion may also result. The first step in checking run-off
losses, therefore, is strictly physical in nature. Good tillage
and plenty of organic matter by encouraging granulation have
much to do with the proper entrance of water into the soil as
well as with its economic utilization therein.
108. Erosion by water and its control.i—While every
one is familiar with the importance of water in the forma-
tion of alluvial and marine soils, the concurrent destructive
action that is going on in the uplands is generally overlooked.
This is due to the fact that erosion is often considered as more
or less uncontrollable, an ill that can not be avoided. In
Wisconsin, for example, 50 per cent. of the tillable land is
subject to erosion of economic importance.” Even in as level a
state as Illinois, 17 per cent. of the area is detrimentally
eroded.2 The waste by erosion is as great in other states,
even those of an arid climate. Davis* has estimated that 870
million tons of suspended material are carried each year into
the ocean by the streams of the United States. Since this is
only a very small fraction of the soil brought down from the
1Davis, R. O. E., Economic Waste from Soil Erosion; U. S. Dept.
Agr., Year Book for 1913, pp. 207-220.
Ramser, C. E., Terracing Farm Lands; U.S. Dept. Agr., Farmers’ Bul.
997, 1918.
Eastman, E. E., and Glass, J. 8., Soil Erosion in Iowa; la. Agr. Exp.
Sta., Bul. 183, Jan., 1919.
Fisher, M. L., The Washed Lands of Indiana; Ind. Agr, Exp. Sta.,
Cire. 90, Feb., 1919.
“Whitson, A. R., and Dunnewald, T. J., Keep Our Hillsides from
Washing ; Wis. Agr. Exp. Sta., Bul. 272, Aug., 1916.
*Mosier, J. G., and Gustafson, A. F., Soil Physics and Management,
p. 358, Philadelphia, 1917.
* Davis, R. O. E., Economic Waste from Soil Erosion; U.S. Dept. Agr.,
Year Book for 1913, p. 213.
THE CONTROL OF SOIL-MOISTURE 205
uplands by running water, erosion is no insignificant factor
in soil management considerations.
Two types of erosion are generally recognized, sheet and
eully. In the former, soil is removed more or less uniformly
from every part of the slope. Gullying occurs where the vol-
ume of water is concentrated, resulting in the formation of
ravines by undermining and downward cutting. Both types
of erosion are serious.
A number of different methods for the effective prevention
and control of erosion may be utilized. Anything that will
increase the absorptive capacity of the soil, such as deep plow-
ing, surface tillage, and increase of organic matter, will lessen
the run-off over the surface. On steep slopes, however, such
influence is of little importance, since during heavy rainfall
absorption is too slow to lessen materially the surface losses.
In cultivating corn and similar crops, it is important that the
last cultivation be across the slope rather than with it. On
long slopes subject to erosion, the fields may be laid out in long
narrow strips across the incline, alternating the tilled crops,
such as corn and potatoes, with hay and grain. The grassed
areas tend to check the surface flow of water. Where the
slopes are subject to very serious erosion, they should either be
reforested or kept in permanent pasture, guarding always
against incipient gullying.
About the only effective means of controlling sheet erosion
is by terracing of some kind. Strong prejudice exists in many
communities against terraces, since they usually waste land,
are often unsightly and are a serious obstacle to harvesting
machinery. The Mangum terrace‘ however, is worthy of es-
pecial attention, since it obviates the really serious objections
to the ordinary terrace while maintaining the desired water
control. The Mangum terrace is generally a broad bank
of earth with gently sloping sides, contouring the field at a
1 First constructed by P. H, Mangum of Wake County, North Caro-
lina.
206 NATURE AND PROPERTIES OF SOILS
grade from 10 to 12 inches to the 100 feet. It is usually
formed by back-furrowing and scraping. The interval be-
tween the embankment depends on the slope. Since the terrace
is low and broad, it may be cropped without difficulty and
offers no obstacle to cultivating and harvesting machinery.
It wastes no land, and eliminates breeding places for insects.
Small gullies, while at first insignificant, soon enlarge intc
deep unsightly ravines. While they may be plowed-in or
otherwise filled up, such a procedure is generally a waste of
time, since the gullies form again with the next heavy wash.
A number of different methods are in use for the control of
gullying, depending on conditions. Staking is a very common
procedure, the size of the stakes increasing with the magni-
tude of the gully. The stakes are usually interwoven with
brush, although stone, straw, and other material may be
utilized. If brush or other loose material is used, it should
be staked to the ground or held down by stone or dirt. Other-
wise, the water will run beneath the fill and no benefit will
result. Dams of earth, concrete, or stone are often installed
with success. They must be supplemented by a tile-drain
outlet, however, with an elbow just above the dam. The dam
checks the water until it rises to the level of the elbow outlet
and is then carried away through the tile. Most of the sedi-
ment is deposited above the dam and the gully is slowly filled.
109. Percolation losses and their control—When at
any time the amount of rainfall entering a soil becomes greater
than its water-holding capacity, losses by percolation will
result. The losses will depend largely on the amount and
distribution of the rainfall and the capability of the soil to
hold moisture. The objectionable features of excessive per-
eolation are two: (1) the actual loss of water, and (2) the
leaching-out of salts that may function as nutrients to plants.
The results from the Rothamsted lysimeter? from 1871-
*Hall, A. D., The Book of the Rothamsted Experiments, p. 22, New
Work, 1917;
THE CONTROL OF SOIL-MOISTURE 207
1913 on a bare clay loam three feet deep are interesting as to
the light they afford regarding actual drainage losses in humid
regions:
TABLE XXXIX
PERCOLATION THROUGH A SIXTY-INCH COLUMN OF BARE CLAY
LOAM. ROTHAMSTED EXPERIMENT STATION, ANNUAL
AVERAGE OF 42 YEARS.
PERCENTAGE
RAINFALL DRAINAGE
12 OF RAINFALL
HELODS INCHES INCHES Ae ADORE
1D Gy ote Sh! 0 a 607% 5.58 82.4
Wire Way oh c5 e 3 5.96 mall! 30.4
DMS AUS. 6 ee 7.83 1.82 23.2
IE Dt NOVee sake oes 8.29 4.50 54.2
Meant otal... 28.85 14.01 48.8
It appears from these figures that the drainage loss is much
lower in summer than winter, the ratio being about one to
three. It is also to be noted that about 50 per cent. of the
rainfall in such a climate as England is lost by percolation
throagh a bare soil. This compares fairly well with Wollny’s*
summary on eighteen soils in England, Switzerland, and Ger-
many. These soils, most of which were bare, showed a loss
of over 41 per cent. of the rainfall by drainage.
Recent results,” due to variable conditions, are by no means
in agreement, ranging from a low to a very high percentage
loss of the rainfall. It seems fair to assume, however, that,
as soils are handled in humid regions, over half of the rain-
fall is lost by percolation and run-off combined.
Percolation seems to be influenced, not only by the amount
1Wollny, E., Untersuchungen iiber die Sickerwassermengen in verschie-
denen Bodenarten; Forsch. a. d. Gebiete d. Agri.-Physik., Band 11,
Seite 1-68, 1888.
For excellent review of literature see Lyon, T. L., and Bizzell,
J. A., Lysimeter Experiments; Cornell Agr. Exp. Sta., Memoir 12, June,
1918,
208 NATURE AND PROPERTIES OF SOILS
of rainfall and its distribution, but also by evaporation, the
character of the soil, and the presence of a crop. As the rain-
fall increases, percolation increases, being much greater in
New York, for example, than in Utah. Evaporation has a
marked influence, reducing drainage losses to a considerable
degree. The drainage through sandy soils is generally larger
than through clayey soils under strictly humid conditions and
where run-off is a factor. When evaporation is high, sandy
soils have been known to percolate very much less than those
of a heavier nature. Field crops, in that they utilize a large
amount of moisture, have always been found to reduce per-
colation losses.
The loss of moisture by percolation is the least objectionable
feature of the phenomenon, since it is often necessary, espe-
cially during the spring and summer, to rid the soil very
quickly of superfluous water. The loss of nutrient salts is
more vital, since the materials so carried away might be used
by plants. The loss of nitrogen, calcium, and potassium from
a bare clay loam at Cornell University * over a period of ten
years averaged, respectively, 69, 398, and 72 pounds an acre
annually. This is equivalent to an acre loss of 419 pounds
of sodium nitrate, 995 pounds of calcium carbonate and 137
pounds of potassium chloride every year, which is a larger
amount of nutrient material than is removed by an average
crop.
Control of percolation is exerted, not so much to save water,
as to conserve nutrients. As water enters a soil it moves
downward and is continually changing into the capillary state.
If the absorptive capacity of the soil is high, little of the rain-
fall may appear as drainage. The presence of organic matter
and the influence of good tillage will do much toward check-
ing drainage losses. Once the absorptive capacity of the soil
1Fraps, G. S., Losses of Moisture and Plant Food by Percolation; Tex.
Agr. Exp. Sta., Bul. 171, 1914.
? Unpublished data. Cornell Agr. Exp. Sta., Ithaca, N. Y.
THE CONTROL OF SOJL-MOISTURE 209
is reached, however, the drainage should be as rapid and com-
plete as possible in order to insure good sanitation. The main-
tenance of a high absorptive capacity for available water and
the facilitation of rapid drainage are the secrets of rational
percolation control.
[h
SEES S
LW iit SSMZ
Fig. 37.—Influence of drainage on the ground water and the extent of
the root zone.
\ oP
MESS
SSO
In this connection it is well to remember that drainage losses
are profoundly affected by cropping. The following data from
the Cornell Experiment Station are especially interesting in
this regard. The data for the Dunkirk and Volusia soils are
for ten and fifteen years respectively :
TABLE XL
AVERAGE ANNUAL LOSS OF WATER BY PERCOLATION FROM BARE
AND CROPPED SOILS. CORNELL LYSIMETER TANKS.
RAINFALL AS
Conprti0Ns (ea etna ot
Dunkirk clay loam: |
Pp aROt ao nce chs 32.41 24.92 76.8
Croppedant..60 ss: 32.41 18.70 Oiled
Volusia silt loam:
LES Hee Soe ane 32.97 Zils 82.3
Cropped...) so764 32.97 20.62 62.5
210 NATURE AND PROPERTIES OF SOILS
TABLE XLI
AVERAGE ANNUAL LOSS OF NUTRIENTS BY PERCOLATION FROM
BARE AND CROPPED SOILS. CORNELL LYSIMETER TANKS.
ANNUAL LOSS IN POUNDS AN ACRE
CONDITIONS
NITROGEN CALCIUM POTASSIUM
Dunkirk elay loam:
Bare cote se ke 69.0 397.9 TRAY
TRObAGIOMIE A wet) Wise 247.1 Dice
GYASRAe ANE Nar A 225 259.9 Gli
Volusia silt loam:
ATG eke iach 51.8 341.4 84.5
Croppedas: an... 10.2 306.4 73.2
The infiuence of the crop on percolation is obvious, the loss
of water by drainage being markedly decreased. The
saving of nutrient is also very marked, especially as regards
the nitrogen. The loss of nitrogen is only about one-seventh
as much from the soils under a rotation, as where the land
was bare, while the saving of calcium and potassium is con-
siderable. The importance of catch- and cover-crops in eco-
nomical soil management need not be emphasized further.
110. Drainage.—While percolation, especially in hu-
mid regions, causes the loss of a large proportion of the
rainfall received and carries away in addition many tons of
1Klippart, J. H., Principles and Practice of Land Drainage; Cin-
cinnati, 1894.
Miles, M., Land Drainage; New York, 1897.
Faure, L., Drainage et Assainissement Agricole des Terres; Paris,
1903.
Elliott, C. G., Drainage of Farm Lands; U.S. Dept. Agr., Farmers’
Bul. 187, 1904.
King, F. H., Irrigation and Drainage, Revised Edition; Part II, New
York, 1909. ~
Warren, G. M., Tidal Marshes and their Reclamation; U. S. Dept.
Agr., Office Exp. Sta., Bul. 240, 1911.
Woodward, S. M., Land Drainage by Means of Pumps; U. S. Dept.
Agr., Office Exp. Sta., Bul. 243, 1911.
Elliott, C. G., Engineering for Land Drainage; New York, 1912.
Parsons, J. L., Land Drainage; Chicago, 1915.
THE CONTROL OF SOIL-MOISTURE 211
soluble material, it is generally wise to facilitate the rapidity
of its action while checking, if possible, its magnitude. The
encouragement of the rate of percolate is spoken of as land
drainage, which is the process of removing the excess or
superfluous water from the soil as rapidly as_ possible.
Excess water, by interfering with aération, sets up unsanitary
conditions within the soil. By draining the land many favor-
able reactions are promoted. Granulation is encouraged,
heaving is checked, while the root zone and water capacity
of the soil are markedly increased. By facilitating aération,
favorable chemical and biological changes are encouraged,
thus increasing the nutrients available for plants. The sum-
total of good drainage is an increase of crop production to
such an extent as to meet the investment costs and pay a hand-
some profit besides.
While the drainage of swamps and the reclamation of over-
flow areas are urgent, the drainage of lands already under
crop is more important. Practical farm drainage is para-
mount in almost every community, even in arid regions where
irrigation must be practiced. Two types of drainage are
feasible—open and closed. Ditch drainage is the usual type
of the first group. Ditches have the advantage of large ca-
pacity and are able to carry water at a low grade. On the
other hand, they waste land, are ineffective and inconvenient,
encourage erosion and demand a yearly up-keep expenditure.
Wherever possible under-drains should be used.
Jeffery, J. A., Text-Book of Land Drainage; New York, 1916.
Fippin, E. O., Drainage in New York; Cornell Agr. Exp. Sta., Bul.
254, 1908.
Brown, C. F., Farm Drainage; Utah Agr. Exp. Sta., Bul. 123,
1913.
Lynde, H. M., Farm Drainage in North Carolina; N. C. Agr. Exp.
Sta., Bul. 234, 1915.
Yarnell, D. L., Trenching Machinery Used for the Construction of
Trenches for Tile Drains; U. 8. Dept. Agr., Farmers’ Bul. 698, 1915.
Leidigh, A. H., and Gee, E. C., Tile Drainage; Tex. Agr. Exp. Sta.,
Bul. 188, 1916.
Hart, R. A., The Drainage of Irrigated Farms; U. S. Dept. Agr.,
Farmers’ Bul. 805, 1917.
212 NATURE AND PROPERTIES OF SOILS
111. Tile drains are the only reliable means of under-
drainage under all conditions. While stone drains’ are
of value in certain cases, they must always be short and
are likely to clog. Besides, their drainage is slow and in-
efficient. On silty soil they do not long remain in service.
The operation of the tile drain is simple. The tile, generally
about twelve inches long with a diameter varying with the
water to be carried, are laid end to end in strings, on the
bottom of a trench of sufficient slope, a carefully protected
outlet being provided. The tile are then covered with earth,
straw or surface soil often being placed directly around the
tile to facilitate the entrance of the water. The superfluous
water enters the tile through the joints, mostly from the
sides. As a consequence, the tops of the joints may be cov-
ered with paper, cloth or even cemented in order to prevent
the entrance of silt or quick-sand. The function of a tile
drain system is twofold: (1) to collect the superfluous water
and (2) to discharge it quickly from the land.
Where the land possesses considerable natural drainage, the
tile are laid along the depressions. This is spoken of as the
natural system of drainage in that the tile facilitate the quick
removal of the water from the places of natural accumulation.
Where the land is level or gently rolling, it often needs uni-
form drainage. A regular system must then be installed.
This may be either of the fishbone or gridiron style, or a
modification or combination of the two, natural drainage being
taken advantage of where possible. Where springs or seep-
age spots occur, cut-off systems must be devised. (See Figs.
38 and 39.)
1Stone drains are built by arranging stone in a properly located and
graded trench in such a manner as to provide a continuous channel
or throat from the upper end of the drain to the lower. One of the
safest modes of construction from the standpoint of clogging is to place
flat stone on edge in the trench with their faces parallel to the walls
of the ditch. The spaces between the stone provide for the movement
of the drainage water.
THE CONTROL OF SOIL-MOISTURE 213
Every regular system consists of two parts, the laterals and
the main drain. The laterals are usually constructed of
three 3- or 4-inch tile, seldom smaller. These laterals should
always enter the main at an angle of about 45 degrees. This
causes a joining of the currents with no loss of impetus and
Fig, 38.—Natural (1) and interception (2) systems for laying tile
drains.
allows the more rapidly moving lateral streams to speed up
the flow in the main drain. The size of the main depends on
the rainfall, the area drained, and the slope. It, of course,
must be larger near the outlet than at any other point. The
following practical table from Elliott + indicates the influence
* Elliott, C. G., Engineering for Land Drainage; p. 108, New York,
1912.
214 NATURE AND PROPERTIES OF SOILS
of area and slope on the size of the main near the outlet of
any system:
TaBLE XLI
GRADES TO A HUNDRED FEET IN DECIMALS OF A FOOT WITH AP-
PROXIMATE EQUIVALENTS IN INCHES.
GRADES TO A HUNDRED FEET IN DECIMALS OF A FOOT WITH
DIAMETER APPROXIMATE EQUIVALENTS IN INCHES
or TILE
(1n INCHES) Y%inech | 1 inch 2 inches | 3 inches | 6 inches | 9 inches
0.04 0.08 0.16 0.25 0.50 0.75
Acres Acres Acres Acres Acres Acres
5 173 19.1 22.1 Zou 32.0 37.0
6 2.3 29.9 34.8 39.6 50.5 59.4
7 39.9 44.1 SHlet 58.0 74.5 87.1
8 Daal 61.4 71.2 80.9 | 103.3 | 121.4
9 74.7 82.2 95.3 | 1084 | 138.1) 1626
10 96.9_| 106.7 123.9 140.6 1792) |) Zitat
i 1hapeey I lary 194.6 | 221.1 281.8 |, 3aL.5
The grade necessary for the satisfactory operation of a tile
drain system varies with the system itself and the portion
under consideration. The grade of the main drain may be
very low, especially if the laterals deliver their water with a
high velocity. In general, the grade will vary from 4 to 20
inches to the hundred feet, 8 inches being more or less ideal.
The depth of the tiles beneath the surface and the distance
between laterals will vary with the soil. With sandy soils
the tile may be placed as deep as 3 or 4 feet. With clayey
soils the depth must be shallower, ranging from 15 to 30
inches, while the interval is reduced as the soil becomes finer
in texture. On a clayey soil the distance between the strings
is sometimes as low as 35 feet although 50 to 70 feet is com-
moner.
The maintenance cost of a tile drain system is low, the only
especial attention needful being at the outlet. The outlet
THE CONTROL OF SOIL-MOISTURE 215
should be well protected, so that the end tiles may not be
loosened and the whole system endangered by clogging with
sediment. It is well to embed the end tile in a masonry or
conerete wall. The last eight or ten feet of tile may even be
replaced by a galvanized iron pipe or with sewer tile, thus
\
i
|
|
|
|
|
|
|
|
N
Fig. 39.—Gridiron and fishbone systems for laying tile drains.
insuring against damage by frost. The water should flow
freely from a tile drain system, as a drowned outlet inter-
feres with efficient drainage. The opening of a tile drain sys-
tem is usually protected by a gate or by wire in such a man-
ner as to allow the water to flow out freely but preventing
rodents from entering in dry weather. (See Fig. 40.)
As with any other improvement, tile drainage must be made
216 NATURE AND PROPERTIES OF SOILS
to pay. If rapid efficient drainage can not be assured at a
reasonable cost and under such conditions that the increased
crops will return a good profit on the investment, tile drains
should not be installed.
112. Evaporation losses.—Evaporation of soil-water takes
place almost entirely at the surface, exceptions being
where large cracks occur, which allow thermal loss directly
from the subsoil. This loss of water by direct evaporation
from the soil may be excessive and may result in direct reduc-
a
IS yy
i
ze
peeves)
ae Oy
ZANE RE AE
A
eo I
Fic. 40.—Cement block at the outlet of a tile drain.
tion of crop yield, a type of loss so familiar that examples
hardly need be cited. In the results with the Rothamsted rain
gauges (see page 207), about 50 per cent. of the annual rain-
fall was regained in the drainage water. Since the gauges bore
no crop, the remaining 50 per cent. must have been lost by
evaporation. It should be noted that in the summer months
under warm temperature, this loss was greatest, amounting
to 75 per cent. of the rainfall. Correspondingly, in the semi-
arid and arid sections of the country where there is little or
no drainage, the rainfall is almost all lost by evaporation.
Evaporation from land surface has an appreciable effect on
THE CONTROL OF SOIL-MOISTURE 217
the amount of rainfall. Even in humid regions, where the
annual rainfall is ample for maximum crop production, the
yields are frequently reduced below the profit point by pro-
longed periods of dry weather in the growing season during
which the loss of water from the plants, coupled with the loss
from the soil and through weeds, exhausts the moisture sup-
ply very rapidly.
While run-off and percolation are directly proportional to
the rainfall, loss by evaporation does not vary to such a de-
gree. The loss by percolation depends almost directly on the
amount of rainfall above the retentive power of the soil. In
years of heavy precipitation losses by percolation increase.
Evaporation from the soil depends largely on the length of
time that the soil surface is moist, and this will not vary
markedly from year to year. The following figures from the
Rothamsted! sixty-inch drain gauge may be quoted in this
regard:
TABLE XLIII
RAINFALL, DRAINAGE AND EVAPORATION AT THE ROTHAMSTED
EXPERIMENT STATION, 1871 To 1912.
RAINFALL [PERCOLATION EVAPORATION
CoNDITIONS
INCHES INCHES INCHES
Maximum rainfall, 1903...) 38.69 24.23 14.46
Mean total for 42 years.... 28.75 13.93 15.32
Minimum rainfall, 1898....} 20.49 7.69 12.80
A rough ealeulation may be made which will show the ap-
portionment of the yearly rainfall in a humid region of the
temperate zone between the four forms of losses—run-off and
percolation, evaporation, and transpiration. The percolation
under a rainfall, say, of 28 inches, as shown by the Rotham-
1Hall, A. D., The Book of the Rothamsted Experiments; p. 22, New
York, 1917.
218 NATURE AND PROPERTIES OF SOILS
sted work, is roughly 14 inches. Run-off and percolation may
be considered as about 50 per cent. The water requirement of
an ordinary crop is about 7 inches. This leaves a loss of 7
inches to be credited to evaporation. In other words, in a
clay loam soil in a climate like that of England, one-half
the rainfall goes as run-off and percolation, while the other
half is divided about equally between the plant and loss by
evaporation. While run-off and percolation may be checked
to some extent, not enough conservation can occur in this di-
rection to tide a crop over a period of drought. Some con-
sideration should, therefore, be directed towards the check-
ing of loss by evaporation, since moisture thus saved means
just that amount added to the water available for the use of
the crop growing on the soil.
113. Evaporation control Any material applied to the
surface of a soil primarily to prevent loss by evaporation or to
keep down weeds may be designated as a mulch. Mulches are
of two general sorts, artificial and natural. In the former case,
foreign material is merely spread over the soil surface. Man-
ure, straw, leaves, and the like may be used successfully.
Such mulches while effective, especially in preventing weed
growth, are not generally applicable to field crops where in-
ter-tillage is practiced, since they would make cultivation im-
possible. Their use is, therefore, limited to such crops as
strawberries, blackberries, and the like.
The second type of mulch is called a soil-mulch since it is
formed from soil itself. With proper tillage, a loose dry layer
of soil may be formed on the surface. Such a layer is designed
to obstruct capillary movement to such an extent as to reduce
evaporation loss toa minimum. In theory a soil-mulch should
be formed as quickly as possible so that the only moisture
sacrificed will be that which is present in the soil forming
the mulch. Moreover, the mulch should be renewed after
every rain and should, except in special cases, be not more
THE CONTROL OF SOIL-MOISTURE 219
than three inches deep. Late in the season, especially for
corn, the cultivation should be shallow to prevent root-prun-
ing.*
For many years cultivation for a soil-mulch has been ad-
vocated for two reasons: (1) checking of evaporation, and (2)
the killing of weeds. Either procedure, if successful, will
allow the crop a larger proportion of the rainfall. Recent
experimental results, however, seem to indicate that a soil-
mulch with an intertilled crop does not check evaporation
compared with a soil uncultivated and kept free of weeds.
This is probably due to the fact, that even with moisture
a limiting factor, the water sacrificed in renewing the mulch
is not offset by that conserved. The tendency of soils, espe-
cially those of a sandy character to self-mulch as well as the
action of the roots of the crop in intercepting the water, may
also be factors. Under greenhouse conditions and in regions
of very little rainfall, the soil-mulch probably does conserve
*Since a great many of the inter-tilled crops are shallow-rooted,
great care should be exercised in cultivation, especially toward the latter
part of the growing season. Corn and potatoes are especially influenced
by root-pruning. The following data? averaged for 7 years are
pertinent :
INFLUENCE OF ROOT-PRUNING ON THE YIELD OF CORN IN BUSHELS TO
THE ACRE. AVERAGE OF 7 YEARS. UNIVERSITY
oF ILLINOIS
TREATMENT YIELD
No cultivation, weeds kept down with hoe.................. 67.7
Nhallowacul tivatloneis creates ithe byraias Melissa as cides ses 70.8
WESP CULGIVATION:,.\0,. 2\0'.s Acie swans oe oaks ai Ses ronetolieis ousvshece st cosas 68.6
Shallowrcultivation, roots unprunedes.. 2... ce. 2. oes 74.8
Shallow cultivation, roots pruned with knife............... 61.6
Buncacewscraped, FOOts ONPLUNeds.. fj)... oie os veiw wee ys wens 80.7
Surface scraped, roots pruned with knife.................. 68.3
* Mosier, J. G., and Gustafson, A. F., Soil Moisture and Tillage for
Corn; Ill. Agr. Exp. Sta., Bul, 181, 1915.
220 NATURE AND PROPERTIES OF SOILS
moisture. The following figures’ are representative of the
data available regarding these points:
TABLE XLIV
MOISTURE CONTENT OF BARE IRRIGATED AND DRY-LAND PLOTS,
TREATED IN VARIOUS WAYS, EXPRESSED IN TOTAL INCHES OF
WATER IN UPPER 6 FEET OF SOIL. GARDEN CITY,
KANSAS, 1914.
IRRIGATED Dry Lanp
marae a | GAIN OR GAIN OR
MAR. 30 |SEPT. 16 Loss. || MAR. 30 |SEPT. 16 aie
6-inch mulch....| 17.6 | 15.9 | —1.7}|| 11.8 | 12.4 |-+ .6
3-inch mulch..... 18.1 | 16.6 | —1.5)| 11.3 | TL.7 )-
Bare surface..... 17.8 | 15.6 | —2.2|| 11.5 | 12.014 5
Weed sine cabs 16.4 9.1 | —7.3]| 10.8 8.0 | —2.8
|
TABLE XLV
EFFECTS OF VARIOUS METHODS OF TILLAGE ON THE YIELD OF CORN
AND THE AVERAGE PERCENTAGE OF MOISTURE IN THE SOIL
TO A DEPTH OF 40 INCHES. AVERAGE OF 8 YEARS’
TEST AT THE UNIVERSITY OF ILLINOIS.”
MEAN RAINFALL, 33.7 INCHES.
AVERAGE
YIELD OF CORN Paneer
TREATMENT BUSHELS
PrER ACRE ue a a
Not plowed or cultivated:
Kept bare of weeds only.... 31.4 23.1
Plowed and seedbed prepared:
Kept bare of weeds only...... 45.9 22.3
Weeds allowed to grow....... 7.3 21.8
Three shallow cultivations.... 39.2 21.9
Call, L. E., and Sewell, M. C., The Soil Mulch; Jour. Amer. Soc.
Agron., Vol. 9, No. 2, pp. 49-61, Feb., 1917.
* Mosier, J. G., and Gustafson, A. F., Soil Moisture and Tillage for
Corn; Tl. Agr. Exp. Sta., Bul. 181, Apr., 1915.
HE CONTROL OF SOIL-MOISTURE 221
The above data, which are amply corroborated by other
investigations,’ indicate that, with an uncropped light silt
loam in a semi-arid region, the soil-mulch is of little practical
importance in conserving moisture. Moreover, the results in
Illinois as well as Kansas are no better on cropped land, the
cultivation seemingly having little influence on either mois-
ture content or crop yield. The importance of a good seed-
bed is very strikingly shown by the Illinois data, as is also the
necessity of weed control. The weeds not only appropriate
moisture that should go to the crop, but at the same time
absorb nutrients that should be utilized in other ways.
Certain general conclusions are unavoidable in respect to
a soil-mulch.? In the first place, a cropped cultivated soil
seems no more effective in preventing evaporation than one
that is cropped and uncultivated. Whether this extends to
bare soil under all conditions has not been conclusively shown.
In the second place, the elimination of weeds seems to be the
most important benefit of cultivation. It must be remem-
bered, however, that cultivation may exert some benefit on
aération of a heavy soil and certainly encourages granulation
to a certain extent.
114. Summary of moisture control.—Moisture control
seems to fall logically under three heads: (1) run-off, (2)
drainage, and (3) evaporation. The detrimental influence of
run-off over the surface is due to erosion, the loss of the water
*Young, H. J., The Soil Mulch; Nebr. Agr. Exp. Sta., 25th Ann.
Rep., pp. 124-128, 1912.
Barker, P. B., The Moistre Content of Field Soils Under Different
Treatments ; Nebr. Agr. Exp. Sta., 25th Ann. Rep., pp. 106-110, 1912.
Cates, J. S., and Cox, H. R., The Weed pier in the Cultivation of
Corn; U.S. Dept. Agr., Bur. Plant Ind., Bul. 257, 1912.
Alway, Ee eles Studies on the Relation of the Noneaaniebla Water of
the Soil to the Hygroscopic Coefficient; Nebr. Agr. Exp. Sta., Res. Bul.
3, 1913.
Burr, W. W., The Storage and Use of Soil Moisture; Nebr. Agr. Exp.
Sta., Res. Bul. 5, 1914.
2 See Call, L. E., and Sewell, M. C., The Soil Mulch; Jour. Amer.
Soc. Agron., Vol. 9, No. 2, pp. "49- 61, Feb., 1917.
222 NATURE AND PROPERTIES OF SOILS
itself being of minor importance. Similarly percolation loss
is important because of the nutrients carried away, rather
than because of the waste of the water. Since a certain
amount of percolation must take place and because a water-
logged soil is unsanitary for plants, rapid drainage is essen-
tial. Of the various methods available, tile drainage is the
most satisfactory. Evaporation loss, as with run-off and per-
eolation, can be but very slightly checked. The soil-mulch is
important in that the cultivation necessary to produce it keeps
down the weeds and in this manner it eliminates serious crop
competition for nutrients and moisture.
CHAPTER XI
SOIL HEAT *
Ir is universally recognized that biological activity is an
energy expression and that such activity will not continue
unless certain temperature relations are maintained. With
higher plants this heat relation has two phases, the tempera-
ture of the air and that of the soil. The former is clearly
a climatic factor and, except on a small scale, is beyond the
control of man. The temperature of the soil, in a similar way,
is subject to no radical regulation, yet soil management meth-
ods provide means whereby certain small but biologically vital
modifications can be made, climatically unimportant but prac-
tically worthy of careful consideration.
115. Importance of soil heat.—Normal plant growth is
practically suspended at a temperature of 40° F., while the
germination of most seeds does not take place even at this
point. In general, it is poor practice to place certain seeds
and plants in soil where growth activities will not occur at
onee, since bacteria and fungi, active at low temperatures,
may sap their vitality and ultimately cause their destruction.
Three groupings of higher plants may be made as far as their
temperature relationships are concerned. Wheat represents
the crops that germinate and grow at relatively low tempera-
tures. Maize requires a medium temperature for proper
growth, while pumpkins and melons typify crops, the heat
requirements of which are very high. The following data
*For a bibliography of the literature of soil heat see Bouyoucos,
G. J., An Investigation of Soil Temperature and Some of the Most
Important Factors Influencing It; Mich. Agr. Exp. Sta., Tech, Bul. 17,
pp. 194-196; 1913.
223
224 NATURE AND PROPERTIES OF SOILS
from Haberlandt! show the need of careful temperature con-
trol in the propagation of plants:
TABLE XLVI
GERMINATION TEMPERATURES
CROP MINIMUM OPTIMUM | MaxIMuM
A Gets PRMMN a MEG eae aoa fai 40° F 84° F 108° F
1 Ee ih eae Ree UN Ue Ne 49 93 105
Paap kam eee 52 93 115
TABLE XLVII
GROWTH TEMPERATURES
CROP MINIMUM OPTIMUM MaxIMUM
Wiheatieid oe cet ee eed 32-40° F T- 18° R 88- 98
IMI ZO RC Hecten cc) keene fate 40-51 88- 98 98-111
Puma kans .2 ceeaess hoe 51-60 98-111 111-122
Other desirable biological activities, especially those due to
bacteria, are impeded if not brought entirely to a standstill by
a temperature of 32° F. Such changes as decomposition of
organic matter, the production of ammonia from nitrogenous
organic matter, the formation of nitrate nitrogen from am-
monia and the fixation of atmospheric nitrogen depend on
heat conditions which, fortunately, are optimum for the de-
velopment of higher plants.
Desirable chemical reactions in the soil are much retarded
by low temperatures, heat greatly accelerating such phe-
nomena. This is especially noticeable in the tropics where
weathering is much more rapid and intense than in temperate
regions. Much of the hydration, oxidation, carbonation and
solution in a temperate climate occurs in the summer when
high temperature lends its aid to such desirable reactions.
1 AHaberlandt, F., Die Oberen und Unteren Temperaturgrenze fiir die
Keimung der Wichtigeren Landwirthschaftlichen Sdmereien; Landw.
Versuchs. Stat., Band 17, Seite 104-106, 1874.
SOIL HEAT 225
The effect of heat on the physical changes within the soil
is often vital. The influence that temperature variation exerts
on percolation, evaporation, and capillary movement of soil-
water; on diffusion of gases, vapors, and salts in solution;
and on osmosis, surface tension and vapor tension phenomena,
may serve as examples of such heat modifications. Moreover,
successive freezing and thawing of the soil greatly aids in
granulation and aération. The aspirating effect of a slight
change in temperature is so tremendous as often markedly to
renew the oxygen supply of the furrow slice.
In order fully to understand the practical and scientific
relationships involved in even a partial control of soil heat,
a certain cycle of events must be recognized. The cycle be-
gins with the acquisition of energy from the sun and the
establishment of certain temperature relations which depend
on absorption activity and the facility with which heat is
transferred from place to place. The important chemical,
physical, and biological transformations within the soil de-
pend as much on such movements as on the intensity of the
temperature factors. Much of the energy so involved is soon
lost from the soil, returning again to the space from which
it came. Thus the cycle is completed, having provided the
temperature conditions necessary for successful crop produc-
tion. (See Fig. 41.)
116. Insolation received by the soil—The sun supplies
practically all of the energy by means of which the soil main-
tains a temperature suitable for its normal activities. Energy
from other sources is negligible. Radiation, the means by
which this transfer is affected, is a free wave movement of
some type. It is an oscillatory phenomenon, the space between
the sun and the receiving body being, so far as is known, en-
tirely unaffected. The leneth' of such oscillations varies from
1The approximate wave lengths are as follows:
MATS eens cue yeoetonsksy ie Ge al ae ... .000270 to .000075 em.
EOI G SW ES co cchiep oes Syeleersve noes) coo .000075 to .000036 em.
Wiltimaavialoletimarcvint. sryocccte eiae ce .000036 to .000019 em.
226 NATURE AND PROPERTIES OF SOILS
the short ultra-violet rays, through the so-called light wave
series to the long infra-red rays, the latter possessing the
greatest heat possibilities. The insolation of energy received
at the upper limits of the earth’s atmosphere varies with the
season and with the position chosen.1
Due to the gases of the atmosphere and especially to clouds
and dust, only a small portion of the total insolation actually
PADIANT
ENERGY
PHIERE REFLECTION
BE IPEFFRACT/ON
EVAPORATION RADIATION
CONDUCTION FPEFLECTION
SLUIPFACE
Pern _-—_CPABSORPTION
COLOR, SLOPE
2-SPECIFIC HEAT
TEXTURE PRISE OF
STRUCTURE TEMPERATURE
MOISTURE
CONDUCTION 3-MOVEMENT
CONVECTION 4-LOSS OF MEAT
ORGANIC DECAY
Fic. 41.—A diagram showing the heat relations of soil.
does work either on the land or water surfaces of the earth.
The atmosphere and its impurities probably deflect on an
average more than three-fourths of the insolation by absorp-
tion, reflection, and refraction. Little or none of such energy
ever reaches the earth itself. Clouds and dust play an im-
portant réle in such interception, affecting to a marked degree
the energy received at any particular location. Part of the
original insolation reaching the earth’s surface is immediately
reflected and is lost as radiant energy, having undergone no
* The earth and its atmosphere receives but one two- billionth of the
sun’s energy. On such a trifling proportion of the sun’s energy depend
almost all of the earth’s activities.
SOIL HEAT 227
transformation and, therefore, having done no work. This
reflection is much greater on sea than on land and greater
from snow than from soil surfaces. Reflection is influenced
to a marked degree by vegetation, stubble, for example, being
more effective than a green field, a forest or even bare soil.
Possibly one-fifth of the earth’s insolation on the average is
absorbed by the land and water surfaces, being the source of
the energy which later functions both statically and dynam-
ically in the soil.
The statement is often made that warm rain carries con-
siderable heat into the soil. Such an assertion is not only
misleading but in most eases entirely incorrect. Precipitation
in general is usually cooler than the soil in temperate regions,
especially in the summer. Rain is spoken of as warm, not
in comparison with soil but with average rain-water tempera-
ture. Even if rain water should be 10° F. warmer than the
soil, a very improbable assumption, an average rain would
raise the temperature of the surface six inches only slightly.
117. Absorption of insolation—The energy received
from the sun functions in a number of ways on reaching the
land surfaces of the earth. It may accelerate chemical re-
actions, it may be absorbed by plants, it may induce certain
changes in form and, lastly, it may be converted into heat.
It is in this latter state that insolation energy plays its most
important part in soil activities, since heat energy may act
in ways that radiant energy finds impossible. Since heat is
commonly conceived as the kinetic energy of the molecules
of a body, it is quite distinct and different from solar radia-
tion, which must encounter some favorable substance before
heat is produced. Temperature is the condition of a body
in respect to its heat energy and is the common mode of ex-
pressing heat intensity.*
1Molecules are in constant motion, colliding with their neighbors, re-
bounding, and quivering. They possess energy which is called heat.
Temperature is determined by the velocity of the molecules and is a
manifestation of heat.
228 NATURE AND PROPERTIES OF SOILS
Certain inherent qualities of the soil as well as its position
tend to influence its capacity to absorb radiant energy. The
effect may be measured in the resultant rise in temperature,
providing all variables are under control. The factors in-
volved are texture, structure, color, and position. Only the
last two are of practical importance.
118. Influence of color on absorption.—It is well known
that a black surface absorbs more energy than a white
one under similar conditions and will register a more rapid
and a higher temperature rise. This is because of a difference
in reflection, the white surface being more effective in this
respect. The same principle has been shown by a number
of investigators to hold with soil... The addition of organic
matter, provided its decomposition has been of the proper
sort, will, other factors being equal, favor a higher soil tem-
perature. Wollny? in experimenting with soil covered with
thin layers of different colored material obtained some inter-
esting field data. The black soil not only exhibited the high-
est temperature but also showed the greatest fluctuation. Min-
imum temperatures were the same regardless of color, while
temperature differences decreased with depth. The curves
in Fig. 42 are typical of Wollny’s results on clear days.
Besides the quite obvious effect of color on rate of energy
absorption, the curves exhibit two other points worthy of
notice. The first is the tendency of the soil temperature to
lag behind that of the air and the second is the equal minima
reached by the two soils. The latter tendency would seem
to indicate that color has little effect on the radiation of heat
by soil.
1 Bouyoucos, G. J., An Investigation of Soil Temperature; Mich. Agr.
Exp. Sta., Tech. Bul. 17, p. 30, 1913.
Lang, C., Uber Warme-absorption und Emission des Boden; Forsch.
a. d. Gebiete d. Agr.-Physik., Band I, Seite 379-407, 1878.
2Wollny, E., Untersuchung tiber den Einfluss der Farbe des Bodens
auf dessen Erwirmung; Forsch. a. a, Gebiete d. Agri.-Physik., Band I,
Seite 43-69, 1878. Also, Untersuchungen iiber den Einfluss der Farbe
des Bordens auf dessen Erwirmung; Forsch, a. a. Gebiete d. Agr.-Phys.,
Band IV, Seite 327-365, 1881.
SOIL HEAT 229
119. The effect of slope on absorption.—The second
phase to be considered in the rise of temperature of a given
soil is the angle of incident of the sun’s rays. The greater
the inclination of a soil from a right angle interception, the
less rapid will be the rise in temperature. As a consequence,
the total insolation received in the tropics to a unit area is
greater than that attained by a corresponding area in the
temperate zone. Moreover, any condition in a temperature
a
BS
Sa
al
ee ae
eee Ay
i
a
eo
4 6 a /0
Fig. 42.—Curves showing the temperature variations of different colored
soils at a four inch depth compared with air temperature. Munich,
June 23, 1876.
region which tends to bring a unit surface more nearly normal
to the sun’s rays will increase its absorbed energy and raise
its average seasonal temperature. In the north temperate
zone this is of course a southerly inclination. The diagram
(Fig. 43) illustrating conditions on the 42d parallel at noon
on June 21 makes clear this relationship.
It is seen that in this case a southerly slope of 20° received
the greatest amount of heat to a unit area with the level soil
230 NATURE AND PROPERTIES OF SOILS
next and the northerly slope last. The amount of heat for
a given area is in the order of 106, 100, and 81, respectively.
Q
Ly
S
oy 7
ay
& i)
x
y\
Ny 120°
v9
gs
Cy
i: oS 3
ATA gto? ean ae
0
Fig. 43.—Diagram showing the distribution of a given amount of radiant
energy on different slopes on June 21, at the 42nd parallel north.
These generalizations have been established by the work of
a number of investigators.*
Wollny? found near Munich that the temperature of south-
* King, F. H., Physics of Agriculture, p. 218. Madison, Wis., 1910.
*Wollny, E., Untersuchungen iiber den Hinfluss der Exposition auf die
SOIL HEAT 231
ward slopes varied with the time of year. For example, the
southeasterly inclination was warmest in the early season, the
southerly slope during mid-season and the southwesterly slope
in the fall. Such a relationship is of course governed entirely
by local climatic conditions, especially cloudiness, and might
not be true of any other place. A southeasterly slope is gen-
erally preferred by gardeners. Orchardists also pay strict
attention to the aspect as it is often a factor in sun-seald and
certain plant diseases.
120. Rise of temperature and the factors involved.—
The rise of temperature of a layer of soil following a given
absorption, depends (1) on the specific heat of the soil, (2) on
the rate at which the heat moves to other parts of the soil
mass, and (3) on the losses of heat to the atmosphere. It is
evident that in a study of the influence of insolation on soil
temperature, specific heat should receive the first attention.
121. Specific heat and soil temperature—The specific
heat of any material may be defined as its thermal capacity
compared with that of water. It is expressed as a ratio to the
quantity of heat required to raise the temperature of a given
amount of a certain substance 1° C. to the quantity needed
to change an equal amount of water from 15° to 16° C.
The specific heat figure for soil generally refers to the heat
eapacity of the dry substance. Under normal conditions, soils
contain variable amounts of pore spaces and consequently
have different weights to the cubic foot. <A specific heat figure
based on weight, therefore, does not give a true idea of the
relative heat capacities of two soils. The expression of spe-
cific heat by volume seems a more rational basis of compari-
son.' The specific heat of the soil is important because of the
relation it has to the warming up of soil in the spring, the
Erwarmung des Bodens; Forsch. a. d. Gebiete d. Agr.-Physik., Band I,
Seite 263-294, 1878. This publication contains a number of other papers
on this subject by Wollny.
1 Weight specific heat of a substance may be expressed by the number
of calories required to raise the temperature of one gram, 1° C. Volume
232 NATURE AND PROPERTIES OF SOILS
rate of cooling in autumn, drainage influences, and like phe-
nomena.
Specific heat data from different investigators do not show
the agreement that might be expected.t| This is probably due
(1) to inaccuracies in the naming of the soils used, (2) to
difference in methods, and (3) to difficulties in technique.
Everything considered, the following table from Ulrich ? dis-
plays in a suitable way the important specific heat phases:
TaBLE XLVII
VOLUME OF SPECIFIC HEAT OF SOIL
WEIGHT VoLUME
SOILS VOLUME Speciric HEAT
SIGs ea he en Oe re ch ees 1.52 .2901
Cay gach try. Bini eStore ky SNe 1.04 .2000
Orgamicymatters oa). fects: Holl . 1639
It is evident that specific heat is partially governed by the
organic matter of the soil and partially by texture and struc-
specific heat is the number of calories necessary to raise the temperature
of one cubic centimeter of the substance one degree. In the case of
soil, weight specific heat may be changed to volume specific heat by
multiplying it by the volume weight, since volume weight is the weight
in grams of one cubic centimeter of dry soil.
The following weight specific heats from Lang,* Patten t and Bou-
youcos ¢ are interesting:
LANG PATTEN Bouyoucos
Coarse sand..... HS Hee domed alS5) | Sand: (ec. ceeens 193
Limestone soil... .249 Sandy loam..... 83" , Gravel oor 204
Omen Olle aoen a4 DN IORI oo4 oso: ALO Clay 728 some .206
Garden soil....). Pegi UCR Me cage cits 194, Loam’. sateen .215
PORE sets) chai sisers ists ATi | Claiyi:ccaeseaereronmets 5210: | Peat: city ecenere 252
* Lang, C., Uber Wirme Capacitiét der Bodenconstituenten; Forsch. a.
d. Gebiete d. Agr.-Phys., Band I, Seite 109-147, 1878.
+ Patten, H. E., Heat Transference in Soils; U. 8. Dept. Agr., Bur.
Soils, Bul. 59, p. 34, 1909.
+t Bouyoucos, G. J., An Investigation of Soil Temperature; Mich. Agr.
Hxpy sta. hech buls l7mp.el2, clues
2 Ulrich, R., Untersuchungen iiber Warmekapazitat der Bodenkonsti-
tuenten; Forsch. a. d. Gebiete d. Agr.-Phys., Band 17, Seite 1-31, 1894.
SOIL HEAT 233
ture. Organic matter will lighten and loosen a soil, and lower
the volume weight. Moreover, its heat capacity is low. The
effect of such an addition is to lower the specific heat figure.
It is apparent also that the finer the texture of the soil, the
lower the specific heat. That is due not to a difference in
chemical composition but to a lowered volume weight. Any
practice, therefore, that tends to vary volume weight will in
a like manner vary specific heat. The farmer may encourage
the warming of his soil by deep and efficient plowing. By
increasing its organic content, he may create a tendency in
the same direction.
One other factor, more important than those already men-
tioned, yet remains to be discussed. This is water, so univer-
sally present in soils and so important in natural soil phe-
nomena. As the specific heat of water is several times greater
than that of the soil constituents, any addition of it must raise
the thermal capacity of the mass. The following data from
Ulrich? show that moisture rather than texture and organic
matter is the controlling factor in normal soil:
TasLeE XLVIII
THE EFFECT OF MOISTURE ON VOLUME SPECIFIC HEAT OF SOIL
(MOISTURE EXPRESSED AS A PERCENTAGE OF THE TOTAL WATER CAPACITY )
Dry 10% 20% 40% 60% 80% | 100%
Sor | WATER] WATER] WATER | WATER | WATER | WATER
cc eee 991 | 330 | 368 | .444 | 520 | 597 | .675
Olay uo. oe. 933 | 294 | .355| .478 | .600 | .723 | .845
Organic matter| .164| 242 | 320 | .476 | .632 | .788 | .945
The overwhelming influence of moisture is at once evident
from these data. Fine texture, because of its high water
eapacity, usually accentuates the dominance of moisture.
Organic matter functions in the same way. While an organic
1 Ulrich, R., Untersuchungen iiber die Warmekapazitat der Bodenkonsti-
tuenten; Forsch. a. d. Gebiete d. Agr.-Phys., Band 17, Seite 27, 1894.
234 NATURE AND PROPERTIES OF SOILS
soil of low volume weight may warm up easily when dry, its
high water content usually markedly retards its temperature
change. A muck soil is usually the last to freeze in winter
and, conversely, the last to thaw in spring. The advantage
of drainage is evident as a wet soil is of necessity colder in
the spring than one that is well drained. This at least par-
tially accounts for the fact that a sandy soil is usually an early
one and is, therefore, of particular value in trucking.
122. Heat movements in soil— While volume weight, or-
ganic matter, and moisture seem largely to control the degree
to which a soil will become heated when exposed to insolation,
it is evident that there must be some mode of energy transfer
whereby such phenomena may be facilitated. Heat movement
is necessary in order that the lower layers of the soil may
become warm enough for proper biological functionings.
Energy transmission both downward and laterally is abso-
lutely essential and deserves as much attention as the factors
influencing insolation absorption.
Two methods of heat transfer function in a normal soil—
conduction and convection. .These modes of energy move-
ment are extremely difficult to analyze, due to the impossi-
bility of controlling one while studying the other.
123. Conduction of heat in soil— While radiation has to
do with the oscillatory transfer of energy conduction relates to
the molecular transmission of heat through any material.
When one part of a substance is heated, the movement of its
molecules is stimulated. These molecules strike their neighbors
with increased force, thus quickening their motion. These in
turn accelerate others until the energy applied at one point
becomes apparent at another. Solids as a class are better con-
ductors than liquids, while liquids in general are superior to
gases in this respect. It must be remembered in studying the
conductivity of heat through soil, that we are dealing with
a heterogeneous mixture of mineral and organic matter con-
taining varying amounts of air and water. The movement
SOIL HEAT 235
of soil heat involves not only the question of conduction
through solids but through liquids and gases as well. More-
over, transfer resistance, which occurs at the boundary of two
substances in contact, has much to do with the rate of trans-
mission. In addition, the air and water of the soil are capable
of considerable movement which makes conductivity studies
extremely difficult due to convection currents.
The heat conductivity of soil is affected by a number of
factors which may or may not lend themselves to field con-
trol. Important among these are texture, structure, organic
matter, and moisture. The influence of the first is clearly
shown by the following comparative data obtained by Bou-
youcos,' with field soils:
TABLE XLIX
RELATIVE CONDUCTIVITY AS MEASURED BY THE TIME REQUIRED
FOR A THERMOMETER 7 INCHES FROM THE SOURCE OF HEAT
TO INDICATE A RISE IN TEMPERATURE
RELATIVE RATE
Som OF CONDUCTIVITY
SUP TET Lge i be i ely eno ne aa a oR oa a 100
PO TIP res. eg ees hea aby chain Gia Bie iss wists 150
(isis = © aoa NMI eer a eee ee 143
ELE Re Si Ie ERS RAAT ae ne 362
These results are comparative only in a qualitative way.
Quantitative determinations are so beset by error that only
few investigators have made any consistent attempt along this
line. Patten’s results” expressed as metric K * (the heat con-
* Bouyoucos, G. J., An Investigation of Soil Temperature; Mich. Agr.
Exp. Sta., Tech. Bul. 17, p. 20, 1913. .
* Patten, H. E., Heat Transfer in Soils; U. S. Dept. Agr., Bur. Soils,
Bul. 59, p. 26-28, 1909.
* The conductivity of a substance is measured by the number of gram-
calories of heat transmitted in 1 second through a cube with 1 centi-
meter edges, when the opposite faces differ in temperature by 1°C. The
calories of heat transmitted (H) will be proportional to the area of the
236 NATURE AND PROPERTIES OF SOILS
ductivity coefficient in C.G.S. units) shows the same general
comparisons as already presented:
TABLE L
CONDUCTIVITY COEFFICIENTS OF DIFFERENT DRY SOILS
Sorns K
WoOarse quanrtyccseireas yoke asim oct nees .000917
Reonardtown loamy ..5-7se ae, ee oe . 000882
Podunk) fine ssandiy: loam sinrcyac. ei ee . 000792
Hagerstown wloamie yi ini. ected ts oat acieretet .000699
Galveston) Clay .ob4 Mice wis eee ee ane .000577
eke Oe. te eee nee eee ee pa .000349
It is evident, in general, that the finer the texture of the
soil, the lower is the conductivity. This cannot be construed
as indicating that the conductivity coefficients of sand and
clay particles are particularly different. The variance ob-
served is adequately explained by the great number of trans-
fers necessary in a fine-textured soil. It is also evident that
the addition of organic matter will lower conductivity.
Humus itself has a low conductivity coefficient and would
markedly affect the transfer resistance by changing the struc-
ture of the soil. Compacting a soil should accelerate heat
transfer due to a more intimate contact of the soil grains and
a consequent diminution of transfer interference. Tillage,
on the contrary, must impede not only the movement of heat
downward in the soil but from the subsoil into the furrow
slice.
The greatest single factor to be considered in heat conduc-
tivity is the moisture content of the soil. The curve (Fig. 44)
faces (A) and to the differences in temperature of the faces (t’—t”),
while it will be inversely proportional to the thickness (d) of the cube.
K is a constant, depending on the material studied.
Ps; A (t’—t””)
H= Nee
SOIL HEAT 237
for fine sandy loam, constructed from Patten’s data,’ illus-
trates its effect and indicates how heavily it must override the
factors already mentioned:
-00300
00200
-00100
0 va 10 15 20 25
Fig. 44.—Conductivity curve for Podunk fine sandy loam, showing the
influence of moisture content upon the rate of heat transfer. The
curve apparently flattens out at a high moisture content indicating
that good conductivity may be obtained at optimum moisture.
At first glance it appears peculiar that the heat movement
through a soil, the mineral constituents of which possess a
conductivity coefficient of about .01066, should be accelerated
by the addition of a liquid possessing a value for K of about
.00149. The explanation lies in the lowering of the transfer
*Patten, H. E., Heat Transfer in Soils; U. S. Dept. Agr., Bur. Soils,
Bull. 59, p. 27, 1909.
238 NATURE AND PROPERTIES OF SOILS
resistance. Heat passes from soil to water about 150 times
easier than from soil to air. As the water increases, the air
decreases and the rate of conductivity is raised. When suf-
ficient water is present to join all of the soil particles, further
additions will have little effect on character of heat movement.
Moisture, optimum for crop growth, amply provides for heat
transfer. The slow warming up of the lower subsoil must not
be taken as an indication of lower conductivity. It is due
rather to a lessened heat supply. As a matter of fact, the
rate of heat transmission has been shown to be more rapid in
the subsoil, due to a greater compaction and to the presence
of more water.
This brief discussion of conductivity shows the vital im-
portance of such a phenomenon to plants in that the necessary
heat is carried broadeast through the soil. While conduc-
tivity is affected to a certain extent by texture, structure, and
organic matter, moisture is the dominant factor. Under nat-
ural conditions, it is necessary to maintain a medium amount
of water in the soil. This moisture condition, fortunately,
supports almost maximum heat conduction. Good tilth and
increased organic matter probably exert their greatest in-
fluence on this type of heat transfer by their influence on soil
moisture.
124. Convection transfer of heat.—Convection, the third
manner by which energy may be conveyed, is a heat transfer
by. means of currents in liquids or gases. It functions by an
actual and obvious movement of matter. In the soil absorp-
tion tends to heat the air as well as the solid substance. This
produces currents due to the expansion and rise of the warmed
gases. It is obvious that such heat movement must always be
lateral or upward, never downward. Such eonvection exerts
its greatest influence in equalizing the temperature of the soil,
overcoming the effects of unequal conduction and uneven ab-
sorption due to vegetation or stone. Air currents as they
escape into the upper air carry considerable heat away from
SOIL HEAT 239
the soil. Such a loss is of little moment, however, compared to
that continually occurring through conduction and radiation.
Some heat is carried downward into the soil by percolat-
ing water. This is a true convection activity. The impor-
tance of such a heat transfer is only conjectural. As percola-
tion is generally intermittent in a soil, it is probable that it
does not modify to any extent the influence exerted by con-
duction.
125. Effect of organic matter on soil temperature.—
Plants entrap a considerable amount of radiant energy from
the sun, part of which is utilized during the growth period.
The remainder exists as latent energy in the tissue. If any
amount of plant remains are incorporated in the soil and de-
cay proceeds, this heat is liberated. Thus a heat transfer is
similar in a way to convection, except that, in this case, the
transfer is by the movement of a solid and the energy is
latent.
To what extent the decay of organic matter is effective in
bringing about any important modification of field soil, it is
difficult to say. In greenhouses and hotbeds perceptible in-
creases are obtained by the use of fresh manure. In the field,
however, where the absorption and loss of heat are very large
and where the organic matter makes up but a small portion
of the soil mass, it is doubtful whether any important heat
increase occurs. Georgeson,’ in Japan during the first twenty
days after an application of eighty tons of manure to the
acre, obtained an increase of only 3.4° F. over a soil un-
treated. Wagner? found an average increase of 1° F. from
the use of twenty tons of barnyard manure to the acre. Bou-
youcos * has obtained the latest data on the subject. Under
*Georgeson, C. C., Influence of Manure on Soil Temperature; Agri.
Sei., Vol. 1, pp. 25-52, 1887.
? Wagner, F., Uber den Einfluss der Dungung, mit Organischen Sub-
stance auf die Bodentemperatur; Forsch. a. d. Gebiete d. Agr.-Phys.,
Band V, Seite 373-405, 1882.
* Bouyoucos, G. J., An Investigation of Soil Temperature; Mich. Agr.
Exp. Sta., Tech. Bul. 17, pp. 180-190, 1913.
240 NATURE AND PROPERTIES OF SOILS
earefully controlled conditions, he found that unless excessive
amounts of manure were added no appreciable effects were
observed. Such results indicate that the heat of decay and
fermentation has little practical effect in modifying the tem-
perature of field soils. Without doubt there are certain local-
ized influences, but how important they may be is beyond
our present knowledge. As far as heat relations are con-
cerned, it seems that organic matter exerts its greatest effects
through a darkening of the color and an increase in the mois-
ture capacity of the soil.
126. Loss of heat—conduction, radiation, and evapora-
tion.— Although small amounts of heat may be carried from
the soil by percolating water, the only important loss is into
the atmosphere above. This loss occurs in three ways, con-
duction, radiation, and evaporation. The loss due to evapora-
tion is easily the least important of the three. Conduction
and radiation have much to do with climatic control, since
the atmosphere receives its energy in large degree from the
earth rather than directly.from the sun. Conduction from
soil to air and vice versa can be modified but to a slight extent
by man, a fortunate provision of nature.
Terrestrial bodies are continually radiating energy waves
into the atmosphere, the change of temperature depending on
whether the receipt of such oscillations exceeds or falls short
of the loss. In the case of the soil, there is a very great dis-
sipation of energy in this way, radiation with conduction
being important climatic controls. The rapid changes in air
temperature are often directly due to these phenomena.
These energy waves of terrestrial origin are very long,?
being within the infra-red group and consequently make
no impression on the eye. They are often spoken of as the
dark rays. Their ‘energy capacity is higher than that of
shorter oscillations. The trapping of heat in a greenhouse
* Terrestrial bodies at ordinary temperatures give out waves varying
in length from .000270 to .001500 cm. The warmer the body, the shorter
the wave length.
SOIL HEAT 241
is partially due to the tendency of the objects within the house
to give off these long rays, which do not pass through the
glass with the facility possessed by the shorter vibrations by
means of which a large proportion of the energy was intro-
duced.
The texture, structure, and color of the soil have little in-
fluence on radiation. Moisture tends to hasten it a trifle,
since water is a better radiator than soil. Mulches, as they
are loose and dry, may check radiation slightly. Artificial
coverings, shelters, and clouds seem to exert the greatest effect.
It is often feasible to protect plants from frost by interfering
with radiation and conduction. Clouds by shutting in heat,
may in some cases prevent a frost that would otherwise occur,
due to the rapid cooling. Snow likewise has a protecting
effect and may often prevent the soil underneath from freez-
ing. While man may influence radiation locally, it is evident
that the total energy loss can be checked but little.
The effect of evaporation on the temperature of the soil is
especially noticeable because of its rapid action. This vapor-
ization of water is caused by an increased molecular activity
and requires the expenditure of a certain amount of heat,*
which results in a cooling effect on the water remaining and
consequently on the soil and air with which it is in contact.
It requires 267.9 kilogram calories to evaporate one pound
of water at 50° F. This is sufficient to lower the temperature
of a cubic foot of saturated clay about 20° F., providing that
all of the energy of evaporation comes from the soil and its
water.
The low temperature of a wet soil is due partially to evapo-
ration and partially to high specific heat. King * found during
*It requires 536.6 gram-calories to evaporate one gram of water at
100°C., while 596.7 calories are necessary if evaporation takes place at
0°C. The calories (C) required to vaporize one gram of water at any
temperature (t) may be caleulated by the formula:
C = 596.73 — .601 t
*King, F. H., Physics of Agriculture, p. 20; Madison, Wis., 1910.
242 NATURE AND PROPERTIES OF SOILS
April that an undrained soil in Wisconsin ranged from 2.5°F.
to 12.5° F. lower than one of the same type well drained.
Parks ! reports data of the same order from England. Drained
and undrained soil held in trays at Urbana, Illinois,? showed
maximum differences of 13.7° F., 9.0° F., and 6.2° F. at
depths of 1, 2, and 4 inches, respectively. The differences
were greatest in the day. Wollny considers that the depres-
sion of temperature due to evaporation is roughly propor-
tioned to the moisture present. Texture, structure, and or-
ganic matter influence the cooling action of evaporation, since
they exert such a marked effect on water capacity and capil-
lary movement. The practical importance of evaporation
study lies in the fact that it can be controlled to such a
marked extent in the field. Such is not true of radiation and
conduction. Windbreaks and shelters have been shown by
King * to reduce evaporation over short distances as much as
25 per cent. This means a conservation of soil energy for
the time being. Thorough under-drainage not only checks
evaporation losses but lowers the specific heat of the soil,
retards its radiation and facilitates convection. This means
a faster warming up, especially of the root zone. Optimum
moisture encourages optimum heat conditions as well as other
favorable phenomena. Drainage, tillage, and organic matter
are the dominant factors in this moisture control.
127. Soil temperature and its variations—The tempera-
ture of the soil at any time depends on the ratio of the energy
absorbed and the heat being lost. The constant change in
this codrdination is reflected in the seasonal, monthly, and
daily soil temperatures. The following data* are representa-
1Parks, J., On the Influence of Water on the Temperature of Soils;
Jour. Roy. Agr. Soc. Eng., Vol. 5, pp. 119-146, 1845.
* Mosier, J. G., and Gustafson, A. F., Soil Physics and Management ;
p. 302; Philadelphia, 1917.
‘King, F. H., The Soil, p. 189; New York, 1906.
‘Swezey, G. D., Soil Temperatures of Lincoin, Nebraska; Nebr. Agr.
Exp. Sta., 16th Ann. Rep., pp. 95-102, 1903.
SOIL HEAT 243
tive of soil temperatures in temperate climates with moderate
rainfall :
TaBLE LI
AVERAGE TEMPERATURE READINGS TAKEN AT LINCOLN,
NEBRASKA, 1890-1902. DEGREES FAHRENHEIT
1 3 6 12 24 36
SEASON AIR Incu |INcHEsS |INcHES |INCHES |INCHES | INCHES
DEEP DEEP DEEP DEEP DEEP DEEP
Summers.) 29.9 | 28:8 | 26:0 | 29.5 | 32:2 | 36.5- | 39s
Autumn...| 49.9 | 54.8 | 53.6 | 51.6 | 48.5 | 45.7 | 443
Spring...) 73.8 | 83.0) 80:9 | 79.1 | 73.8 | 69.0 | 66.2
Winter. . Or eaO4s | Ooi W575 |) 59.5 | 60.5
It is apparent that the seasonal variations of temperature
are considerable even at the lower depths. The surface layers
vary more or less in accord with the air temperature and,
therefore, exhibit a greater fluctuation than the subsoil. In
general, the surface soil is warmer in spring and summer than
the lower layers but cooler in fall and winter. The soil, on
the average, is warmer than the air in winter. This occurs
because the air responds more quickly to a change in solar
insolation than the soil.
The curves showing the monthly march of soil temperature
at Lincoln, Nebraska (Fig. 45), reveal the lag of the tempera-
ture change in the subsoil due to slow heat penetration. It is
also noticeable that the monthly range in temperature change
in the surface soil is higher than that of the air. The abso-
lute range is, of course, greater for the air. It must be kept
in mind that changes in soil temperature are gradual, while
the air may vary many degrees in an hour.
The daily and hourly temperature of the air and soil in
the temperate zone may show considerable agreement or
marked divergence according to whether the weather control
is cyclonic or solar. With solar control and a clear sky the
air temperature rises from morning to a maximum at about
244 NATURE AND PROPERTIES OF SOILS
two o’clock. It then falls rapidly. The soil, however, does
not reach its maximum temperature until later in the after-
noon, due to the usual soil lag. This retardation is greater
and the temperature change less as the depth increases.* The
substratum of a soil shows little daily, or even monthly, varia-
tion and is affected, if at all, by seasonal changes only. The
80 LE. SS
i Z Ss
e ----+--5
= A AN eNeall aeetga SSy
60 PS ° YON hoe Ss
. of ‘.
3 / Y\ Ap ee
50 NO aa a WS
y, on GIT
pee \ me
40 Lt Nene
en ee 72, ag
30 Le See
-———_*- is —
20
JAN. FESR. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT, NOV. DEC.
Fig. 45.—Curves showing the average monthly temperature readings at
various soil depths. Average of twelve years, Lincoln, Nebraska.
curves in Fig. 46, comparing soil and air temperatures at
Munich? on a bright day in May, substantiates some of the
statements above:
128. Control of soil temperature.—The most important
factor in the control of soil heat is obviously moisture. Good
1The following laws hold in a general way:
1. The lag of the temperature wave is proportional ta the depth.
2. The diurnal amplitude of the temperature oscillation decreases in
geometric progression as the depth increases in arithmetic progression.
If the temperature variation at the surface was 24°F and at 6 inches
deep 12°F, according to this law the diurnal variation at 12 inches
would be 6°F and at 18 inches 3°F.
2 Wollny, E., Untersuchungen tiber den Einfluss der Pflanzendecke und
der Beschattung auf die Physikalischen Eigenschaften des Boden;
Forsch. a. d. Gebiete d. Agr.-Physik., Band VI, Seite 197-256, 1885.
SOIL HEAT 245
drainage, and a proper structural development, sufficient or-
ganic matter and deep and careful plowing, favor optimum
moisture conditions. Such moisture regulation means a low-
ered specific heat, rapid conductivity, and good convection.
The increase of soil organic matter may act directly in heat
control by darkening the color and thus increasing absorp-
M 2 4 6 o
Fig. 46.—Curves showing the hourly temperature of a bare soil at a
depth of four inches and of the air just above the soil in Ger-
many, May 26. (Data from Wollny.)
tion. A soil-mulch, being dry, not only may check evapora-
tion but at the same time may lower radiation.
Any method of handling the land which tends to benefit its
physical condition, better its tilth and control its moisture,
tends at the same time towards a proper heat control. The
whole question may be summarized by saying that, if a farmer
adopts a proper system of moisture control and at the same
time employs methods that continually encourage a_ better
246 NATURE AND PROPERTIES OF SOILS
physical condition of the soil, the problem of the control of
soil heat will be solved automatically. The farmer will then
have brought about the best conditions for heat absorption
and will have facilitated conduction and convection, retarding
at the same time losses by evaporation and radiation.
CHAPTER XII
SOIL AIR
THE soil is a porous mass of material of which only about
one-half is solid matter. The pore space that results is occu-
pied by water and by air in a constantly varying proportion.
When a soil is in good condition for crop growth, the air
space rarely makes up more than from 20 to 25 per cent. of
its volume. The texture of the soil and the amount of mois-
ture are obviously the main controls. The individual air
spaces of the soil are more or less continuous and seem to
maintain a fairly complete communication between the vari-
ous horizons. The better the granulation of the soil and
the greater the number of cracks and burrows, the easier and
quicker is this communication. The air of the soil is either
directly in contact with the roots and the soil bacteria or
separated from them by only a thin layer of moisture or col-
loidal material.
The air of the soil is not merely a continuation of the atmo-
spheric air into the interstitial spaces. As it is enclosed by the
soil complexes and by the soil-moisture movement does not
take place readily. Hence it is greatly influenced by its local
surroundings. This leads to important differences between
the atmospheric air and the soil air, the character of the latter
depending on a variety of conditions in which the physical,
chemical and biological properties of the soil play a large
part.
129. Composition of soil air—The air of the soil differs
from that of the outside atmosphere in that it contains more
water-vapor, a much larger proportion of carbon dioxide, a
247
248 NATURE AND PROPERTIES OF SOILS
correspondingly smaller amount of oxygen, and slightly larger
quantities of other gases, including ammonia, methane, hydro-
ven sulfide, and the like, formed by the decomposition of
organic matter. The percentage of nitrogen is practically the
same in all cases. The following average data quoted from
three different sources show the comparative compositions
as far as the carbon dioxide, oxygen, and nitrogen are con-
cerned. All other gases are included with the nitrogen fig-
ures.*
TasBLE LII
AVERAGE COMPOSITION OF SOIL AIR AND ATMOSPHERIC AIR
PERCENTAGE BY VOLUME
LocaATION
CO, - O, Nz
Soil Air
Germany 4.707 .20 20.60 79 .20
TOWAros A creek .20 20.40 79.40
Bngland4, 32.5, 20 20.65 79.20
Atmospheric Air
Bneland:*, 52)... .03 A0G0T 190)
Russell and Appleyard,’ in their study of the soil atmo-
sphere, found that there are really two types of soil air. The
first one occupies the portion of the pore space not taken
1 Atmosphere air carries about .93 per cent. of argon, with very small
amounts of other inert gases such as krypton, xenon, helium and neon.
These gases are of course present in the soil.
2Lau, E., Beitrige zur Kenntnis der Zusammensetzung der vm Acker-
boden befindlichen Luft; Inaug. Diss., Rostock, 1906.
*Jodidi, S. L., and Wells, A. A., Influence of Various Factors on
Decomposition of Soil Organic Matter; Ia. Agr. Exp. Sta., Res. Bul.
Noss, Oct. 1LOUa
*Russell, E. J., and Appleyard, A., The Atmosphere of the Soil: Its
Composition and the Causes of Variation; Jour. Agr. Sci., Vol. VII,
Part 1, pp. 1-48, 1915.
° Russell, E. J., and Appleyard, A., The Atmosphere of the Sotl: Its
Composition and the Causes of Variation; Jour. Agr. Sei., Vol VII,
Part 1, pp. 1-48, 1915.
SOIL AIR 249
up by water, is free to move from place to place and is satu-
rated or nearly saturated with water-vapor. It is the soil
atmosphere most commonly referred to and its composition
is set forth in the above tabulation. After this air was drawn
off Russell and Appleyard found that still more air could
be removed by applying suction. This air at first carried
considerable oxygen but by continuing the suction almost pure
earbon dioxide was obtained. The amount of gas removed
by lowering the pressure varied directly with the moisture
content of the soil and consequently it may be considered as
air largely absorbed by the moisture of the soil complexes.
Two types of atmosphere, therefore, exist in the soil. One,
the ordinary soil air, is comparatively rich in oxygen. The
other, absorbed by the soil moisture, is very low in oxygen
but very high in carbon dioxide. Obviously they insensibly
merge. The biological significance of these atmospheric types
is very important. Their simultaneous presence admits of
both aérobie and anaérobic biological activity. For example,
rapid nitrate formation might be progressing but no accumu-
lation would be evident, due to just as rapid a synthetic activ-
ity of the anaérobic forms.*
It must not be assumed from the data above quoted that
the composition of the soil air is at all constant or that it is
approximately the same in every soil. The soil is dynamic
in nearly every phase and is nowhere more changeable than
in its atmospheric composition. This variability will of course
be more marked and more important in the air which occupies
the interstitial spaces, although the absorbed air will show
some fluctuation. The compositions of the air of several soils,
as determined by Boussingault and Lewy? are quoted in the
following table:
*Gainey, P. L., Real and Apparent Nitrifying Power of Soils; Science,
N. S., Vol. 39, pp. 35-37, 1914.
Doryland, C. J. T., Influence of Energy Material upon the Relation of
Soil Microorganisms to Soluble Plant Food; N. Dak. Agr. Exp. Sta.,
Bul. 116, pp. 318-399, 1916.
* Johnson, S. W., How Crops Feed, p. 219; New York, 1891.
250 NATURE AND PROPERTIES OF SOILS
TasBLE LIII
PERCENTAGE BY VOLUME
CHARACTER OF SOIL
CO, O, N,
Sandy subsoil of forest....... 24 —— ——
Loamy subsoil of forest...... 8) 19.66 79.55
Surface soil of forest........ xsill To ow Tae
GIES ACSI OyT ERM nes ncn nae ns GPRD .66 19'299 79.35
Soil one year after manuring| .74 19.02 80.24
Soil freshly manured........ 1.54 18.80 79.66
Vegetable mold compost...... 3.64 16.45 (Keen
The differences in the ‘composition of the atmosphere of
different soils and the variability noticeable within the same
soil are due primarily to two factors: (1) the production of
carbon dioxide, and (2) oxidation. These will be discussed
in the above mentioned order.
130. The carbon dioxide of the soil air.—The presence
of carbon dioxide in soils may be due in small part to in-
filtration from the atmospheric air, there being a tendency
for the carbon dioxide, which is heavier than nitrogen and
oxygen, to settle out. It may also have a purely chemical
origin. The latter source is much more probable. The ab-
sorption of the bases of carbonates or bicarbonates would
obviously release carbon dioxide. This probably does not take
place, however, to any great extent in a natural soil. When
ground limestone is added, such a reaction does occur. Car-
bon dioxide in appreciable amounts might for a short time
thus be liberated through chemical reaction. The addition
*MaclIntire, W. H., The Carbonation of Burnt Lime in Soils; Soil
Sei., Vol. VII, No. 5, pp. 325-446, 1919. See also, The Non-existence
of Magnesium Carbonate in Humid Soils; Tenn. Agr. Exp. Sta., Bul.
107, 1914,
SOIL AIR 251
of lime has been shown by several investigators to increase
the carbon dioxide production.+
There is now no doubt that biological activities are largely
JUNE JULY AUGUST SEPT.
Fig. 47.—Diagram showing the amount of carbon dioxide in air from
Volusia silt loam limed and unlimed and cropped to oats.
responsible for the occurrence of the large quantity of carbon
dioxide in the soil air. There are two distinet processes in-
*Bizzell, J. A., and Lyon, T. L., The Effect of Certain Factors on
the Carbon Dioxide Content of Soil Air; Amer. Soe. Agron., Vol. 10,
No. 3, pp. 97-112; Mar. 1918.
Potter, R. S., and Snyder, R. S., Carbon Dioxide Production in Soils
and Carbon and Nitrogen Changes in Soils Variously Treated; Ta. Agr.
Exp. Sta., Res. Bul. 39; Feb. 1916.
Plummer, J. K., Some Effects of Oxygen and Carbon Dioxide on Nitri-
fication and Ammonification in Soils; Cornell Agr. Exp. Sta., Bul. 384;
Dec. 1916.
252 NATURE AND PROPERTIES OF SOILS
volved: (1) the physiological action of bacteria by which
they absorb oxygen and give off carbon dioxide, and (2) the
excretion of carbon dioxide by roots. (See Fig. 47.)
Recent work' has clearly shown that higher plants, espe-
cially during their most rapid growth, markedly increase the
amount of carbon dioxide gas in the soil. Stoklasa? concluded
that the microorganisms in an acre of soil to a depth of four
feet may produce between sixty-five and seventy pounds of
carbon dioxide a day for two hundred days in the year, and
that during the growing period the roots of oats or wheat
would give off nearly as much more. Turpin® finds that the
crop often produces, during its period of active growth, many
times as much carbon dioxide as is produced by soil organ-
isms. He minimizes the influence of the decaying root par-
ticles of the crop occupying the soil on the carbon dioxide
content of the soil air.
In any particular soil, the two major controls of carbon
dioxide production seem to be temperature and rainfall.t The
former apparently is dominant in a temperate humid region
from November to May. During the remainder of the year,
the moisture content of the soil and the amount of rainfall
are the direct controls. Bacterial numbers and nitrate ac-
*Stoklasa, J., and Ernest, A., Beitrdge zur Losung der Frage der
Chemischen Natur des Wurzelsekretes; Jahr. Wiss. Bot., Bd. 46, Seite
55-102, 1909.
Aberson, J. H., Hin Beitrag zur Kenntnis der Natur der Wurzelaus-
scheidunger; Jahr. Wiss. Bot., Bd. 47, Seite 41-56, 1910.
‘Russell, E. J., and Appleyard, A., The Influence of Soil Conditions
on the Decomposition of Organic Matter in the Soil; Jour. Agr. Sei.,
Vol. VII, Part 3, pp. 385-417, 1917.
Bizzell, J. A., and Lyon, T. L., The Effect of Certain Factors on
the Carbon Dioxide Content of Soil Air; Amer. Soe. Agron., Vol. 10,
No. 3, pp. 97-112, Mar. 1918.
*Stoklasa, J., Methoden cur Bestimmung der Atmungsintensitat der
Bakterien im Boden. Zeit, f. d. Landw. Versuchswesen in Oesterreich,
Band 14, Seite 1243-79, 1911.
’Turpin, H. W., The Carbon Dioxide of the Soil Air; Cornell Agr.
Exp. Sta., Memoir 32, April 1920.
* Russell, E. J.. and Appleyard, A., The Atmosphere of the Soil: Its
Composition and the Causes of Variation; Jour. Agr. Sci., Vol. VII,
Part 1, pp. 1-48, 1915.
SOIL AIR 253
cumulation seem to fluctuate with the carbon dioxide, while
the oxygen curve is almost the exact reciprocal. Other in-
fluences of a minor nature enter in, such as the character of
the crop growing on the soil, heavy rainfall, oxygen dissolved
in the rain, and rapid changes of temperature. (See Fig.
48.)
While plowing, application of lime, drainage, and other
practices have a great influence on the proportion of oxygen
2 ala
OLH
PER CENT OF C
oS
ll ill
ATLL MTs
Li!
I AY HT NTL
A iaanaidundd QlMweaancniilantanalincraclnat
FEBR. MARCH APRIL MAY JUNE JULY AUG,
Fig, 48.—Carbon dioxide in air from Dunkirk clay loam bare and from
the same soil cropped to oats, 1918. (After Turpin.)
and carbon dioxide in the soil air, the addition of organic
matter seems to have the most profound effect. At the
Rothamsted Experiment Station,! the carbon dioxide content
of the air from two soils was studied. One soil (Broadbalk
field) had been manured for a number of years while the other
(Hoos) had not received such a treatment:
*Russell, E. J.. and Appleyard, A., The Atmosphere of the Soil: Its
Composition and the Causes of Variation; Jour. Agr. Sci., Vol. VII,
Part 1, p. 25, 1915.
254 NATURE AND PROPERTIES OF SOILS
TABLE LIV
EFFECT OF FARM MANURE ON THE CARBON DIOXIDE CONTENT OF
SOIL AIR. ROTHAMSTED, ENGLAND
PERCENTAGE OF CO, BY VOLUME
TREATMENT
May 15|May 25| June 10| JUNE 12) JuLy 7 |JuLy 27
Manured soil..... 22 Be nly 06 36 .oD
Unmanured soil...) .10 O07 08 07 .08 09
l
Although the formation of carbon dioxide in the soil is in-
fluenced to a marked degree by the decomposition of organic
matter, the effect is by no means proportional to the quantity
of organic matter present. The rate of decomposition varies
greatly, and where this is depressed, as sometimes occurs in
muck or forest soils, the content of carbon dioxide is relatively
low. A high percentage of organic matter is in itself likely
to prevent a proportional formation of carbon dioxide, since
the accumulation of the gas may inhibit further activity of
the decomposing organisms.
131. Oxidation and its effect on the composition of the
soil air.—Oxidative processes in the soil are of two general
types, those due to chemical reactions alone and those due
to biochemical transformations. The purely chemical oxida-
tion may be illustrated best by recalling the processes of soil
formation.t Here it was noted that certain minerals, espe-
cially those carrying iron, were susceptible to the influence of
oxygen. The following reactions show how olivine may as-
sume water and then produce ferric oxide through oxidation:
3MgFeSiO, + 2H,O = H,Mg,Si,0, + SiO, + 3FeO
4FeO + O, = 2Fe,0,
This is illustrative of the complex reactions which are con-
tinually taking place and which tend materially to decrease
the oxygen of the soil air.
+See Chapter II, par. 16, of this text.
SOIL ATR 255
Biochemical oxidation, however, is usually rapid and is a
much more important factor in the oxygen control of the air.
Not only do all bacteria require oxygen for their growth, but
they are continually producing compounds that require oxy-
gen in their molecules. Carbon dioxide is an _ oxidation
product. Its formation reduces the oxygen of the air and its
presence causes a dilution. Sulfofication and nitrification are
well known examples. The reactions for the process of nitri-
fication illustrate in addition the production of carbon dioxide
by chemical means:
ONH, + 30, = 2HNO, + 2H,0
2HNO, -- CaCO, = Ca(NO,), + H,O + CO,
Ca(NO,). + O, = Ca(NO,),
132. Function of the carbon dioxide of the soil_—The
solvent action of carbon dioxide is probably one of its most
important functions in the soil. Constant biological activities,
combined with the seasonal cropping influences, maintain this
solvent and keep it continually in contact with the solution
surfaces of the soil. Although a very weak acid when dis-
solved in water, its rapid formation and continuous action is
productive of marked effects.
The availability of almost all of the plant nutrients is due
either directly or indirectly to the action of carbon dioxide.
Its influence on the potash of orthoclase, the phosphoric acid
of tri-caleium phosphate and the calcium of calcium carbonate
are well known examples:
2K AlSi,0, + 2H,0 + CO, = H,Al,Si,0, + 48i0, + K,CO,
Ca,(PO,). + 2H,O + 2C0O, = CaH,(PO,), + 2CaCO,
CaCO, + H,O + CO, = CaH,(CO,),
Stocklasat has correlated the carbon dioxide production
*Stoklasa, J., Methoden zur Bestimmung der Atmungsintensitiét der
Bakterien im Boden; Zeit. f. d. Landw. Versuchswesen in Oesterreich,
Band 14, Seite 1243-79, 1911.
256 NATURE AND PROPERTIES OF SOILS
with the quantity of phosphates found in the drainage water
from certain soils. Some of his results are given in Table LV:
TABLE LV
P,O, IN DRAINAGE | RELATIVE PRODUC-
WATER TION OF CO,
Sorn (MILLIGRAMS TO A
Get eeme AN | POUND OF SOIL IN 24
HOURS)
eames esos tc Se 4.6 titi
Cleve. hee eae en Aa 7
Tlie Sonera ae eee 8 5, oe 16
Orcamicisoil pve ce. es 7.4 25
Stoklasa considers that the production of carbon dioxide
is a measure of the intensity of bacterial action in the soil,
and that in consequence of this activity the phosphorus is
rendered soluble. |
As far as biological activity is concerned, carbon dioxide
seems to be a factor only insofar as it dilutes the oxygen.'
This seems to be especially true of those bacterial processes
involved in the formation of nitrates. When it exists to the
exclusion of the oxygen, it produces anaérobic conditions but
in this respect it functions in exactly the same way as does
nitrogen or any other inert gas. Physiologically it seems to
have no detrimental effects. Carbon dioxide increases so
markedly with an increase in nitrate production that its
presence can not be depressing.”
133. Importance of oxygen in the soil air— Oxygen is
the all-important gas of the soil air. Without it no weather-
*Plummer, J. K., Some Effects of Oxygen and Carbon Dioxide on
Nitrification and Ammonification in Soils; Cornell Agr. Exp. Sta., Bul.
384, Dec. 1916.
Also, Owen, W. L., Effect of Carbonates upon Nitrification; Ga. Agr.
Exp. Sta., Bul. 81, 1908.
*Neller, J. R., Studies in the Correlation Between the Production
of Carbon Dioxide and the Accumulation of Ammonia by Soil Organ-
isms; Soil Sci., Vol. V, pp. 225-241, 1918.
Stoklasa, Julius, Methoden zur biochemischen Untersuchung des
Bodens ; Handb. Biochem. Arbeitsmeth., Bd. 5, 8. 843-910, 1912.
SOIL AIR 207
ing would occur, no minerals would break down, and no solu-
tion would be possible. Oxidation must go on rapidly and
continuously in the normal soil, not only for chemical but for
biological reasons as well. By it the organic matter that
would soon accumulate to the exclusion of higher plant life is
disposed of, and its nutrient materials are brought into a
condition in which they may be absorbed by roots. The
presence of oxygen is essential either directly or indirectly
to the organisms that facilitate decomposition. Through such
a process, roots of past crops, as well as other organic matter
that has been plowed under, are rapidly changed in the soil.
The processes of decay give rise to products, chiefly carbon
dioxide, that are solvents of mineral matter, and leave the
nitrogen and ash constituents more or less available for plant
use.
Oxygen is also necessary for the germination of seeds and
the growth of roots. These phenomena, although not involv-
ing the removal of large quantities of oxygen, are entirely de-
pendent on its presence in considerable amounts.
134. Volume of the soil air—The amount of air in soils
is determined by their physical properties, the variability in
any particular soil being due to certain changes to which such
a soil is normally subject from time to time. The factors
that influence the volume of air in soil are: (1) texture; (2)
structure; (3) organic matter; and (4) moisture content.
It is a well recognized fact that the finer the texture, the
better the granulation and the larger the amount of organic
matter, the greater is the amount of pore space. Since about
the same proportion of the pore space is filled with water in
every soil when it is in optimum condition for crop growth,
it is obvious that with finer texture, better granulation and
increased organic matter, there will be a greater amount of
air present.
Russell, E. J., and Appleyard, A., The Influence of Soil Conditions
on the Decomposition of Organic Matter in the Soil; Jour. Agr. Sci.,
Vol. VIII, Part 3, pp. 385-417, 1917.
258 NATURE AND PROPERTIES OF SOILS
It must also follow that the larger the proportion of the
interstitial space filled with water, the smaller will be the
quantity of air contained. This does not mean that the soil
with the higher percentage of water will contain the least air.
The percentage pore space, which is determined by the tex-
ture, structure, and organic matter is a consideration also.
These three factors, together with moisture content, are in-
volved in the following formula for calculating air space:
% Air Space = % Pore Space — (%H,O X Vol. Wt.)
If one soil, containing 30 per cent. of water, has a pore
space of 50 per cent. and a volume weight of 1.3, its air space
would be 11 per cent. of the total soil volume. Another soil
with 20 per cent. of moisture, a pore space of 40 per cent.
and a volume weight of 1.6 would, on the other hand, con-
tain only 8 per cent. of air. The above formula, however,
is irremediably inaccurate in two respects. It does not allow
for the air dissolved in the soil-moisture nor does it compen-
sate for the influence of the gelatinous colloidal material that
exists in the interstices especially of a heavy soil.
135. Movement of soil air—There seems to be a slow
but constant movement of air through the interstitial spaces
of a normal soil in an attempt to create a homogeneous com-
position within the soil as well as to establish equilibrium with
the atmospheric air. The major controls of such movement
are (1) moisture and (2) temperature changes. The minor
influences are (1) diffusion and (2) fluctuations in atmo-
spheric¢ pressure.
As water, when present in a soil, occupies certain of the
interstitial spaces, it decreases the air space when it enters
the soil and increases it when it leaves. The downward move-
ment of rain-water produces a movement of soil air by forcing
it out through the drainage channels below, while at the same
time a fresh supply of air is drawn in behind the wave of
saturation as the water passes down from the surface. The |
SOIL AIR 259
movement thus occasioned extends to a depth where the soil
becomes permanently saturated with water. Twenty-five per
cent. of the air in a soil may be driven out by normal change
in moisture content. Capillary movement, whether it be pro-
duced by evaporation, plant action or other normal forces,
likewise produces movement of the soil air. In fact, every
readjustment of soil-moisture, however slight, will produce
a corresponding adjustment of the air films.
It is generally considered that the effect of normal tempera-
ture change on the contraction or expansion of the soil air is
so slight as to produce but little movement. Ramann says,‘
“*Sinee the coefficient of expansion of gas is only 1/273 to a
degree Centigrade and since the temperature fluctuations to
the depths of from four to eight inches are small, the diurnal
exchange of gas is consequently slight.’’ Bouyoucos,? by rais-
ing the temperature of both dry and moist soil held in a
properly controlled apparatus, was able to measure the
amount of air actually expelled. He found in every case that
the gases driven off markedly exceeded the theoretical
amounts.
TABLE LVI
EFFECT OF TEMPERATURE ON THE AMOUNT OF AIR EXPELLED FROM
MOIST SOILS
CuBiIc CENTIMETERS OF AIR EXPELLED ea
PER | PER |FRoM ONE-HALF CuBIC Foot or Sorn|® ae ue
Son, CENT | CENT N-
Mots-| Po- panes
TURE |ROSITY
0-10°C} 10°-20°C | 20°-30°C} 30°-40°C ere
IOS
Sandy loam} 11.0 | 48.2} 289) 354 382 419 250
Silt loam. .| 18.6 | 47.0} 326) 335 428 465 244
Chay eck 25.3 | 50.3 | 363} 382 428 503 261
BGaticio ais o 92.0 | 38.6 | 466 | 512 559 657 200
+Ramann, H., Bodenkunde, Seite 386; Berlin, 1905.
*Bouyoucos, G. J., Effect of Temperature on Some of the Most
Important Physical Processes in Soils; Mich. Agr. Exp. Sta., Tech. Bul.
22, pp. 50-62, 1915.
260 NATURE AND PROPERTIES OF SOILS
Not only are the amounts of air expelled larger than the
theoretical figures, but the differences rise with the tempera-
ture. With a change of 40° C. it is to be expected that the
actual gas expelled will exceed the theoretical from 1.2 to 2.7
times, depending on the soil and its condition. This apparent
discrepancy is due to the expansion of the aqueous vapor in
the soil air and to the liberation of absorbed gases with a rise
in temperature.
Diurnal fluctuations in temperature often rise as high as
15° C. for the upper six inches of soil in the summer months.!
When it is remembered that monthly and seasonal differences
are even greater than the diurnal and that this respiring effect
continues day after day, the importance of temperature in
relation to air movement cannot be minimized. If a six-inch
layer of soil is raised from 5° C. to 20° C. in temperature,
about 10 per cent. of its atmosphere will be expelled, pro-
viding the actual expansion is twice the theoretical.
The wide difference in the compositions of soil and atmo-
spheric gases give rise to diffusion movements, especially of
the oxygen and carbon dioxide. This tendency towards equi-
librium is also important in the readjustments within the soil.
As oxidation and carbon dioxide production do not occur
equally in all parts of the soil, diffussion movements might
easily be induced. The readjustments and equalizations be-
tween the soil air proper and that absorbed by the soil-mois-
ture are probably largely diffusive. Although diffusion phe-
nomena are slow, Buckingham? considers them quite impor-
tant.
Waves of high or low atmospheric pressure, frequently in-
volving a change of 0.5 inch on the mercury gauge, are con-
stantly following each other eastward across the continent.
Low pressure allows the soil air to expand and issue from
1See Swezey, G. D., Soil Temperature at Lincoln, Nebraska; Nebr.
Agr. Exp. Sta., 16th Ann. Rep., pp. 95-102, 1903.
? Buckingham, E., Contributions to Our Knowledge of Aération of
Soils; U.S. Dept. Agr., Bur. Soils, Bul. 25, 1904.
SOIL AIR 261
the soil, while a high pressure following causes the outside
air to enter. An appreciable, but not important, movement
of soil air is produced in this way. Gusts of wind, by affect-
ing the air pressure, would function in the same way but
presumably would influence only the superficial air spaces.
136. Practical modification of soil air——The ordinary
operations of tillage greatly influence the ventilation of the
soil. When a soil is plowed, the bottom of the furrow is ex-
posed directly to the air, and, by the separation of adhering
particles and aggregates of particles, air is brought into con-
tact with portions that previously have been shut off from
atmospheric influence. It is partly because of its effect on
soil ventilation that plowing is beneficial. The necessity for
its practice is obviously greater in a humid region and on a
heavy soil than in a region of light rainfall and on a light
soil. The practice of listing corn in semi-arid regions, by
which the soil is sometimes left unplowed for a number of
years, would fail utterly on the heavy soils of a humid region.
Subsoiling, by loosening the subsoil, increases the ventila-
tion at the lower depths. Rolling and subsurface packing
both diminish the volume and the movement of air. Their
essential difference is in their effect on moisture rather than
on air. Harrowing and cultivation have the opposite effect,
and both may under certain conditions increase the produc-
tion of nitrates in the soil by promoting aération.
Farm manures, lime, and other amendments that improve
the structure of the soil have for that reason a beneficial
action on soil aération. By their effect on the physical con-
dition of the soil, they increase its permeability, and by stim-
ulating oxidation and carbon dioxide production they induce
diffusion.
Under-drainage, by lowering the water-table and removing
the soil-water from the larger capillary spaces, markedly in-
fluences the aération of the soil and thus profoundly modifies
the chemical and biological activities therein. There is a
262 NATURE AND PROPERTIES OF SOILS
very considerable movement of air in and out of tile drains,
which cannot fail to influence the aération of the soil above.
The influence of irrigation on the soil is much like that of
rainfall. The alternate filling and emptying of the interstitial
spaces with water causes a very considerable change of air.
The roots of plants left in a soil after the crop has been
harvested decay and leave channels in the soil through which
air penetrates. Below the furrow slice, where the soil is not
stirred and where it is usually more dense than at the surface,
this affords an important means of aération. The absorption
of moisture from the soil by roots also causes the air to pene-
trate, in order to replace the water withdrawn.
137. Resume.—The air of the soil differs from the atmos-
pheric air in being relatively lower in oxygen and compara-
tively very much higher in carbon dioxide. It is generally
saturated with water-vapor. The percentage of nitrogen and
other gases is about the same as in the atmosphere. The
major portion of the soil atmosphere exists in the larger inter-
stices. Its movement in most cases is due to moisture and
temperature changes, although diffusion and fluctuations in
barometric pressure are of some importance. A minor portion
of the soil air is dissolved in the soil-water, the absorptive
influences of the soil complexes probably playing a part also.
Carbon dioxide is the predominating gas in the minor por-
tion, which maintains an equilibrium with the more active
soil air largely by diffusion.
While the amount of air in the soil varies with the texture,
structure, and organic matter, the moisture content seems to
be the dominant factor with volume as well as with movement.
Although plowing, tillage, and manuring profoundly influence
the soil air and its relationships to normal chemical and bio-
logical reactions, natural forces and processes, once the crop
is on the soil, seem to control aération.
CHAPTER XIII
THE ABSORPTIVE PROPERTIES OF SOILS *
Ir has been known from very early times that soils were
able to take up and tenaciously hold such materials as salts
and dyes. Aristotle, for example, noticed that sea water was
purified when passed through sand. This capacity of soil
to absorb and fix, more or less completely, materials added
to it is called absorption. The earliest quantitative experi-
ments were made by H. 8S. Thompson in England. He found
that the soil was able to absorb considerable quantities of
ammonia from ammonium sulfate, the acid radical being
liberated. The importance of absorption phenomena has since
attracted much attention, both from the practical and the
theoretical standpoint.?
138. Types of absorption— Two general types of absorp-
tion are usually recognized, physical* and chemical. In the
former case the absorbed material is supposed to be concen-
trated on the surfaces of the absorbing substance, no chemical
reaction taking place. The absorptive capacity of charcoal
and cotton for dyes is a good example of such a phenomenon.
In many cases, however, absorption is due to chemical reac-
*The literature on absorption by soils is so complicated and contra-
dictory that only those concepts which are more or less definitely estab-
lished and which have a practical bearing on soil management will be
considered.
* A good review of literature will be found as follows:
Patten, H. E., and Waggaman, W. H., Absorption by Soils; U. S.
Dept. Agr., Bur. Soils, Bul. 52, 1908.
Prescott, J. A., The Phenomenon of Absorption in its Relation to
Soils; Jour. Agr. Sci., Vol. VIII, No. 1, pp. 111-130, Sept., 1916.
° Physical absorption is sometimes spoken of as adsorption. The ten-
dency at present is toward the elimination of this term.
263
264 NATURE AND PROPERTIES OF SOILS
tion. The tenacity with which soils absorb and hold phos-
phorie acid is probably due to the change that the soluble
form undergoes almost immediately in the soil,! producing
the sparingly soluble tri-calecium phosphate (Ca,(PO,),) or
the practically insoluble iron and aluminum phosphates
(FePO, and AIPO,).
While it is generally considered that most of the material
absorbed by soil, whether the action is chemical or physical,
is concentrated at the surfaces of the solid material, there is
some evidence that part of it penetrates, forming a solid solu-
tion. For example, the longer a gas is held at high pressure
within an absorbing material, the less will be released when
the pressure is lowered. Again, while most absorption is
almost instantaneous, the final equilibrium is very slow. Such
phenomena have given rise to a theory of molecular invasion.
In the soil it is impossible to know whether the absorption
of any material has been purely physical, purely chemical, or
due to both actions. In all probability both types of fixation
occur. When a potassium compound is added to a soil, the
potassium is taken up very readily. The fixation at first is
probably physical. This type of absorption generates chem-
ical reactions catalytically and the remainder, and possibly
the greater proportion of the fixation, is probably chemical
in nature.
139. Causes of absorption— Way? was the first to ad-
vance any definite explanation of absorption. After study-
ing the absorptive capacity of double silicates of sodium and
aluminum, he decided that the phenomenon was purely chem-
Cal, (PO): 4 2CaH,(CO:), = Ca,(PO)): a 4H.0 =, 460;
Soluble Insoluble
2Way, J. T., On the Power of Soils to Absorb Manure; Jour. Roy.
Agr. Soc., England, Vol. 11, pp. 313-379, 1850. Also, On the Power of
Soils to Absorb Manure; Jour. Roy. Agr. Soc., England, Vol. 13, pp.
123-143, 1852. Also, On the Influence of Lime on the ‘‘ Absorptive
Properties’’ of Soils; Jour. Roy. Agr. Soc., England, Vol. 15, pp. 491-
515, 1854,
THE ABSORPTIVE PROPERTIES OF SOILS 265
ical. Warington! also believed in the chemical hypothesis.
Liebig, however, regarded absorption as largely physical. Van
Bammelen 2 was the first to direct attention to the importance
of both organic and inorganic colloidal matter to absorption
phenomena. This type of explanation seems the most plau-
sible in light of present knowledge of the colloidal state of cer-
tain soil constituents and from the fact that a soil very often
does not remove different bases in chemically equivalent
amounts.’ The fact that a soil apparently saturated with one
base is able to absorb quantities of another is additional argu-
ment against a purely chemical explanation.
In the soil, especially if it is of a clayey nature, there always
exist certain quantities of hydrated aluminum silicates of
indefinite chemical constitution. They are generally colloidal
in nature. Such materials, as well as those of an organic
character, possess high absorptive capacities, not only be-
cause of their tremendous surface exposures but also because
of their tendeney to react quickly and easily with substances
in the soil solution. According to Van Bemmelen, who made
1Warington, R., On the Part Taken by Oxide of Iron and Alumina
in Absorptive Action of Soils; Jour. Chem. Soc., (London), Vol. 6,
pp. 1-19, 1868.
2 Van Bemmelen, J. M., Die Absorptionsverbindungen und das Absorp-
tionsvermogen der Ackererde; Landw. Vers. Stat., Band 35, Seite 75,
1888. Also, Die Absorption, Dresden, 1910.
*The uncertainty regarding the real explanation of absorption is
shown by the controversy of Weigner, who holds to the colloidal theory,
with Gans, who believes the phenomenon is chemical.
Weigner, G., The Chemical or Physical Nature of Colloidal Aluminum
Silicates Containing Water; Centrbl. f. Min. u. Palaontol., No. 9, pp.
262-272, 1914.
Gans, R., Concerning the Chemical or Physical Nature of Colloidal
Water-containing Aluminum Silicates; Centrbl. f. Min. u. Palaontol.,
No. 22, pp. 699-712; No. 23, pn. 728-741, 1914.
‘The absorptive capacity of the soil is often ascribed to zeolites.
The presence of zeolites in the soil, however, is extremely improbable.
Water and the absence of oxidizing agents are essential for their for-
mation. They are products of hydrometamorphism and not of weather-
ing. It seems probable that the processes of weathering are not only
opposed to zeolite formation but would destroy those already present.
Merrill, G. P., Weathering of Micaceous Gneiss; Bul. Geol. Soc. Amer.,
Vol. 8, pp. 162-166, 1879.
266 NATURE AND PROPERTIES OF SOILS
a very exhaustive study of the subject, the following colloidal
materials may function in the soil:
1. Partially decayed remains of plant and animal tissue.
2. Colloidal iron, aluminum, and silica.
3. Colloidal silicates formed through weathering.
Van Bemmelen also credits crystalline silicates with some
absorptive power, but he does not consider such action par-
ticularly important.
The combinations produced by absorption are often weak,
it being possible to leach out the substances held in the water
of the colloidal gels. The following example of one kind of
absorption is given by Van Bemmelen! and shows how com-
plex the phenomenon may become: ten grams of a hydrogel
having the composition SiO,.4.2 H,O, shaken with 100 cubie
centimenter solution of 20 molecular equivalent KCl, absorbed
0.8 to 1.1 molecular equivalent of the dissolved substance.
The absorption in this case was as if the solution had been
diluted with 4.2 to 5.8 centimeters of water. As the amount
of gel water in 10 grams of hydrogel of SiO, is about 5 cubic
centimeters, the assumption may be made that the dissolved
substance is taken up in equal concentration by the gel water.
Ten grams of hydrogel of SiO, shaken with 100 cubic centi-
meter solution of 50 molecular equivalent KCl—that is, two
and a half times the concentration of the former solution—
absorbs two and a half times as much, or 2.1 to 2.5 molecular
equivalent. This applies also to concentrations five times
stronger than the first mentioned above, but beyond that the
relation is not so simple. It serves, however, to illustrate
the manner in which the absorption takes place from dilute
solutions.
140. The absorptive capacity of soils.2»—The absorptive
+*Van Bemmelen, J. M., Die Absorptionsverbindungen und das Ab-
sorptionsvermogen der Ackererde; Landw. Vers. Stat., Band 35, Seite
75, 1888.
2A few important citations are as follows:
Peters, E., Ueber die Absorption von Kali durch Ackererde; Landw.
Ver. Stat., Bd. 2, Seite 113-151, 1860.
THE ABSORPTIVE PROPERTIES OF SOILS 267
capacity of any particular soil for gases, water, or salts in
solution, under any particular condition, depends on the tex-
ture of the soil and on the time during which the action is
allowed to continue. The absorptive power of a soil may be
determined by percolating a solution of known strength
through a column of the soil or by shaking the sample with
a definite amount of the solution. The following data from
Parker! were obtained by shaking a 35-gram portion of soil
for two days with a solution carrying the equivalent of about
6.5 grams of KCl:
TasLE LVII
EFFECT OF TEXTURE ON THE ABSORPTION OF POTASSIUM.
PoTAsSsiuM ABSORBED
Sor, TYPE EXPRESSED AS MILLIGRAMS
or KCl,
CIES GE Nace ack pein es tae ee 32D
Mecathumi clay loam, ..6 ssn. sins oe oo sss 240
Carreiteton OAM pita aes Actoas eosie es 225
iNoriolke-samdy loam. 2s... 4.8.25. «40% 148
Sullivan, E. C., The Interaction Between Minerals and Water Solu-
tions; U. S. Geol. Survey, Bul. 312, 1907.
Morse, F. W., and Curry, B. E., Reactions Between Manurial Salts and
Clay, Mucks and Soils; N. H. Agr. Exp. Sta., 29th Ann. Rep., pp. 271-
293, 1908.
Demolon, A., and Bronet, G., Sur la Pénétration des Engrais Solubles
dans les Sols; Ann. Agron., Tome 28, pp. 401-418, 1911.
Bogue, R. H., Absorption of Potassium and Phosphorus Ions by
Typical Soils; Jour. Phys. Chem., Vol. 19, No. 8, pp. 665-695, 1915.
McCall, A. G., Hildebrandt, F. M., and Johnston, E. S., The <Ab-
sorption of Potassium by the Soil; Jour. Phys. Chem., Vol. 20, No. 1,
pp. 51-63, 1916.
McBeth, J. G., Fixation of Ammonia in Soils; Jour. Agr. Res.,
Vol. IX, No. 5, pp. 141-155, 1917.
Wyckoff, M. L., Absorption of Ammonium Sulfate by Soils and Quartz
Sand; Soil Sci., Vol. III, No. 6, pp. 561-564, 1917.
Kelley, W. P., and Cummins, A. B., Chemical Effect of Salts on
Sotls; Soil Sci., Vol. XI, No. 2, pp. 139-159, Feb., 1921.
*Parker, E. G., Selective Absorption by Soils; Jour. Agr. Res., Vol. 1,
No. 5, pp. 179-188, Dee., 1913.
268 NATURE AND PROPERTIES OF SOILS
It is noticeable that the absorption increases with the fine-
ness of the texture, indicating that the heavier the soil, the
greater is the amount of material present that possesses marked
capacity for fixation. Organic matter, in general, does not
seem as efficacious as mineral material in absorptive reac-
tions, especially those involving salts.
7
ed |
e
a
ue
eee
2a
oO 200 400 600 S00 1000 7200 CL.
Fig. 49.—Curves showing the absorption of K in parts per million by
various soils from a solution containing 200 parts to the million of
K. The volume of the percolate is used as the abscissas.
The influence of time on absorption is shown by the follow-
ing data from Schreiner and Failyer.t In this case 100 gram
portions of soil were treated with 500 ¢.c. of a mono-calcium
phosphate solution carrying 100 parts per million of PO,. The
1Schreiner, O., and Failyer, G. H., The Absorption of Phosphates
and Potassium by Soils; U. S. Dept. Agr., Bur. Soils, Bul. 32, p. 9,
1906.
THE ABSORPTIVE PROPERTIES OF SOILS 269
parts per million of PO, absorbed after certain intervals of
time are given below. (See also Fig. 49) : 1
TABLE LVIIT
EFFECT OF TIME AND TEXTURE ON THE ABSORPTION OF PO, FROM
A SOLUTION OF CaH,(PO,)>.
PO, ABSORBED IN PARTS
PER MILLION
TIME -
CLAYEY |FINE SANDY
Soin Soin
SIMUMULEES yn oe Pin ec oe ke epee ta 400 2aD
ALU MEITETA GES cs) Ss Sa clohs, cea awed aaah 410 250
TEC LO 12 t 2 ee aes a Car ee 415 260
rue TAROT LETS oe SORE eee ASR RE he 435 315
21 LEO LETS Rag gp CD one RR) 440 335
2 5] ANTE epee RS PR ea 445 370
It must not be inferred that, when a solution is brought
in contact with a soil, it always becomes weaker because of
absorption. Negative absorption may occur in which the sol-
vent is taken up more rapidly than the solute. Concentra-
tion is thus induced.
141. Selective absorption.?—The fixation phenomena by
the soil, whether physical or chemical, is of two types: (1) the
absorption of molecules, the compound being taken up un-
changed; and (2) the absorption of ions. In the first case,
*The law which appears to govern absorption of phosphates and
potash by the soil may be expressed mathematically as follows:
dy 2.
ae K (A—Y)
in which K is a constant, A the maximum quantity possible for the soil
to absorb and y the quantity actually fixed when v, volume of the
solution, has percolated through. A short discussion of the mathematics
of this law may be found in the following publication: Schreiner, O.,
and Failyer, G. H., The Absorption of Phosphates and Potassium by
Soils; U. S. Dept. Agr., Bur. Soils, Bul. 32, pp. 23-24, 37-39, 1906.
*A very good discussion of selective absorption is found in the
following: Parker, E. G., Selective Absorption by Soils; Jour. Agr.
Res., Vol. 1, No. 5, pp. 179-188, 1913.
270 NATURE AND PROPERTIES OF SOILS
if a residue is left, it is unchanged except in concentration.
Such would be the case in the absorption of certain dyes, of
gases and of hydroxides of various kinds, where the molecule
is fixed intact. This first form of absorption is by no means
as important as the selective absorption of ions.
Certain compounds, ealled electrolytes,t tend when in solu-
tion to ionize or split up into ions. Thus potassium nitrate,
a neutral salt, breaks up into K* and NO-, ions, the degree
of ionization depending on the concentration of the solution.
When such a solution is brought into contact with soil, the
latter usually, but not always, exerts a greater affinity for the
basic ion, leaving an excess of the acid radical in solution.
The water present furnishes small amounts of H* and OH-
ions, thereby encouraging the formation of KOH, which is
absorbed intact, together with the K+ and OH~ ions. This
action, therefore, leaves the Ht and NO-, ions preponderant in
the solution, which is of necessity acid in reaction due to the
hydrogen ion concentration. This selective absorption may be
demonstrated with any neutral salt and any neutral absorbent,
the resultant extract always being acid due to the selective
absorption of the basic ions.
142. Substitution of bases.°—Associated with the selec-
tive absorption of bases from solution there is a liberation of
1 According to the theory of the electrolytic-dissociation or ioniza-
tion, many compounds under certain conditions break up into electrically
charged portions called ions. Ions may be single atoms or a group of
atoms. Many inorganic substances are almost completely ionized. A
few organic compounds exhibit marked dissociation but many are not
appreciably affected.
Water dissociates into H+ and OH- ions to the extent of about .00001
of a per cent. or 1 part in 10,000,000. An acid yields hydrogen ions
and other ions carrying the remainder of the molecules. Alkalies give
hydroxyl ions and other ions consisting of the remaining portion of the
molecules. The acidity or alkalinity of a solution is determined by its
hydrogen-ion concentration.
?Van Bemmelen, J. M., Das Absorptionsvermogen der Ackererde;
Landw. Vers. Stat., Band 21, Seite 135-191, 1877.
Sullivan, E. C., The Interaction beiween Minerals and Water Solu-
tions; U. S. Geol. Survey, Bul. 312, 1907.
Wiegner, G., Zum Basenaustausch in der Ackererde; Jour. Landw.,
Band 60, Seite 111-150, 197-222, 1912.
THE ABSORPTIVE PROPERTIES OF SOILS 271
other bases from the soil, which appear in the filtrate as ions
and in combination with acid radicals. Such phenomena may
be considered as mere basic exchange, pushed forward by the
mass action of the ion absorbed, and is called substitution of
bases. The change may be illustrated as follows:
KCl + X, Silicate = X,Cl + K Silicate
It is unlikely that this reaction actually takes place to any
extent in fertilizer practice.t. It is more probable that the
acid produced by the selective absorption liberates the bases
from their loose union with the hydrated aluminum silicate
complexes.
HCl + X, Silicates = X,Cl + H Silicates
A dilute solution of potassium chloride filtered through a
soil will produce a filtrate containing some calcium, mag-
nesium, or chloride or all of these salts and some potassium
chloride. The more dilute the solution, the larger will be the
proportion retained, but the less the total quantity absorbed.
Peters * treated 100 grams of soil with 250 cubic centimeters
of a solution of potassium salts, and found that the potassium
of separate salts was retained in different proportions, and
that the more concentrated solutions lost relatively less than
the weaker ones, although more actual potassium was re-
moved from the former.
TasBLE LIX
GRAMS OF K,O GRAMS OF K,O
ABSORBED FROM A ABSORBED FROM A
SOLUTION 1/10 NorMAL Souvu- | 1/20 NormMat Souvu-
TION TION
150) I ae a 0124 .1990
RENO amy aes se 3362 2098
ECO Mo aeeitns 2 oe TAT 3134
1Parker, E. G., Selective Absorption by Soils; Jour. Agr. Res., Vol. 1,
No. 5, p. 180, 1913.
*Peters, E., Uber die Absorption von Kali durch Ackererde; Landw.
Vers. Stat., Band 2, Seite 113-151, 1860.
272 NATURE AND PROPERTIES OF SOILS
The same bases are not always absorbed in the same propor-
tion by different soils; one soil may have a greater absorp-
tive power for potassium, while another may retain relatively
more ammonia. They seem to be somewhat interchangeable,
as any absorbed base may be released by a number of others
in solution. The absorptive power of a soil for certain bases
is reflected in the composition of the drainage water from the
soil. The latter varies with the soil, and a soluble fertilizer
applied to one soil will have a different effect on the composi-
tion of drainage water than if applied to another soil. This
is well illustrated from lysimeter experiments by Gerlach *
at Bromberg. Several soils were used, a portion of each being
fertilized and unfertilized respectively. The lysimeters were
1.2 meters deep and contained 4 cubic meters of soil. The
drainage water was collected and analyzed for four years.
The first year there was no crop, the second year potatoes were
erown, the third oats, and the fourth rye. The following re-
sults were obtained :
TABLE LX
AVERAGE COMPETITION OF DRAINAGE WATER IN PARTS PER MIL-
LION. BROMBERG.
TOTAL On-
Sor TREATMENT N NO, | GANIC} K,O CaQ
Moor, Soles 26. Mertilized ||) 32-7 |) 30:0 | i274 32e2 405
Untreated | 65.0 | 60.3 | 4.7 | 26.2 507
Sand low in or-
ganic matter...| Fertilized| 25.5 | 25.1 A} 25.1 92
Untreated | 20.9} 20.4 uy 8.5 90
Sandy loam high
in organic
matter. ..... Fertilized| 67.8 | 64.6 | 3.1] 70.2 399
Untreated | 69.5] 66.1 | 3.4] 47.4 414
Gerlach, U., Uber die durch sickerwasser dem Boden Entzogenen
Menge Wasser und Nahrstoffe; Il. Landw. Zeitung, 30 Jahrgrange, Heft
95, Seite 871-881, 1910.
THE ABSORPTIVE PROPERTIES OF SOILS 273
143. Importance of absorption—Absorption is impor-
tant, not only because it allows the soil to retain certain nutri-
ents against excessive leaching, but because it facilitates the
condensation and concentration of gases within the soil.t Rus-
sell and Appleyard? have shown that the inner soil air is
held very tightly and must in consequence be under consid-
erable pressure. Such gas absorption tends to force reactions
which otherwise would be very slow. A part of the catalytic
power of the soil may be accounted for in this way. Moreover,
the absorption of water by the soil is by no means unimportant.
It is because of such phenomena that the moisture of the soil
occurs in various forms and possesses distinctly different re-
lationships to the plant.
The selective absorption of the basic ions by soils of every
type is important in a number of ways. In the first place,
potassium, calcium, magnesium, and iron function in the soil
as bases. Selective absorption tends to conserve these nutri-
ents to the exclusion of their acid radicals, which are readily
lost in drainage. Phosphorus, however, has a different status,
for although it is held as a part of an acid radical (PO,), it is
saved from leaching by the insolubility of the compounds
which tend to form. In the second place, selective absorption
apparently produces residues when fertilizers are added and
these residues are almost always acid. Sodium nitrate, am-
monium sulphate, potassium chloride, and potassium sulphate
will leave an acid residue in the soil solution unless influenced
by extraneous factors, such as the addition of lime or the ac-
tion of plants.
*Patten, H. E., and Gallagher, F. E., Absorption of Vapors and Gases
by Soils; U. S. Dept. Agr., Bur. Soils, Bul. 51, 1908.
McGeorge, W., Absorption of Fertilizer Salts by Hawaiian Soils ; Haw.
Agr. Exp. Sta., Bul. 35, p. 32, 1914.
Cook, R. C., Factors Affecting the Absorption and Distribution of
Ammonia Applied to Soils; Soil Sci., Vol. II, No. 4, pp. 305-344, 1916.
? Russell, E. J., and Appleyard, A., The Atmosphere of the Soil: Its
Composition and the Causes of Variation; Jour. Agr. Sci., Vol. VII,
Part 1, pp. 1-48, 1915.
274 NATURE AND PROPERTIES OF SOILS
The acidity of soils, which is a function not only of the soil
solution but of the solid portions also, is frequently attributed
to certain absorptive phenomena, one idea being that, due
to physical and chemical absorption of bases, a concentra-
tion of the hydrogen ion is produced and actual acidity re-
sults. Basie exchange seems to liberate iron and aluminum,
the salts of which easily hydrolize and yield acid solutions.
If, as some investigators maintain, the toxic principle of the
so-called acid soils is active aluminum, manganese or similar
elements, absorption may again be the activating phenomenon,
since an unsatisfied absorptive capacity, especially for cal-
cium and magnesium, seems to favor the presence of such
constituents in the soil solution.
The absorptive power of the soil is a controlling factor as
far as the composition and concentration of the soil solution
is concerned. Any study of the dynamic relationships of the
water solution that exists in the soil interstices and in the col-
loidal complexes which coat the soil particles, must reckon
with absorption phenomena and all of the factors which tend
to influence them.
CHAPTER XIV
THE SOIL SOLUTION
THE soil is a heterogeneous mixture of solids, gases, and a
liquid. The mineral constituents come from the debris of
rock, the organic matter is derived from plant and animal
tissue, while through and around these complex materials the
water and gases of the soil circulate in ever-changing propor-
tions. Minute organisms are also present in great numbers,
aiding, through their enzymic activities, the intricate trans-
formations. As a result of the reactory inter-relations of the
soil components, a solution is generated which tends to come
into equilibrium with the solids and gases with which it is
in contact. As it is from this source that plants obtain their
mineral nutrients, the soil solution and its control demand
especial attention.
The fundamental error of many soil conceptions has been
to regard the soil as a static system. Chemical, physical, and
biological activities are admitted, but they have been regarded
as of little importance in influencing the soil mass as a whole.
Such a conception is in error as every constituent of the soil
is dynamic. The presence of large amounts of material in
a colloidal state makes the constaney of any particular con-
dition impossible over any extended period.
In studying the soil solution, especially as to its composi-
tion and concentration, the phenomenon of absorption can
not be ignored. The tendency of certain portions of the soil
to go into solution, while other parts are absorbing both the
solvent and the solute, must be reckoned with. Moreover,
the losses of nutrients to the plant and through leaching are
275
276 NATURE AND PROPERTIES OF SOILS
a factor to be considered. Obviously the concentration and
composition of the soil solution is first of all a function of
the absorptive capacity of the soil complexes, modified by the
rate of solution and the magnitude of crop and leaching
activities.
144. Absorption and the soil solution.—In a bare moist
soil, where there is no evaporation or leaching to disturb
equilibrium ‘tendencies, the soil presents a_ three-phase
system. The phases are: (1) the solution surfaces,
(2) the absorptive or colloidal surfaces, and (3) the
SOLUTION
SURFACES
ABSORPTION
ia Sore
COMPLEXES SOLUTION
Fig. 50.—Diagram showing the equilibrium tendencies that exist between
the solution surfaces, the colloidal complexes and the soil solution.
soil solution itself. When solution takes place, the con-
stituents so affected are acquired in part by the soil mois-
ture as a solute and in part by the absorptive complexes.
There is a constant attempt at equilibrium, which of course
is never attained as long as solution continues. Under field
conditions, many other disturbing factors enter. The rate
of solution may vary, and the capacity and character of the
absorbing colloidal complexes are always changing. Moreover,
the amount of water in the soil is never constant, due to
drainage and evaporation. The feeding of the plant, as re-
1This term refers to the soil surfaces from which solution takes
place.
THE SOIL SOLUTION 277
gards both water and nutrients, and losses by leaching, must
always be considered. In addition, the effect of tillage as
well as the common practices of adding farm manure, plow-
ing under of green-crops and applying fertilizers and lime,
are constantly effective in obstructing equilibrium adjust-
ments.! (See Fig. 50.)
The soil solution is, therefore, markedly dynamic in char-
acter, constantly changing in composition and concentra-
tion. Its important control is absorption, the absorptive sur-
faces acting as a depository, in which active reserve nutrients
are held. As the solution is depleted in any constituent,
quicker adjustment takes place between the solvent and the
colloidal complexes than is possible between the solution and
the solution surfaces. Rapid adjustments, as far as the sup-
ply of nutrients for plants is concerned, is possible only be-
cause of the absorptive properties of the colloidal complexes
of the soil.
145. Methods of studying the soil solution.—Questions
regarding the soil solution are difficult to answer because no
adequate procedure has been devised for extracting a repre-
sentative sample of the solution as it existed in the soil. More-
over, no wholly satisfactory method has been perfected for
its measurement in place. Various extractive methods have
been tried. Briggs and McLane? attempted to sample the
solution by the use of a centrifuge developing a force of two
or three thousand times that of gravitation. When the soil
contained a rather large quantity of capillary water, a small
amount of it could be removed in this way.
1Bouyoucos has shown that even under controlled conditions the
equilibrium between finely ground minerals and water is not absolute
or real due to the complex hydration and hydrolysis which continually
occur. Bouyoucos, G. J., Rate and Extent of Solubility of Mimerals
and Rocks under Different Treatments and Conditions; Mich. Agr. Exp.
Sta., Tech. Bul. 50, July, 921.
? Briggs, Lyman J., and McLane, John W., The Moisture Equivalent of
Soils; U. S. Dept. Agr., Bur. Soils, Bul. 45, pp. 6-8, 1907.
278 NATURE AND PROPERTIES OF SOILS
Another device, perfected by Briggs and McCall,: consists
of a close-grained, unglazed porcelain tube, closed at one end
and provided at the other with a tubulure, by which it can
be connected with an exhausted receiver. This tube is mois-
tened and buried in the soil. If the moisture content of the
soil is sufficient to reduce the pressure of the capillary water
surface in the soil to less than half the difference between the
pressure inside and outside of the tube, there will be a move-
ment of water inward. The water may be collected and ana-
lyzed.
More recently Van Suchtelen has used another method to
obtain the soil solution. He replaces the soil-water by means
of paraffin in a liquid state, at the same time subjecting the
soil on a filter to suction. The displaced water is considered
to represent the soil solution. Later Van Suchtelen and Itano
substituted pressure for suction, modifying the apparatus to
meet the new procedure. This apparatus has been further
perfected by Morgan.* Lipman‘ has proposed a method in
which very high pressure, a minimum of 53,000 pounds to the
square inch, is utilized in squeezing out the soil-water.°®
All such methods are open to the objection that the sample
is not representative. The soil solution changes both in con-
1 Briggs, L. J., and McCall, A. G., An Artificial Root for Inducing
Capillary Movement of Soil Moisture; Science, N. S., Vol. 20, pp.
566-569, 1904.
2Van Suchtelen, F. H. H., Methode zur Gewinnung der Natiirlichen
Bodenlosung; Jour. f. Landw., Band 60, Seite 369-370, 1912.
*Morgan, J. F., The Soil Solution Obtained by the Oil Pressure
Method; Mich. Agr. Exp. Sta., Tech. Bul. 28, Oct., 1916.
4 Lipman, C. B., A New Method of Extracting the Soil Solution; Univ.
Cal. Pub., Agr. Sci., Vol. 3, No. 7, pp. 131-134, 1918. Ramann, E., et al.,
have proposed a similar method but with less pressure. Internat. Mit. f.
Bodenkunde, Bd. 6, Seite 27, 1916.
For a good criticism of this method, see Northrup, Zea, Science,
N.S., Vol. XLVII, No. 1226, p. 638, June 1918.
°Ischerekov in 1907 used ethyl alcohol to displace the water in a
soil column utilizing only the force of gravity. Parker claims that
this method is of considerable value. He found that data so obtained
compared closely with that obtained from the water extract method.
Parker, F. W., Methods of Studying the Concentration of the Soil
Solution; Soil Sci., Vol. XII, No. 3, pp. 209-232, 1921.
THE SOIL SOLUTION 279
centration and composition so readily that the addition of ex-
traneous material or the exertion of unnatural pressure defeat
the object of the determination. Moreover, the soil solution is
probably not homogeneous and unless practically all of it is
removed a sample of value cannot be obtained. The signifi-
cance of such a sample, if it were attained, is questionable,
as it is impossible to know the proportion of the soluble nu-
trients that may actually be appropriated by the growing
plant.
The method of obtaining soil extracts has been used to a
greater extent than any other in studying the soil solution.
Water is the usual solvent. The Bureau of Soils filter method *
is commonly followed. As might be expected, it is purely
arbitrary in its procedure, the idea being to make the results
comparative rather than strictly quantitative. Soil and water
in the proportions of 1 to 5 are mixed, stirred three minutes
and allowed to stand twenty minutes. The supernatant liquid
is then forced through a Pasteur-Chamberland filter and a
clear extract obtained for analysis.
The solution obtained is not representative of the soil-water
and its solutes. It is only an extract of the soil. The addi-
tion of a large amount of water is a disturbing factor. The
concentration of the extract is also modified by the absorptive
power of the soil, being relatively greater for a sandy than
for a clayey soil. Moreover, the differential influence of the
solvent comes into play, for as soon as solution begins, the
solvent is no longer pure water but a solution of constantly
changing efficiency. Nevertheless, the work of Hoagland,
Stewart and Burd ? indicates that there is not only a relation-
1Schreiner, O., and Failyer, G. H., Colometric, Turbidity and Titra-
tion Methods Used in Soil Investigations; U. 8. Dept. Agr., Bur. Soils,
Bul. 31, 1906.
? Hoagland, D. R., The Freezing Point Method as an Index of Varia-
tions in the Soil Solution Due to Season and Crop Growth; Jour. Agr.
Res., Vol. XII, No. 6, pp. 369-395, 1918.
Stewart, G. R., Effect of Season and Crop Growth in Modifying the
Soil Solution; Jour. Agr. Res., Vol. XII, No. 6, pp. 311-368, 1918.
280 NATURE AND PROPERTIES OF SOILS
ship between the water extract of a soil and its productivity,
but a correlation with the strength of the soil solution as well.
The extract method is especially valuable in studying the
nitrates of the soil solution. As nitrate nitrogen does not
suffer as much absorption as do the nutrient bases, that which
appears in the extract is a fair measure of the strength of the
soil solution insofar as this constituent is concerned.
The only method for measuring the concentration of the soil
solution 2n situ is that of Bouyoucos.' This is known as the
depression of the freezing point method. It is possible, when
dealing with a pure solution of a known salt, to calculate its
concentration by determining how much the freezing point is
lowered or depressed below 0° C. This principle is applied
to the soil by using a Beckman thermometer and the proper
control apparatus. As the soil solution carries a great num-
ber of different ions in unknown proportions, it is impossible
to ealeulate even the concentration with accuracy, a factor
of somewhat doubtful validity being utilized. The procedure
gives nothing regarding the presence of specific ions nor are
its results uniform, due to the variable dissociation of the salts
present. Nevertheless the method has thrown much lght
on the many difficult problems of the soil and its solution.
146. Qualitative composition of the soil solution.—Once
the dynamic character of the soil solution is conceded, three
points of importance immediately demand attention: (1) the
qualitative composition of the soil solution and its concentra-
tion 7n toto, (2) the quantitative composition, and (8) the
factors most important in influencing both the composition
and the concentration of the solution.
It must be recognized at the outset that the soil solution
Burd, J. S., Water Extractions of Sotls as Criteria of their Crop
Producing Power; Jour. Agr. Res., Vol. XII, No. 6, pp. 297-309, 1918.
Hoagland, D. R., Martin, J. C., and Stewart, G. R., Relation of the
Soil Solution to the Soil Extract; Jour. Agr. Res., Vol. XX, No. 5,
pp. 381-395, 1920.
+ Bouyoucos, G. J., Further Studies on the Freezing Point Lowering of
Soils; Mich. Agr. Exp. Sta., Tech. Bul. 31, Nov., 1916.
THE SOIL SOLUTION 281
is generally dilute except in arid regions under conditions of
alkali. The concentration probably very seldom exceeds 30,-
000 parts per million and is normally very much lower. More-
over, the greater proportion of the solute is in an ionic state,
molecules appearing only when the concentration is relatively
high. It is well to note that the plant absorbs most of its
nutrients in the ionic condition.
From the knowledge obtained by the analysis of soil ex-
tracts, it is safe to assume that all of the common bases and
acid radicals normally occur in the soil solution. Thus, K*,
Na*, Mg**, Ca**, Fe*t*+, Al** and NH,* ions may be expected
as well as such ions as SO%, 8i0%, Cl, POz, NO;, NO; and
CO. Since water dissociates slightly, Ht and OH- ions will
also be present. The reaction of the solution will depend on
its hydrogen-ion concentration and may be alkaline, neutral
or acid as the case may be. Most soil solutions seem to be
slightly acid,' possibly due to the action of carbon dioxide.
Morgan ? found on an examination of the solutions obtained
from soils by the oil pressure method that, as the moisture in-
creased, the concentration of the solution decreased. These
findings are amply corroborated by the work of Bouyoucos ®
with the depression of the freezing point method. The latter
presents data regarding the actual concentrations at various
moisture contents, which seem to indicate the general differ-
ences that may be expected between soils of different types.
*Gillespie, L. J., The Reaction of Soil and Measurements of Hydro-
gen-ion Concentration; Jour. Wash. Acad. Sci. Vol. 6, No. 1, pp.
7-16, 1916.
Sharp, L. T., and Hoagland, D. R., Acidity and Adsorption in Soils
as Measured by the Hydrogen Electrode; Jour. Agr. Res., Vol. VII,
No. 3, pp. 123-145, 1916.
Hoagland, D. R., Relation of the Concentration and Reaction of the
Nutrient Medium to the Growth and Absorption of the Plant; Jour.
Agr. Res., Vol. XVIII, No. 2, pp. 73-117, 1919.
*Morgan, J. F., The Soil Solution Obtained by the Oil Pressure
Method; Mich. Agr. Exp. Sta., Tech. Bul. 28, 1916.
* Bouyoucos, G. J., Further Studies on the Freezing Point Lowering
of Soils; Mich, Agr. Exp. Sta., Tech. Bul. 31, pp. 14-15, 1916.
282 NATURE AND PROPERTIES OF SOILS
TasLE LXI
THE CONCENTRATION OF THE SOLUTION OF VARIOUS SOILS AS DE-
TERMINED BY THE DEPRESSION OF THE FREEZING POINT. EX-
PRESSED IN PARTS PER MILLION BASED ON DRY SOIL.
Som, MOISTURE ee e RA || MoIsTURE Cone ate
2 Pea Me To P. P.M.
Superior clay... 18.8 29,268 39.4 415
Miami silt loam. 8.8 19,560 36.0 707
Carrington loam 15.2 16,390 38.5 463
Plainfield sand. 5.0 6,342 24.6 366
PEA ihe: cos arerenes 61.3 23,3383 208.5 2,222
147. Quantitative composition of the soil solution —
Data regarding the relative or actual quantities of the nutri-
ent elements in the soil solution are not only very meagre but
unreliable. Morgan! found, on comparing the solutions ob-
tained from different soils by the oil pressure method, that the
potassium (K) might vary from 4 to 180 parts per million
based on dry soil; the phosphorus (PO,) from .2 to 4.6, and
the calcium (Ca) from 6 to 1000 parts per million. King,” in
his extensive work with soil extracts, found the nitrate nitro-
gen (NO,) extremely variable, ranging from a fraction of a
part per million to more than 150 parts per million in the same
soil at different times. A greater fluctuation is to be expected,
however, in the nitrate nitrogen than with the other elements,
since the presence of soluble nitrogen in the soil solution is due
very largely to biological activity. The following figures from
Morgan, although the different samples should not be com-
pared, show what may be expected in general regarding the
concentration of particular elements in the soil solution.
1Morgan, J. F., The Soil Solution Obtained by the Oil Pressure
Method; Mich. Agr. Exp. Sta., Tech. Bul. 28, 1916.
*King, F. H., Investigations in Soil Management; U. 8. Dept. Agr.
Bur. Soils, Bul. 26, 1905.
THE SOIL SOLUTION 283
TABLE LXII
THE AMOUNTS OF POTASSIUM, PHOSPHORUS, AND CALCIUM IN THE
SOLUTION OF VARIOUS SOILS AS DETERMINED BY THE OIL
PRESSURE METHOD. EXPRESSED IN PARTS PER MILLION
BASED ON DRY SOIL.
Parts PER MILLION
MOISTURE
Sorts PER-
CENTAGE K PO, Ca |NH,-+NO,
+NO,
Fine sandy loam. 29 7.18 | 1.54 9.10 91
Medium sandy
Oana ess Fs 27.2 9.82 | 141 12.75 | 13.56
Clyde fine sandy
hoa hace ks. 41.9 12.44 | 1.85 | 37.12 3.80
Miami silt loam..| 37.8 27.02 | 4.64 | 25.93 1.20
Miami elay...... 24.5 11.08 | 1.13 10.56 1.61
| EOE Ree rane aera 13229) 139 San | 2198) tot) 33.00
Morgan’s data indicate that the least variation may be ex-
pected in the phosphorus (PO,) content, which does not differ
greatiy in different soil solutions nor does it vary to any great
extent in the same soil. Potassium (K) and especially cal-
cium (Ca) show considerable fluctuation, as does the nitrate
nitrogen (NO,), as has already been emphasized. The figures
of Morgan correlate fairly well with the data obtained by the
Bureau of Soils? by means of centrifugal extraction. The
potassium (K) averaged about 28 parts per million based on
the solution, the calcium (Ca) 32, and the phosphorus (PO,)
8 parts per million.
148. Influence of season and crop on the soil sclution.—
It has already been emphasized that the concentration and
the composition of the soil solution suffer wide fluctuations.
The principal causes of such variations are as interesting as
Cameron, F. K., The Soil Solution; p. 40, Easton, Pa., 1911.
284 NATURE AND PROPERTIES OF SOILS
they are important since they have a bearing not only on the
chemical and biological phenomena within the soil but also
on its plant relationships.
The broadest and most general factors affecting the soil
solution are season and crop. Whether the soil is fallow or
covered with vegetation, a great seasonal influence is evident
on the soil and its solution. Stewart,’ working in California
with extracts from thirteen soils held in large containers,
found notable fluctuations of nitrates, calcium, potassium, and
magnesium both in bare and cropped earth. The phosphates
did not show great variation. The soluble nutrients were
markedly higher in the bare soils, the differences between the
various types being quite noteworthy. The good soils seemed
to have the more concentrated soil solution, a conclusion al-
ready reached by a number of investigators.2, When crops
were growing on these soils, the concentration of soluble nu-
trients not only was lower than with the fallowed areas, but
it was about the same in every type of soil. The inherent
solution capacity of the different soils was roughly indicated
by the crop growth. Hoagland’s* study of the concentration
1Stewart, G. R., Effect of Season and Crop Growth in Modifying
the Soil Solution; Jour. Agr. Res., Vol. XII, No. 6, pp. 311-368, 1918.
*Snyder, H., The Water-Soluble Plant Food of Soils; Science, N. 8.,
Vol. 19, No. 491, pp. 834-835, 1904.
King, F. H., Investigations in Soil Management; Madison, Wis.,
1904.
King, F. H., Investigations in Soil Management; U. S. Dept. Agr.,
Bur. Soils, Bul. 26, 1905.
Mitscherlich, E. A., Hine Chemische Bodenanalyse fiir Pflanzen-
physiologische Forschungen; Landw. Jahrb., Bd. 36, Heft 2, S. 309-369,
1907.
Lyon, T. L., and Bizzell, J. A., The Plant as an Indicator of the
Relative Density of the Soil Solutions; Proc. Amer. Soc. Agron., Vol.
IV, pp. 35-49, 1912.
Hall, A. D., Brenchley, W. E., and Underwood, T. M., The Soil Solu-
tion and the Mineral Constituents of the Soil; Philosoph. Trans. Roy.
Soc., London, Series B, Vol. 204, pp. 179-200, 1913.
Pantanelli, E., Ricerche Sulla Concentrazione del Liquide Circolante
nei Terreni Libici; Bul. Orto Bot. R., Univ. Napoli, T. 4, pp. 371-383.
* Hoagland, D. R., The Freezing Point Method as an Index of Varia-
tions in the Soil Solution Due to Season and Crop Growth; Jour. Agr.
Res., Vol. XII, No. 6, pp. 369-395, 1918,
THE SOIL SOLUTION 285
of the solution in these soils through the growing season by
the freezing point method corroborates the conclusions drawn
from the water extracts. The investigation also indicates that
large amounts of nutrients are made available by cultivation,
fallowing, and cropping and that, from the standpoint of the
soil solution, the ordinary farm practices are inherently sound.
Hoagland’s data regarding some of the soils studied is given
in Table LXIII. The moisture content was approximately the
same for each soil.
TABLE LXIII
THE CONCENTRATION OF THE SOIL SOLUTION IN PARTS PER MIL-
LION FROM A GOOD AND POOR SOIL EACH FALLOWED OR
CROPPED TO BARLEY.
FERTILE SOIL Poor Soin
DATE ; ;
FALLOW - CROPPED FALLOW CROPPED
emmys ke Suet 2000 1200 1100 600
Ail O22 seer 1700 500 800 200
Ts To 8 LAN ae 1800 700 1300 400
OCheeor is. d 5s 4300 1900 2900 900
Deer Sno fee 58 3400 1500 1800 1000
J22] 6c bp) ee eee 4200 1900 2700 1800
aes tos 2. 2 a's 6700 3800 6300 3700
Further investigations of Hoagland with Martin * indicate
that the effect of cropping on the soil solution persists for
a considerable period. A marked relationship was also noted
between the soil solution and the physical condition of the
soil, due to a change in the colloidal matter with season. An
increase in colloidal matter was noted when the soil solution
was depleted of its solutes by plant activities.
Hoagland, D. R., and Martin, J. C., Effect of Season and Crop
Growth on the Physical State of the Soil; Jour. Agr. Res., Vol. XX,
No. 5, pp. 397-404, 1920.
286 NATURE AND PROPERTIES OF SOILS
149. Other factors influencing the soil solution.—A num-
ber of other conditions, which are really phases of season,
influence both the concentration and the composition of the
soil solution. Among these are temperature, leaching, and
the moisture content of the soil. As the soil warms up in the
spring, reactions of all kinds are stimulated and an increase
in concentration generally results. If considerable rain-water
enters the soil, the soil solution is much diluted. It is also
changed in composition, due to the equilibrium adjustments
that of necessity occur. The following data from Bouyoucos *
show the influence of change in moisture on the concentra-
tion of the soil solution:
TABLE LXIV
CONCENTRATION OF THE SOLUTION OF CERTAIN SOILS AT VARIOUS
MOISTURE CONTENTS. LOWERING OF THE FREEZING
POINT METHOD.
Sorts MOISTURE ae MOgEE ce
To P. P. M. % P. P. M.
AMG s < Atlee 2.60 3,939 21.98 303
Sandy loam.... 8.30 13,639 21.53 606
POAT anges ev 11.18 13,780 20.97 848
Silt loam. .2e... 17.40 20,1538 34.76 1061
Clayatee tee 18.80 28,940 36.50 1030
If the soil is moistened beyond its water-holding capacity,
it is obvious that drainage losses will occur, which will deplete
the soil of valuable constituents. Increase of moisture, there-
fore, may modify the soil solution temporarily or permanently,
according to conditions.
Tillage and the addition of various materials also have a
1Bouyoucos, G. J., The Freezing Point Method as a New Means of
Measuring the Concentration of the Soil Solution Directly in the Soil;
Mich. Agr, Exp. Sta., Tech. Bul. 24, 1915,
THE SOIL SOLUTION 287
remarkable influence on the soil solution, especially increasing
its concentration during the warmer seasons. Plowing and
cultivation by stimulating biological activity may enhance ni-
trate production to a marked degree in a short time. Aération
will often increase the available mineral elements by the en-
couragement of reactions which favor solution. The addition
of salts of various kinds has been shown by Bouyoucos? to
influence the soil solution profoundiy. The compounds added
affected different soils in a diverse manner. When neutral
salts were added, the soil solution was increased from 35 to
100 per cent. of the added strength of the salts. In the case
of phosphate salts the increase was very much less.
150. The soil solution and productivity——As the crop
obtains its nutrients from the soil solution, there must be a
direct relationship between the fertility of the soil and the con-
centration and composition of the soil solution. The data
quoted from Hoagland indicate in a broad way that a fertile
soil is capable of maintaining a more concentrated soil solu-
tion than is a poorer one. The work of other investigators
amply corroborates this assumption.? One rather convincing
experiment may be quoted.
Hall, Brenchley, and Underwood * analyzed the water ex-
tract from certain plats on the Rothamsted Experiment Sta-
tion farm, the fertilizer treatment and the yields of which
had been recorded for a long term of years. Complete analyses
of the soil from the several plats were also made:
1 Bouyoucos, G. J., The Freezing Point Method as a Means of Studying
Velocity Reactions Between Soils and Chemical Agents and Behavior of
Equilibrium; Mich. Agr. Exp. Sta., Tech. Bul. 37, 1917.
Also, Rate and Extent of Solubility of Soils under Different Treat-
ments and Conditions; Mich. Agr. Exp. Sta., Tech. Bul. 44, 1919.
See also, Spurway, C. H., The Effect of Fertilizer Salt Treatments on
the Composition of Soil Extracts; Mich. Agr. Exp. Sta., Tech. Bul. 45,
1919.
*See citations page 284.
* Hall, A. D., Brenchley, W. E., and Underwood, T. M., The Soil
Solution and the Mineral Constituents of the Soil; Phil. Trans. Roy.
Soe., London, Series B, Vol. 204, pp. 179-200, 1913.
288 NATURE AND PROPERTIES OF SOILS
TABLE LXV
YIELDS TO THE ACRE OF CROPS, AND COMPOSITION OF SOIL AND
WATER EXTRACT OF SOIL. ROTHAMSTED EXPERIMENT
STATION FARM. ENGLAND.
COMPLETE ANALY-
WATER EXTRACT
YIELD TO sIS
TREATMENT THE ACRE
(POUNDS)| P.O, K,O P.O, K,O
% %o Pp. P.M. | P. P.M.
Untreated: >.4...c2 1276 .099 183 525 3.40
De ey ate «UN Os a ae 2985 102 257 808 | 30.33
IN == PO tngee aan 3972 3 248 3.900 3.88
N+ K,0:4- P,0,:)) 5087) © 182° | 826 4 025s
Farm manure... . 6184 176 167 4.463 | 26.45
151. Summary.—tThe solution as it exists in a normal
soil is highly dynamic. Its concentration and composition
are fundamentally governed by rate of solution, by absorp-
tion, and by the amounts of the various solutes in the solution
itself. Many factors are active in preventing a condition of
equilibrium between these three phases. Those of especial
importance are season and crop. Temperature, moisture con-
tent, and leaching are subfactors of season. Tillage of all
kinds and the addition of manures, lime, and fertilizers are
practical means of modifying the soil solution more to ade-
quately meet the needs of the crop. In fact, all of the com-
mon practices so successfully used in economic soil manage-
ment attain their end through a modification and control of
the soil solution.
CHAPTER XV
THE REMOVAL OF NUTRIENTS FROM THE SOIL BY
CROPPING AND LEACHING
THE soil solution, because of its dynamic character, offers
two sources of loss for nutrient materials, one of which should
be economically encouraged, while the other should be reduced
by suitable control to as low a point as is consistent with good
soil management. These two sources of exhaustion are (1)
cropping and (2) leaching or drainage. One is a legitimate
expenditure; the other is a waste, which within certain limits
in a humid region is unavoidable.*
152. Intake of water by plants—osmosis.—Plants ob-
tain their raw materials from the air and the soil, the former
furnishing the carbon and the oxygen, most of the water and
the nutrients proper coming from the soil. Although many
constituents, some necessary and some incidental, pass into
the plant from the soil, for convenience of discussion two
groups may be established: (1) water, and (2) nutrients prop-
er. It must be kept in mind, however, that water, while per-
forming certain mechanical functions, has a nutrient relation-
ship also.
The most important mechanical principle governing the ab-
sorption of water by the plant is osmosis.2, The abstract phe-
nomenon should be clearly in mind before its plant relation-
ships are considered. A bag of collodion (pig’s bladder or
parchment paper will do as well) is filled with a strong solu-
1Gases, such as carbon dioxide, nitrogen and possibly ammonia, may
be lost from the soil also.
? Water may also be taken up by colloidal absorption which is called
imbibition. This is common in seeds.
289
290 NATURE AND PROPERTIES OF SOILS
tion of cane-sugar. The walls of such a bag are semi-permea-
ble, that is, certain materials will pass through readily while
others will pass but slowly. For example, the sugar mole-
cules penetrate with difficulty, while the water finds the walls
of the bag but a slight obstacle.
If this collodion bag with its sugar solution is attached to a
capillary tube and immersed in pure water, it at once becomes
distended and the liquid will rise in the capillary tube, indi-
cating an unequal pressure within the system. The pressure
develops because of the separation of the pure water and the
sugar solution by a membrane that is penetrated at different
rates by the molecules and ions in contact with it. A tendency
towards equalization of course occurs and, as the water moves
in faster than the sugar moves out, a pressure is developed
within the bag which becomes apparent by the rise of the
liquid in the capillary tube. Such a phenomenon is called
osmosis and the pressure osmotic pressure. Such force prob-
ably has much to do with the movement of plant saps and
fluids. Under such conditions as those maintained in the ex-
periment, the water tends to move from the dilute solution to
the more concentrated one.
Suppose the collodion bag be considered as typical of the
cells, which form the feeding surface of an active rootlet, and
the sugar solution the relatively concentrated and partially
colloidal cell contents. The water outside the bag will, of
course, represent the dilute soil solution which bathes the roots.
With such substitutions it can readily be seen why the plant
exerts an osmotic ‘‘pull’’ and how the water moves through
the cell-wall. Such a transfer will continue until the move-
ment of the water in the soil becomes too slow for normal
plant activities. Wilting then occurs. (See Fig. 51.)
In alkali soils, where the soil solution becomes very concen-
trated, the process above described may be reversed. Out-
ward osmosis then occurs and plasmolysist may result.
+Plasmolysis is a separation of the plasma from the cell-wall due to a
REMOVAL OF NUTRIENTS FROM THE SOIL 291
Bouyoucos ' has suggested that the phenomena of wilting may
be due, at least partially, to plasmolysis since he has shown
by observing the depression of the freezing point that the soil
solution becomes very concentrated at low moisture contents.
Such a conception of water absorption is simple, yet it often
leads to erroneous ideas regarding the intake of nutrients by
plants. The amount of any particular nutrient absorbed by
the plant is not determined by the quantity of water taken up,
since water and nutrients enter more or less independently.
The large amount of water imbibed by the plant, later to be
lost by transpiration, cannot be accounted for on the basis of
a very dilute soil solution and the necessity of rapid trans-
piration in order to facilitate the entrance of sufficient nutrient
substance.
153. Absorption of nutrients by plants—diffusion—The
solution in a normal fertile soil is not only rather dilute
in toto but a great proportion of the nutrients therein are in
the ionic condition. While both molecules and ions are pre-
sented to the absorbing surfaces of the plant, it is only the
latter that penetrate to any great extent, although some mate-
rials, especially those of an organic nature, do enter in a
molecular condition. The presence of water is, of course, nec-
essary for both ionic and molecular penetration, but only as a
medium for diffusion. Its movement into the plant is, there-
fore, of no very great moment in the actual diffusion process,
as the phenomenon is called, although the approach of the
nutrients to the feeding surfaces is considerably influenced by
capillary activity.
The tendency of diffusion is to equalize the concentration
of a solution as to the ions and molecules of its solute, the
molecules and ions of different salts moving more or less inde-
loss of water. It is a shrinkage of the protoplasm and when carried
beyond a certain point permanently injures the cell.
1Bouyoucos, G. J., The Freezing Point Method as a New Means of
Measuring the Concentration of the Soil Solution Directly in the Soil;
Mich. Agr. Exp. Sta., Tech. Bul. 24, 1915.
292 NATURE AND PROPERTIES OF SOILS
pendently. The absorption of nutrients by plants, in its
simplest analysis, is but a working out of this phenomenon.
Thus, if the concentrations of K* ions is high in the soil
solution and low within the cell, the potassium will move
inward in response to diffusion forces, providing, of course,
the ions can pass through the cell wall. This penetration is
entirely independent of the entrance of water, as far as the
ent a SS
ne eT oe
SD et een y
Sh... ES anes
soil particles clinging to root-hairs.
Above, root-hairs much enlarged.
Root-hairs are simple tube-like pro-
longations of the border cells.
movement of the latter is concerned. Moreover, the equaliza-
tion of one ion is more or less unrelated to the concentration
equilibrium of any other. The osmosis of the water, on the
other hand, is a phenomenon dependent on sum-total concen-
tration plus the semi-permeable membrane.
154. Differential diffusion——The intake of nutrients is
by no means as simple as the above explanation might lead one
to assume, due to the complications interposed by the presence
of a semi-permeable membrane. The passage of ions and mole-
cules through the cell-wall and the protoplasmic membrane
ad
REMOVAL OF NUTRIENTS FROM THE SOIL 293
may be a simple mechanical infiltration, although it is prob-
ably accompanied by a chemical reaction, or by a change in
the colloidal state of the membrane or both. Moreover, differ-
ent ions and molecules do not pass through the same cell-wall '
with equal facility. Thus, one kind of ions may pass through
very readily while another kind may encounter extreme diffi-
culty in responding to diffusion tendencies.
Differential diffusion may be ascribed to two conditions:
(1) different relationships between the cell-wall and the ions
and molecules of the entering material; and (2) differences
in the rate at which the entering molecules and ions are
utilized in the metabolic activities of the cell in particular and
the plant as a whole. The first case has been partially ex-
plained. If a compound ionizes into A and B ions and if A
ions, due to their relationship to the colloidal cell-wall, enter
more easily, a residue of B ions will be left in the soil solution.
The second case may be illustrated by assuming the pres-
ence of potassium chloride in the soil solution. It ionizes
K* and Cl- ions. Now conceive that these ions diffuse through
the cell-wall with equal facility in response to equilibrium
tendencies. If the potassium ions are used by the cell as
rapidly as they enter and are removed from solution, more
potassium will be absorbed. This might continue until the
potassium ions in the soil solution become much reduced in
number. If the chlorine, on the other hand, is but slightly
utilized by the plant, little will be drawn from the soil after
the initial equalization. Thus, a residue of chlorine might be
left from this type of differential absorption. This applica-
tion of diffusion principles shows the possibility, or even more,
the probability of plants leaving residues in the soil solution.
What the residues from different fertilizers may be and what
is the practical importance of such differential actions are
pertinent questions.
*The term cell-wall as used here refers to the cell-wall proper plus
the protoplasmic membrane.
294 NATURE AND PROPERTIES OF SOILS
155. Fertilizer residues may be developed in two gen-
eral ways: (1) by selective absorption by the soil; and (2) by
differential diffusion into the plant. Regarding the first case
(see par. 141), it has already been established that soils
ordinarily absorb the basic ions more strongly than the acid
radicals, thus tending to leave an acid residue in the soil solu-
tion. Sodium nitrate, ammonium sulfate, calcium nitrate,
potassium chloride and potassium sulfate, therefore, tend to
produce an acid residue, when they are first added to a soil.
The final result, however, cannot be determined until the
action of the crop is known. If the crop especially utilizes
the cation or basic radical, it will intensify the selective ab-
sorption of the soil and a still more pronounced acid residue
will result. This would be the case with ammonium sulfate,
potassium sulfate, and potassium chloride. If, however, the
anion or acid radical is utilized to the greater extent, the ac-
tion of the soil absorption would be nullified and an alkaline
residue would tend to develop. This is especially true with
sodium nitrate when applied in large amounts over a term of
years, the physical condition of the soil becoming impaired
due to the presence of sodium carbonate."
One other condition is possible. If the plants should use
the cation and anion of a fertilizer salt in equal proportions,
no residue would result. This seems to happen to an approxi-
mate degree with ammonium nitrate, potassium phosphate,
potassium nitrate, and ammonium phosphate. Such salts are
extremely valuable in long-continued experiments, where the
disturbing effects of fertilizer residues are to be avoided.
Monoecalecium phosphate, the important constituent of acid
phosphate, needs especial consideration. When added to the
soil, it immediately reverts to the tricalcium form if active
calcium is present.2, Even with the large amount of gypsum
1Hall, A. D., The Effect of the Long Continued Use of Sodium Nitrate
on the Constitution of the Soil; Trans. Chem. Soc. (London), Vol. 85,
pp. 950-971, 1904.
* CaH,(PO,). + 2CaH,(CO,),—=Ca,(PO,). + 4H,0 + 4CO,
REMOVAL OF NUTRIENTS FROM THE SOIL 295
carried by acid phosphate, the effect does not seem to be
towards acidity even after long periods of application.
This discussion, brief as it is, brings out a little studied
phase of crop and fertilizer interaction. How the plant util-
izes a particular fertilizer after it is once in the soil, what
residues are left, and the importance of such residues, are
questions of fundamental concern. The possibility of plants
influencing the soil and the fertilizers added, as well as the
soil and fertilizer influencing the crop, is well worth attention.
156. Do plants directly aid in the preparation of their
nutrients?—The conception commonly held regarding the
plant is that its direct relation to the soil is more or less
passive. Indirectly, of course, it may exert a considerable
influence on the availability of the nutrients. In view of the
knowledge regarding fertilizer residues and the new concepts
as to possible root exudates, the idea that the plant may
directly aid in the preparation of its own nutrients is becom-
ing more and more plausible.
Such influences, if recognized, might occur in three ways:
(1) through the action of carbon dioxide, known to be given
off in large amounts by roots; (2) through the influence of
organic and inorganic acids other than carbonic acid; and
(3) by catalytic agents, enzymic or non-enzymic.
In a rich, moist soil the number of root-hairs is very large
and the relationship between the rootlets and the soil particles
very intimate. When in contact with a particle of soil or
colloidal complex, the root-hair in many cases almost incloses
it, and by means of its mucilaginous wall forms a contact so
close as to make the solution held between the particle and the
cell-wall distinct from that in the soil proper. Carbon dioxide,
excreted under such conditions, may assume a solvent power
entirely unique and independent of the amount produced.
1Conner, S. D., Acid Soils and the Effect of Acid Phosphate and
Other Fertilizers Upon Them; Jour. Ind. and Eng. Chem., Vol. 8, No. 1,
pp. 35-40, Jan. 1916.
296 NATURE AND PROPERTIES OF SOILS
The plant might thus facilitate special conditions and aid ma-
terially in the preparation of its own nutrients.
Sachs,' and later other investigators, grew plants of various
kinds in soil and other media in which was placed a slab of
polished’ marble or dolomite or calcium phosphate, covered
with a layer of washed sand. After the plants had made
sufficient growth the slabs were removed, and on the surfaces
were found corroded tracings, corresponding to the lines of
contact between the rootlets and the minerals.
Czapek * repeated the experiments of Sachs, using plates
of gypsum mixed with the ground mineral that he wished
to test, and this mixture he spread over a glass plate. Cza-
pek found that, while plates of calcium carbonate and of
calcium phosphate were corroded by the roots, plates of alu-
minum phosphate were not. He concludes that if the tracings
are due to acids excreted by the roots, these acids must
be those that have no solvent action on aluminum phos-
phate. This would limit the excreted acids to carbonic,
acetic, proprionic, and butyric. By means of micro-chem-
ical analyses of the exudations of root-hairs grown in a
water-saturated atmosphere, Czapek found potassium, mag-
nesium, calcium, phosphorus, and chlorine in the exudate. He
concludes that the solvent action of roots is due to acid salts
of mineral acids, particularly acid potassium phosphate. He
has not proved, however, that the exudations were not from
dead root-hairs or from the dead cells of the root cap. In
either case they would have some solvent action, but whether
sufficient to make them of importance is doubtful. This ob-
jection makes the possible exudation of organic and inorganic
acids somewhat questionable.
Molisch * found that root-hairs secrete a substance having
‘Sachs, J., Aujlésung des Marmors durch Mais-Wurzlen; Bot. Zeitung,
18 Jahrgang, Seite 117-119, 1860.
2Ozapek, J., Zur Lehre von den Wurzelausscheidung ; Jahrb. f. Wiss.
Bot., Band 29, Seite 321-390, 1896.
*Molisch, H., Uber Wurzelausscheidungen und deren Einwirkung auf
REMOVAL OF NUTRIENTS FROM THE SOIL 297
properties corresponding to those of an oxidizing enzyme.
His work has been repeated by others, who have failed to ob-
tain similar results, but lately Schreiner and Reed! have
demonstrated an oxidizing action of roots that is apparently
due to a peroxidase. Oxidation alone, however, would hardly
suffice to account for the solvent action accompanying the de-
velopment of roots, although it is doubtless an important
function and useful in other ways.
Schreiner and Sullivan? have demonstrated the presence
of reducing substances in media in which plants were grow-
ing. This work has recently been corroborated by Lyon and
Wilson,? working with maize, oats, peas, and vetch. They
found that the solutions in which the plants had been growing
exhibited both reducing and oxidizing phenomena. Reducing
substances were always present, but whether oxidizing mate-
rials were so consistently produced could not be definitely
decided. The peroxidases were rendered inactive by boiling
the solutions. The reducing substances did not always disap-
pear with such treatment. This would throw some doubt upon
the enzymic character of the reducing materials and suggest
that non-enzymic catalytic exudates are a possibility.
The interstices between the larger particles of a normal
soil are at least partially filled with colloidal material of a
more or less gel-like nature. Moreover, the surfaces of some
soil grains may be somewhat coated with the same material.
Roots of growing plants have been found to cause coagula-
tion of at least some colloids, possibly by leaving an acid
residue in the nutrient solution by reason of the selective
Organische Substanzen; Sitzungsber. Akad. Wiss. Wien-Math. Nat., Band
96, Seite 84-109, 1888. Abstract in Chem. Centrlb. f. Agr. Chem., Band
17, Seite 428, 1888.
*Schreiner, Oswald, and Reed, H. S., Studies on the Oxidizing Powers
of Roots; Bot. Gazette, Vol. 47, p. 355, 1909.
* Schreiner, O., and Sullivan, M. K., Studies in Soil Oxidation; U. 8S.
Dept. Agr., Bur. Soils, Bul. 73, 1910.
*Lyon, T. L., and Wilson, J. K., Liberation of Organic Matter by
Roots of Growing Plants; Cornell Agr. Exp. Sta., Memoir 40, July, 1921.
298 NATURE AND PROPERTIES OF SOILS
absorption of bases and rejection of the acid radicals of the
dissolved salts. It is conceivable that the root-hairs, by re-
moving bases from the solution existing between the cell-wall
and the colloidal covering of the soil particle, may cause
coagulation of the colloidal matter and thus lberate the nu-
trient materials held by absorption. The liberated material,
being of a readily soluble nature, would be taken up by the
solution between the rootlet and the soil particle, from which
the root-hair could readily absorb it. Such an hypothesis
would account for the ability of plants to obtain a quantity
of nutrients far in excess of that accounted for by the solvent
action of pure water, and even beyond what many investi-
gators are willing to attribute to the solvent action of water
charged with carbon dioxide.
157. The present status of the question.—The available
evidence on excretion of acids other than carbonic by the
roots of plants does not admit of any very satisfactory conclu-
sion as to their relative importance in the acquisition of plant
nutrients. There can be no doubt, however, that carbon
dioxide resulting from root exudation and from decomposi-
tion of organic matter in the soil plays a very prominent part
in this operation. The very large quantity of carbon dioxide
in the soil, amounting in some eases to nearly 10 per cent. of
the soil air, or several hundred times that of the atmospheric
air, must aid greatly in dissolving the soil particles.
Whatever may be the concentration of the soil-water, it
seems probable that the liquid that is found where the root-
hair comes in contact with the soil particle, and that is sepa-
rated, in part at least, from the remainder of the soil-water,
must have a composition different from that found elsewhere
in the soil. Many plants grown in solutions of nutritive salts
have few or no root-hairs, but absorb through the epidermal
tissue of the roots. The special modification by which the
root-hairs come in intimate contact with the soil particle and
almost surround it, indeates a direct relation between the
REMOVAL OF NUTRIENTS FROM THE SOIL 299
soil particles and the plant, as well as between the soil-water
and the plant. Such a condition complicates in no small
degree the practical questions of soil management and plant
nutrition.
158. Why crops vary in their ability to thrive on dif-
ferent soils —It is very commonly recognized that crops of
different kinds vary in their ability to obtain nourishment
from the soil. The difference between the nitrogen, phosphoric
acid, potash, and lime taken up by an average corn crop and
a wheat crop of average size is striking. The terms ‘‘weak
feeders’’ and ‘‘strong feeders,’’ so often heard, indicate the
practical field relationships. Aside from the fact that crops
do not all need the same quantities of nutrients these differ-
ences in ability to grow normally on different soils may be
due either to (1) a larger absorbing system or (2) a more
active absorptive capacity.
Plants with large root systems may be expected to absorb
greater amounts, not only of water but of nutrients also.’
Such a development is especially important in time of drought
and in addition gives the plant a greater area from which to
draw nutrients. Water, as well as nutrients, does not move
through any great distance towards the imbibing and ab-
sorbing surfaces. Root development, while of some impor-
tance in explaining the differences in the feeding capacities
of plants, is probably by no means as important as differences
in the absorption activity.
The absorptive activity of a plant under any given condi-
tion of soil, climate, and stage of growth depends on: (1) the
concentration and composition of the cell-sap; (2) the char-
acter of the cell-wall; (3) the activity of the cell in elabo-
rating and removing from solution the materials absorbed;
(4) the extent to which exudates—whether these be carbon
*Gile, P. L., and Carrero, P. L., Absorption of Nutrients as Affected
by the Number of Roots Supplied with the Nutrient; Jour. Agr. Res.,
Vol. IX, No. 3, pp. 73-95, 1917.
300 NATURE AND PROPERTIES OF SOILS
dioxide, organic or mineral acids and their salts or enzymes
—act on the colloidal and non-colloidal soil constituents; and
(5) synergistic relationships in the soil solution or the cell-
wall.
The concentration and composition of the cell-sap deter-
mines not only the osmotic relationship but has much to do
with diffusion tendencies. The ability of the plant to obtain
water and nutrients is thus directly affected by such condi-
tions. The character of the cell-wall has of course an im-
portant influence on such phenomena. If the cell-wall is
easily penetrated, it may greatly facilitate the absorbing ¢a-
pacity of the plant. If it is slowly penetrated or exerts spe-
cial differential influences, it might have a great deal to do
with the differences observed between certain plants. The
character of the cell-wall has already been shown to be in-
volved in the development of certain residues in the soil.
The rate at which materials are utilized within the plant
is also a factor. If ions or molecules are used rapidly and
thus removed from solution, the diffusion of similar ions and
molecules is hastened. Such activity would also influence
osmotic relationships to a marked extent. This has already
been discussed under differential diffusion.
It is readily conceivable that exudates, insofar as they are
capable of directly affecting the solubility of nutrients, might
produce marked differences between plants as far as their
absorbing activities are concerned. <A crop producing active
exudates of any kind should be able, other conditions being
equal, to grow to better advantage, especially on a soil in
which the necessary nutrients are somewhat unavailable.
The absorption of electrolytes by plants seems to be influ-
enced by the presence of other nutrient ions. True? has
shown that K+ ions when accompanied by Ca** ions are readily
absorbed by the seedlings of certain plants. When the same
1True, R. H., The Function of Calcium in the Nutrition of Seedlings;
Jour. Amer. Soe. Agron., Vol. 13, No. 3, pp. 91-107, 1921.
REMOVAL OF NUTRIENTS FROM THE SOIL 801
concentration of potassium is offered in single solution, this
nutrient is more or less neglected by the seedlings. This rela-
tionship, by which the calcium ions make the potassium physi-
ologically available, is spoken of by True as synergism and
probably has a great deal to do with the penetration of nu-
trient ions into the plant. It is no doubt of considerable im-
portance in acid soils where the active calcium is low.
159. The absorptive capacity of different crops.—
Cereals have the power of utilizing the potassium and phos-
phorus of the soil to a considerable degree, but they generally
require fertilization with nitrogen salts. Most of the cereals,
such as wheat, rye, oats, and barley, take up the principal
part of their nitrogen early in the season, before the nitrifica-
tion processes are sufficiently operative to furnish a large
supply of nitrogen; hence nitrogen is the fertilizer constituent
that usually gives good results, and should be added in a
soluble form. Wheat, in particular, needs a large amount of
available nitrogen early in its spring growth. Since it is a
““delicate feeder,’’ it does best after a cultivated crop or a
fallow, by which the nitrogen has been converted into a soluble
form. Oats ean make better use of the soil nutrients and do
not require so much manuring. Maize is a very ‘‘coarse
feeder,’’ and, while it removes a large quantity of plant nu-
trients from the soil, it does not require that this shall be
added in a soluble form. Farm and other slowly acting ma-
nures may well be applied for the maize crop. The long
growing period required by maize gives it opportunity to
utilize the nitrogen as it becomes available during the summer,
when ammonification and nitrification are active. Phosphorus
is the substance usually most needed by maize.
Grasses, when in meadow or in pasture, are greatly bene-
fited by manures. They are less vigorous ‘‘feeders’’ than the
cereals, have shorter roots, and, when allowed to grow for
more than one year, the lack of aération in the soil causes the
+The term is used here in the sense of cooperation.
302 NATURE AND PROPERTIES OF SOILS
ond
decomposition of soil organic matter to decrease. There is
usually a more active fixation of nitrogen in grass lands than
in cultivated lands, but this nitrogen becomes available very
slowly.
Different soils and climatie conditions necessitate varied
methods of manuring for grass. Farm manures may well be
applied to meadows in all situations, while the use of available
nitrogen in commercial fertilizers is generally profitable.
Most of the leguminous crops are deep-rooted and are vigo-
rous ‘‘feeders.’’ Their ability to take nitrogen from the air
makes the use of that fertilizer constituent unnecessary ex-
cept in a few instances, such as young alfalfa on poor soil,
where a small application of nitrate of soda is usually bene-
ficial. Phosphoric acid and often lime are the substances most
beneficial to legumes on most soils.
Many crops will utilize very large quantities of nutrients
if they are in a form in which they ean be used. Phosphates
and nitrogen are the substances generally required, the latter
especially by beets and carrots. In growing vegetables the
object is to produce a rapid growth of leaves and stalks rather
than seeds, and often this growth is made very early in the
season. As a consequence a soluble form of nitrogen is very
desirable. Farm manure should also have a prominent part
in the treatment, as it keeps the soil in a mechanical condition
favorable to the retention of moisture, which vegetables re-
quire in large amounts, and it also supplies needed fertility.
The very intensive method of culture employed in the produc-
tion of vegetables necessitates the use of much greater quan-
tities of manures than are used for field crops, and the e ereat
value of the product justifies the practice.
160. Quantities of nutrients removed by crops.—The
utilization of nutrient substances by crops is a constant source
of loss of fertility to agricultural soils. In a state of nature
the loss in this way is comparatively small, as the native vege-
tation falls on the ground, and in the process of decomposi-
REMOVAL OF NUTRIENTS FROM THE SOIL 303
tion the ash is almost entirely returned, while there is a large
gain of organic matter and often an increase in nitrogen as
well. Under natural conditions the soil usually increases in
fertility ; for, while there is some loss through drainage and
other sources, this is more than counterbalanced by the action
of the natural agencies of disintegration and decomposition,
while the fixation of atmospheric nitrogen affords a constant,
though small, supply of that important soil ingredient.
When land is placed under cultivation a very different
condition is presented. Crops are removed and only par-
tially returned at best to the soil as manure and crop resi-
due. A certain proportion of the soil nutrients are, therefore,
permanently withdrawn. The point of vital importance,
however, is that only a part of the total supply of soil con-
stituents will ever become available, the portion withdrawn
each year by cropping being a more serious consideration
than is generally supposed.
The following table, computed by Warington,' shows the
quantities of nitrogen, potash, phosphorie acid, lime and sulfur
trioxide * removed from an acre of soil by some of the common
erops. The entire harvested crop is included.
TaBLE LXVI
A N | K,0 | CaO | P.O, | SO,
CRor YIELD fast) (LBS.) | (LBS.) (ED (LBS. )| (LBS. )
Wheat. si. 30 bushels | 1727) 48 | 28.8) 9.2 | 21.1 | 15.7
Barley. -)-. =: 40 bushels | 157 | 48 | 35.7| 9.2 | 20.7 | 14.3
Oats oe! 45 bushels | 191 55 | 46.1 | 11.6 | 19.4 | 19.7
Mazes... 2 25) 30 bushels | 121 | 43 | 36.3 18.0 | 12.0
Meadow Hay| 1% tons | 203] 49 |50.9 | 32.1 | 12.3 |113
Red Clover.| 2 tons | 258 | 102 | 83.4 | 90.1 | 24.9 | 15.4
Potatoes....| 6 . tons TAT 4 Gea eae | Di 5
*Warington, R., Chemistry of the Farm; pp. 64-65, London, 1894.
?From Hart, E. B., and Peterson, W. H., Sulphur Requirements of
Farm Crops in Relation to the Soil and Air Supply; Wis. Agr. Exp. Sta.,
Res. Bul. 14, 1911.
304 NATURE AND PROPERTIES OF SOILS
Before the question of possible soil exhaustion can be dis-
cussed adequately, the losses of nutrients in the drainage
water must be considered as another source of loss in addition
to the cropping influences already noticed.
161. Qualitative composition of drainage water.—In
theory, at least, the qualitative composition of drainage water
should be the same as that of the soil solution; that is, in it
should be found all of the common bases and acid radicals.
Actually, however, due to the absorptive power of the soil,
certain constituents appear in very slight amounts. Phos-
phorus, for example, often occurs in drainage only in traces,
as do the nitrites, ammonia, and carbonates. The principal
bases lost by leaching are calcium, magnesium, potassium,
and sodium. The important acid radicals of drainage water
are the nitrates, chlorides, sulfates, and bicarbonates.
As might be expected, the constituents appearing in drain-
age are extremely variable not only when different soils are
compared but also within the same soil at different periods.
Phosphorus may be leached from some soils in measureable
quantities, while from others the amount may be negligible.
Nitrate nitrogen is usually an important constituent in all
drainage water during the summer, especially that from a bare
soil. In the winter and early spring nitrates decrease in
amount. The method of soil treatment as to cultivation, ma-
nuring, liming, or fertilizing may also markedly influence the
qualitative composition of the water draining from field soil.
162. Quantitative composition of drainage water.— While
but little reliable data regarding the composition and
especially the concentration of the soil solution are available
at the present time, much exact information has been obtained
regarding drainage water. The concentration of drainage
water is much lower than that of the soil solution and much
less variable. The total concentration seems to be governed
more by the amount of water leaching through than by any
other factor. Other seasonal conditions of course come into
REMOVAL OF NUTRIENTS FROM THE SOIL 305
play. In total concentration, drainage water seldom exceeds
500 parts per million. It is thus much more dilute than the
average soil solution. This difference holds for the separate
constituents as well as for the concentration in toto.
The following data, as compiled by Hall,’ give some idea
of the quantitative composition of the drainage water from
the clay loam soil of the Rothamsted Experimental Farm.
The drainage water was obtained from tile drains, a line of
which extended under each of the variously treated plats.
The data is a mean of five collections, 1866 to 1868.
TABLE LXVII
Parts PER MILLION BASED ON SOLUTION
TREATMENT Se
NOs NH3 P2205 K,0 CaO MgO Na,O Fe.O3 Cl SOz SiO,
No manure...... 3.9 UPA 1 383 mse |) sal | styl 6.0 Bat | LOw?, 24.7) 10.9
Farm manure, 14
WHS a5 a50en00 UGS |) 16 = Bik (aTae | 429) | 18e7 |) 2:6) 20:7) | 10621) 35.7
Minerals? only..| 5.1 STS meg: 5.4 |124.3] 6.4 | 11.7 4.4 |11.1 66.3] 15.4
Minerals plus 600
Ibs. (NH,4)oSO4] 16.9 | .27 | .17 OT 197-8) 8:9 | 10:6 ||) 20 39:4. || 89.7209
Minerals plus 550
lbs. NaNOs...)18.4 | .24 | — 4.1 |118.1| 5.9 | 56.1 5.1 |12.0 | 41.0] 10.6
It is immediately noticeable that ammoniacal nitrogen and
phosphoric acid are lost in drainage to but a slight degree.
Calcium appears in the highest concentration with sulfur
next. Nitrates and potash are present in appreciable quan-
tities but are quite variable.
The influence of treatment is particularly obvious on the
parts per million of nitrate nitrogen, lime, and sulfur appear-
ing in the drainage, the addition of farm manure increasing
all of these constituents as well as the concentration of the
potash, soda, and chlorine. The application of sodium nitrate
increased the nitrate nitrogen as well as the soda, potash, and
1 Hall, A. D., The Book of the Rothamsted Experiments; pp. 237-239,
New York, 1917.
* By minerals are meant the phosphoric acid, potash, lime, and other
constituents left as ash when plants are burned.
306 NATURE AND PROPERTIES OF SOILS
lime. The two latter constituents are probably liberated by
basic exchange. The addition of any fertilizer seems espe-
cially to increase the lime in the drainage water. This is prob-
ably due to the development of acid fertilizer residues. In
general, it seems that the more productive the soil and the
heavier the fertilization, the higher the concentration of the
constituents in the drainage water.
It is not always the case, however, that a manured soil
loses more nutrient material than an unfertilized one. Ger-
lach! reports experiments with soil tanks at the Bromberg
Institute of Agriculture, in which five soils rationally fertil-
ized yielded larger crops and lost in the main less nitrogen
and lime in the drainage water than the same soils unmanured.
The loss of potash was slightly greater from the manured than
from the unmanured soils. Apparently the stimulation that
the plants received from the fertilizer enabled them to make
such a good growth that they absorbed more soluble nitrogen
and lime in excess of the unfertilized plants than was added
in the fertilizer, and nearly as much potash.
The most serious losses of plant nutrients in drainage are
those of the nitrogen and calcium, both of which losses are to
a certain extent unavoidable. These losses are also very
closely related, rising and falling together. Nitrogen is lost
as the nitrate while the calcium is leached out due to the
presence of the bicarbonate and nitrate radicals. While loss
of lime goes on continually, it is of necessity particularly
large during periods of rapid nitrate accumulation. Nitrogen
is a high-priced fertilizer constituent, while a continued loss
of lime tends to produce soil acidity. About the only means
of conserving either of these constituents is to maintain a crop
on the soil, especially during the warmer seasons.
1Gerlach, M., Uber die durch Sickerwasser dem Boden Entzogenen
Menge Wasser und Nahrstoffe; Ulus. Landw. Zeitung, 30 Jahrgang,
Heft 95, Seite 871-881, 1910. Also, Untersuchungen iiber die Menge und
Zusammensetzung der Sickerwasser; Mitt. K. W. Inst. f. Landw. in
Bromberg, Band 3, Seite 351-381, 1910.
REMOVAL OF NUTRIENTS FROM THE SOIL 307
163. Quantities of nutrients removed by drainage and
cropping.—Now that an adequate conception has-been pre-
sented regarding the composition of soil drainage water and
also of the nutrients removed by cropping, it is interesting to
note what the combined result may be on the same soil. Such
information can be obtained only in a few instances. The
following data from the lysimeters at the Cornell Experiment
Station! are valuable in this respect.2 The soil used was a
Dunkirk silty clay loam.
TABLE LX VIII
AVERAGE ANNUAL LOSS OF NUTRIENTS BY PERCOLATION AND
CROPPING. CORNELL LYSIMETER TANKS.
AVERAGE OF 10 YEARS.
POUNDS TO THE ACRE PER YEAR
CONDITION
N P.O; K,0 CaO So,
Drainage losses
Ave iafos: 69.0 — 86.4 557.0 132.0
Rotation... .. 7.3 — 68.7 345.9 108.5
Grassi. Dee — 74.0 363.8 111.0
Crop removal
iBarey t.t.28 — — — — —
Rotathioms...|' 10:5 43.5 105.4 24.3 41.0
VAS). keke 54 28.6 74.0 12.8 29.2
Total loss
Barents 6 69.0 — 86.4 557.0 132.0
Rotation....| 77.8 43.5 174.1 370.2 149.5
Grass... ses 56.9 28.6 158.0 376.6 140.2
1 Unpublished data, Cornell Agr. Exp. Sta., Ithaca, N. Y.
7A study was made at the New Jersey Experiment Station of the
nitrogen losses from a loam soil in cylinders under a five-year rotation
of corn, oats, wheat and timothy for 20 years, treated in various ways
as to lime, manure and fertilizers. The average loss of nitrogen from
the surface ten inches of soil for 15 years was 103 pounds annually
due to cropping and leaching. Data were obtained by analyzing the
soil and the crops. Lipman, J. G., and Blair, A. W., Nitrogen Under
Intense Cropping ; Soil Sci., Vol. XII, No. 1, pp. 1-16, July, 1921.
308 NATURE AND PROPERTIES OF SOILS
The first outstanding feature of the above table is the con-
trol on drainage losses exerted by cropping. The loss of
nitrate nitrogen is reduced to an exceptionally low figure,
while the saving of potash, sulfur, and lime is quite apprecia-
ble. No phosphoric acid is lost even from the bare soil. The
losses due to cropping and leaching combined from a planted
soil are generally but little greater than the drainage losses
alone from a soil kept continuously bare except in the cases
of the phosphoric acid and the potash.
The next point of interest is the difference in the nutrients
removed by a rotation of crops, such as maize, oats, wheat,
and hay as compared with permanent meadow. The latter,
although absorbing less nutrients than the rotation crops,
exert as marked a conserving effect on the nutrients appear-
ing in the drainage as do the crops in rotation. The compara-
tive removal of nutrients from the soil by cropping and leach-
ing are well shown by the following diagram, in which the
weight of the symbols indicates where the loss of any par-
ticular nutrient is the greater.
RELATIVE LOSSES OF NUTRIENTS FROM A PLANTED SOIL THROUGH
CROPPING AND DRAINAGE
PHOS-
SULFUR
NITROGEN| PHORIC PotasH | Lime area
ACID
Cropping loss..... N P.O. K,O CaO SO;
Drainage loss.... N P30: K;0 CaO so,
164. Possible exhaustion of the soil.—It is interesting at
this point to compare the amounts of nutrients removed an-
nually from a soil cropped in rotation with the amounts which
are present in an average soil to the depth of four feet. As-
suming reasonable figures for the pounds of sulfur trioxide,
lime, phosphoric acid, nitrogen, and potash and considering
that these nutrients are wholly available, the following sig-
REMOVAL OF NUTRIENTS FROM THE SOIL 309
nificant data are obtained. The losses of nutrients by drain-
age and rotation cropping are from the figures already quoted
regarding the Cornell lysimeter soils.
TABLE LXIX
SHOWING THE NUMBER OF YEARS A SOIL TO THE DEPTH OF FOUR
FEET WOULD SUPPLY NUTRIENTS FOR CROP GROWTH,
PROVIDING THAT ALL OF THESE CONSTITUENTS
WERE UNIFORMLY AVAILABLE
POUNDS
POUNDS TO REMOVED
CONSTITUENTS THE DEPTH OF |ANNUALLY BY YEARS
Four FEET CROPPING AND
DRAINAGE
SO ee urs, 12,000 84.51 142
OG SRO te st ie a 85,000 370.2 229
LEO 2a a 16,000 43.5 367
INN cl Ral nae 15,000 46.81 303
LEO) 2 MA oe SU 250,000 174.1 1,485
While the subsoil supplies large amounts of plant nutrients,
it must be remembered that only a small proportion of the
soil constituents, especially the. phosphoric acid and potash,
ever become available either in surface or subsoil. Moreover,
crop yields decrease as the nutrients, even those most readily
available, are reduced. The above figures for duration of
crop growth are, as a consequence, merely conventional but
they indicate the probability of even a very fertile soil be-
coming quickly exhausted.
Moreover, when it is considered that the soil must be de-
pended on to furnish food for humanity and domestic animals
as long as they shall continue to inhabit the earth, the supply
of plant nutrients becomes a matter of grave concern.
The visible sources of supply, to replace or supplement
* Sixty-five pounds of SO, are added an acre each year in rain-
water while 31 pounds of N are added yearly to the acre in rain and
through the free-fixing activity of organisms (pars, 222, 236 and 238).
310 NATURE AND PROPERTIES OF SOILS
those in the soils now cultivated, are, for the mineral sub-
stances, the subsoil and the natural deposits of phosphates,
potash salts, and limestone; and for nitrogen, deposits of
nitrate, the by-products of coal distillation, and the nitrogen
of the atmosphere. The last of these is inexhaustible, and the
exhaustion of the nitrogen supply, which a few years ago was
thought to be a matter of less than half a century, has now
ceased to cause any apprehension.
The conservation or extension of the supply of mineral
nutrients is now of extreme importance. The utilization of
city refuse and the discovery of new mineral deposits are
developments well within the range of possibility, but neither
of these promises to afford more than partial relief. The
utilization of the subsoil through the gradual removal by nat-
ural agencies of the topsoil will, without doubt, tend constantly
to renew the supply. The removal of topsoil by wind and
water erosion is, even on level land, a very considerable factor.
The large amount of sediment carried in streams immediately
after a rain, especially in summer, gives some idea of the ex-
tent of this shifting. This affects chiefly the surface soil, and
thereby brings the subsoil into the range of root action.
There is little doubt that a moderate supply of plant nu-
trients will always be available in most soils, but for progres-
sive agriculture the use of green-manures, legumes and farm
manures must be supplemented by judicious and economical
application of lime and certain fertilizer constituents.
CHAPTER XVI
CHEMICAL ANALYSIS OF SOILS
No PHASE of soil science has received as much popular rec-
ognition as chemical analysis, nor is any other technical soil
procedure so little understood in general and at the same
time so greatly overrated. Many persons feel that a soil
analysis should completely solve the many problems, both
theoretical and practical, regarding the economic management
of the soil, especially as to its fertilizer needs. In the hght
of such general misunderstanding in regard to the research
and applied value of chemistry to soils, a consideration of the
question seems opportune at this point, especially as the dis-
eussion of the phenomena of absorption and the characteristics
of the soil solution have just been presented.
For convenience in treatment, chemical analyses, as applied
to soils, may be grouped under two heads—total or bulk
analyses and partial or extraction methods. In the former the
total amount of certain constituents are determined regard-
less of their chemical combinations and character. In the
latter group of methods only a portion of certain important
materials are removed and analyzed, the chemical combina-
tion being to a certain extent a factor in the amount of any
constituent extracted.
165. Bulk analysis—organic carbon and nitrogen.1—
1The sampling of the soil is an important consideration in any
analytical work. The sample should be representative and is_ best
taken with a soil auger. In sampling small areas, such as plats, a num-
ber of borings are usually made to the depths required and thoroughly
mixed. This composite is quartered until a sample of the required size
311
312 NATURE AND PROPERTIES OF SOILS
The methods of determining the amount of organic matter in
any soil have already been discussed (par. 60), the conclusion
being that the figure for organic carbon, or this figure multi-
plied by 1.724, was the most reliable indication of the organic
content of a soil.
Fig. 52.—Auger used
in the field exam-
ination of soil and
in taking samples.
Note modified ecut-
ting edge.
The bomb method is cited as one of the
more suitable procedures for obtaining
the organic soil carbon.
The method for estimating the soil
humus, although it is not a bulk method,
should be considered at this point because
of its close relationship to the determina-
tion of organic carbon. The modified
Grandeau procedure (par. 61) is used for
humus estimation and is supposed to dis-
tinguish between the more active and less
active organic matter. Of the two
methods the determination of organic car-
bon is by far the more accurate. As
there is also some doubt about the com-
parative activity of the material ex-
tracted by the Grandeau procedure the
figure for organic carbon seems in general
the more significant and it is the deter-
mination usually made. The estimation
of soil humus may, therefore, be con-
sidered as a chemical method of sec-
ondary importance except in special
cases.
The total nitrogen of the soil is determined by either the
Kjeldahl, the modified Kjeldahl, or by the Gunning method.
The determination of nitrogen is such a common laboratory
is obtained. Where large areas are involved, as in the case of a soil
survey, only one sample, representative of the soil type being studied, is
usually taken.
CHEMICAL ANALYSIS OF SOILS 313
procedure that it is worth while to consider the principles in-
volved. About 10 grams of dry soil are placed in a Kjeldahl
flask with about 30 e.c. of strong sulfuric acid and 0.7 gram
of mercuric oxide or its equivalent in metallic mercury. The
mixture is boiled vigorously until the solution is clear. The
flask is then removed from the flame and, while hot, potassium
permanganate is added in small quantities to complete the
oxidation until, after shaking, the liquid remains a green or
purple color. The nitrogen of the soil, no matter what has
been its combination, is now in the form of ammonium sulfate
[(NH,).SO,], the mercury acting as a catalytic agent and
the permanganate as an oxidizer.
After cooling, the contents of the flask are diluted with
about, 200 ¢.c. of water, zine dust or a few pieces of granu-
lated zine are added to prevent bumping and 25 «ec. of
potassium sulfid are poured in with shaking. Next a sodium
hydroxide solution, suffcient in amount to neutralize the acid,
is carefully poured down the side of the flask. The flask is
then connected with a condenser and the contents cautiously
mixed by shaking. The ammonia set free by the alkali is dis-
tilled over into a standard acid, the excess acid being titrated
with a standard alkali, using a suitable indicator. When the
amount of standard acid neutralized is known, the amount of
nitrogen, which has passed over in the form of ammonia, may
be calculated and expressed as a percentage, based on the
original dry sample of soil. (See Fig. 53.)
*The method described above is the Kjeldahl method. See Official
and Tentatwe Methods of Analysis of the Assoc. Official Agr. Chemists,
p. 314, 1920.
This method does not determine the nitrogen in the nitrate form.
If this is desired a modified procedure must be followed. As the
nitrate nitrogen in most soil is low compared to the nitrogen in other
combinations, the objection just made to the regular Kjeldahl method
is not serious.
Snyder, R. 8., Determination of Total Nitrogen in Soils Containing
Rather Large Amounts of Nitrates; Soil Sci., Vol. VI, No. 6, pp. 487-
490, 1918.
314 NATURE AND PROPERTIES OF SOILS
166. Bulk analysis—complete solution of the soil—By
the use of hydrofluoric acid or by fusion with potassium and
sodium carbonate, the entire soil mass may be decomposed and
Fig. 53.—Front and side view of a Kjeldahl distilling battery. (A),
Kjeldahl flask; (B), trap; (C), condenser tank; (D), receiving flask
containing standard acid and (E), Bunsen burner.
its constituents determined.t The amount of lime (CaO) or
any other constituent,? may thus be expressed in percentage
1 Wiley, Harvey W., Principles and Practices of Agricultural Chemical
Analysis, Vol. 1, pp. 398-399, 1906.
*Schollenberger presents some interesting data regarding the pro-
CHEMICAL ANALYSIS OF SOILS 315
based on dry soil or in pounds to the acre to any suitable
depth. This method gives only the total of any constituent
and tells nothing regarding its availability to crops, although
a marked deficiency in any element may thus be detected. A
rock will often show greater amounts of the mineral elements
than a fertile soil.t
167. Partial analysis of the soil for mineral constitu-
ents.— When it was realized that a bulk analysis of the soil,
especially for the mineral constituents, gave no information
as to the availability of certain elements or as to the fertilizer
needs of the soil, extraction methods were devised. Such
methods, of whatever character they may be, are designed to
portion of organic and inorganic phosphorus in Ohio soils. The figures
are an average of twelve types.
ORGANIC P.O,
SoILs LOL AS PER CENT rita
tae OF TOTAL
% % %
Cultivated
O=BY7Sin ChESsaccaoe etc eicis .0433 34 14
HeLomINCHES tess) \ciatere cialciors .0345 20 .07
Virgin
OBR MIN CHESS hea.zs.thsl<caie cos: 0587 24 19
Wl ANCHES Se 55.8 os ses sauce .0381 21 .08
Schollenberger, C. J., Organic Phosphorus Content of Ohio Soils;
Soil Sei., Vol. X. No. 2, pp. 127-141, 1920.
For methods of determining organic phosphorus, see Potter, R. S.,
The Organic Phosphorus of Soil; Soil Sci., Vol. II, No. 4, pp. 291-
298, 1916.
Rost, C. O., The Determination of Soil Phosphorus; Soil Sci., Vol.
IV, No. 4, pp. 295-311, 1917.
Potter, R. S., and Snyder, R. S., The Organic Phosphorus of Soil;
Soil Sei., Vol. VI, No. 5, pp. 321-332, 1918.
Schollenberger, C. J., Organic Phosphorus of Soil: Experimental Work
on Methods for Extraction and Determination ; Soil Sci., Vol. VI, No. 5,
pp. 365-395, 1918.
*Sulfur is determined by a separate method. Official and Tentative
Methods of Analysis of the Assoc. of Official Agr. Chemists, p. 317, 1920.
See also, Hart, E. B., and Peterson, W. H., Sulphur Requirements of
Farm Crops in Relation to the Soil and Air Supply; Wis. Agr. Exp.
Sta., Res. Bul. 14, 1911.
316 NATURE AND PROPERTIES OF SOILS
give information regarding the availability of the plant nutri-
ents within the soil. They may be listed under three heads:
(1) digestion with strong acids, (2) digestion with dilute
acids, and (3) extraction with water. These methods will be
discussed in the order mentioned.
168. Digestion with strong acids.—While surfuric, ni-
tric, and hydrochloric acids have all been used as solvents,!
the one most commonly employed is hydrochloric acid of
1.115 specific gravity.2 It has been used to such an ex-
tent that it may be considered the standard solvent, and a
statement of a chemical analysis of a soil in this country may
be considered as based on this solvent unless otherwise stated.
An analysis by this method is supposed to show the propor-
tion of nutrient materials in a soil that is in a condition to
be used ultimately by plants at the time when the analysis is
made. The nutrient materials that are not dissolved by
treatment with hydrochloric acid are assumed to be in a
condition in whch plants cannot use them. The difficulty
with this assumption is that, while treatment with hydro-
ehlorie acid of a given strength marks a definite point in the
solubility of the compounds in the soil, it does not bear a
uniform relation to the natural processes by which these
compounds become available to plants.
This method is not only arbitrary but it is artificial as well.
1The following analyses of the same soil quoted from Snyder are
interesting in this regard. Snyder, H., Soils; Minn, Agr. Exp. Sta.,
Bul. 41, p. 66, 1895.
EXTRACT ToraL | K,O CaO | MgO | P.O; SO,
% Jo % % %o %
FEC Me ae eis hc 18,80 42 5 AQ lear 08
HEIN Ostet teh ose e556 | 30 30 32 23 08
HiSO, Sea c | 19.55 by ‘53 ‘52 26 10
=>
* Official and Provisional Methods of Analysis; U.S. Dept. Agr., Bur.
Chem., Bul. 107 (revised), pp. 14-18, 1908.
CHEMICAL ANALYSIS OF SOILS 317
While it is supposed to measure the permanent fertility? of
a soil, there is no reason to suppose that there is any rela-
tionship between the nutrients extracted by a strong acid
in the laboratory and the amounts of the same constituents
absorbed by crops over a period of fifty or one hundred years.
Moreover, productivity is not necessarily controlled by the
amounts of available nutrients in a soil. This further vitiates
the data obtained by such an analysis.
Snyder? has analyzed a number of Minnesota soils by
means of digestion with strong hydrochloric acid, decompos-
ing the acid-insoluble residues by fusion and determining
their composition. Veitch * has analyzed certain Maryland
soils by the hydrochloric acid method and by means of com-
plete solution. A few examples are given below to show how
soils may vary in the solubility of their constituents in strong
hydrochloric acid:
TABLE LXX
PERCENTAGE OF SOIL CONSTITUENTS INSOLUBLE IN
HCl, sp. GR. 1.115
Sorts K,o | cao | Mgo | P,0, | So,
Minnesota (Snyder)
Maes ERAVEN or cye fers wn 94 20 58 40 74
Elo le F=5 0 eee a 81 61 76 45 90
Experiment Station...| 838 41 36 18 20
Maryland (Veitch)
Colmmiiiay - 5. «ors 95 90 34 66 —
Ghesapeake: 7 0.626 <2 67 82 29 15 “=
Hudson River Shale..| 738 Bit 28 0 —
169. Digestion with dilute acids—A great number of
different acids have been used in a dilute condition for ex-
* Fertility is used here in the sense of potential productivity, the
nutrients in the soil being considered as the controlling factor.
*Snyder, Harry, Soils; Minn. Agr. Exp. Sta., Bul. 41, p. 35, 1895.
® Veitch, F. P., The Chemical Composition of Maryland Soils; Mad.
Agr. Exp. Sta., Bul. 70, p. 103, 1901.
318 NATURE AND PROPERTIES OF SOILS
tracting soils, the idea being in every case to determine the
amount of the mineral nutrients immediately available to
crops. The scope is thus narrower than in the digestion with
strong acids, by which the permanent fertility is sought.
Two acids have been commonly utilized in the extraction of
soils with dilute solvents: one per cent. citric acid proposed by
Dyer,’ and one-fifth normal nitric acid.2— Dyer adopted the
one-per-cent. strength as the result of an investigation in which
he determined the acidity of the juices in the roots of over
one hundred species or varieties of plants representing twenty
different natural orders. The implication is that plants pro-
duce a solvent action on a soil in proportion to the acidity of
their juices, but an examination of Dyer’s figures does not
show that the size of the crop ordinarily produced by the plants
would in many cases correspond to the acidity of their juices.
Thus, of the Crucifere, the horse-radish has several times the
acidity of the Swedish turnip or of the field cabbage, although
the crop produced by the former is much less than that of the
latter two.
Dyer’s method gave results on Rothamsted soils that en-
abled him to estimate their refative productivity. On other
soils and in the hands of other investigators, however, the
method is unsatisfactory. In soils rich in calcium and low in
iron and aluminum, it may often show the amounts of easily
soluble phosphoric acid and potash.
In ease of manipulation, the fifth normal nitric acid is
preferable to the one-per-cent. citric acid, which is rather
tedious to work with. It has been utilized nearly as exten-
sively in this country as has the latter in Great Britain. Its
use has been confined largely to the determination of the
readily available phosphoric acid and potash in the soil, as
* Dyer, Bernard, On the Analytical Determination of Probably Avatl-
able ‘‘Mineral’’ Plant Food in Soils; Jour. Chem, Soc., Vol. LXV,
pp. 115-167, 1894.
? Official and Provisional Methods of Analysis; U.S. Dept. Agr., Bur.
Chem., Bul. 107 (revised), p. 18, 1908.
CHEMICAL ANALYSIS OF SOILS 319
has the citric acid method. It is obvious that some materials
are more readily soluble than others, and for that reason the
method will distinguish between phosphorus and potassium
in different forms. The calcium phosphates are supposed to
be entirely soluble in this strength of acid. According to
Fraps,' it dissolves iron and aluminum phosphates to only a
slight extent, thus distinguishing between these forms of phos-
phorus and ealcium phosphate. Fraps finds also that no
potassium is removed from orthoclase and microcline, that less
than 10 per cent. is dissolved from glauconite and biotite, and
that from 15 to 60 per cent. is dissolved from muscovite,
nephelite, leucite, apophyllite, and phillipsite, minerals known
to be rather easily available.
There are several factors, however, that make the use of
one-fifth normal nitric acid an uncertain guide to the avail-
able phosphoric acid and potash in the soil. When a soil is
treated with the acid, some of it is neutralized by the reac-
tions that result and thus its strength is lessened. This may
have no relation to the quantities of phosphoric acid or potash
dissolved. Some analysts correct for the neutralization and
some do not. Again, as with concentrated hydrochloric acid,
the degree of solubility of the soil constituents in the nitric
acid may not correspond with the ability of the plant to ob-
tain these substances. With this, as with the other methods
discussed, the objection holds that the results cannot be taken
as an infallible guide to the productiveness of a soil, or to its
fertilizer needs. The artificial extraction of a soil in the
laboratory cannot be expected to simulate the action of a
crop even for one year.
170. Extraction with water.—As carbon dioxide is a
universal constituent of the water of the soil, and without
+ Fraps, G. 8., Active Phosphoric Acid and Its Relation to the Needs
of the Soil for Phosphoric Acid in Pot Experiments; Tex. Agr. Exp.
Sta., Bul. 126, pp. 7-72, 1909.
Also, The Active Potash of the Soil and Its Relation to Pot Expert-
ments; Tex. Agr. Exp. Sta., Bul. 145, pp. 5-39, 1912.
320 NATURE AND PROPERTIES OF SOILS
doubt a potent factor in the decomposition of the mineral
matter, it has been proposed to use a solution of carbon diox-
ide as a solvent in soil analysis. The amounts of soil con-
stituents taken up by this solvent are much less than are taken
up by any of the others heretofore mentioned, but all mineral
substances used by plants are soluble in it to some extent.
The amount of phosphoric acid is so small as to make its
detection by the gravimetric method difficult. Like other
methods employing very weak solvents, this is open to the
objection that much of the material dissolved cannot be re-
moved because of the absorptive power of the soil, and as this
varies with the character of the soil, adequate comparisons
eannot be made. Water charged with carbon dioxide has been
very largely replaced by pure water in making such extrac-
tions.
When soil is digested with distilled water, all the mineral
substances used by plants are dissolved from it, but in very
small quantities. It has been proposed to employ this extract
for soil analysis on the ground that it is a natural solvent
and dissolves only those nutrients in a condition to be used
by plants. By determining the moisture content of the soil
and using a known quantity of water for the extraction, the
parts per million of the extracted nutrients may be expressed
on the basis of the dry soil or of the solution. The aqueous
extract does not by any means contain the entire quantity of
nutrients which were in the soil solution and is not an exact
measure of the fertility in this form. Absorption holds back
an undetermined and variable quantity of the important con-
stituents and thus vitiates the method, especally for compar-
ing different soils. The method, however, is very valuable for
comparing the same soil at different times, especially as re-
gards the nitrates. The nitrate radical is not absorbed to any
great degree by the soil and presents a very fair measure of
the concentration of the soil solution as far as this constituent
is concerned.
CHEMICAL ANALYSIS OF SOILS 321
The water extract method generally followed in this country
is that established by the Bureau of Soils. One hundred
grams of soil are mixed with 500 cubic centimeters of water
and stirred for three minutes. After standing twenty minutes
the supernatant liquid is filtered through a Pasteur-Chamber-
land filter under pressure. It is then ready for analysis.
Colometric and turbidity methods are usually employed in de-
termining the amounts of the constituents removed.t The
method is of greatest use in estimating the nitrate content of
soils.
The quantity of extracted materiai depends on the absorp-
tive properties of the soil, on the amount of water used in the
extraction, and on the number of extractions. Analyses of
the aqueous extract of a clay and of a sandy soil from the
Cornell University farm serve to illustrate the greater reten-
tive power of the former for nitrates. Sodium nitrate was
applied to a clay soil and to a sandy loam soil at the rate of
640 pounds to the acre. Analyses of aqueous extracts some
ninety days later showed the following:
TABLE LXXI
NITRATES INSOIL
KIND oF SoIn FERTILIZER (Parts per
million)
Wlaya eee te Sodium nitrate 7.8
Claire tere sae a hes No fertilizer 1.8
Sandy loam........ Sodium nitrate 150.0
any. MOaMr«is.s 5 ni x No fertilizer 29.7
There was apparently a much greater retention of nitrate
by the clay soil, as shown by a comparison of the fertilized
and unfertilized plats on both soils.
*Schreiner, O., and Failyer, G. H., Colorimetric, Turbidity and Titra-
tion Methods Used in Soil Investigations; U. S. Dept. Agr., Bur. Soils,
Bul. 31, 1906.
322 NATURE AND PROPERTIES OF SOILS
Schulze? extracted a rich soil by slowly leaching one kilo
with pure water, one liter of water passing through in twenty-
four hours. The extract for each twenty-four hours was
analyzed every day for a period of six days. The total amounts
dissolved during each period were as follows:
TaBLE LXXII
| ToTAL MATTER
SUCCESSIVE EXTRACTION| DISSOLVED VOLATILE INORGANIC
GRAMS GRAMS GRAMS
LEuibigst eae ts ee ls ae ’ 00D 340 195
NCCOMCm ey cee occ 120 Oi .063
Geet as ae” 261 On .160
JeMODU ete vse ee Shenae .203 .083 120
MyiiGhie Seok ieines. o00o a 0% .260 082 178
Sixth...........-4) .200 O77 123
It will be noticed that the dissolved matter, both organic
and inorganic, fell off markedly after the first extraction.
Later extractions were doubtless supplied largely from the
substances held by absorption, which gradually diffused into
the water extract as the tendency to maintain equilibrium of
the solution overcame the absorptive action. With the re-
moval of the absorbed substances the equilibrium between
the absorption and solution surfaces and the surrounding so-
lution is disturbed, diffusion and solution are increased, and
more material gradually passes from the soil into the solution.
In this way, a more or less uniform and continuous extraction
is mantained.
In spite of the obvious defects of the water extraction
method the work of Hoagland, Burd and Stewart? seems to
indicate that such data, if obtained over an extended period,
Schulze, F., Uber den Phosphorsaure-Gehalt des Wasser-Auszugs der
Ackererde; Landw. Vers. Stat., Band 6, Seite 409-412, 1864.
? Burd, J. S., Water Extractions of Soils as a Criteria of their Crop-
CHEMICAL ANALYSIS OF SOILS 323
are a good comparative measure of the concentration and
composition of the soil solution (see par. 145). They also con-
sider water extractions as criteria of the crop-producing power
of a soil so studied. The practical value of such a method as
a means of estimating fertility is, however, somewhat ques-
tionable, since much time and labor are required to make the
necessary extractions and analyses before conclusions at all
reliable may be drawn.
171. Fertility evaluation by means of chemical analyses.
—The important part that chemistry plays in soil investiga-
tion and research should not be overlooked. Nor can a satis-
factory presentation of soil phenomena, whether with a tech-
nical or an applied bearing, be made without the use of some
chemistry. Chemistry, in fact, is the fundamental science
that is most utilized in soil study.
In spite of these relationships, the value of chemistry in the
direct solution of practical fertility problems is neither abso-
lute nor final. The objections already raised to the digestion
of the soil, either with concentrated or dilute acids, shows the
inadequacy of these methods so far as practical problems are
concerned.
Of all the chemical analyses discussed those that have to do
with the determination of organic carbon, total nitrogen, total
ealeium and phosphoric acid are of outstanding value. Or-
ganic matter is such an important soil constituent that a
knowledge of its amount cannot fail to throw much light on
the physical and chemical condition of the soil. Much of the
soil nitrogen is carried by the organic matter and becomes
available in much larger proportion than do the mineral
nutrients. An analysis for total nitrogen is, therefore, a
Producing Power; Jour. Agr. Res., Vol. XII, No. 6, pp. 297-309, 1918.
Stewart, G. R., Effect of Season and Crop Growth in Modifying the
Soil Extract; Jour. Agr. Res., Vol. XII, No. 6, pp. 311-368, 1918.
Hoagland, D. R., The Freezing Point Method as an Index of Varia-
tions in the Soil Solution Due to Season and Crop; Jour. Agr. Res.,
Vol. XII, No. 6, pp. 369-395, 1918.
324 NATURE AND PROPERTIES OF SOILS
fairly reliable guide in some eases to the fertility of the soil
under specific consideration.
Although the relationship of organic matter and nitrogen
to soil fertility is so close that certain generalized tables ‘ may
be cited for the interpretation of chemical data, no close cor-
relation is possible, especially where soils of markedly different
character are compared. So many other factors may enter
that practically no opinion can be formed regarding the prod-
uctivity of a soil unless other and more detailed data are
available.
An interesting example of where the nitrogen content fails
to indicate the relative fertility of two soils is found in certain
unpublished data from the Cornell Agricultural Experiment
Station. Two soils are being studied in the lysimeter tanks—
Dunkirk silty clay loam and Volusia silt loam. In Table
LXXIII is given the nitrogen and calcium content of these
soils and the pounds of nitrogen removed to the acre by maize,
oats, and barley, respectively, for the years 1915, 1916, and
1917. The treatment and handling of the soils compared has
been the same.
While the nitrogen, phosphoric acid and potash contents of
these soils are about the same, a marked difference is noted in
their productivity. This may be due, at least partially, to
the calcium content, which is rather high in the Dunkirk,
especially in the subsoil. In comparing soils over wide areas
1The following tentative classification of soils on the basis of their
percentages of organic matter and nitrogen is offered for generalized
field use:
PERCENTAGE OF PERCENTAGE OF
DESCRIPTION OrGANIC MATTER NITROGEN
TGR AED tly sos 5s Ne: ahlle EADS cm 02 30. | | ate
Mie davmisy ek eas ioee: ce nena eee encle 3.0- 6.0 -10- .25
Jebel) Coe anidicdoobnoooodopeo6ee 6.0-10.0 © .25- .40
Wainy Wel b6cooccanaaconpooodc above 10.0 above .40
bo
on
CHEMICAL ANALYSIS OF SOILS 3
TABLE LX XIII
THE PERCENTAGES OF NITROGEN AND CALCIUM IN THE DUNKIRK
SILTY CLAY LOAM AND THE VOLUSIA SILT LOAM AND THE
NITROGEN REMOVED BY CERTAIN CROPS. CORNELL
LYSIMETER TANKS.
PouNDS oF N REMOVED
Cad N PER ACRE
SoILs % %
MAIZE | OATS | BARLEY
1915 1916 1917
Dunkirk silty clay loam... 53.6 | 62.3| 44.0
TOMI SLPS OO) ae eee eR Pee 040 | 134
Second Loot. 2. . 2k en 280 | .062
AITGEOOG oe alk exe wc a 490 | .064
EM GutbherOGbcl a scl ob os 1.530 | .054
Molusia- sultloami.......¢ +. Deda hei. tl 18:8
1 SLT eeS Ft 070) eS er ea 230 | .145
DECOM LOOT oe cles «cle 165 | .052
IM ATW 076 thin 010) Ree ne Ie .260 | .059
OUEGNE LOOLies 6 teckel 365 | .050
and in a general way there is often some correlation between
the amount of calcium present and the productivity. In
humid regions soils high in lime are usually fertile. Within
certain limits, therefore, calcium becomes significant in fer-
tility studies.*
Some idea concerning the relative value of the various chem-
ical methods, especially those dealing with potash, lime, phos-
phorie acid, and magnesia, may perhaps be obtained by com-
paring actual data. Burd? has analyzed a number of soils,
1Shedd, O. M., A Proposed Method for the Estimation of Total
Calcium in Soils and the Significance of this Element in Soil Fertility;
Soil Sci., Vol. X, No. 1, pp. 1-14, 1920.
*Burd, J. 8., Chemical Criteria, Crop Production and Physical Classi-
fication in Two Soil Classes; Soil Sci., Vol. V, No. 6, pp. 405-419, 1918.
326 NATURE AND PROPERTIES OF SOILS
some good, some poor, by several different methods. Repre-
sentative figures are given below:
TaBLE LX XIV
CHEMICAL COMPOSITION OF A GOOD AND A POOR SOIL AS
INDICATED BY SEVERAL DIFFERENT METHODS
PERCENTAGE OF
CONDITIONS
K,0 | CaO | MgO | P,O,
Bulk analysis
Productive silt loam. . 2... .<’. 1-98") 1-485) 2:66 20
Unproductive silt loam....... 185) oOr he a-od 21
Concentrated HCl digestion
Produchiversilt loam. ...s56 54 0a) 1431-2246 22
Unproductive silt loam........ 89 | 1.48 | 3.32 20
One per cent. citric acid
Productive silt loam.......... 089 | 452°) 22077 |eahom
Unprodnuctive sult loam.) 70... 0389 | 422 | 144 | 072
Water extract p.p.-m. | p.p.m.| p.p.m. | p.p.m.
Productive silt loamis. 223.2. .. 57 127 40 12
Unproductive silt loam........ 02 45 | ~ 28 5
A comparison of the figures from the good and poor soil
Seems to indicate no differences large enough to warrant opin-
ions regarding their relative fertility, except in the case of the
water extracts. These latter figures, however, are seasonal
averages and required as long a time to procure as was neces-
sary to grow a crop. Such fertility measurement is not as
practicable as actually using the crop as an indicator.
172. Resume.—The conclusion that chemical analyses are
of but little direct practical value as a guide to soil prod-
uctivity is unavoidable. In spite of the great importance of
chemistry in research and teaching, it fails to indicate either
the permanent or the immediate fertility of the land. No
chemical method is capable of showing substantial and con-
stant differences between soils producing within 20 per cent.
CHEMICAL ANALYSIS OF SOILS 327
of each other. Even if an analysis should show the nutrients,
which would be available over a term of years, it would still be
inadequate, since available nutrients are only one of a great
number of factors which govern productivity. This produc-
tivity equation may be indicated as follows:
Productivity = Texture X structure < organic matter <
moisture < available nutrients * soil reaction & weather «
plant disease X care of farmer, etc., ete.
The factors of this equation are variables, their importance
in determining productivity depending on many things. An
accurate knowledge of the available soil nutrients, even if
procurable, would aid but little in solving such an equation.
The solution of individual or community fertility problems
is best accomplished by the aid of experienced and technically
trained men, who understand the scientific principles under-
lying the common field procedures and who also are in touch
with the experiences of farmers over wide and diverse areas.
Such men may advise not only in regard to the crops that
should be grown but also as to their rotation, management,
and fertilization from seeding until harvest. These men may
also institute such codperative experiments and tests as will
best throw. light on fertility problems untouched by practical
experience.
*The samples sent to a chemical laboratory by farmers are gen-
erally improperly taken and consequently are not representative. It
would be unwise to analyze such soils even if the methods were capable
of showing all that could be wished for.
CHAPTER XVII
ALKALI SOILS 1
Ir HAS already been shown that soils are acted on by a great
variety of weathering agents which gradually render soluble
a portion of the most susceptible constituents. This soluble
material becomes a part of the soil solution and may come in
contact with the roots of any crop growing on the land. In
humid regions, where a large quantity of water percolates
through the soil, this soluble matter has little opportunity to
accumulate.” In arid regions, however, where loss by drainage
is slight, these salts may often collect in large amounts. Dur-
ing periods of dry weather they are carried upward by the
capillary rise of the soil-water, while during periods of rain-
fall they may move downward again in proportion to the leach-
ing action. At one time the lower soil may contain consid-
erably more soluble salt than the upper; at another time the
condition may be reversed, in which case the solution in con-
tact with roots may contain so much soluble matter that vege-
tation is injured or destroyed. This excess of soluble salts
usually has a marked alkaline reaction, but in any ease it pro-
duces what is termed an alkali soil.
Large areas of land in every continent carry soluble salts
to such an extent that alkali injury is either actual or poten-
*For a complete and satisfactory treatise on alkali see Harris, F. S.,
Soil Alkali, New York, 1920.
*Peat soils in humid regions may sometimes contain high concentra-
tions of salts, commonly non-toxic, and lower concentrations of ex-
tremely toxic salts.
Conner, S. D., Excess Soluble Salts in Humid Soils; Jour. Amer. Soc.
Agron., Vol. 9, No. 6, pp. 297-301, 1917.
328
ALKALI SOILS 329
tial. It is estimated that 13 per cent. of the irrigated land of
the United States contains sufficient soluble salts seriously to
interfere with crop growth. This alone amounts to nine mil-
lion acres and does not include the millions of acres not under
the ditch that are affected to a marked degree by alkali. Sim-
ilar figures are available from other continents and, since
alkali conditions can be alleviated and controlled to a certain
extent, the importance of the subject becomes apparent.
Entirely aside from the economic aspects, alkali is of great
interest scientifically, offering a research field of such range
and complexity as to involve many sciences. A greater por-
tion of the practical information regarding alkali and its con-
trol has arisen from the purely scientific interest that has
been directed towards this peculiar soil condition.
173. Composition of alkali—It has been emphasized pre-
viously that the solution of a normal humid-region soil is of
such dilution as to be largely ionic in character except in
periods of low moisture content. In a soil affected with
alkali it is obvious that the molecular state is dominant and
that certain salts may exist and function as definite entities.
Thus the following bases may be expected to be present—
sodium, potassium, magnesium, calcium, and sometimes am-
monium. The common acid radicals are chlorides, sulphates,
carbonates, bicarbonates, phosphates, and nitrates. The salts
that are present and their proportion not only in the soil solu-
tion but as a precipitant will vary with conditions.
The following table indicates not only the salts that may be
present but the composition of the alkali as reported by a
number of different investigators. (See table LX XV, p. 330.)
174. White and black alkali—Sulfates and chlorides of
the alkalies, when concentrated on the surface of the soil,
produce a white incrustation, which is very common in alkali
regions during a dry period as a result of the evaporation of
moisture. Incrustations of this character are called white
alkali.
330 NATURE AND PROPERTIES OF SOILS
TABLE LXXV
COMPARISON OF ALKALI EXPRESSED IN PERCENTAGE OF THE DIF-
FERENT SALTS PRESENT.
Wyss biter BILLInes, Mont.’| Yuma, Ariz.?
Re lege ,|-————
Sar z Bi eae) |a as : SURFACE 0-72
Bk Eee: Seag CRUST eee CRUST | Gaus
KOM ee 16 | — 5.6 | —— | — 4.0 | 22.0
KESO, cee ty gg Se) 6.) ea eee
RECO AN eerie ot —}| —
Na,SO,.. — | 25.3 | — | 856 | 35.1 | —]} —
NaNO...) - 93.1 |. 19.8 | 2.1) — Se
Na,CO,. 2 191806) | 13.8 (eo 7 os
NaCl wee. 6.6 | 14.7 | —— | === | 8d | ise
Na EO) S| 1 hs Ree ee a ee ee ee
MeSQ,..... aos ee ee ne nr pe yt
MeCho..4.. 12-70) Se ee el een
CaGyy... VT Be eee eee ea ae 2 ee
NaHCO, — | — | 36.7 6 | 22.0 2 |) 20
WasOne . 2: 21.5 | —— iL) mind ae €A\(0)50) 6.6 | 32.2
@ai(HCO,),)' 4h 21) 6 ba) ee ee
Me(HCO,);)| > 22) both 22) eS
(N).CO, | 0) A) eee
Carbonates of the alkalies, particularly sodium carbonate,
dissolve organic matter from the soil, thus giving a dark color
to the solution and to the inerustation. For this reason, alkali
containing large quantities of these salts is called black alkali.
Black or brown alkali may also be produced by calcium chlo-
ride or by an excess of sodium nitrate.
Black alkali is much more destructive to vegetation than is
the white. A quantity of the latter which would not seriously
*Headden, W. P., The Fixation of Nitrogen; Colo. Agr. Exp. Sta.,
Bul. 155, p. 10, 1910.
* Hilgard, E. W., Soils, p. 442, New York, 1906.
* Dorsey, C. W., Alkali Soils of the United States; U. S. Dept. Agr.,
Bur. Soils, Bul. 35, 1906.
ALKALI SOILS 331
interfere with the growth of most crops might completely pre-
vent the development of useful plants if the alkali were black.
175. Origin of alkali—While the presence of alkah and
its influence on plants has been known for centuries, it is
only within recent years that its probable mode of origin has
been understood. The soluble salts have undoubtedly come
- from the materials which have formed the soils, the reactions
being as complex as the ordinary transformations which take
place in soil formation.
Some soils have been laid down as deltas in arms of the
ocean. If these bodies of water later are cut off from the sea
and gradually dry up under arid conditions, an alkali soil
will be left. In a similar way saline lakes may disappear and
soils heavily charged with alkali will result.
The commonest mode of origin for alkali soil is through
ordinary weathering under conditions of aridity. Almost any
rock will give rise to soils rich in alkali salts if leaching is not
a feature in the weathering processes. In western United
States the origin of much of the soil affected to the greatest
degree with alkali is associated with strata originally carrying
much soluble material. When such rock forms soil, the alkali
arises not only from the decomposition of the minerals of
which the rock is composed, but is greatly reinforced by the
soluble salts already present. The Cretaceous and Tertiary
beds in Utah, Colorado, and Wyoming are of this character,
having been laid down in brackish water. They naturally
give rise to soils high in alkali.t
One fact that is often overlooked in practice is that the
amount of alkali in the surface layers of soil may be greatly in-
creased by improper handling. Rapid evaporation after rain
or irrigation will carry the soluble salts toward the surface and
deposit them near to or in the root zone. Again, over-irriga-
1Stewart, R., and Peterson, W., Origin of Alkali; Jour. Agr. Res.,
Vol. X, No. 7, pp. 331-353, 1917. See also, Breazeale, J. F., Forma-
tion of Black Alkali in Calcareous Soils; Jour. Agr. Res., Vol. X, No.
11, pp. 541-589, 1917.
302 NATURE AND PROPERTIES OF SOILS
tion may produce leaching into lower lands, an alkali condition
generally resulting if the areas so affected remain water-logged
for a long time.
Very often alkali is localized in small areas called alkali
spots. These vary in size from a few square yards to several
acres. In years of good rainfall these areas may be pro-
ductive, but in dry years they are often quite sterile. Their
origin is generally due to seepage, the ground water being
near enough the surface to allow a concentration of salts by
eapillarity, especially in dry seasons.
A very peculiar type of alkali spot occurs in the Grand
Valley of Colorado and elsewhere, the predominant salt being
the nitrate, which does not usually occur in large amounts
as alkali. Two theories have been advanced to account for the
presence of the nitrate salts. One hypothesis’ is that the
surrounding shales are comparatively rich in nitrates and that
the alkali accumulation is a leaching and seepage process. The
other theory is biological in nature.? Such soils are capable
of rapid nitrogen fixation by means of their bacterial flora.
The idea is advanced that the nitrogen is fixed from the air
very rapidly in these spots and later oxidized to the nitrate
form. Whatever the origin of the soluble salts the fact re-
mains that such spots are quite destructive, spreading very
rapidly until whole orchards are wiped out.
Water used for irrigation is very often heavily charged with
alkali, especially where any amount of the water previously
applied to the soil finds its way back into the streams. At
Canon City, Colorado, the Arkansas River is very pure. At
a point 120 miles below the soluble salts have been known
1Stewart, R., and Peterson, W., The Nitric Nitrogen Content of the
Country Rock; Utah Agr. Exp. Sta., Bul. 134, 1914.
Also, Further Studies of the Nitric Nitrogen Content of the Country
Rock; Utah Agr. Exp. Sta., Bul. 150, 1917.
*Headden, W. P., The Fixation of Nitrogen in Colorado Soils; Colo.
Agr, Exp. Sta., Bul. 186, 1913.
Sackett, W. G., and Isham, R. M., Origin of the Niter Spots in
Certain Western Soils; Science, N. 8., Vol. 42, pp. 452-453, 1915.
ALKALI SOILS 333
to reach a concentration of 2200 parts per million. The quan-
tity of soluble salts that may be present in irrigation water
before it is unfit for use depends on certain conditions. This
amount will vary with the crop, the rainfall, the soil, the
composition of the alkali, and a number of other factors.
A
aa a aS is
eee
‘ ‘SD
‘ =
a / ‘
et et
2
DEPT Ed OFRGOVL JIN FEET:
Fic. 54.—Diagram showing the amount and composition of alkali salts
at various depths in a soil at Tulare, California. (After Hilgard.)
GR BERZSERE
eee eee
a Gar aak
PUTOUNTS OF ALKALI IN 100 OF SO/l,
Where the alkali is of the sodium sulfate type rather high
concentrations are admissible, running as high as 1000 parts
per million. Water carrying black alkali must be used with
great caution. Table LX XVI indicates the concentration that
may be expected in normal irrigation water.
The preponderance of sodium chloride is almost always a
feature, not only in alkali water but also in soils affected with
alkali salts. This may be explained as due to differential ab-
334 NATURE AND PROPERTIES OF SOILS
TaBLE LX XVI
ANALYSIS OF SOME TYPICAL ALKALINE RIVER WATER OF WESTERN
UNITED STATES.1
ToTAL PERCENTAGE OF TOTAL SOLIDS AS
STREAM Soups
p-p.m.) Cl | SO,|CO;| Na | K | Ca | Mg| SiO,
Malad River, Utah ....| 4,395 | 50.0] 2.9) 4.7)37.4
Sevier River at Delta,
Wits erreraeerseslevenners W316) P2524 os |ev7 29) Gea eee ero | ieee
Rio Grande, Texas ....| 791 | 21.6/30.1 | 11.5/14.8] .8/13.7) 3.0) 3:8
Mill Creek, Montana ..|3,747 | 7.4/17.3 | 35.1/23.5 | 1.4|10.1] 2.2] .7
San Benito, California.| 936 | 13.8/29.0 | 38.3)13.1| 5.4] 6.6] 7.7] 2.6
Buckeye Canal, Arizona] 1,972 | 39.9) 7.3 | 9.6)24.9 26) 16, On earn leech
sorption of ions by the soil. Sodium and chlorine ions seem
to be about as little absorbed by the soil as any of the com-
mon soil constituents. They are thus readily carried through
the soil and are free to accumulate in considerable amounts
at points where they may become noticeable. Their union of
necessity produces large quantities of sodium chloride or com-
mon salt.”
176. Effect of alkali on crops.—The presence of rela-
tively large amounts of salts dissolved in water and brought
into contact with a plant cell has been shown to cause a shrink-
age of the protoplasmic lining of the cell. This action, called
plasmolysis, increases with the concentration of the solution
until the plant finally dies. The phenomenon is due to the
osmotic movement of the water, which passes from the cell
towards the more concentrated soil solution. The nature of the
salt, the species, and even the individuality of the plant, as
well as other factors, determine the exact concentration at
which the plant succumbs. The carbonates of the alkali bases
have, in addition, a corroding effect on the plant tissues, dis-
* Harris, F. S., Soil Alkali, p. 232; New York, 1920.
? Dorsey, C. W., Alkali Soils of the United States; U. S. Dept. Agr.,
Bur. Soils, Bul. 35, 1906.
ALKALI SOILS 335
solving the parts of the plant with which they come into con-
tact. Such action is not as important as plasmolysis and when
it does occur is most noticeable at the root crown. (See
Fig. 55.)
Indirectly, alkali may influence plants by its effect on soil
tilth, soil organisms, and fungous and bacterial growths. Mar-
chal,t for example, found that the formation of nodules, con-
taining the nitrogen-fixing organisms, did not develop well
Fig. 55.—(1) Cross-section diagram of a normal plant cell. (2) Cell
after plasmolysis has taken place.
on pea roots in nutrient solutions when certain concentra-
tions of salts were maintained. Ammonium salts were injuri-
ous at a concentration of 500 parts per million. Potassium and
sodium salts retarded the nodule development at 5000 and 3333
parts to the million respectively. The quantity of alkali that
will cause injury to ammonifying and nitrifying bacteria
varies from 250 to 4000 parts per million, depending on con-
ditions.
177. Resistance of different plants to alkali—The fac-
tors that determine the tolerance of plants toward alkali are:
* Marchal, E., Influence des Sels minéraux nutritifs sur la Production
des nodosités chez le Pois; Compt. Rend. Acad. Sci. (Paris), Tome 133,
No. 24, p. 1032, 1901.
336 NATURE AND PROPERTIES OF SOILS
(1) the physiological constitution of the plant, and (2) the
rooting habit. The former is little understood, so much de-
pending on the character of the alkali solution, the nature
of the cell-wall, and the character and activity of the cell con-
tents. It has long been known that the toxicity of two salts
when together is considerably less than the sum of their detri-
mental action when used alone. This ameliorating or antagon-
istic action varies for different salts, seeming to be greatest
when calcium and magnesium are involved. This is but an
example of the complexities which arise when an attempt is
made to study the physiological relationships of alkali injury.
The rooting habit of plants in their relation to alkali toler-
ance is more easily understood. The advantage is always with
deep-rooted crops, such as alfalfa and sugar-beets, probably
because a portion of the root may be in a less strongly impreg-
nated part of the soil.
The tolerance of many plants to alkali has been studied in
water culture. Such results are not of great practical value,
however, as it is only in soil that all of the numerous factors,
such as absorption, antagonism, and physical conditions, come
into play. Harris and Pittman? found that organic matter
in a soil had a marked ameliorating influence on alkali injury,
especially from sodium carbonate. High moisture was also an
important factor in lowering the toxicity of soluble salts.
Guthrie and Helms,’ using a rich garden loam, found the fol-
lowing concentrations slightly affecting or entirely preventing
germination and growth of certain crops. (Table LX XVII.)
Of the cereals, barley and oats are the most tolerant, these
being able, in some eases, to produce good crops in soil con-
taining two-tenths per cent. of white alkali. Of the forage
crops, a number of valuable grasses are able to grow on soil
1Harris, F. S., and Pittman, D. W., Soil Factors Affecting the
Toxicity of Alkali; Jour. Agr. Res., Vol. XV, pp. 287-319, 1918.
2 Guthrie, F. B., and Helms, R., Pot EHaperiments to Determine the
Limits of Endurance of Different Farm Crops for Certain Injurious Sub-
stances; Agr. Gaz., N. S. Wales, Vol. 14, No. 2, pp. 114-120, 1903.
ALKALI SOILS 337
TABLE LX XVII
EFFECT OF CERTAIN CONCENTRATIONS OF SALTS ON CROPS. EX-
PRESSED IN PARTS PER MILLION.
NaCl Na,CO,
CONDITION
WHEAT |BARLEY RyrE | WHEAT |BARLEY RYE
Germination affected. | 500 | 1000 | 1000 | 3000 | 2500 | 2500
Germination prevented) 2000 2500 | 4000 5000 6000 5000
Growth affected...... 500 | 1000 | 1500 | 1000 | 1500 | 2500
Growth prevented....| 2000 | 2000 | 2000 | 4000 | 4000 | 4000
containing considerably more than two-tenths per cent of al-
kali. Timothy, smooth brome, and alfalfa are the cultivated
forage plants most tolerant of alkali, although they do not
equal the native grasses in this respect. Cotton also tolerates
a considerable amount of alkali.
Loughridge,’ after experiments and observation for a num-
ber of years, has obtained data regarding the resistance of
various crops to the several alkali salts. His results are given
in part as follows, expressed in pounds to an acre to a depth of
four feet. (See table LX XVIII, page 338.)
Although in general the results as to the resistance to alkali
of the various crops are so conflicting, the Bureau of Soils,’
in its alkali mapping, has been able to make a rough classifi-
eation as follows. (See table LX XIX, page 338.)
178. Conditions that influence the effect of alkali—It
has already been mentioned that organic matter and a high
moisture content of the soil tended to alleviate alkali toxicity.
Should, however, a previously wet soil become dry, the solu-
tion, originally very dilute, would become concentrated and
1Loughridge, R. H., Tolerance of Alkali by Various Cultures; Calif.
Agr. Exp. Sta., Bul. 133, 1901. See also Kearney, T. H., and Harter,
L. L., Comparative Tolerance of Various Plants for the Salts Com-
mon in Alkali Soils; U. S. Dept. Agr., Bur. Plant Ind., Bul. 113, 1907.
2 Dorsey, C. W., Alkali Soils of the United States; U. S. Dept. Agr.,
Bur. Soils, Bul. 35, pp. 23-25, 1906.
338 NATURE AND PROPERTIES OF SOILS
TaBLE LXXVIII
CROP Na,SO, Na,CO, NaCl pene
Grapes.teoccor 40,800 7,990 9,640 45,760
Oranges ia Sone 18,600 3,840 3,360 21,840
IRGAES awe Mee 17,800 1,760 1,360 20,920
Applesicmespre an 14,240 640 1,240 16,120
Peaches........- 9,600 680 1,000 11,280
RUC a 7 MUR ge 9,800 960 1,720 12,480
Barley inches 12,020 12,170 5,100 25,020
Sugar Beet..... 52,640 4,000 5,440 59,840
NOrehuims. 2s. : 61,840 9,840 9,680 81,360
PNG aa eaves a0 5 102,480 2,360 5,760 110,320
Saltiushstee.! 554 125,640 18,560 12,520 156,720
consequently toxic. High moisture should, therefore, be
maintained at least as long as the crop is upon the soil.
The distribution of the alkali at different depths may have
an important bearing as to its effect on plants. Young plants
and shallow-rooted crops may be entirely destroyed by the
concentration of alkali at the surface, while the same quantity
evenly distributed through the soil, or carried by moisture to
a lower depth, would have caused no injury. A loam soil, by
TABLE LX XIX
PERCENTAGE OF | PERCENTAGE OF
ToTAL SALTS IN} BLACK ALKALI CROPS
Son IN Soin
.0O— .20 .0O— .05 |All crops grow
.20— .40 .05— .10 |All but most sensitive
AO— .60 .10— .20 |Old alfalfa, sugar beet, sorghum,
barley
.60—1.00 .20— .80 |Only most resistant plants
1.00—38.00 above .30 |No plants
ALKALI SOILS 389
reason of its greater water-holding capacity and absorptive
power, will contain more alkali without injury to plants than
will a sandy soil. Certain of the alkali salts exert a deflocculat-
ing action on clay soils and effect an indirect injury in that
way.
In irrigated regions the injurious effects of alkali are in
many cases developed only after irrigation has been practiced
for a few years. This is due to what is known as a ‘‘rise of
alkali’’ and comes about through the accumulation, near the
surface of the soil, of salts that were formerly distributed
throughout a depth of perhaps many feet. Before the land
was irrigated the rainfall penetrated only a slight depth into
the soil, and when evaporation took place salts were drawn to
the surface from only a small volume of soil. When, however,
irrigation water is turned on the land, the soil becomes wet to
a depth of perhaps fifteen or twenty feet. During the por-
tion of the year in which the soil is allowed to dry large quan-
tities of salts are carried toward the surface by the upward-
moving capillary water.
Although these salts are in part carried down again by the
next irrigation the upward movement constantly exceeds the
downward one. This is because the descending water passes
largely through the non-capillary interstitial spaces, while the
ascending water passes almost entirely through the capillary
channels. The smaller spaces, therefore, contain a consider-
able quantity of soluble salts after the downward movement
ceases and the upward movement begins. In other words, the
volume of water carrying the salts downward in the eapil-
lary spaces is less than that carrying them upward through
these spaces. Surface tension causes the salts to accumulate
largely in the capillary spaces, and it is, therefore, the direc-
tion of the principal movement through these spaces that de-
termines the point of accumulation of the alkali.
There are large areas of land in Egypt, in India, and even
in France and Italy, as well as in this country, that have suf-
340 NATURE AND PROPERTIES OF SOILS
fered in this way, and not infrequently they have reverted
to a desert state.
179. Alkali vegetation.—There are a great number of
plants that seldom grow on soils other than those affected with
alkali. Davy? states that there are 197 species restricted to
alkali soils in California. Such plants are generally recog-
nized by the farmers in the district as indicators of alkali.
Care should be taken, however, in thus classifying alkali land.
Such plants should occupy the land to the exclusion of less
tolerant species. Some of the plants? whose presence should
cause one to surmise alkali conditions are as follows:
Greasewood Inkweed
Alkali-heath Tussock-grass
Salt-grass Bushy samphire
Salt-bush Spike-weed
Cressa Rabbit bush
Sage-brush, which is so often associated in popular literature
with alkali, does not grow on land which carries a great amount
of soluble salts. In locating land it is, therefore, a good indi-
eator of alkali-free conditions, especially if it is growing vig-
orously.
180. The handling of alkali lands.*—Ordinarily there
are two general ways in which alkali lands may be handled in
order to avoid the injurious effects of soluble salts. The first
of these is eradication, the second may be designated as con-
trol. In the former case an attempt is made actually to elimi-
*Davy, J. B., Investigations on the Native Vegetation of Alkali
Lands; Calif. Exp. Sta. Rep., 1895-97, pp. 53-75.
? Harris, F. S., Soil Alkali; Chap. VI? New York, 1920.
5 Dorsey, C. W., Reclamation of Alkali Soils; U. 8. Dept. Agr., Bur.
Soils, Bul. 34, 1906. Also, Hilgard, E. W., Utilization and Reclamation
of Alkali Soils; New York, 1911. Also, Brown, C. F., and Hart, R. A.,
Reclamation of Seeped and Alkali Lands; Utah Agr. Exp. Sta., Bul. 111,
1910. Also, Dorsey, C. W., Reclamation of Alkali Soils at Billings,
Montana; U. S. Dept. Agr., Bur. Soils, Bul. 44, 1907. Also Harris,
F.S., Soil Alkali; Chaps. XII, XIII and XIV; New York, 1920.
ALKALI SOILS 341
nate by various means some of the alkali. In the latter, meth-
ods of soil management are employed which will keep the salts
well distributed throughout the soil. In many cases soils
would grow excellent crops if the alkali could only be kept
well distributed through the soil layers so that no concentra-
tion that is toxic could occur, at least within the root zone.
In general, steps should be taken toward the control of alkali,
whether eradication is attempted or not. Under irrigation,
careful attention is always wise.
181. Eradication of alkali—Of methods designed at
least partially to free the soil of alkali the commonest are:
(1) leaching with under-drainage, (2) correction with gyp-
sum, (3) seraping, and (4) flushing. Of the various methods
for removing an excess of soluble salts, the use of tile drains
is the most thorough and satisfactory. When this method is
used in an irrigated region heavy and repeated applications
of water must be made, to leach out the alkali from the soil
and drain it off through the tile. When used for the ameliora-
tion of alkali spots in a semi-arid region, the natural rainfall
will often in time effect the removal.
In laying tiles it is necessary to have them at such a depth
that the soluble salts in the soil beneath them will not readily
rise to the surface. This will depend on those properties of the
soil governing the capillary movement of water. Three or
four feet in depth is usually sufficient, but the capillary move-
ment should first be estimated.
After the drains have been placed the land is flooded with
water to a depth of several inches. The water is allowed to
soak into the soil and to pass off through the drains, leaching
out part of the alkali in the process. Before the soil has
time to become very dry the flooding is repeated, and the
operation is kept up until the land is brought into a satis-
factory condition.
Crops that will stand flooding may be grown during this
treatment, and they will serve to keep the soil from puddling,
342 NATURE AND PROPERTIES OF SOILS
as it is likely to do if allowed to become dry at the surface.
If crops are not grown, the soil should be harrowed between
floodings. The operation should not be earried to a point
where the soluble salts are reduced below the needs of the
crop... The use of gypsum on black alkali land has sometimes
been practiced for the purpose of converting the alkali carbon-
ates into sulfates, thus ameliorating the injurious properties
of the alkali without decreasing the amount. The quantity
of gypsum required may be estimated from the amount and
composition of the alkali. The soil must be kept moist, in
order to bring about the reaction, and the gypsum should be
harrowed into the surface, not plowed under. The reaction
is as follows:
Na.CO, + CaSO, = CaCO, + Na,SO,
When soil containing black alkali is to be tile-drained, it
is recommended that the land should first be treated with gyp-
sum, as the substitution of alkali sulfates or carbonates causes
the soil to assume a much less compact condition and thus fa-
cilitates drainage. It also prevents the loss of organic matter
dissolved by the carbonate of soda and the soluble phosphates,
both of which are precipitated by the change.
Removal of the alkali incrustation that has accumulated at
the surface is sometimes resorted to. Very often the rise of
alkali is encouraged by applications of irrigation water, which
is allowed to evaporate unretarded. The salts are thus carried
upward by the eapillary movement of the soil-water. This
*It has been suggested that elemental sulfur could be used to advan-
tage in alkali land, especially where carbonates and bicarbonates abound.
Sulfur generally oxidizes in the soil quite readily, producing an acid
[see par. 221]. Instead of trying to remove all of the alkalinity by
leaching, it might be more practicable to add sulfur.
Lipman, J. G., Sulfur on Alkali Lands; Soil Sci., Vol. II, No. 3,
p. 205, 1916.
Hibbard, P. L., Sulfur for Neutralizing Alkali Soil; Soil Sei., Vol,
XI, No. 5, pp. 385-387, 1921.
ALKALI SOILS 343
method of alkali eradication is never very efficient, and is often
dangerous, as it encourages the presence of very large amounts
of alkali salts in the surface soil.
Often alkali accumulations may be washed from the soil sur-
face by turning on a rapidly moving stream of water. The tex-
ture of the soil, as well as the slope of the land, must be just
right for such a procedure. Generally so much water enters
the soil that the land remains heavily impregnated with alkali
salts. Both this method and the previous, even if successful,
are only temporary. Moreover, lands carrying so much alkali
as to admit of either one of these procedures may be so heavily
charged as never to yield to any form of either eradication
or control.
182. Control of alkali—Where excessive amounts of
soluble salts do not exist in a soil the control of the alkali with
a view of keeping it well distributed in the soil column is the
best practice. The retardation of evaporation is, of course, the
main object in this procedure. The intensive use 6f the soil-
mulch is, therefore, to be advocated, especially in all irrigation
operations where alkali concentrations are likely to occur.
Such a method of soil management not only saves moisture, but
also prevents the excessive translocation of soluble salts into
the root zone. This method of control is the most economical,
the cheapest, and the one to be advocated on all occasions, no
matter what may have been the previous means of dealing with
the alkali situation. Certain soils that are strongly impreg-
nated with alkali may be gradually improved by cropping with
sugar-beets and other crops that are tolerant of alkali and
that remove large quantities of salts. This is more likely to be
efficacious where irrigation is not practiced. Certain crops,
moreover, while somewhat seriously injured when young, are
very resistant once their root systems are developed. A good
example is alfalfa, the young plants being very tender while
the mature ones are extremely resistant. Temporary eradica-
344 NATURE AND PROPERTIES OF SOILS
tion of alkali may allow such a crop to be established. Farm
manure has been found especially useful in this respect.t The
crop once well established will then maintain itself in spite of
the concentrations that may occur later.
* Lipman, C. B., and Gericke, W. F., The Inhibition by Stable Manure
of the Injurious Effects of Alkali Salts in Soils; Soil Sci., Vol. VII,
No. 2, pp. 105-120, 1919.
CHAPTER XVIII
SOIL ACIDITY
A CHEMICAL or physico-chemical viewpoint regarding the
soil and its solution is essential in explaining many of the phe-
nomena, especially those relating to higher plants and their
nutrition. Since plants respond so markedly to their chemical
environment, the importance of soil reaction has long at-
tracted much attention. Two conditions are popularly recog
nized in this respect—soil alkalinity or alkali and soil acidity.
The former condition can only occur where soluble salts may
concentrate in the soil and is confined largely to arid and semi-
arid regions. Soil acidity, on the other hand, is common only
in kumid sections. So widespread is it occurrence and so
marked is its influence on crop yields that its importance in
a practical way surpasses that of soil alkali.
183. General nature of soil acidity..—The nature of soil
acidity is so little understood that it is impossible to define
or explain it except in the most general terms. So-called soil
acidity may be considered for practical purposes as a more
or less unfavorable condition for plant growth, arising in the
soil through a lack of certain active bases such as calcium and
magnesium and which in practice is alleviated by the addition
of some form of lime.?
Technically three reasons may be suggested as accounting
for the harmful effects of soil acidity: (1) unfavorable hydro-
*MacIntire, W. H., The Nature of Soil Acidity with Regard to its
Quantitative Determination; Jour. Amer. Soc, Agron., Vol. 13, No. 4,
pp. 137-161, 1921.
*Lime in an agricultural sense refers to all of the compounds of ¢al-
cium and magnesium commonly utilized in correcting soil acidity.
345
346 NATURE AND PROPERTIES OF SOILS
ven ion concentrations ;+ (2) presence of substances harm-
ful to plant growth such as active aluminum, manganese and
the like, the presence of which is usually accompanied by a
hydrogen ion concentration beyond neutrality; and (3) im-
proper nutrition arising from a lack of calcium as a nutrient
or as a synergistic agent in facilitating the entrance of other
nutrient ions into the plant.”
184. Hydrogen ion concentration—A number of condi-
tions are possible if the toxic influence of soil acidity is due to
an actual acid. The harmful effect might be due to an ab-
normally high hydrogen ion concentration arising from (1)
soluble organic or inorganic acids in the soil solution. Again
it might be due to (2) insoluble acids or acid salts which, on
reaction with water, produce acidity. In this case, the hydro-
gen ion concentration of the soil solution at any particular time
would not be a measure of the so-called soil acidity.* A harm-
ful hydrogen ion influence may also be ascribed (3) to soluble
acids, either organic or mineral, absorbed by the soil complexes
and which would become active only under certain conditions.
An additional feature of the actual acidity theory may lie in
(4) the selective absorption of bases by the soil, by which acid-
ity might be developed from neutral or even ‘alkaline salts.
If the actual acidity explanation is entertained, any one or all
of these phases might be considered as contributing to the dele-
terious effects so noticeable on certain plants.
185. Active toxic bases.—The explanation of the harm-
ful effects of so-called soil acidity as being due to the presence
of active toxic bases has of late received much attention. The
1Hydrogen is the one essential constituent of all acids. When dis-
solved in water, acids dissociate, the hydrogen ion becoming active. The
strength of an acid is determined by its hydrogen ion concentration.
*True speaks of this codperative relationship as synergism. By_ it
calcium makes other nutrients physiologically available. True, R. H.,
The Function of Calcium in the Nutrition of Seedlings; Jour. Amer.
Soe. Agron., Vol. 13, No. 3, pp. 91-107, 1921.
*Rice, F. E., and Osugi, S., The Inversion of Cane Sugar by Soils
and Allied Substances and the Nature of Soil Acidity; Soil Sci., Vol. V,
No. 5, p. 347, 1918.
SOIL ACIDITY 347
presence of active aluminum in so-called acid soils has been
known for some time. Abbott, Conner, and Smalley ! showed
in 1913 that aluminum salts were the toxic agents in a certain
unproductive soil. In 1918, Hartwell and Pember? proved
quite definitely that, for certain soils and for certain crops,
the aluminum ion was the injurious factor rather than the
hydrogen ion that accompanied it. The work of Mirasol * indi-
cates that active aluminum is usually present in acid soils.*
Although soluble iron is seldom present to an excess, its
ferrous salts are known to be toxic to a greater extent than
acids of the same concentration.®° While soluble iron may ac-
company active aluminum, it is questionable whether it ac-
tually figures in acidity effects. The toxic influence of man-
g@anese is more probable, since it is more soluble in an acid than
a neutral soil. While it is extremely toxic to plants above
a certain concentration the recent work of Funchess*® with
* Abbott, J. B., Conner, S. D., and Smalley, H. R., Soil Acidity, Nitri-
fication and the Toxicity of Soluble Salts of Aluminum; Ind. Agr. Exp.
Sta., Bul. 170, 1913.
* Hartwell, B. L., and Pember, F. R., The Presence of Aluminum as a
Reason for the Difference in the Effect of So-called Acid Soil on Barley
and Rye; Soil Sci., Vol. VI, No. 4, pp. 259-277, 1918.
*Mirasol, J. J., Aluminum as a Factor in Soil Acidity; Soil Sci.,
Vol. X, No. 3, pp. 153-192, 1920.
*See also, Kratzman, E., Zur Physiologischen Wirkung der Aluminium
Salz auf die Pflanze; Chem. Ztg., Jahrgang 38, S. 1040, 1914.
Ruprecht, R. W., Toxic Effect of Iron and Aluminum Salts on Clover
Seedlings; Mass. Agr. Exp. Sta., Bul. 161, 1915.
Miyake, K., The Toxic Action of Soluble Aluminum Salts upon the
Growth of the Rice Plant; Jour. Biol. Chem., Vol. 25, No. 1, pp.
23-28, 1916.
Conner, 8S. D., Liming in Its Relation to Injurious Inorganic Com-
pounds in the Soil; Jour. Amer. Soc. Agron., Vol. 13, No. 3, pp. 113-
124, 1921.
*Conner, S. D., Liming in Its Relation to Injurious Inorganic Com-
ee in the Soil; Jour. Amer. Soc. Agron., Vol. 13, No. 3, p. 114,
1921.
*Funchess, M. J., Acid Soils and the Tozicity of Manganese; Soil
Sci., Vol. VIII, No. 1, p. 69, 1919.
See also, Kelly, W. P., The Influence of Manganese on the Growth
of Pineapples; Haw. Agr. Exp. Sta., Bul. 23, 1909.
Skinner, J. J., and Reid, F. R., The Action of Manganese Under Acid
and Neutral Soil Conditions; U. S. Dept. Agr., Bul. 441, 1916,
348 NATURE AND PROPERTIES OF SOILS
Alabama soils indicates that it is probably of minor importance
as compared with aluminum. A toxic effect from magnesium
is possible, especially if there is not enough ealcium to prevent
it from exerting a poisonous influence. The presence of alumi-
num or iron in an active form is generally accompanied by a
high hydrogen ion concentration due to hydrolysis,! which
takes place readily in many soils.
186. Lack of nutrients——Less is known regarding this
condition than of the two previously discussed. The lack of
sufficient nutritive calcium in an acid soil has often been sug-
gested.? In addition, it may be possible that some plants re-
quire more calcium and other bases for their metabolic proec-
esses when growing on a so-called acid soil, due to the gen-
eration of particular conditions within the cells. Plants like
alfalfa absorb large amounts of calcium and may find an acid
soil especially unfavorable on this account.
True * has shown that the presence of calcium in consider-
able amount is necessary when certain plants are growing in
nutrient solution, that other nutrient ions may penetrate the
plant cells. Potassium, for example, was but slightly absorbed
even when present in large amounts, unless a certain concen-
Hydrolysis is a double decomposition in which one of the inter-
acting substances is water. The water produces H+ and OH- ions,
the former uniting with the non-metallic portion of the substance and
the hydroxyl with the remainder.
Active basic radicals give, with feeble acids in water, salts which
are alkaline. Active acids and active bases give neutral salts. Active
acids and less active bases yield salts which are acid in reaction.
A feeble base and a feeble acid may produce a salt which is either
acid or alkaline. Ammonium sulfide (NH,).S in solution is alkaline,
since the ammonium hydroxide which tends to form is more dissociated
than the hydrogen sulfide which also is present. Aluminum silicates in
water hydrolize readily and since aluminum hydroxide is less dissociated
than silicic acid, the hydrogen ions predominate over the hydroxyl ions
and an acid reaction results.
See Truog, E., Soil Acidity: Its Relation to the Growth of Plants;
Soil Sci., Vol. V, No. 3, pp. 169-195, 1918.
Also, Soil Acidity: Its Relation to the Acidity of the Plant Juices;
Soil Sci., Vol. VII, No. 6, pp. 469-474, 1919.
° True, R. H., The Function of Caleiwm in the Nutrition of Seed-
lings; Jour. Amer, Soc. Agron., Vol. 13, No. 3, pp. 91-107, 1921.
SOIL ACIDITY 349
tration of calcium ions was provided. This relationship,
spoken of as synergism, may be seriously interfered with by
so-called soil acidity.
187. The present status of the question.—Each of the
general hypotheses which have been advanced to explain the
detrimental influence of soil acidity has considerable plausible
evidence in its support. Cane-sugar, which is inverted only
in the presence of an acid, was found by Rice and Osugi' to
be inverted in soils, even when the water extracts from these
same soils were neutral or even alkaline. This seemed to indi-
eate that the acidity was actual and was inherent with the soil
mass rather than with the soil solution. This would also sug-
gest the presence of insoluble or absorbed acids that might be
liberated by hydrolysis, thus producing a harmful hydrogen
ion concentration. Other equally valuable data are available
on this phase of soil acidity. The work of Hartwell and Pem-
ber ? and of Mirasol,* however, is even more conclusive in re-
gard to aluminum as a toxic agent, especially as they studied
the problem from the plant standpoint.
Conner,* investigating the comparative influence of sulfuric
acid and aluminum sulfate on plants, has obtained some in-
teresting data corroborating the work of Hartwell and Pember.
By comparing a given hydrogen ion concentration with the
same hydrogen ion concentrations plus equivalent amounts of
aluminum ions, he was able to demonstrate the greater toxicity
of aluminum to barley and rye in water culture. Since soluble
aluminum so often accompanies an unfavorable hydrogen ion
Rice, F. E., and Osugi, 8., The Inversion of Cane Sugar by Soils
and Allied Substances and the Nature of Sotl Acidity; Soil Sci.
Vol. V, No. 5, pp. 333-358, 1918.
? Hartwell, B. L., and Pember, F. R., The Presence of Aluminum
as a Reason for the Difference in the Effect of So-called Acid Soil on
Barley and Rye; Soil Sci., Vol. VI, No. 4, pp. 259-277, 1918.
*Mirasol, J. J., Aluminum as a Factor in Soil Acidity; Soil Sci.,
Vol. X, No. 3, pp. 153-193, 1920.
“Conner, S. D., Liming in Its Relation to Injurious Inorganic Com-
pounds in the Soil; Jour. Amer. Soe. Agron., Vol. 13, No. 3, pp. 113-
124, 1921.
390 NATURE AND PROPERTIES OF SOILS
concentration, the importance of aluminum in acidity cannot
be avoided.
TaBLE LXXX
RELATIVE WEIGHTS OF BARLEY AND RYE GROWN IN WATER CUL-
TURE. THE HYDROGEN ION CONCENTRATION IS EX-
PRESSED IN PH.1
H Ion RELATIVE WEIGHTS
TREATMENT CoNCENTRA-
TION PH BARLEY | RYE
Cee ny sree Men ae el 6.3 100 100
ESO POE Ie, ier i 93 95
CSOD euseatae mr 4.2 68 65
ESO ics dotted ee 3.9 73 65
ASO pee! me: see 3.9 55
47
The only conclusion possible at the present time is that
there are probably several kinds of acidity and many degrees
of the same acidity as far as toxic influences are concerned.
Moreover, dissimilar plants seem to be affected differently by
the same acidity, while the same plants respond diversely at
different times. Hoagland? and others* have demonstrated
that some plants grow better in a slightly acid medium, which
1The hydrogen ion concentration of an acid in solution is a measure
of the dissociation of that acid and of its strength. The specific acidity
of pure water is taken as 1, the number of grams of H+ ions to a liter
being .0000001 or 10-7. The exponent of the power is taken as an expres-
sion of the acidity. Pure water has a PH value of 7, which is approxi-
mate neutrality. An acid solution containing 4000 times more H+ ions
would have a PH value of 3.4.
* Hoagland, D. R., Relation of the Concentration and Reaction of
the Nutrient Medium to the Growth and Adsorption of the Plant;
Jour. Agr. Res., Vol. XVIII, No. 2, pp. 73-117, 1919.
*Gillespie, L. J., The Reaction of the Soil and Measurements of
Hydrogen ion Concentration; Jour. Wash. Acad. Sci., Vol. 6, No. 1,
pp. 7-16, 1916.
Sharp, L. T., and Hoagland, D. R., Acidity and Adsorption in Soils
as Measured by the Hydrogen Electrode; Jour. Agr. Res., Vol. VII,
No. 3, pp. 123-145, 1916.
Gillespie, L. J., and Hurst, L. A., Hydrogen-ion Concentration—Soil
Type—Common Potato Scab; Soil Sci., Vol. VI, No. 3, pp. 219-236,
1918.
SOIL ACIDITY 351
seems to indicate that the hydrogen ion concentration less
than a Ph value of 7, so often reported in so-called acid soils,
is concomitant with a toxic constituent or with malnutrition
and is not in itself the harmful agent.t This argument, how-
ever, does not admit that the hydrogen ion is not in many
cases the true explanation of the toxicity of certain acid soils,
nor does it suggest that lack of nutrients may not be a serious
consideration.
In light of the explanations offered above, it is evident that
the term soil acidity is inadequate to express the inorganic
toxicity that accompanies a hydrogen ion concentration below
Ph 7, as the condition referred to is, in many cases, not due to
the hydrogen ion in detrimental concentration.” Since the
term is of long standing and since so-ealled acid soils almost
invariably yield an acid reaction with litmus paper, the phrase
will continue in use in spite of its misleading inference.
188. Why soil acidity develops.*—No matter what hypoth-
1 Joffe found that while alfalfa plants experienced difficulty in becom-
ing established in soils having high hydrogen ion concentrations due
to the addition of sulfuric acid, once the seedlings became established
they showed normal color and vigor and made excellent growth on soils
having a Ph value as low as 3.8.
Joffe, J.S., The Influence of Soil Reaction on the Growth of Alfalfa;
Soil Sci., Vol. X, No. 4, pp. 301-307, 1920.
2 Researches on Danish soils extending from 1916 to 1920 show that
the Ph value on different soils may vary from 3.4 to 8.0. A rather
constant relationship was observed between the type of vegetation and
the hydrogen ion concentration, many species being found only on
soils within a certain range of Ph values. In water culture studies
so-called acid-soil plants grew best at a Ph of about 4. Alkaline-soil
plants seemed to give the strongest growth at a Ph of 6 to 7.
Olsen, C., The Concentration of the Hydrogen Ions in the Soil;
Science (N. S.), Vol. LIV, No. 1405, pp. 539-541, Dec. 2, 1921.
*White, J. W., Studies in Acid Soils; Ann. Rep. Penn. State Col.,
1912-1913, pp. 55-104,
Skinner, J. J., and Beattie, J. H., Influence of Fertilizers and Soil
Amendments on Soil Acidity; Jour. Amer. Soe. Agron., Vol. 9, No.
1, pp. 25-35, 1917.
Conner, S. D., Soil Acidity as Affected by Moisture Conditions of the
Soil; Jour. Agr. Res., Vol. XV, No. 6, pp. 321-329, 1918,
Martin, W. H., The Relation of Sulfur to Soil Acidity and to the
Control of Potato Scab; Soil Sci., Vol. IX, No. 6, pp. 393-408, 1920.
302 NATURE AND PROPERTIES OF SOILS
esis may be considered as best explaining soil acidity, sci-
entific and practical men are agreed that the addition of cer-
tain compounds of calcium and magnesium tend to alleviate
the detrimental condition. Conversely, almost every one is
willing to admit that the most reasonable cause of its develop-
ment is the loss or inactivity of certain bases. A lack of cal-
cium seems especially prone to allow an increased hydrogen
ion concentration to develop and may at the same time en-
courage the activity of certain toxic bases or produce malnu-
trition. The tendency of all soils in a humid region is, there-
fore, towards acidity, their condition depending on the activ-
ity of certain factors which seem to produce such a condition.
The four important factors generally specified as encour-
aging acidity are: (1) leaching losses, (2) cropping losses,
(3) absorption phenomena within the soil, and (4) fertilizer
residues.
The loss of nutrient bases from the soil has already been
emphasized (par. 163) and the importance of such removal is
evident from the standpoint of plant nutrition. Over a period
of ten years, the removal of nutrients from the Cornell lysi-
meter soils,t by drainage and rotation cropping together,
amounted to 3702, 1741, and 942 pounds to the acre, respec-
tively, for lime (CaO), potash (K,O), and magnesia (MgO).
The loss of such amounts of bases cannot but permit the rapid
development of soil acidity. No matter how well supplied
the soil may be with favorable bases, it will in time become
acid.
Absorption, in its influence on soil acidity, produces its
effect by rendering certain bases inactive rather than by
removing them from the soil. When the activity of such bases
as calcium is reduced by absorptive influences, not only does
the hydrogen ion concentration of the soil solution tend to in-
crease, but the hydrolysis of compounds carrying aluminum
and similar bases seems to be encouraged. The acidity as de-
* Unpublished data, Cornell Agr. Exp. Sta., Ithaca, N. Y.
SOIL ACIDITY 353
veloped may have a nutritive relationship as well as a toxic
effect.
When fertilizer salts are added to the soil, the basic ions
are usually absorbed to a greater degree than the acid radi-
cals. This tends to develop actual acidity in the soil solution,
which may in itself be toxic or may facilitate the development
of detrimental ions. If the erop utilizes the basic ion of the
fertilizer added to a greater extent than the acid radical, it
will aid in the development of acidity. If the plant, on the
other hand, absorbs the acid radical, it will tend to counter-
act the selective absorption by the soil. The combined influ-
ences of soil and crop on ammonium sulfate tend to develop
acidity, while the effect on sodium nitrate is toward alkalinity.
A salt such as potassium nitrate should leave no residue.
The decomposition of organic matter, especially when green-
manures are plowed under, is often considered as increasing
the acidity of the soil. Such may be the case at the beginning
of the decomposition process, but the data‘ available on the
subject seem to indicate that organic matter, if it exerts any
influence on acidity, tends to reduce rather than accentuate
it. This result may occur through the liberation of bases
from the organic matter as decomposition proceeds.
189. Relative tolerance of acidity by plants.—Since so
many intermediate influences are possible in acid soils, and
since plants respond so differently to these influences, it is im-
possible to forecast the relative resistance of different crops
on the same soil. The response of the same crop on differen*
acid soils is likewise difficult to foretell.
It is known that certain crops are often more tolerant to
soil acidity than others. Of the common weeds sheep sorrel,
1White, J. W., Soil Acidity as Influenced by Green Manures; Jour.
Agr. Res., Vol. XIII, No. 3, pp. 171-197, 1918.
Stephenson, R. E., The Effect of Organic Matter on Soil Reaction;
Soil Sci., Vol. VI, No. 6, pp. 413-439, 1918.
Howard, L. P., The Reaction of the Soil as Influenced by the De-
composition of Green Manures; Soil Sci., Vol, IX, No. 1, pp. 27-38,
1920.
304 NATURE AND PROPERTIES OF SOILS
paint-brush, daisy, and plantain seem especially resistant.
This does not mean, however, that they grow better on an
extremely acid soil than on one that is slightly acid or neutral.
Some of the common crops that are tolerant of acidity are
strawberry, blackberry, watermelon, red-top, Rhode Island
bent-grass, cowpea, soybean, rye, millet, and buckwheat. Such
crops as alfalfa, red clover, timothy, maize, oats, barley, cab-
bage and sugar-beet seem to be susceptible in various degree
to acid conditions.
Reasons for the above differences are not as yet known, since
plants apparently alike in every other respect differ in their
reaction to the same acid condition. The following pairs of
plants may be listed as examples: watermelon and musk-
melon, blackberries and raspberries, apple and quince, turnip
and beet, beans and alfalfa, red-top and timothy, rye and
barley. The first of each pair mentioned will grow well on
acid soils, while the second crop in each case is very detri-
mentally affected.t
190. Tests for soil acidity..—The great importance of
soil acidity to plant growth has directed much attention
towards methods for determining the acidity of the soil.
1 Hartwell, B. L., Need for Lime as Indicated by Relative Toxicity of
Acid Soil Conditions to Different Crops; Jour. Amer. Soc. Agron., Vol.
13, No. 3, pp. 108-112, 1921.
2Some of the important methods are compared and discussed in the
following articles:
Sechollenberger, C. J., Relation Between the Indications of Several
Lime-requirement Methods and the Soil Content of Bases; Soil Sci.,
Vol. III, No. 3, pp. 279-288, 1917.
Christensen, H. R., Haperiments in Methods for Determining the
Reaction of Soils; Soil Sci., Vol. IV, No. 2, pp. 115-178, 1917.
Stephenson, R. E., Soil Acidity Methods; Soil Sci. Vol. VI, No. 1,
pp. 33-52, 1918.
Blair, A. W., and Prince, A. L., The Lime Requirement of Soils
According to the Veitch Method, Compared with the Hydrogen-Ion
Concentration of the Soil Extract; Soil Sci., Vol. IX, No. 4, pp. 253-
259, 1920.
Hartwell, B. L., Pember, F. R., and Howard, L. P., Lime Require-
ment as Determined by the Plant and by the Chemist; Soil Sci., Vol.
VII, Ne. 4, pp. 279-282, 1919.
SOIL ACIDITY 399
Such methods may be divided, for convenience of discussion,
under two heads: quantitative determinations and qualita-
tive tests. In the first case the methods devised purport to
give the lime requirement of the-soil. The second group of
methods attempts to determine whether the soil is acid and
may in addition give some general idea as to the degree of
acidity.
191. Lime-requirement determinations.—A great num-
ber of methods has been advanced for the determination of the
lime requirement of soils. The methods may for convenience
be grouped under three heads: (1) those using a neutral salt,"
(2) those utilizing a basie substance,* and (3) miscellaneous
procedures.
In the first group, some neutral salt such as potassium ni-
trate is added to the soil and the amount of actual acidity
developed is determined under suitable control. The actual
acidity produced by selective absorption and basic exchange
is thus taken as a measurement of the soil acidity and is gen-
erally figured to pounds of lime to the acre.
In the second group some basic substance, preferably that
which is used in practice to correct acidity, is added to the
soil. The amount of the basic substance necessary to render
the soil alkaline or neutral is determined in pounds to the
*The Hopkins methods utilize potassium nitrate or sodium chloride.
Caleium acetate is used in the Jones method.
Hopkins, C. G., Knox, W. H., and Pettit, J. H., Ad Quantitative
Method for Determining the Acidity of Soils; U. S. Dept. Agr., Bur.
Chem., Bul. 73, pp. 114-121, 1903.
Jones, C. H., Method for Determining the Lime Requirement of
Soils; Jour. Assoc. Off. Agr. Chemists, Vol. I, No. 1, pp. 43-44, 1915.
*The Veitch method utilizes calcium hydroxide, the Tacke method
calcium carbonate and the method proposed by Hutchinson and Mac-
Lennan calcium bicarbonate.
Veitch, F. P., Comparison of the Methods for the Estimation of
Soil Acidity; Jour. Amer. Chem. Soc., Vol. 26, pp. 637-662, 1904.
Tacke, Br., Uber die Bestimmung der freien Huwmussduren; Chem.
Ztg., Bd. 21, Heft. 20, S. 174-175, 1897.
Hutchinson, H. B., and MacLennan, K., The Determination of the
Lime Requirement of the Soil; Chem. News, Vol. 110, p. 61, 1914.
396 NATURE AND PROPERTIES OF SOILS
acre. Calcium hydroxide and calcium carbonate are often
used.
Many investigators consider that the hydrogen ion concen-
tration of the soil solution is a fair measure of the lime re-
quirement of a soil.1 They thus assume that the concentra-
tion of the hydrogen ion is a comparative indication of the
amount of lime necessary to alleviate the detrimental influ-
ences due to acidity. Bouyoucos? claims that the depression
of the freezing point (see par. 145) may be used to measure
soil acidity. He found that the depression of the freezing
point was less for a neutral soil than for one either acid or
alkaline.
192. The Veitch method.—In order to show something
of the procedure necessary in determining the lime require-
ment of the soil, the Veitch method, which utilizes calcium
hydroxide, will be briefly described. Eleven and and one-fifth
grams of soil are placed in a suitable Erlenmeyer flask and
treated with a standard lime-water solution. The amount of
soil taken and the strength of the calcium hydroxide solution
are such that each cubic centimeter of the latter absorbed by
the soil indicates the need of 300 pounds of calcium oxide
to the acre. A number of samples are run at the same time,
receiving progressively larger amounts of lime-water. The
tGainey, P. L., Soil Reaction and Growth of Azotobacter; Jour.
Agr. Res., Vol. XIV, No. 7, pp. 265-271, 1918.
Gillespie, L. J., and Hurst, L. A., Hydrogen Ion Concentration—
Soil. Type—Common Potato Scab; Soil Sci., Vol. VI, No. 3, pp. 219-
236, 1918.
Plummer, J. K., Studies in Soil Reaction as Indicated by the Hydro-
gen Electrode; Jour. Agr. Res., Vol. XII, No. 1, pp. 19-31, 1918.
Joffe, J. H., Hydrogen Ion Concentration Measurements in Sotls in
Connection with Their Lime Requirements; Soil Sci., Vol. IX, No. 4,
pp. 261-266, 1920.
Blair, A. W., and Prince, A. L., The Lime Requirement of Soils
According to the Veitch Method Compared with the Hydrogen Ion Con-
centration of the Soil Eatract; Soil Se:., Vol. IX, No. 4, pp. 253-259,
1920.
*Bouyoucos, G. J., The Freezing Point Method as a New Means of
Determining the Nature of Acidity and Lime Requirements of Sotls;
Mich, Agr. Exp. Sta., Tech. Bul. 27, 1916,
SOIL ACIDITY 307
samples are brought to dryness over a steam bath and then
taken up with about 100 cubic centimeters of water. The
samples, after shaking, are allowed to settle, and the super-
natant liquid is treated with phenolphthalein. By the use
of a number of samples with varying amounts of lime-water,
the amount of the reagent necessary to neutralize the soil can
be approximately determined.
The objections that can be urged against the Veitch method
may serve to indicate the difficulties that are in general en-
countered in using most of the methods for determining the
lime requirement of soils. The method is, in the first place,
very artificial, there being no assurance that the amount of
calcium absorbed is the same as that necessary to neutralize
the soil under field conditions. In the second place, it is
subject to considerable error. Even with the most careful
manipulation, the method is hardly accurate within 300
pounds of calcium oxide to the acre.
If the results from such a method are to be applied directly
to practical liming it must be assumed that the amount of lime
necessary to neutralize an acid soil is the same as that capable
of alleviating the acidity for a particular crop. In lght
of the variable influences of acidity on plants, this is an un-
scientific assumption to say the least. Acidity itself is too
intangible a condition. Moreover, it is in many cases not only
inadvisable but also unprofitable to satisfy the full lime re-
quirement of a soil. Some crops are unharmed or may even
be benefited by moderate acidity. The selection of a lawn
grass, for example, which is tolerant to acidity may allow
the suppression of certain troublesome weeds that would
spring up if the soil was limed.
Since the results from lime-requirement methods must be
so radically modified to suit field conditions, they seem but
little better in a practical way than qualitative tests, which
distinguish only in a general manner between different de-
grees of acidity. The rapidity and simplicity of qualitative
358 NATURE AND PROPERTIES OF SOILS
tests give them an advantage over the somewhat questionable
lime-requirement determinations. As the amount of lime
applied is at best only an estimate, a simple test, rationally
correlated with the many other factors that must be consid-
ered, may prove as satisfactory as a more complicated pro-
cedure.
193. Qualitative tests for acidity—litmus paper.—Per-
haps the oldest test for acidity is the use of litmus paper.
This may be used alone or in connection with some sensitiz-
ing agent. Potassium nitrate, a neutral salt, is often utilized
in this capacity. As has already been explained (par. 141),
the addition of such a salt, especially to a soil lacking in ac-
tive bases, results in a marked selective absorption and the
development of a hydrogen ion concentration. In using litmus
paper and potassium nitrate it is assumed that the selective
absorption and basic exchange is an approximate measure of
the so-called soil acidity.
The procedure is as follows: A small amount of the soil
to be tested is placed in a small dish or other container and
moistened with a neutral potassium nitrate solution. A thick
batter is produced by mixing. The soil is then smoothed
down and one end of a strip of neutral litmus paper is care-
fully applied. The reddening of the paper is an indication
of acidity, while the rate of the reaction is a rough measure
of the degree. The portion of the paper not in contact with
the soil may be used for comparison when the change is slight.
The unused end may even be moistened with distilled water
to make the comparison more accurate.
194. The zinc-sulfide test—Another qualitative test
based on the same general principles has more recently been
* Barlow, J. T., Soil Acidity and the Litmus Paper Method for Its
Detection; Jour. Amer. Soc. Agron., Vol. 8, No. 1, pp. 23-30, 1916.
Karraker, P. E., The Value of Blue Litmus Paper from Different
Sources as a Test for Soil Acidity; Jour. Amer. Soc. Agron., Vol. 10,
No. 4, pp. 180-182, 1918.
SOIL ACIDITY 359
developed. This is the zine-sulfide method.t The soil sample,
usually 10 grams, is placed in an Erlenmeyer flask and treated
with an excess of neutral calcium chloride and zine sulfide.
About 75 cubie centimeters of water are added. The mixture
is boiled for one minute to control frothing and to develop
uniform ebullition. A strip of moistened lead acetate paper
is now laid over the mouth of the flask and allowed to remain
there exactly three minutes, the boiling being continued at
a uniform rate. The reactions involved in the test are as fol-
lows:
Soil + xCaCl, (neutral) ss Ca, Soil + xHCl
2HCl + ZnS = ZnCl, + HS
H.S (Expelled by boiling) + Pb(C,H,0,), = PbS
(black) + 2C,H,0,
The selective absorption and basic exchange of the soil de-
velops actual acidity, which produces hydrogen sulfide from
the zine sulfide. The gas is driven off against the lead acetate
paper, producing a black color. The principle involved is the
same as that already explained for the litmus test, a different
means being employed for measuring the actual acidity de-
veloped.
195. Comparison and criticism of qualitative tests —A
comparison and criticism of these two methods will amply
show the advantages and disadvantages of qualitative tests ”
*Truog, E., New Method for the Determination of Soil Acidity;
Science, N. 8., Vol. 40, pp. 246-248, 1914.
Truog, E., Testing Soils for Acidity; Wis. Agr. Exp. Sta., Bul. 312,
1920.
* There are a number of other qualitative tests for acidity, of which
the following may be mentioned:
Ammonia test.—In this test the soil is placed in a bottle and treated
with a strong solution of ammonia. After shaking, the soil is allowed
to settle, the depth of the color developing in the supernatant liquid
being considered as indicating the degree of acidity. This color depends
on the amount and character of the soil organic matter rather than on the
acidity.
Acid test for carbonates.—In this test a sample of the soil is treated
with a few drops of dilute hydrochloric acid. Effervescence indicates the
360 NATURE AND PROPERTIES OF SOILS
in general. The litmus paper test is simple and rapid. It
ean be used with equal facility in the laboratory and field.
While its readings may not correlate very definitely with the
actual amount of lime that should be applied, it gives a basis
for an estimate that in practice should include a number of
factors besides so-called soil acidity. One objection to the
method lies in the difficulty of obtaining sensitive litmus paper.
Again the intensity of the color change is not great and in the
hands of an inexperienced person may seem insignificant. In
spite of its limitations, it is one of the best practical qualita-
tive tests for soil acidity now available.
The zinc-sulfide test is much more striking than the litmus
test and thus is more easily interpreted. On account of the
marked change of color there is always a temptation to read
into this test a quantitative value which it does not possess
to any greater degree than does the litmus paper method.
The zine sulfide test is not as rapid as the litmus test, nor is
it a satisfactory field method. Moreover, it is more complex
and requires a much more extensive technique. Again it does
not distinguish between a neutral and an alkaline soil. Lit-
mus paper, on the other hand, indicates alkalinity and acidity
with equal facility. The zine-sulfide test is not a method
suited for those inexperienced in laboratory procedure. The
deductions from the two tests, however, should be approxi-
mately the same.
196. Resume.—Soil acidity is a more or less unfavorable
biological condition, which develops in soils due to the lack or
presence of sufficient favorable bases in the carbonate or bicarbonate
forms. A soil, however, may be alkaline and yet fail to effervesce.
Potassium sulfo-cyanate test——A new test has recently been proposed
in which a sample of soil held in a test-tube is treated with an alcoholic
solution of potassium sulfo-cyanate (KSCN). If the supernatant liquid
turns red, soluble iron is present, the degree of color indicating the
amount. It is assumed that the soluble iron is a comparative measure
of the active aluminum in the soil and that aluminum is the toxic
constituent.
Comber, N. M., A Qualitative Test for Sour Soils; Jour. Agr. Sci.,
Vol. 10, part 4, pp. 420-424, 1920.
SOIL ACIDITY 361
inactivity of certain bases, especially those which tend to-
wards soil alkalinity. These necessary bases may be rendered
inactive by absorption phenomena or may be actually lost
through leaching and cropping. The specific and usually de-
leterious influence of so-called soil acidity may be due to an
excessive hydrogen ion concentration or to toxic bases such
as aluminum, iron, and manganese, which become active when
ionic calcium and similar bases are lacking, thus encouraging
a hydrogen ion accumulation. It is not improbable that in
some cases the detrimental influence may be improper nutri-
tion, either due to a lack of calcium as a nutrient or as a syner-
gistic agent necessary for the absorption of other nutrients
by plants. These detrimental conditions are alleviated in
practice by the application of some form of lime.
A number of different methods has been devised to ascer-
tain quantitatively the lime requirements of soils. They are
all more or less inaccurate. Moreover, the lime requirement
of a soil and the lime necessary for best plant growth on that
soil are not of necessity the same. Plants respond very differ-
ently to the diverse conditions that may develop in the various
acid soils and it is seldom necessary or practicable entirely to
neutralize a very acid soil in order to correct its deleterious
condition. While lime-requirement methods are valuable in
research, qualitative tests are sufficient in practice. The
amount of lime that should be applied is determined not only
by the degree and nature of the acidity but also by the char-
acter of the crops, the length of rotation, the system of fer-
tilization, and similar factors. At best the amount of lime
that should be applied to the acre is but an estimate based
on many conditions, of which acidity is one. A qualitative
test seems as satisfactory a basis for such an estimate as a
more carefully controlled quantitative determination.
CHAPTER XIX
LIMING THE SOIL?
WuueE soil acidity is a condition but imperfectly under-
stood, most investigators are agreed that it is due to a lack or
inactivity of certain bases, especially those that tend to reduce
the hydrogen ion concentration of the soil solution and to
give the soil an alkaline reaction. The correction of acidity
obviously les in the addition of compounds which carry the
necessary bases in such forms that the acidity may be partially
or wholly alleviated.
The base most commonly used to correct acidity is calcium,
although magnesium is often applied, especially in connec-
+The following publications may be of interest:
Hopkins, C. G., Ground Limestone for Acid Soils; Ill. Agr. Exp. Sta.,
Cire. 110, 1907.
Ellett, W. B., Lime for Virginia Farms; Va. Agr. Exp. Sta., Bul. 187,
1910.
Brown, P. E., Bacteriological Studies of Field Soils: The Effects of
Lime; Ia. Agr. Exp. Sta., Res. Bul. 5, 1912.
Whitson, A. R., and Weir, W. W., Soil Acidity and Liming ; Wis. Agr.
Exp. Sta., Bul. 230, 1913.
Frear, W., Sour Soils and Liming; Penn. Dept. Agr., Bul. 261,
1915.
Miller, M. F., and Krusekopf, H. H., Agricultural Lime; Mo. Agr.
Exp. Sta., Bul. 146, 1917.
Mooers, C. A., Ground Limestone and Prosperity; Tenn. Agr. Exp.
Sta., Bul. 119, 1917.
Shorey, E. C., The Principles of the Liming of Soils; U. S. Dept. Agr.,
Farmers’ Bul. 921, 1918.
McCool, M. M., and Millar, C. E., Some General Information on Lime
and Its Uses and Functions in Soils; Mich. Agr. Exp. Sta., Special Bul.
91, 1918.
‘Agee, Alva., The Right Use of Lime in Soil Improvement; New York,
1919,
Hudelson, R. R., Keeping Soils Productive; Mo. Agr. Exp. Sta., Cire.
102, 1921.
362
LIMING THE SOIL 363
tion with calcium. Calcium is employed because it is not only
effective with all types of acidity but because it is ecompara-
tively cheap and plentiful. Potassium in active form is too
expensive, sodium is likely to generate harmful compounds
in the soil, while magnesium in large amounts is sometimes
harmful. Calcium compounds may be applied in excess and
yet no harmful effects on plant growth are ordinarily lkely
to result."
197. Forms of lime.—The term lime correctly used re-
fers only to calcium oxide (CaO). In a popular and agri-
cultural sense the scope of the word has been broadened to
include all of the commercial compounds of calcium and mag-
nesium commonly applied to the soil to correct the so-called
acidity. The term in its agricultural sense refers to the fol-
lowing compounds either alone or in mixture: calcium oxide
(CaO), magnesium oxide (MgO), calcium hydroxide (Ca-
(OH),), magnesium hydroxide (Mg(OH),), calcium ear-
bonate (CaCO,), and magnesium carbonate (MgCO,). Such
compounds as gypsum (CaSO,.2H,O), mono-calcium phos-
phate (CaH,(PO,),), and calcium silicate (Ca,Si0,), insofar
as they are carriers of calcium, also might be spoken of as lime.
As might be expected, liming materials do not appear on the
market as single compounds of magnesium or calcium, nor
are they by any means pure. The better grades of the oxides
and hydroxides are generally used in the trades, the more im-
pure materials having an outlet as agricultural ime. The car-
bonated forms of lime have a number of different sources and
vary to a marked degree in purity. Lime, in whatever form
it may appear on the market, almost always carries magnesium
as well as calcium, the latter usually predominating.
Three general groups of lime, as it is commercially handled,
Floyd, B. F., Some Cases of Injury to Citrus Trees Apparently
Induced by Ground Limestone; Fla. Agr. Exp. Sta., Bul. 137, 1917.
Wyatt, F. A., Influence of Calcium and Magnesium Compounds on
Plant Growth; Jour. Agr. Res., Vol. VI, No. 16, pp. 589-619, 1916.
0604 NATURE AND PROPERTIES OF SOILS
may be recognized: (1) burned lime,’ (2) water-slaked or
simply slaked lime,? and (3) carbonated lime.*
The devices for producing burned lime are various, rang-
ing from the farmer’s lime heap to the immense eylindrical
kilns of commerce. In any case the general result is the same.
The limestone with which the kiln is charged is decomposed by
the heat, carbon dioxide and other gases are discharged, and
calcium and magnesium oxides are left behind.* The purity of
burned lime, as it is sold for agricultural purposes, is quite
variable, ranging from 60 to 98 per cent. of calcium and mag-
nesium oxides. As high as 40 per cent. of burned lime may
be magnesium oxide, if the original stone was dolomitic. The
impurities of burned lime consist of the original impurities
of the limestone, such as chert, clay, iron compounds, and the
like, as well as unburned fragments of the stone. These ma-
terials are often partially screened out before the product ap-
pears on the market.
Slaked lime is produced by adding water to the burned
product, a hydroxide resulting from the direct union of the
oxides of calcium and magnesium with water.° Often some
of the calcium and magnesium oxides remain unslaked. Four
lime compounds may, therefore, appear in freshly slaked lime,
besides the original impurities of the burned materials. Com-
1Often spoken of as burnt lime, oxide of lime and quick lime. It
may be purchased either in the lump form or in a finely ground condi-
tion. It is highly caustic and reacts readily with water.
* Incorrectly designated in trade as hydrated lime or lime hydrate.
It is strongly alkaline and quite caustic but not to the degree exhibited
by calcium and magnesium oxides. Calcium hydroxide and magnesium
hydroxide are soluble in cold water to the extent of about 17 parts and
.09 parts in 10,000, respectively.
®The carbonated forms of lime are often incorrectly spoken of as
lime carbonate and carbonate of lime. Calcium and magnesium carbo-
nates are soluble in pure cold water to the extent of only about .13 and
1.06 parts in 10,000, respectively. The reaction to litmus is slightly
alkaline.
*CaCO, + Heat — CaO + CO,
MgCO, + Heat = MgO + CO,,
> CaO + H,O= Ca (OH)..
MgO + H,O = Mg(OH),.
LIMING THE SOIL 365
mercial slaked lime ranges in composition from 60 to 75 per
cent. of lime expressed as calcium plus magnesium oxides.
Both the burned and slaked forms of lime tend to absorb ecar-
bon dioxide from the air, producing calcium and magnesium
earbonate. This is called air-slaking."
A number of lime compounds are sold under the head of
earbonated lime. Of these pulverized or ground limestone is
the most common. There is also bog lime or marl, oyster
shelis and artificial carbonates. The latter are by-products
from certain industries. All of these are quite variable in
their content of calcium and magnesium carbonates. Pul-
verized limestone may vary in purity from 75 to 98 per cent.,
90 per cent. being a fair average. Highly magnesian stone is
generally avoided, although stone carrying from 15 to 20 per
cent. of magnesium carbonate is often used. The magnesium
carbonate, however, usually makes up less than 5 per cent. of
the lime present.
The figures * quoted in table LX XI (see page 366) show the
average composition of liming materials offered for sale in
Pennsylvania from 1916 to 1920 inclusive.
198. Determining the need for lime——The lack of lime
in the soils of humid regions is so universal that liming will
generally increase crop growth. For example, 72 per cent. of
the soils of Pennsylvania * are sour, while 75 per cent. of the
cultivated lands of Indiana‘ show acidity by the ordinary
tests. While it is safe to assume that the productivity of
three-fourths of the soils in the eastern part of the United
States would be raised by liming, it is a question in many cases
whether such treatment would pay.
1Ca(OH),. + CO,= CaCO, + H.O.
Mg(OH), + CO, = MgO, + H.O.
bea eee J. W., Lime Report; Penn. Dept. Agr., Vol. 4, No. 2, Feb.
® White, J. W., Lime Requirements of Pennsylvania Soils; Penn. Agr.
Exp. Sta., Bul. 164, 1920.
*Wiancko, A. T., Conner, S. D., and Jones, 8. C., The Value of Lime on
Indiana Soils; Ind. Agr. Exp. Sta., Bul. 213, 1918.
366 NATURE AND PROPERTIES OF SOILS
TasLeE LXXI
NUMBER 5) | INSOLU-
Form or LIME OF Res MgO BLE
SAMPLES ° |Marrrr
Burned lime (low mg.)... 59 70.01 209 (| alg
Burned lime (high mg.).. + 02.23 | 33.07 | 2.81
Slaked lime (low mg.)....| 242 64.26 3.10 |) ole
Slaked lime (high mg.)..| 107 48.87 | 28.07 | 1.58
Pulverized limestone...... 161 47.83 3.19 | 6.82
Pulverized oyster shell.... + 47,60 .O9: |: .Oehe
Artificial carbonate....... 72 50.70 2.52 ; 1.29
Ma) DS Soi cae Ane eA RL 22 46.75 1.00 | 5.90
The first point to be determined in deciding whether or
not lime should be applied is in regard to the .acidity and its
degree. The litmus or zine sulfide test will supply this in-
formation, although a quantitative determination may be
made. The general degree of acidity, unless it is very high,
is not sufficient, however, in deciding whether it would be
wise to lime the soil. The nature of the crops is a factor,
as well as the type of the rotation, the fertilizer to be used,
and to what extent farm manure and green-crops are utilized.
Often special considerations are involved, such as scab on
potatoes, which is encouraged by liming. All of the factors
mentioned, as well as the experiences of the community with
lime, should be considered in deciding whether liming would
pay. If the increased crops that will probably result from
an application of lime will not pay a good interest on the
investment, then liming is not to be advised. An application
sufficient to make possible the production of good crops of
clover or alfalfa is probably all that can be used profitably.
1The tests are discussed in Chapter XVIII.
LIMING THE SOIL 367
199. Form of lime to apply.—The experimental data
regarding the relative effectiveness of the different forms of
lime are not only meagre but also somewhat contradictory.
In practice it is best to assume that the effectiveness of the
lime depends on the amount of magnesium and calcium ear-
ried and is influenced to a much less degree by the particular
combinations in which these bases may occur. For example,
one and a half tons of medium to finely ground limestone
carrying 50 per cent. of calcium oxide should be as effective
as one ton of burned lime analyzing 75 per cent. caleium oxide.
While there is a difference in the rapidity with which the
various forms react, there seems to be but little difference be-
tween them over the period of a rotation when they are ap-
pled in chemical equivalent amounts.
Accepting this relationship as a practical working basis,
four factors must be considered in deciding what form of
agricultural lime to apply. These factors are as follows:
(1) chemical equivalents, determined by chemical combina-
tion and purity; (2) cost a ton, freight on board; (3) freight;
and (4) cost of haul and application to the land.
It is evident that, if the various forms of lime are equally
effective in chemical equivalent quantities, once these amounts
are determined the question becomes a problem in arithmetic.?
The importance of the factors above listed can best be shown
by working out an actual case.”
1CaO x 1.32 = Ca(OH), MgO x 1.44—=Mg(OH),
CaO x 1.78 = CaCO, MgO x 2.09 — MgCo,
Ca(OH), X .76—Ca0d Mg(OH), x .69=MgO
Ca(OH), Xx 1.35 = CaCO, Mg(OH), X 1.44— MgCo,
CaCO, x .56—CaO MgCO, X .48= MgO
CaCO, X .74=Ca(OH), MgCO, x .69 —=Meg(OH),
CaO X .70—=MgO MgO x 1.39 =CaO
* Calcium oxide and calcium hydroxide have an advantage over ground
limestone in percentages of calcium carried and possibly in initial ac-
tivity. They are, however, more disagreeable to handle and do not
mix with the soil so well since they tend to lump on becoming moist.
Partially or wholly carbonated lumps are often found in the soil years
after the caustic lime has been applied.
368 NATURE AND PROPERTIES OF SOILS
Suppose that slaked lime carrying 70 per cent. of calcium
oxide (CaQ) sells in carload lots at $8.00 a ton and that pul-
verized limestone of a fair degree of fineness costs in bulk
$4.50 and analyzes 50 per cent. of calcium oxide. Assume the
freight as $3.00 a ton and the cost of hauling to the farm and
applying to the land as $1.00 more.
The application of 1 ton of the agricultural slaked lime
would cost $8.00 + $3.00 + $1.00 = $12.00. It would be
necessary to apply 1.4 tons of the limestone to every ton of
slaked lime. This would amount to $6.30 + $4.20 + $1.40
= $11.90. The difference in this case is very slight be-
tween the two forms. lLessening the freight or shortening
the haul would give the advantage to the limestone, while in-
creasing these would favor the use of slaked lime.
It is obvious from such calculations that a flat reeommenda-
tion cannot be made in a county or community regarding the
lime to use. Each individual case should be calculated, con-
sidering the cost items already mentioned.
200. Amount of lime to apply.—The possibility of an
application of lime paying and the form to purchase can usu-
ally be determined with considerable assurance. Such is not
the case, unfortunately, regarding the amount of a given kind
of lime to apply to the acre. So many factors, of which soil
reaction is only one, are active in determining crop growth
that acre applications are at best estimates and often admit-
tedly guesses. Not only the degree of acidity but the texture
and the structure of the soil, the crops grown in rotation, the
length of the rotation, the fertilizers used, the amount of farm
manure added in a given period, and similar conditions must
be considered. In ordinary practice, it is seldom economical
to apply much more than a ton of limestone or its equivalent
to the acre, unless the soil is very acid and the promise for
increased crop yield exceptionally good. In many eases, it
seems unnecessary entirely to correct the acidity of a soil in
order to promote normal crop growth. The following figures,
LIMING THE SOIL 369
while merely tentative, serve in a general way as guides in
practical liming operations for a four- or five-year rotation
with average soils. The general degree of acidity may be
estimated from a qualitative test.
TABLE LX XXIT
SUGGESTED AMOUNTS OF AVERAGE PULVERIZED LIMESTONE THAT
SHOULD BE APPLIED TO THE ACRE UNDER
VARIOUS CONDITIONS.!
LIMESTONE—POUNDS TO THE ACRE
ACIDITY
Sanpy Loam CLAY LoAmM
WiGGer ALG! Wo olka. becce ee 1200+1500 1800-2500
SILT O10 oo eae et ee Coe 1800+-2500 2500-3000
201. Changes of lime in the soil When calcium oxide or
calcium hydroxide are added to the soil, they undergo a very
rapid transformation, especially if the soil is moist. The
oxide takes up water and becomes the hydroxide, while the
latter almost as quickly changes to the carbonate. The reac-
tions are as follows:
CaO + H,O = Ca(OH),
Ca(OH), + CO, = CaCO, + H,0
It is generally supposed that when once the carbonate is
formed in the soil or added as pulverized limestone, it is more
*The equivalent amounts of burned or slaked lime may readily be
calculated from the chemical equivalents already quoted. Caleulate for
example the amount of slaked lime, carrying 65 per cent. of CaO and
5 per cent. of MgO, necessary to equal an application of 2000 pounds of
adequately pulverized limestone containing 48 per cent. of CaO and 2
per cent. of MgO. The 5 per cent. of MgO in the slaked lime and the
2 per cent. of MgO in the limestone are equivalent in neutralizing capacity
to 6.9 and 2.8 per cent. of CaO, respectively. The slaked lime and the
limestone, therefore, carry the equivalent of 71.9 and 50.8 per cent. of
200 50
CaO, respectively. 2S 1413 pounds, the amount of slaked
lime necessary to equal 2000 pounds of the limestone.
370 NATURE AND PROPERTIES OF SOILS
or less stable, except for slow solubility. In most cases, how-
ever, the carbonate, especially magnesium carbonate, is rap-
idly decomposed and earbon dioxide is given off, the bases
presumably entering the unsaturated aluminum silicates
which are likely to be present in acid soils."
The actual loss of lime in drainage water occurs through
the influence of carbon dioxide which changes the insoluble
carbonate to the soluble bicarbonate. The bicarbonate is
washed out as such or ionizes, the calcium and the magnesium
being lost in the ionic state. The presence of nitrates in the
soil, either from biological activity or from fertilizers, also
greatly facilitates the loss of lime from the soil in drainage.
Such influence is to be especially expected during the summer
and fall. In spite of the direct effect of carbon dioxide and
nitrates on the loss of lime, the controlling factor seems to be
the amount of water passing through the soil rather than its
concentration. The following unpublished data from the
Cornell University lysimeters show the losses of lime that may
be expected under different conditions.2 These figures are
averages of ten years’ work with Dunkirk silty clay loam.
TABLE LX XXIII
AVERAGE ANNUAL LOSS OF NITROGEN AND LIME BY LEACHING.
CORNELL LYSIMETERS. AVERAGE OF 10 YEARS.
PouNDS TO THE ACRE PER YEAR
ConDITION LIME EX- LIME EX-
NITROGEN | PRESSED AS | PRESSED AS
CaO CaCO,
Iara: SOM ckew etree 69.0 597.0 993.6
otatlonavetic cos eee hee 345.9 617.1
Grasse eee Ae 2.5 363.8 648.9
1MacIntire, et al., The Non-existence of Magnesium Carbonate in
Humid Soils; Tenn. Agr. Exp. Sta., Bul. 107, 1914.
?Complete data on these lysimeters will be found in par. 163.
LIMING THE SOIL 371
202. Effect of lime on the soil—In heavy soils there is
always a tendency for the fine particles to become too closely
associated. Such a condition interferes with air and water
movement. The granular structure that should prevail is
somewhat encouraged by the addition of lime, especially the
caustic forms. In practice, however, the amounts of lime ap-
plied are generally too small to have much importance in this
respect.
Chemically, lime brings about many complex changes in
the soil. Basic exchange is forced and certain mineral nu-
trients tend to become more available. The hydrogen ion
concentration is lowered and deleterious bases, such as alumi-
num and manganese, are forced back into less active combi-
nations. Oxidation processes seem also to be stimulated, thus
favoring the elimination of organic toxins, which often de-
velop when improper decay takes place. The charge that
quicklime in normal amounts produces a rapid and detri-
mental oxidation of the soil organic matter is probably an
over-statement.t While lime of all kinds promotes the oxida-
tion of organic matter, calcium oxide, when added in rational
amounts, is probably no more active over the term of the rota-
tion than calcium carbonate.
Most of the favorable soil organisms and some of the un-
favorable ones, such as those that produce potato-scab, are
benefited by judicious liming. The bacteria that fix nitrogen
from the air, either alone or in the nodules of some legumes,
are especially stimulated by the application of lime. The
change of ammoniacal nitrogen to the nitrate form, which is a
biological phenomenon, requires active basic material. Other-
wise this necessary transformation will not proceed. The
decomposition of both carbohydrate compounds (fermenta-
tion) and of nitrogenous materials (putrefaction) depends on
lime, that the decay products may be favorable.
1MacIntire, W. H., The Carbonation of Burned Lime in Soils; Soil
Sei., Vol. VII, No. 5, pp. 325-446, May, 1919.
372 NATURE AND PROPERTIES OF SOILS
Of the general and specific influences of lime just men-
tioned the correction of acidity is the one commonly ascribed
to it in the popular mind. The mere correction of the soil
reaction, however, is probably no more important than a
number of other direct and indirect influences of lime. It is
evident that the benefits that may result from liming a soil
will accrue from a combination of influences rather than from
one effect alone.
203. Crop response to liming.—Much experimental work
has been done in various parts of the world in determining
the relative response of different crops to liming and the rea-
son for certain well-known differences. As might be expected,
the results, while in close agreement as to some crops, show
striking disagreements as to others. This is to be expected,
since the varying conditions of the experiments would have a
marked influence on the response of the plants under con-
sideration.
Of legume crops, alfalfa and red and white clovers respond
most markedly to lime. The response of soybeans, garden
peas and field peas, while less, is still quite noticeable. Alsike
clover is more tolerant to acidity than red clover and, as the
soil of a region declines in active bases, it is common to find
it gradually replacing the latter. Japanese clover, cowpeas,
vetch, and field beans do not seem to be greatly benefited by
lime.
Of the non-legumes that are favorably influenced by lime,
blue-grass, maize, timothy, oats, barley, wheat, and sorghum
may be mentioned. Rye is less benefited by liming than is
barley. Red-top, cotton, strawberries, and potatoes do not
seem to be particularly stimulated by liming. Certain plants,
such as blueberries, watermelons, and rhododendron are ac-
tually injured by the use of lime.
There are a number of reasons why plants may be benefited
by lime, these reasons being numerous and complex enough
to account for the differences in response among common
LIMING THE SOIL 373
crops. The possible influences of lime on plants may be listed
as follows: (1) direct nutritive action; (2) synergistic rela-
tionships either in the soil solution or in the cell-wall; (3) re-
moval or neutralization of toxins of either an organic or inor-
ganic nature; (4) effect on plant diseases; (5) liberation of
mineral nutrients; and (6) encouragement of the biological
preparation of nutrient materials.
In some eases the calcium may function as a direct nutrient ;
in others the intake of nutrients may be facilitated by the
presence of calcium and magnesium; while in still other cases
the elimination or alleviation of a toxic condition may be the
important result. It is easy to conceive that any two or all
three of these relationships might be fulfilled simultaneously
by hme. The stimulating influence of lime might also make
the plant a more active agent and thus encourage it to aid
to a greater extent in the preparation of its own nutrients.
Certain diseases may be retarded or even entirely suppressed
by lime, as is the ‘‘finger-and-toe’’ disease of the Crucifere.
The lberation of mineral nutrients, such as potash and
phosphoric acid, by the addition of lime, is somewhat uncer-
tain although it evidently does occur in many eases.1. The
process is probably a more or less complicated physical or
chemical change. The stimulation to plants by such an ac-
tion is difficult to establish, since so many disturbing factors
are active in obscuring the results. Lime is undoubtedly very
important in the use of acid phosphate, the active compound
of which is mono-caleium phosphate (CaH,(PO,).). In the
presence of active calcium, the reversion compound is
(Ca,(PO,).,),? rather than the very insoluble iron and alumi-
num phosphates (FePO, and AIPO,).
The formation of nitrates proceeds rather slowly in most
*Plummer, J. K., The Effects of Liming on the Availability of Soil
Potassium, Phosphorus and Sulfur; Jour. Amer. Soc. Agron., Vol. 13,
No. 4, pp. 162-171, 1921.
*CaH,(PO,), + 2CaH,(CO,),—= Ca,(PO,), + 4H,O + 4CO,
374 NATURE AND PROPERTIES OF SOILS
acid soils, since there is but little active basic material to
stimulate the nitrifying organisms directly or to neutralize
the nitrous acid that is formed.t The addition of lime is the
most economical method of supplying this base. This response
of the nitrifying bacteria to lime is a matter of great moment
to crops that need large amounts of nitrate nitrogen and may
account in some cases for the early response of certain crops
to liming. The tolerance of some plants to acid soils might be
accounted for on the supposition that they need but small
amounts of nitrogen or are able to absorb their nitrogen in
forms other than the nitrate.
204. Method and time of applying the lime.—Although
lime is lost rapidly from most soils, appearing in the drain-
age water in large amounts, it does not seem to correct to any
great extent the acidity of the soil layers through which it is
earried.2 Lime applied at the soil surface will tend to disap-
pear, but will have little effect on the soil below. The action
of lime seems to be a contact phenomenon and the more thor-
oughly it is mixed with the soil, the greater will be the num-
ber of active focii and the more rapid and effective will be the
results of the treatment.
Lime is best applied to plowed land and worked into the soil
as the seed-bed is prepared. It should be thoroughly mixed
with the surface three to five inches of soil. Top-dressing of
lime is seldom recommended except on permanent meadows
and pastures. The time of year at which lime is applied is
immaterial, the system of farming, the type of rotation, and
such considerations being the deciding factors. The soil
should not be too moist when the application is made, as the
12NH, + 30, = 2HNO, + 2H,0.
2HNO, + CaCO, = Ca(NO,), + H.O + CO,.
Ca(NO;), + O; = Ca(NO;)..
? Wilson, B. D., The Translocation of Calcium in a Soil; Cornell Agr.
Exp. Sta., Memoir 17, 1918.
Stewart, R., and Wyatt, F. A., Limestone Action on Acid Soils; Ill.
Agr. Exp. Sta., Bul. 212, 1919.
LIMING THE SOIL 375
lime, especially the slaked and ground burned forms, tends to
ball badly and thus thorough distribution is prevented.
A lime distributer should be used, especially if the amount
to be applied is at all large. A manure-spreader can be util-
ized and even an end-gate seeder may be pressed into service.
Small amounts of lime may be distributed by means of the
fertilizer attachment on a grain drill. As with the applica-
tion of any material, the evenness of distribution is as im-
portant as the form and amount of lime used and should by no
means be neglected.
A discussion of the application of lime is never complete
without some consideration being given to the place in the
rotation at which the liming is best done. In a rotation of
maize, oats, wheat, and two years of clover and timothy, the
lime is often applied when the wheat is seeded in the fall. It
can then be spread on the plowed ground and worked in as
the seed-bed is prepared. Its effect is thus especially favor-
able on the new seeding. Thorne! has shown, however, in
certain Ohio experiments, that maize is affected more favor-
ably than any of the crops above mentioned and as the money
value of this increase is practically as much as that from the
hay, he favors applying the lime to the maize. With pota-
toes in the rotation, the lime should follow the potato crop,
especially if scab is prevalent. In practice the place of lime
in the rotation is usually determined by expediency, since the
vital consideration is, after all, the application of lime regu-
larly and in conjunction with a rational rotation of some kind.
205. The calcium and magnesium ratio.—A physiological
balance seems to be necessary in a nutrient solution in con-
tact with a normally growing plant. This balance varies with
the plant and with numerous other conditions. The reason
for such antagonistic action between the ions of certain ele-
ments is difficult to explain and many theories have been ad-
+Thorne, C. E., The Maintenance of Fertility. Liming the Land;
Ohio Agr. Exp. Sta., Bul. 279, 1914.
376 NATURE AND PROPERTIES OF SOILS
vanced. Loew,’ in 1901, worked out the optimum ratio for
a number of different plants growing in water culture. He
found that both calcium and magnesium alone were toxic and
it was only when the ratio of these ions fell within certain
limits that the toxicity disappeared. This ratio varied be-
tween 1 of CaO to 1 of MgO and 7 of CaO to 1 of MgO.
The question was immediately raised as to the advisability
of using limestone or even burned and slaked lime, the mag-
nesium eontent of which approached in any degree the cal-
cium present. Recent field and laboratory tests have shown,
however, that magnesium salts may be applied in ordinary
amounts alone or with calcium compounds with impunity.’
The absorptive capacity of the soil seems to take care in a
very effective way of any toxicity that might result from a
soil solution physiologically unbalanced.
206. The fineness of limestone—The hardness of the
stone, its purity, and its fineness are items of extreme im-
portance to the manufacturer of pulverized lime. The softer
the limestone, the easier the grinding and the finer the product
with a given expenditure of power. The higher the percent-
age of calcium and magnesium, the greater is the effectiveness
of a given quantity. The farmer, other conditions being more
or less equal, is especially interested in the fineness of the
product. It is a well-known fact that the finer the division of
any material, the more rapid the solution. This, however,
1 Loew, O., The Physiological Role of the Mineral Nutrients of Plants ;
U.S. Dept. Agr., Bur. Plant Ind., Bul. 1, p. 53, 1901.
*Gile, P. L., and Ageton, C. U., The Significance of the Lime-Mag-
nesia Ratio in Soil Analyses; Jour. Ind. and Eng. Chem., Vol. 5, pp.
33-35, 1913.
Thomas, W., and Frear, W., The Lime-Magnesia Ratio in Soil Amend-
ments; Jour. Ind. and Eng. Chem., Vol. 7, No. 12, pp. 1042-1044,
Dee. 1915.
Lipman, C. B., A Critique of the Hypothesis of the Lime-Magnesia
Ratio; Plant World, Vol. 19, No. 4, pp. 83-105, Apr. 1916.
Wyatt, F. A., Influence of Calcium and Magnesium Compounds on
Plant Growth; Jour. Agr. Res., Vol. VI, No. 16, pp. 589-619; 1916.
Stewart, R., and Wyatt, F. A., Limestone Action on Acid Soils; Il.
Agr. Exp. Sta., Bul, 212, 1919.
LIMING THE SOIL 377
is not the only importance of fineness. Lime produces its in-
fluence largely through contact, and the finer the lime is
ground, the more thorough is the mixing with the soil and
the greater the number of operating focil.
White! presents the following significant data as a result
of certain laboratory and greenhouse studies at State College,
Pennsylvania.
TaBLE LXX XIV
A COMPARISON OF VARIOUS GRADES? OF LIMESTONE WHEN
APPLIED AT THE SAME RATES.
100 MESH] 689 | 90-40 | 8-12
COR DUETS dienes MesuH | Meso | MEsH
Solubility in carbonated water.| 100 | 57 | 45 | 28
Value in correcting acidity....| 100 57 27 18
Mormation of nitrates. «2.2... 100 94 56 12
lamtemrowtlsncs ies oo. s kee 100 69 22 5)
These figures show that the finer grades of limestone are
much more rapidly effective. Further data by the same au-
1White, J. W., The Value of Limestone of Different Degrees of Fine-
ness; Penn. Agr. Exp. Sta., Bul. 149, 1917. Also, Thomas, W., and
Frear, W., The Importance of Fineness of Sub-division to the Utility of
Crushed Limestone as a Soil Amendment; Jour. Ind. and Eng. Chem.,
Vol. 7, No. 12, pp. 1041-1042, 1915.
Broughton, L. B., et al, Tests of the Availability of Different Grades
of Ground Limestone; Md. Agr. Exp. Sta., Bul. 193, 1916.
Kopeloff, N., The Influence of Fineness of Division of Pulverized
Limestone on Crop Yield as Well as the Chemical and Bacteriological
Factors in Soil Fertility; Soil Sci., Vol. IV, No. 1, pp. 19-67, 1917.
Frear, W., The Fineness of Lime and Limestone Application as Re-
lated to Crop Production; Jour. Amer. Soc. Agron., Vol. 13, No. 4,
pp. 171-174, 1921.
?Lime is graded by sieves carrying a certain number of meshes to the
linear inch. An 80-mesh sieve has 80 openings to the linear inch or 6400
to the square inch. Screens rated as carrying the same number of meshes
often do not give the same grade of material, due to a difference in the
size of wire used. Material of 60 to 80 mesh refers to those sizes that
will pass through a 60-mesh but will be held by an 80-mesh screen.
A standardization of sieves and methods of expressing such analyses is
much needed.
378 NATURE AND PROPERTIES OF SOILS
thor indicate that while the coarser lime is less rapid in its
action, it remains in the soil longer and its influence should
be effective for a greater period of years.
TABLE LXXXV
DECOMPOSITION OF LIMESTONE DURING THE THREE YEARS
AFTER APPLICATION.
PERCENTAGE OF DECOMPOSITION
MESH
HiegH CALCIUM HicgH MAGNESIUM
STONE STONE
100 mesh and smaller... 92.4 91.2
60) .to0..80) meshs. 2k. 342 81.5 (Wee
20: to, 40° mesh 5 425... 46.7 34.9
Sito 2 emesh va. eae 14.9 5.9
The conclusion is likely to be drawn that limestone should
be ground as finely as possible. Such an assumption is at
fault in several ways. In the first place, very fine lime is
difficult to handle and unpleasant to distribute. Again, the
cost of grinding increases very rapidly with the fineness, being
entirely too expensive compared with the results attained.
Moreover, finely ground material does not possess the lasting
qualities of the coarser lime. Because of the cost of grinding
the stone to a very fine condition and the rapidity with which
such material disappears from the soil, a medium ground
lime seems to be a more desirable commercial product. Such
material has enough of the finer particles to give quick re-
sults and yet enough of the coarser fragments to make it last
over the period of the rotation. A pulverized limestone, all
of which will pass a 10-mesh sieve, 70 per cent. of which
will pass a 50-mesh sieve and 50 per cent. of which will pass
a 100-mesh sieve, should give excellent results and yet be
cheap enough to make its use worth while.
The following figures show in an approximate way the
LIMING THE SOIL 379
mechanical composition of limestone on sale in Pennsylvania
for 1920':
TaBLe LXXXVI
MECHANICAL COMPOSITION OF SOME LIMESTONE OFFERED FOR
SALE IN PENNSYLVANIA IN 1920.
AMOUNT PASSING SIEVE, MESH
LIMESTONE
10 Bele ly 00
Re orders os cit Sec aul 100 98 92
EN OE eee al ee 100 99 88
Sy ck oh eect ERNE EAE ed OV a ee 100 89 73
NT ree oe ie foee b ohOk Sok 100 70 58
Fy yo sate eee ee 100 57 50
(0): a napa ere) cai aay se 100 44 34
207. Gypsum and other soil amendments.—Gypsum, in
which form calcium sulfate (CaSO,.2H,O) is usually applied
to soil, has been used for years and was popular long before
commercial fertilizers were available to any extent. The use
of gypsum was probably familiar to the Romans. It fre-
quently goes by the name land plaster. It is widely distribu-
ted in nature and easily ground. Its beneficial effect has been
noted, particularly with clover and alfalfa, crops which re-
spond especially to potash. Its popularity has waned in recent
years, however, since its effectiveness on soils where it has
long been used has apparently decreased. This possibly has
been due in part to the acid residue that ultimately must re-
sult from the use of such material and to the failure to lib-
erate potassium—a property with which it has very gen-
erally been credited and which, when applied to some soils,
it may possess. The experimental work in this respect is
somewhat conflicting, possibly due to the fact that the con-
pen elnee, J. W., Lime Report; Penn. Dept. Agr., Vol. 4, No. 2,
1921.
380 NATURE AND PROPERTIES OF SOILS
ditions of contact between the soil and the gypsum were ab-
normal. MeMillar’ found that the potash of certain Minne-
sota soils treated with one per cent. of gypsum was appre-
ciably influenced three months after the application. When
gypsum has proven beneficial to crop growth, the effect may
have been due to the nutrient influence of the sulfur it con-
tains or to the potash liberated from its soil combinations.
The use of gypsum as a soil amendment is now seldom recom-
mended, especially if the other forms of lime are available.
Sodium chloride has a marked effect on the productivity of
some soils, especially when certain crops such as asparagus
are grown. Wherein its effectiveness lies is not well under-
stood. Increased fertility arising from the addition of sodium
and chlorine, which are plant constituents, is probably not
the reason of its influence, as these substances are usually
available in soils far beyond any possible plant requirement.
When common salt shows a beneficial influence, it is probably
due to its tendency to liberate certain mineral nutrients such
as potassium, calcium, and magnesium. Since it tends to
leave an acid residue in the soil and since some form of lime
will generally give better and more permanent results, the
use of common salt is not recommended except in certain
cases. :
The use of di-calcium silicate (Ca,Si0,) in an experimental
way as a liming material has recently received some attention.
Cowles,” in 1917, presented data from which he concluded that
1MeMillar, P. R., Influence of Gypsum upon the Solubility of Potash
in Soils; Jour. Agr. Res., Vol. XIV, No. 1, pp. 61-66, 1918.
Morse, F. W., and Curry, B. E., The Availability of Soil Potash in
Clay and Clay Loam Soils; N. H. Agr. Exp. Sta., Bul. 142, 1909.
Bradley, C. E., The Reaction of Lime and Gypsum on Some Oregon
Soils; Jour. Ind. and Eng. Chem., Vol. 2, No. 12, pp. 529-530, 1910.
Briggs, L. J., and Breazeale, J. F., Availability of Potash in Certain
Orthoclase-bearing Soils as Affected by Lime or Gypsum; Jour. Agr.
Res., Vol. VIII, No. 1, pp. 21-28, 1917.
Cowles, A. H., Calcium Silicates as Fertilizers. Metal. Chem. Eng.,
Vol. 17, pp. 664-665, 1917.
LIMING THE SOIL 381
this compound was of greater value than either ground lime-
stone or slaked lime as an amendment. He also concluded
that silicon was an essential element in plant nutrition. Hart-
well and Pember,' in 1920, found di-calcium silicate approxi-
mately equal to limestone insofar as the correction of acidity
was concerned. Lettuce was used as an indicator. They
found no indication that the silicon was of any value, but, as
their experiments were with soil, this, of course, does not op-
pose the idea that silicon is an essential element in the growth
of plants.
Hartwell and Pember concluded that the beneficial influ-
ence of phosphorus and calcium compounds added to the soil
might, in many cases, be due to the precipitation of active
aluminum quite as much as to the supplying of nutrients or
the correction of actual acidity. Such a conception of the
influence of liming materials may ultimately mean an in-
crease in the number and nature of the compounds that may
be used as soil amendments.
208. Importance of lime in soil improvement.?—The in-
fluence of successively liming a soil over a period of years
may tend to raise or lower the fertility of the soil, according
to the system of soil management that accompanies the appli-
eations of the lime. The use of lime alone will undoubtedly
increase crop yield for a time. Basic exchange will be en-
1 Hartwell, B. L., and Pember, F. R., The Effect of Dicalcium Silicate
on an Acid Soil; Soil Sci., Vol. X, No. 1, pp. 57-60, July, 1920.
7A number of general references on the importance of lime were
given at the beginning of the chapter. See also,
Wiancko, A. T., et al., The Value of Lime on Indiana Soils; Ind. Agr.
Exp. Sta., Bul. 213, 1918.
Stewart, R., and Wyatt, F. A., Limestone Action on Acid Soils; Il.
Agr. Exp. Sta., Bul. 212, 1919.
Lipman, J. G., and Blair, A. W., The Lime Factor in Permanent
Soil Improvement ; Soil Sci., Vol. IX, No. 2, pp. 83-114, Feb. 1920.
Hartwell, B. L., and Damon, 8. C., Six Years’ Experience in Improving
a Light Unproductive Soil; Jour. Amer. Soc. Agron., Vol. 13, No, 1,
pp. 37-41, Jan. 1921.
382 NATURE AND PROPERTIES OF SOILS
couraged, soil bacteria will be stimulated, and more nutrients
will become available for crop use. Such stimulation, how-
ever, will soon wane, and if nothing is returned to the land,
productivity must ultimately drop back to even a lower level
than before the lime was applied.
Lime is, to a great extent, a soil amendment and as it in-
creases crop growth, the draft on the soil becomes larger.
Greater effort is necessary, therefore, in order to maintain
the fertility of the land when lime is used than when such ap-
plications are not made. Farm manure, crop residues and
green-manures should be utilized to the fullest extent and
when these are insufficient to keep up the potash and phos-
phorie acid of the soil, commercial fertilizing materials must
be resorted to. Lime improperly used exhausts the soil, but
when properly and rationally applied it becomes one of the
important factors in the mamtenance of a more or less con-
tinuous productivity.
It is interesting in this connection to consider certain fig-
ures from the Ohio Experiment Station.t Maize, oats, wheat
and clover and timothy were grown in a five-year rotation
on both limed and unlimed plats fertilized in various ways.
The results of table LXX XVII (page 383) are averages for a
period of twelve years.
It is immediately evident that the effectiveness of the lime
was increased by the use of both fertilizers and farm manure.
Conversely, the returns from the fertilizers and the manure
were markedly influenced by the lime. The lime increased
the effectiveness of the acid phosphate 20 per cent. The in-
creases with the acid phosphate plus potassium chloride and
with the complete fertilizers were 22 and 10 per cent., re-
spectively. Lime increased the returns of farm manure only
4 per cent., indicating that manure itself may function as a
Thorne, C. E., The Maintenance of Soil Fertility. Liming the Land;
Ohio Agr. Exp. Sta., Bul. 279, 1914.
LIMING THE SOIL 383
TABLE LXX XVII
RELATIVE ROTATION VALUES OF CROP INCREASES DUE TO LIMING
AND FERTILIZING A STANDARD ROTATION OVER A TWELVE-
YEAR PERIOD. OHIO EXPERIMENT STATION. THE ACID
PHOSPHATE TREATMENT IS TAKEN AS 100 FOR
THE LIME GAIN AND ALSO FOR THE
UNLIMED FERTILIZER GAIN.
GAIN FROM F'ER-
GAIN Mr teh Esa
FERTILIZERS TO THE ROTATION FROM CS
LIME
UNLIMED| LimEp
CIA PHOS BATES ss 5, Sse Sale ral ccs 2 100 100 120
Acid phosphate plus potassium
IMCL OMe ee aoe c t ccexs bos tacee mois 114 142 173
Acid phosphate, potassium
chloride and sodium nitrate..... 119 Die 255
Memanmers IGMONSs @h)..as0 ss obese ees 113 287 300
soil amendment. These figures serve in a definite way to em-
phasize the correlation between liming and the other factors
that must be considered in soil improvement and fertility
maintenance,
CHAPTER XxX
SOIL ORGANISMS, CARBON, SULFUR, AND
MINERAL CYCLES
A vast number of organisms, both vegetable and animal,
live in the upper layers of the soil and determine to a very
large degree its dynamic character.?, By far the greater por-
tion of these organisms belong to plant life, producing those
changes, both organic and inorganic, which control, in large
degree, the productivity of the soil. While most of the or-
ganisms are so minute as to be seen, if visible at all, only by
the aid of a microscope, a small proportion attain the size of
the larger rodents. For convenience of discussion the life of
the soil may be classified into macro-organisms and mucro-
organisms.
209. Macro-organisms—animal forms.—Of the macro-
organisms in the soil, the animal types are chiefly (1) rodents,
(2) worms, and (38) insects; and the plant forms (1) the
large fungi and algx, and (2) roots.
The burrowing habits of rodents—of which the ground
squirrel, the mole, the gopher, and the prairie dog are familiar
examples—result in the pulverization of considerable quanti-
*General references:
Lipman, J: G., Bacteria in Relation to Country Life; New York,
1908.
Conn, H. W., Agricultural Bacteriology; Philadelphia, 1918.
Marshall, C. E., Microbiology; Philadelphia, 1917.
?It has been estimated that every acre of soil contains at least 2000
pounds of living material exclusive of roots. If these organisms were
confined to a surface foot of soil, weighing, when moist, 4,000,000 pounds
to the acre foot, they would make up .05 per cent. by weight of the nor-
mal field soil.
384
SOIL ORGANISMS 385
ties of soil. While the effect is rather beneficial and is analo-
gous to tillage, the activities of these animals are generally
unfavorable to agricultural operations and such soil inhabi-
tants have been more or less exterminated in arable land.
The common earthworm is the most conspicuous example of
the benefits that may accrue from the presence of animals.
Darwin, as the result of careful measurements, states that the
quantity of soil passed through these creatures may under
favorable conditions in a humid climate, amount to ten tons
of dry earth to the acre annually. The earthworm obtains its
nourishment from the organic matter of the soil, but takes
into its alimentary canal the inorganic matter as well, ex-
pelling the latter in the form of casts after it has passed en-
tirely through the body. The ejected material is to some ex-
tent disintegrated, and is in a flocculated condition. The holes
left in the soil serve to increase aération and drainage. The
activities of the worms bring about a notable transportation
of lower soil to the surface, which aids still more in effecting
aeration. Darwin’s studies led him to state that from one-
tenth to two-tenths of an inch of soil is yearly brought to the
surface of land in which earthworms exist in numbers normal
to fertile soil.
Earthworms naturally seek a heavy compact soil, and it is
in soil of this character that they are most needed because of
the stirring and aération that they accomplish. Sandy soil
and that of arid regions, in which are found few or no earth-
worms, are not usually in need of their activities.
There is a less definite, and probably a less effective, action
of a similar kind produced by insects. Ants, beetles, and the
myriads of other burrowing insects and their larve effect a
considerable movement of soil particles, with a consequent
aeration of the soil. At the same time they incorporate into
the soil a considerable quantity of organic matter.
210. Macro-organisms—plant forms.—The larger fungi
are chiefly concerned in bringing about the first stages in the
386 NATURE AND PROPERTIES OF SOILS
decomposition of woody matter, which is disintegrated by the
penetrating mycelia of the fungi. These break down the
structure, and thus greatly facilitate the work of the decay
bacteria. Action of this kind is largely confined to the forest
and is not of great importance in cultivated soil. Another
function of the large fungi is exercised in the intimate, and
possibly symbiotic, relation of the fungal hyphe to the roots of
many forest trees, in soil where nitrification proceeds very
slowly, if at all, for nitrates are apparently not abundant in
forests.
Alge, except in special cases, do not exist in the soil to
any large extent. Certain Colorado soils,t however, seem to
contain appreciable numbers of this form. While the pres-
ence of both the larger fungi and the alge is interesting, their
importance in soil fertility is probably rather slight.
The roots of plants are important in the soil both by con-
tributing organic matter and by leaving, on their decay, open-
ings which render the soil more permeable to air and water.
The dense mass of roctlets, with their minute hairs, that is left
in the soil after every harvest, furnishes a well-distributed
supply of organic matter, which is not confined to the furrow
slice, as is artificially incorporated manure. The action of
roots on the soil is not by any means entirely physical. Dur-
ing the life of the plant the elimination of tissue and the
presence of exudates make the rootlets rather important chem-
ical agents.2, The chemical and biological importance of de-
caying organic matter has already been adequately empha-
sized.*
211. Micro-organisms—protozoa.—The micro-organisms
of the soil belong to the following groups: (1) protozoa, (2)
fungi and alge, (8) actinomyces, and (4) bacteria.
1Robbins, W. W., Alge in Some Colorado Soils; Colo. Agr. Exp. Sta.,
Bul. 184, 1912.
*See paragraphs 156 and 157.
*See paragraphs 64 and 132.
SOIL ORGANISMS 387
While nematodes, rotifers, and similar organisms are some-
times found in soil, the protozoa are the only important micro-
scopic animal group usually present. The importance of
protozoa in soils was especially emphasized in 1909 by Russell
and Hutchinson,’ who maintained that the protozoan flora so
interfered with the ammonia-producing bacteria as materially
to lower the productivity of the soil. Partial sterilization
seemed to alleviate this condition, possibly by killing the
harmful protozoa. The findings of Russell and Hutchinson
have resulted in much research as to the importance of proto-
zoa in a normal soil.
While Waksman ? found that the presence of protozoa was
concomitant with low bacterial numbers, he does not consider
all protozoa harmful to biological activities. Fellers and All-
son,* in an examination of New Jersey soils, found protozoa in
every sample, the number of species ranging from two to
twenty-eight. Soils rich in organic matter or containing large
amounts of water carried the greater number. Besides the
104 species of protozoa identified in New Jersey soils, ten
genera of alge and six of diatomes were isolated. Nematodes
were common. The number of protozoa ranged from a very
few to as high as 4500 to a gram of soil. When occurring in
such numbers, these animals must be of considerable impor-
* Russell, E. G., and Hutchinson, H. B., The Effect of Partial Sterili-
zation of Soil on the Production of Plant Food; Jour. Agri. Sci., Vol.
III, pp. 111-144, 1909. Also, The Effect of Partial Sterilization of
Soil on the Production of Plant Food. II. The Limitation of Bace-
terial Numbers on Soils and Its Consequences; Jour. Agr. Sci., Vol. V,
part 2, pp. 152-221, 1913.
?Waksman, S. A., Protozoa as Affecting Bacterial Activities in the
Soil; Soil Sci., Vol. II, No. 4, pp. 363-376, 1916. Also, Sherman,
J. M., Studies on Soil Protozoa and Their Relation to the Bacteria;
I. Jour. Bact., Vol. 1, No. 1, pp. 35-66, 1916. II. Jour. Bact., Vol. 1,
No. 2, pp. 165-184, 1916.
Kopeloff, N., and Coleman, D. A., A Review of Investigations in
Soil Protozoa and Soil Sterilization; Soil Sci., Vol. III, No. 3, pp.
197-269, 1917.
*Fellers, C. R., and Ailison, F. E., The Protozoan Fauna of the
Soil of New Jersey; Soil Sci., Vol. IX, No. 1, pp. 1-24, 1920.
388 NATURE AND PROPERTIES OF SOILS
tance in soils, although it is doubtful whether they are detri-
mental except under special conditions."
212. Micro-organisms—fungi and alge.—Of the higher
fungi, molds are the only group that apparently attain any
particular importance in soils, although yeasts have been found
to occur and may in special cases exist in considerable num-
bers. It is only recently, however, that fungi have received
much attention, although their presence has been noted many
times. Such common genera as Fusarium, Mucor, Aspergillas,
and Pencillium are usually present in normal soils. In gen-
eral, a large amount of organic matter is conducive to the
activity of such fungi. Molds occur in soils in both the active
and the spore stage and probably pass their various life cycles
entirely in the soil.
Waksman,” in a detailed study of soil fungi, found that
most of the organisms were capable of producing considerable
ammonia from nitrogenous organic matter. A large propor-
tion of the fungi isolated were also able to decompose cellulose
rather rapidly. Different soils seemed to have a distinct and
characteristic fungal flora. Over one hundred distinct species
of fungi were isolated by Waksman belonging to thirty-one
genera. Some pathogenic species, such as different Fusaria
and Alternaria, were found. The numbers ranged from 80,-
000 to a gram of soil under forest conditions to 14,000,000
to a gram in a meadow soil. The numbers were usually larger
1Koch, G. P., Studies on the Activity of Soil Protozoa; Soil Sci.,
Vol. II, No. 2, pp. 163-181, 1916.
2Waksman, S. A., Soil Fungi and Their Activities; Soil Sci., Vol.
II, No. 2, pp. 103-155, 1916. Also,
McLean, H. C., and Wilson, G. W., Ammonification Studies with Soil
Fungi; N. J. Agr. Exp. Sta., Bul. 270, 1914.
Kopeloff, N., The Effect of Soil Reaction on Ammonification by
Certain Soil Fungi; Soil Sci., Vol. V, No. 1, pp. 541-574, 1916.
Coleman, D. A., Environmental Factors Influencing the Activity of
Soil Fungi; Soil Sci., Vol. V, No. 2, pp. 1-66, 1916.
Brown, P. E., The Importance of Mold Action in Soil; Science, N. S.,
Vol. XLVI, No. 1182, pp. 171-175, 1917.
Conn, H. J., The Microscopic Study of Bacteria and Fungi in Soil;
N. Y. State Agr. Exp. Sta., Tech. Bul. 64, 1918.
SOIL ORGANISMS 389
in the surface soil. While the microscopic alge are probably
present in soils, it has never been shown that they are of
practical importance.
213. Actinomyces.—The actinomyces are a_ filamentous
form of organisms, widely distributed in nature and are prob-
ably more nearly related to the bacteria than to the molds,
although they produce spores and develop into branching
forms of considerable complexity. Their production of aérial
hyphe is quite unlike the habits of bacteria. These thread
organisms exist in the soil in both the vegetative and the
resting stage and often make up quite a large proportion of
the soil flora. They are extremely difficult to study, since
they produce hard compact growths. It is questionable also,
whether the growths produced artificially are exactly like
those occurring in the soil.
Hiltner and Stormer! found that 20 per cent. of the soil
organisms developing on gelatin plates inoculated from the
soil were actinomyces. Conn? reports a range from 11 to 75
per cent. under similar cultural conditions. The average was
38 per cent. Conn estimates that 20 per cent. of the average
flora consists of actinomyces. The organisms were generally
greater in meadow soil than in cultivated land, indicating
the relationship of these thread forms to cellulose decomposi-
tion. McBeth* found actinomyces of wide distribution in
soils and he concludes that they are undoubtedly an impor-
tant factor in the decomposition of the cellulose of the soil
organic matter.
1 Hiltner, L., and Stormer, K., Studien tiber die Bakterienflora des
Ackerbodens; Kaiserliches Gesundheitsamt, Biol. Abt. Land-u. Forstw.,
Bd. 3, 8. 445-545, 1903.
Conn, H. J., A Possible Function of Actinomycetes in Soil; Jour.
Bact., Vol. 1, No. 2, pp. 197-207, 1916.
°’McBeth, I. G., Studies on the Decomposition of Cellulose in Soils;
Soil Sci., Vol. I, No. 5, pp. 437-487, 1916. Also,
Waksman, S. A., and Curtis, R. E., The Actinomyces of the Soil;
Soil Sci., Vol. 1, No. 2, pp. 99-134, 1916.
Waksman, S. A., Cultural Studies of Species of Actinomyces; Soil
Sci., Vol. VIII, No. 2, pp. 71-207, 1919.
390 NATURE AND PROPERTIES OF SOIL
214. Bacteria.—Of the several forms of micro-organisms
in the soil, bacteria are probably the most important. In fact,
the abundant and continued growth of higher plants on the
soil is absolutely dependent on the presence of bacteria.
Through their action chemical changes are brought about
which result in the solution of both organic and inorganic
material necessary for the life of higher plants, and which,
in part at least, would not otherwise be available.
Bacteria are single cell organisms and are probably the
simplest forms of life with which we have to deal. They are
generally much smaller than yeasts, multiplying by elongat-
ing and dividing into half. They are, therefore, often called
fission fungi. Molds multiply by budding. The activities of
both groups are similar, in that they produce their effects
very largely by the production of enzymes.!| The importance
of enzymic influences must constantly be borne in mind in all
biological transformations in the soil.
Bacteria are very small, the larger individuals seldom ex-
ceeding one or two microns (.001 to .002 m.m.) in diameter.
In the soil there is good reason to suppose that there are
many groups which are too small to be seen under the micro-
scope. Such organisms may, therefore, function as a part of
the colloidal matter of the soil. Many of the soil bacteria
are equipped with extremely delicate vibrating hairs called
flagella, which enable the organisms to swim through the
1 Bacteria, as well as most fungi, bring about their important trans-
formations largely by means of enzymes. These enzymes are catalytic
agents and are generally considered as colloidal in nature. A number of
transformations may be accelerated by enzymes, the exact reaction de-
pending on the nature of the enzyme itself. The change in the soil of
ammonia (NH,) to the nitrate form (NO,) is an example of oxidation
and is spoken of as nitrification. The reversal of this action is desig-
nated as reduction and is probably not entirely enzymic. A splitting
action is very common. The breaking up of glucose into alcohol and
carbon dioxide is an example of this (C.H,,O, = 2C,H,OH + 2C0O,).
A fourth reaction that may be hastened by enzymic influence is hydrol-
ysis. Cane-sugar may thus quickly produce glucose and fructose
(Ci3H22011 4° H,0 = C.H,20, hr C,Hi20.).
SOIL ORGANISMS 391
soil-water. The shape of bacteria is varied in that they may
be nearly round, rod-like, or spirals. In the soil the rod-
shaped organisms seem to predominate.
As already stated, the primary method of multiplication
of bacteria is by simple division, the process being very rapid
under favorable conditions. The phenomena frequently takes
place in thirty minutes. This almost unlimited capacity to
increase in numbers is extremely important in the soil since
it allows certain groups quickly to assume their normal func-
tions under favorable conditions, even though their numbers
were originally small.t Bacteria may thus be considered as
a force of tremendous magnitude in the soil, held more or
less in check by conditions, but ever ready to exert an influ-
ence of profound importance on crop growth.
In the soil bacteria probably exist as mats or clumps,
called colonies, on and around the soil particles wherever food
conditions are favorable. Natural and artificial forces tend
to break up these colonies and, as many groups are flagellated,
bacteria becomes well distributed through the soil. In gen-
eral the greatest numbers are found in the surface layers of
the soil, since conditions of temperature, aération, and food
are here more favorable. Many of the soil bacteria are able
to produce spores, thus presenting both a resting and a vege-
tative stage. The production of spores is often extremely
important as it allows the organisms to survive unfavorable
conditions of many kinds.
The number of bacteria present in soil is quite variable as
many conditions markedly affect their growth. The meth-
ods” of determining the numbers are extremely inaccurate,
1If a single bacterium and every subsequent organism produced sub-
divided every hour, the offspring from the original cell would be about
17,000,000 in twenty-four hours. In six days the organisms would greatly
surpass the earth in volume. Under actual conditions such multiplication
would never occur, due to lack of food and other limitations.
The counting of soil bacteria is generally carried out somewhat as
follows: A small sample of soil (usually .5 gram) is placed in a sterile
Erlenmeyer flask and treated with 100 cc. of sterile water. The sample
392 NATURE AND PROPERTIES OF SOILS
since many organisms cannot grow in the artificial media
commonly used. Moreover, it is almost impossible to break
up the clump of colonies in such a way as to determine the
number of individuals present. It is fairly certain, however,
that the numbers of bacteria in soil are very large, possibly
ranging from 500,000 to 100,000,000 to a gram of dry soil.
Good soils seem, in general, to carry the greatest numbers.
The bacterial flora, as well as the other soil organisms, fluctu-
ate markedly with season, the numbers usually being great-
est in the summer months.
215. Conditions affecting bacterial growth.1—Many con-
is then well shaken in order to produce a suspension containing the
bacteria originally present in the soil. Dilutions of 1 to 20,000, 1 to
100,000 and 1 to 200,000 based on the original soil sample are made.
Gelatin or agar plates are then inoculated, three from each dilution.
After adequate incubation the colonies on the plates are counted, each
colony supposedly representing one original organism. The numbers of
bacteria that were present in the original soil are then calculated. The
agar or gelatin of the plates generally receive a sterile extract from the
soil together with certain added materials, organic or inorganic, in order
that the growth of the bacteria may be hastened.
Such a count does not represent by any means all of the bacteria of
the soil, as some groups will not develop at all, while others require
special media. Slowly growing groups of organisms, that would prob-
ably appear if time were given, escape the count, since the plates are so
quickly covered by more abundant growths. The suspension from the
soil, used to inoculate the plates, does not contain all of the organisms
as single individuals, since it is impossible completely to break down the
clump formation. This tends to make the counts too low. Special
media and technique are of course necessary in studying fungi, alge
and actinomyées.
1Rahn, Otto, The Bacterial Activity in Soil as a Function of Grain-size
and Moisture Content; Mich. Agr. Exp. Sta., Tech. Bul. 16, 1912.
Plummer, J. K., Some Effects of Oxygen and Carbon Dioxide on Nitri-
fication and Ammonification in Soils; Cornell Agr. Exp, Sta., Bul. 384,
1916.
Greaves, J. E., and Carter, E. G., Influence of Barnyard Manure
and Water Upon the Bacterial Activities of the Soil; Jour. Agr. Res.,
Vol. VI, No. 23, pp. 889-926, 1916.
Brown, P. E. The Influence of Some Common Humus-forming Mate-
rials of Narrow and of Wide Nitrogen-carbon Ratio on Bacterial Num-
bers; Soil Sci., Vol. 1, No. 1, pp. 49-75, 1916.
Waksman, S. A., Bacterial Numbers in Soils, at Different Depths and
in Different Seasons of the Year; Soil Sci., Vol. I, No. 4, pp. 363-380,
1916.
Gainey, P. L., The Effect of Time and Depth of Cultivating a Wheat
SOIL ORGANISMS 393
ditions of the soil affect the growth of bacteria. Among the
most important of these are the supply of oxygen and mois-
ture, the temperature, the presence of organic matter, and
the acidity or the basicity of the soil.
All soil bacteria require for their growth a certain amount
of oxygen. Some bacteria, however, can continue their activ-
ities with much less oxygen than can others. Those requir-
ing an abundant supply of oxygen have been called aérobic
bacteria, while those preferring little air are designated as
anaérobic bacteria. This is an important distinction, because
those bacteria that are of greatest benefit to the soil are, in
the main aérobes, and those that are injurious in their action
are chiefly anaérobes. However, it seems likely that an
aérobie bacterium may gradually accommodate itself within
certain limits to an environment containing less oxygen, and
an anaérobic bacterium may accommodate itself to the pres-
ence of a larger amount of oxygen. It is quite possible that
the aérobic and anaérobie organisms function in the soil at
the same time, since a portion even of a well aérated soil is
always highly charged with carbon dioxide. It is not improb-
able, also, that there exists a more or less beneficial inter-
relation between the two general groups.
Bacteria require moisture for their growth, optimum water
for higher plants seemingly being the best moisture for the
development and activity of favorable soil organisms of all
kinds. With a decrease of moisture the soil becomes well
aérated, while an excessive water supply tends to encourage
anaerobic conditions. Moisture, when aération and tempera-
ture are favorable, seems to be the main control of biological
changes within the soil.
Soil bacteria, like other plants, continue life and growth
Seed-Bea upon Bacterial Activity in the Soil; Soil Sci., Vol. II, No. 2,
pp. 193-204, 1916.
Greaves, J. E., and Carter, E. G., Influence of Moisture on the Bac-
terial Activities of the Soil; Soil Sci., Vol. X, No. 5, pp. 361-387, 1920.
394 NATURE AND PROPERTIES OF SOILS
under a considerable range of temperature. Freezing, while
rendering bacteria dormant, does not kill them, and growth
begins slightly above that point.’ It has been shown that
some nitrification occurs at temperatures as low as from 37°
to 39° F. It is not, however, until the temperature is con-
siderably higher that bacterial functions are pronounced.
From 70° to 110° F. their activity is greatest, and it dimin-
ishes perceptibly below or above those points. The thermal
death point of most forms of bacteria is between 110° and
Fig. 56.—Some important decay organisms found in soils. (a), Acti-
nomyces threads; (b), a colony of Actinomyces; (e) and (d), Pro-
teus vulgaris; (e), B, fluorescens; (f), B. subtilis.
160° F., but the spore forms even resist boiling. Only in
some desert soils does the natural temperature reach a point
sufficiently high actually to destroy bacteria, and there only
near the surface. In fact, it is very seldom that soil tempera-
tures, other conditions being favorable, become sufficiently
high to curtail bacterial activity.
The presence of a certain amount of organic matter is es-
sential to the growth of most, but not all, forms of soil bac-
*In the seasonal study of bacteria it has been repeatedly noticed that
the counts increased during the winter, especially after a freeze followed
by a thaw. It was considered for a time that a special winter flora was
present, and was able to multiply in the soil-water which failed te freeze.
It is now considered that this increase is only apparent, the freezing
having disrupted the bacterial clumps, thus increasing the number of
colonies appearing on the plates during incubation.
SOIL ORGANISMS 395
teria. The organic matter of the soil, consisting as it does of
the remains of a large variety of substances, furnishes a suit-
able food supply for a very great number of forms of organ-
isms. The action of one set of bacteria on the cellular matter
of plants embodied in the soil produces compounds suited to
other forms, and so from one stage of decomposition to another
this constantly changing material affords sustenance to bac-
terial flora, the extent and variety of which it is difficult to
conceive. A soil low in organic matter usually has a lower
bacterial content than one containing a large amount, and,
under favorable conditions, the beneficial action, to a certain
point at least, increases with the content of organic substance;
but, as the products of bacterial life are generally injurious
to the organisms producing them, such factors as the rate
of aération and the basicity of the soil must determine the
effectiveness of the organic matter.
The so-called acidity of the soil is probably as important
a factor in bacterial activity as it is to higher plants.. In
general, favorable soil organisms of all kinds seem to func-
tion better in a soil carrying sufficient active base to generate
conditions favorable for higher plants. An exception some-
times occurs, however, notably in the case of the ‘‘finger-and-
toe’’ disease of certain Crucifere, which is retarded by
liming.
The activities of many soil bacteria result in the formation
of acids which are injurious to the bacteria themselves, and
unless there is present some base with which these can com-
bine, bacterial development is inhibited by such products.
This is one of the reasons why lime is so often of great benefit
when applied to soils, and especially to those on which alfalfa
and red clover are growing. For the same reason the
presence of lime hastens the decay of organic matter in
certain soils, and the conversion of nitrogenous material
into compounds available to the plants. As showing the
value of lime in the process of nitrate formation it has been
396 NATURE AND PROPERTIES OF SOILS
pointed out that in the presenee of an adequate supply of
ealeium the availability of ammonium salts is almost as high
as that of nitrate salts, but where the supply of calcium is
insufficient the value of ammonium salts is relatively low.
216. Organisms injurious to higher plants.—While the
macro-organisms may, under certain conditions, be detri-
mental to the growth of higher plants, it is the smaller in-
habitants of the soil that attract especial attention in this re-
spect. While protozoa may, under special circumstances, be
extremely detrimental, injurious organisms are confined
mostly to fungi and bacteria. They may be entirely parasitic
in their habits or only partially so, while they may injure
higher plants by attacking the roots or even the tops. Those
that infest parts of the plant other than the roots are not
strictly soil organisms, as they pass only a part of their
eyele in the soil. Some of the more common diseases pro-
duced ‘by soil organisms are: wilt of cotton, cowpeas, water-
melon, flax, tobacco, tomatoes, and other plants; damping-off
of a large number of plants; root-rot; and galls.
Injurious fungi or bacteria may live for long periods in
the soil, if the conditions necessary for their growth are main-
tained. Some of them will die within a few years if their host
plants are not grown on the soil, but others are able‘to main-
tain existence on almost any organic substance. Once a
soil is infected it is likely to remain so for a long time, or
indeed indefinitely. Infection easily occurs. Organisms from
infected fields may be carried on implements, plants, or rub-
bish of any kind, in soil used for inoculation of leguminous
crops, or even in stable manure containing infected plants
or in the feces resulting from the feeding of such plants.
Flooding of land by which soil is washed from one field to
another may be a means of infection.
Prevention is the best defense from diseases produced by
such soil organisms. Once a disease has procured a foothold,
it is often. impossible to eradicate all its organisms. Rota-
SOIL ORGANISMS 397
tion of erops is effective for some diseases, but entire absence
of the host crop is often necessary. The use of lime is bene-
ficial in the case of certain diseases. Chemicals of various
kinds have been tried with little success. Steam sterilization
is a practical method of treating greenhouse soils for a num-
ber of diseases. The breeding of plants immune to the dis-
ease affecting its particular species has been successfully car-
ried out in the case of the cowpea and cotton, and can doubt-
less be accomplished with others.
In regions in which farming is confined largely to one
crop or to a limited number of cereals, it is the common ex-
perience that yields decrease greatly in the course of a score
of years after the virgin soil is broken. The cause for this
is attributed by Bolley,! in large measure, to a diseased con-
dition of the plants, due to the growth of various fungi that
inhabit the soil and attack the crops grown on it. He reports
that he experimented with pure cultures taken from wheat
grains, straw, and roots, and has demonstrated that certain
strains or species of Fusarium, Helminthosporium, Alter-
naria, Macrosporium, Colletotrichum, and Cephalothecium
are directly capable of attacking and destroying growing
plants of wheat, oats, barley, brome-grass, and quack-grass,
and that within limits the disease may be transferred from
one type of crop to another.
217. The beneficial influences of soil organisms.— While
the macro-organisms of the soil are usually beneficial to
higher plants, the more important relationships are occupied
by the micro-organisms. The micro-organisms of the soil take
an active part in removing dead plants and animals from the
surface of the land, and in bringing about the other oper-
ations that are necessary for the production of higher plants.
The first step in preparation for plant growth is to remove the
remains of plants and animals that would otherwise accumu-
late to the exclusion of higher plants. These are decomposed
1 Bolley, H. L., Wheat; N. Dak. Agr. Exp. Sta., Bul. 107, 1913.
398 NATURE AND PROPERTIES OF SOILS
through the action of organisms of various kinds, the inter-
mediate and final products of decomposition assisting plant
production by contributing nitrogen, and certain mineral
compounds that are a directly available source of plant nutri-
ents, and also by the effect of certain of the decomposition
products on the mineral substances of the soil, by which they
are rendered soluble and hence available to plants.
Through these operations the supply of carbon and nitro-
gen required for the production of organic matter is kept in
circulation. The complex organic compounds in the bodies
of dead plants or animals, in which condition higher plants
cannot use them, are, under the action of micro-organisms,
converted by a number of stages into the simple compounds
used by plants. In the course of this process, a part of the
nitrogen is sometimes lost into the air by conversion into free
nitrogen, but fortunately this may be recovered and even
more nitrogen taken from the air by certain other organisms
of the soil.
Higher fungi and actinomyces are particularly active in
the early stages of decomposition of both nitrogenous and
non-nitrogenous organic matter. Molds are capable of am-
monifying proteins, and even re-forming complex protein
bodies from the nitrogen of ammonium salts. Certain of the
molds and of the alge are apparently able to fix atmospheric
nitrogen, and contribute in addition a supply of carbohy-
drates required for the use of the nitrogen-fixing bacteria.
While the higher fungi are important in such transforma-
tions, their activities in almost every stage are excelled by
those of the bacteria. Because of this, the vital biological
transformations within the soil are generally ascribed to bac-
terial action, the bacteria receiving the greatest attention of
the numberless organisms making up both the soil flora and
fauna.
218. Biological cycles——Because of a lack of knowledge
regarding the flora and fauna of the soil, it is obviously im-
SOIL ORGANISMS 399
possible to discuss in detail the transformations caused by
individual species of organisms or even by groups of related
species. From the standpoint of soil fertility such an at-
tempt is unnecessary, as a practical understanding of the
changes through which a given soil constituent passes as
it is prepared for plant nutrition, is much more important
than the possession of specific knowledge regarding the organ-
isms concerned. As a consequence it has become customary
to discuss the biological transformations of the more impor-
tant soil constituents, including as much regarding the speci-
fice organisms and groups of organisms involved as is con-
sistent with a clear fertility viewpoint.t Four cycles are gen-
erally recognized, as follows: (1) the carbon eycle, (2) the
sulfur cycle, (3) the mineral cycle, and (4) the nitrogen
eycle.
219. The carbon cycle.—Since all organic compounds
carry carbon, nitrogenous as well non-nitrogenous materials
are involved in the carbon cycle. Nevertheless attention will
be directed for the time being only toward the carbon and the
changes that it undergoes from the time it enters the soil
until it is removed either by aération, leaching, or by plant
absorption.
Most of the carbon compounds enter the soil as plant tissue,
although animal remains contribute appreciable amounts.
These carbonaceous materials are immediately attacked in the
soil by a host of different organisms capable of producing
fermentation. While such bacteria as Bacillus subtilis, Ba-
cillus mycoides, and the like have a great deal to do with the
decay processes, they are by no means the only agents. Most
of the microscopic fungi, as well as the larger fungi and alge,
* There are two general ways of studying the soil flora. A classification
of the organisms may be attempted. This requires the isolation and
study of individuals and has so far met with but little success. The
second approach is a biochemical one, in which the transformations oc-
curring in the soil are studied first, the specific organisms involved being
a secondary consideration. The determination of the capacity of the
soil to produce ammonia is an example of this method of study.
400 NATURE AND PROPERTIES OF SOILS
aid in the initial transformation, being particularly effective
in decomposing cellulose. The actinomyces, present in such
large numbers, seem to be especially fitted for the breaking
down of such resistant material.
The result of these complex decomposition processes is the
formation of a partially decayed group of carbon-bearing
material, some being quite simple while others are extremely
complicated. The change is accompanied through its entire
course by the formation of carbon dioxide and water, the end-
products of carbohydrate decay. The same heterogeneous
group of soil organisms, which initiate the simplification of
carbonaceous materials, seem to continue the process until
only the end products and the more resistant portions of the
original tissue remain.
The transformations above discussed are not the only
sources of carbon dioxide within the soil. Some carbon diox-
ide is brought down in rain-water, while still more is given off
by the roots of living plants (see par. 156). Moreover some
earbon dioxide is obtained from the inorganic matter of the
soil, especially if the land has recently received an applica-
tion of limestone. The reactions within the soil seem to de-
compose such carbonates rather readily, carbon dioxide being
given off (see par. 201).
226. The loss of carbon from the soil.—Carbon diox-
ide, the importance of which has already been fully discussed
(par. 132), may suffer transformation in a number of ways
in the soil. It may be lost (1) to the atmospheric air; (2)
it may react with the mineral constituents of the soil and be
held at least temporarily by the soil mass; or (8) it may be
removed by leaching. Since the soil-water is always more or
less charged with carbon dioxide and since ‘it carries car-
bonate and bicarbonate salts, considerable carbon is continu-
ally being removed in this way. In this regard the figures
from the Cornel lysimeter tanks! are especially interesting.
1 Unpublished data. Cornell Agr. Exp. Sta., Ithaca, N. Y.
SOIL ORGANISMS 401
The data are expressed in pounds to the acre and are averages
of ten years’ experimentation. The carbon was lost as the
bicarbonate, only traces of carbonates being present. (See
table LXX XVIII, page 402).
i
COs, GY je
TQ T-ASE
= GREEN FARM
“S.. MANURE MANURE
-
~
SNe,
SOIL DECAY
REACTIONS \4 PARTIALLY DECOMPOSED
MATERIALS
CARBO N=
ae pain)
a BIOLOGICAL
ACTIVITIES
REACTIONS
Fig. 57.—Diagram showing the transformations of carbon, commonly
spoken of as the ‘‘carbon cycle.’’
LEAC :
LOSSES
It is apparent that a drainage loss of about 1200 pounds
of bicarbonate (HCO,) may be expected each year to the
acre, without considering the carbon dioxide which is respired
to the atmosphere. This latter loss probably at least equals,
if it does not greatly exceed, the loss of carbon in the bicar-
bonate form. Together they cause a disappearance of several
hundred pounds of carbon a year under the conditions main-
402 NATURE AND PROPERTIES OF SOILS
TABLE LXXXVIII
LOSS OF CARBON FROM THE SOIL IN DRAINAGE, EXPRESSED IN
POUNDS TO THE ACRE PER YEAR. CORNELL LYSIMETERS.
HCO, CARBON
ERE USE (POUNDS) (POUNDS )
Bane, :SOtlc i Geta eet sete eel tees 1391 273
TROCA TOMS ache eee wetter 1350 265
(GRASS he Aoi pa se ene eine in eGo ae 11938 234
tained in the Cornell lysimeters. The application of two tons
of green-manure to the acre would be necessary to replace
even the drainage loss cited above.
Small amounts of carbon may be removed by means other
than drainage or diffusion into the atmospheric air. Nu-
merous investigators! have shown that plants are capable
of assimilating various organic materials. Recently it has
been demonstrated that higher plants may utilize a consid-
erable variety of carbohydrate compounds.” Such materials,
when thus assimilated, no doubt supply the plant with en-
ergy and thus are foods rather than nutrients. The ready
response of certain crops, such as maize, to applications of
farm manure lends plausibility to the theory that considerable
carbon may be removed from the soil by plants and that the
carbon dioxide of the air is not the only immediate source of
the element carbon.
221. The sulfur cycle—Sulfur is an essential plant nu-
1 Hutchinson, H. B., and Miller, N. H. J., The Direct Assimilation a
Inorganic and Organic Forms of Nitrogen by Higher Plants; Centrlb. f
Bakt., II, Band 30,8. 513-547, 1911.
3 Mazé, je , Influence, sur le ‘développement de la plante, des substances
minérales qui s’accumulent dans ses organes comme résidus d’assimila-
tion; Compt. Rend. Sci., Paris, Tome 152, pp. 783-785, 1911.
Ravin, P., Nutrition carbonée des plantes a l’aide des acides organique
libres et combinés ; Ann. Sci. Nat. Bot., Ser. 9, No. 18, pp. 289-446;
1913.
Knudson, L., Influence of Certain Carbohydrates on Green Plants;
Cornell Agr. Exp. Sta., Memoir 9, July 1916.
SOIL ORGANISMS 403
trient, being utilized by such crops as alfalfa, turnips, and
cabbage in much larger amounts than is phosphorus. <Al-
though sulfur probably seldom becomes a limiting factor in
crop production (see par. 264), where rational methods of
soil management are practiced, its transformations in the soil
are of great importance.
Sulfur is absorbed by the plant as the sulfate ion and con-
sequently all forms of soil sulfur must be changed to the sul-
fate before the plant may benefit to any degree. This trans-
formation of sulfur, both organic and inorganic, to the sul-
fate form, insofar as it is biological, has been termed by
Lipman,' sulfofication. The reactions involved after hydro-
gen sulfide or free sulfur are formed may be written as fol-
lows:
2H.S + 30, = 2H,SO,
S-+ H,O + 0, = H.SO,
H.SO, + CaH,(CO,), = CaSO, + 2H,0 + 2CO,
2CaSO, + O, = 2CaSO,
While the oxidation reactions cited above are not entirely
biological, purely chemical changes occurring to a slight de-
gree, the decay processes preceding them are due wholly to
bacterio'ogical and allied influences. The organisms involved
in sulfofication are probably many, including the higher forms
of fungi as well as bacteria. The organisms that function in
the carbon cycle no doubt are active in the sulfur transfor-
mations as well.
The possible sources of the sulfur which is found in the
sulfur cycle are four: (1) plant and animals tissue, (2) fer-
tilizers, (3) rain-water, and (4) the inorganic sulfur of the
soil itself. The organic source is probably the most impor-
tant means by which the sulfur supply of the soil is aug-
mented in practice. The addition of farm manure and the
turning under of crop residues and green-manures will do
*Lipman, G. J., Suggestions Concerning the Terminology of Soil
Bacteria; Bot. Gaz., Vol. 51, pp. 454-460, 1911,
404 NATURE AND PROPERTIES OF SOILS
much to retard the sulfur reduction which is constantly oe-
curring. Fertilizers, such as acid phosphate, ammonium sul-
fate, and potassium sulfate, may also be valuable sources of
sulfur. The amount of sulfur carried down in rain-water is
largely in the sulfate form and is quite variable, ranging from
a few pounds of SO, yearly to the acre to over 160 pounds.
The rainfall addition at Ithaca,) New York, is about 65
pounds of SO, to the acre a year, while Stewart’ reports a
yearly gain to the acre of 113 pounds at the University of
Illinois. The inorganic sulfur of the soil also constantly
tends to enter the sulfur cycle and must be reckoned with in
any study of sulfofication.
222. Loss of sulfur from the soil.—The loss of sulfur
from the soil under normal agricultural conditions occurs
in two ways: (1) losses in drainage, and (2) removal by
cropping. Unless such losses ean adequately be met by ad-
ditions of sulfur or sulfur compounds, it is obvious that this
element will become a limiting factor in crop growth. The
figures? from the Cornell lysimeters are very instructive in
this regard. The soil used was a Dunkirk silty clay loam.
TaBLE LXXXIX
AVERAGE ANNUAL LOSS OF SULFUR (as SO,) BY PERCOLATION
AND CROPPING. CORNELL LYSIMETERS. AVERAGE OF 10 YEARS.
PouUNDS TO THE ACRE OF SO, Lost THROUGH
CONDITION
DRAINAGE Crop ToTAL
Bare esol sree: 13220 — 132.0
Rotations a ae ee 108.5 41.0 149.5
Girassieoe na eoyee ee: 111.0 29.2 140.2
1 Wilson, B. D., Sulfur Supplied to the Soil in Rain Water; Jour.
Amer. Soc. Agron., Vol. 13, No. 5, pp. 226-229, 1921.
2Stewart, R., Sulfur in Relation to Soil Fertility; Il. Agr. Exp. Sta.,
Bul. 227, 1920.
* Unpublished data, Cornell Agr. Exp. Sta., Ithaca, N. Y.
SOIL ORGANISMS 405
Since the sulfur added to the soil at Ithaca, New York,
amounts to only 65 pounds of SO, yearly to the acre, other
sources of sulfur assume considerable importance in fertility
practice. It seems probable, however, that the judicious
use of fertilizers carrying sulfur in conjunction with farm
manure, green-manure and crop residues, will adequately
eare for the sulfur needs of the average soil (see par. 264).
223. Factors influencing sulfofication.—The sulfofying
activities of the soil flora are greatly influenced by conditions
within the soil. Brown! has found that the addition of farm
manure and green-manure greatly stimulates sulfofication, al-
though carbohydrates alone seem to exert a depressing influ-
ence. Lime, unless applied in very large amounts, encour-
aged the transformation of the sulfur compounds, increas-
ing the amount of sulfates present in the soil. The reason
for this influence is evident from the reactions already quoted.
The partial oxidation of hydrogen sulfide or of free sulfur
produces sulfurous acid (H,SO,), which exerts a retarding
influence on further action, unless a base, such as calcium or
magnesium, is present to form a salt of this acid.
Brown’s results also indicate the preponderant influence
of aération, moisture, and organic matter on sulfofication.
Optimum conditions for crop growth, as far as these factors
are concerned, seem also to be optimum for the transforma-
tion of sulfur compounds in the soil. These same conditions
also favor satisfactory reactions within the carbon cycle as
well.
*Brown, P. E., and Kellogg, EK. H., The Determination of the Sul-
fofying Power of Soils; Jour. Biol. Chem., Vol. XXI, No. 1, pp. 73-89, .
1915.
Brown, P. H., and Johnson, H. W., Studies in Sulfofication ; Soil Sci.,
Vol. I, No. 4, pp. 339-362, 1916.
Brown determines the sulfofying power of soil by adding .1 gram of
- NaS or free sulfur to 100 grams of fresh soil, adjusting the moisture
content to optimum and incubating from five to ten days. The sulfates
are then determined by shaking the soil with water for seven hours,
filtering and precipitating the sulfates with barium chloride. The
amounts of sulfates are estimated in a sulfur photometer. An untreated
sample of soil should be run as a check,
406 NATURE AND PROPERTIES OF SOILS
224. The sulfur compost.—It has been noted by a num-
ber of experimenters that the presence of sulfur compounds
in the soil and especially elemental sulfur tends to develop
considerable acidity. The cause of this acidity has already
been explained. In 1916, Lipman? and his co-workers sug-
gested that a practical use be made of sulfofication in ren-
dering certain mineral nutrients, such as potash and phos-
phorie acid, available. Lipman devised a compost of sulfur
and raw rock phosphate. His results seem to indicate that
sufficient acid might be formed by biological oxidation ap-
preciably to influence the solubility of the rock phosphate.
Brown and Warner? later used a compost of sulfur, farm
manure and raw rock phosphate. Remarkable increases in the
solubility of phosphoric acid, measured by extraction with
a solution of ammonium citrate, were recorded. The results
of Lipman, Brown, and Warner have been corroborated by
Ames and Richmond,? and Shedd.*| Ames and Boltz® in
1919 found that sulfur composted with feldspar appreciably
influenced the solubility of potash. Such results as those
recorded above indicate the importance of sulfofication in
the soil under ordinary circumstances, as well as a possible
value in a more intensified procedure.
The practicability of using sulfur composts on the farm
1Lipman, J. G., et al., Sulfur Oxidation in the Soil and Its Effects on
the Availability of Mineral Phosphates; Soil Sei., Vol. Il, No. 6,
pp. 499-538, 1916.
Brown, P. E., and Warner, H. W., Production of Available Phos-
phorus from Rock-Phosphate by Composting with Sulfur and Manure;
Soil Sci., Vol. IV, No. 4, pp. 269-282, 1917.
%Ames, J. W., and Richmond, T. E., Effect of Sulfofication and
Nitrification on Rock Phosphate; Soil Sei., Vol. VI, No. 4, pp. 351-364,
1918.
4Shedd, O. M., Effect of Oxidation of Sulfur in Soils on the Solu-
bility of Rock-Phosphate and on Nitrification; Jour. Agr. Res., Vol.
XVIII, No. 6, pp. 329-345, 1919.
> Ames, J. W., and Boltz, G. E., Effect of Sulfofication and Nitrifica-
tion on Potassium and Other Soil Constituents; Soil Sci., Vol. VII,
No. 3, pp. 183-195, 1919. See also, Tottingham, W. E., and Hart, E. B.,
Sulfur and Sulfur Composts in Relation to Plant Nutrition; Soil Scei.,
Vol. XI, No. 1, pp. 49-65, 1921.
SOIL ORGANISMS 407
is yet to be determined, and will depend on a number of fac-
tors. The soil must, of course, be deficient in the constituent
composted with sulfur. Otherwise, an application of sulfur
alone would give just as good results. Again the cost of
composting must be reckoned with. It yet remains to be
proven by crop growth whether the efficiency of sulfur is any
greater when it is composted with such materials as raw rock
phosphate and farm manure and applied to the soil, than
when these materials are added separately.
225. The mineral cycle.——The strictly mineral constitu-
ents of the soil seem to undergo as complex and intricate
transformations as do the elements that are considered as
more closely related to the soil organic matter, such as ecar-
bon, nitrogen and sulfur. While a part of the mineral cycle
is purely chemical or physico-chemical, the biological phase
is by no means unimportant. In fact, were it not for the in-
fluence of organisms within the soil, little or no mineral mat-
ter, such as phosphoric acid and potash, would ever become
available to higher plants.
When plant or animal tissue enters the soil, it undergoes
decay in the manner already described, the ash constituents
being liberated and either utilized directly by higher plants
again or converted into a part of the soil mass. The main
source of the mineral nutrients for any plant is of course the
inorganic portion of the soil rather than the organic part.
It is thus necessary to investigate what influence, if any, soil
organisms have on such material.
The action of organisms on the inorganic portions of the
soil is of two kinds: (1) direct, and (2) indirect. In the
former the soil organisms themselves attack the mineral mat-
ter, rendering part of it available. Some of this soluble ma-
terial is absorbed by the organisms, becoming a part of the
eell contents. When the fungus or bacterium dies, this ma-
terial through decay again becomes available and may be
used by higher plants. While most soil organisms probably
408 NATURE AND PROPERTIES OF SOILS
function to a certain extent in this direction, some are es-
pecially active. It is known that B. mycoides, B. mesentert-
cus and B. megatherium are capable of assimilating phos-
phorus in considerable quantities, while such organisms as
Beggiotoa and Ophidomonas store up sulfur in large amounts.
In the same way iron, potassium, calcium, and like elements
may be utilized. While such biological action is at the time
a direct competition with higher plants, more mineral ma-
terial is ultimately available in the soil through such activ-
ities.
While the direct effects of organisms on soil minerals is
no doubt very important, the direct influences seem to be
more vital in a practical way. While this indirect influence
may be in part enzymic, it is probably largely due to the
production of carbon dioxide, which accompanies all types of
life processes. The sulfurous acid and nitrous acid of the
sulfur and the nitrogen cycles, respectively, are also active
to a certain extent. The preceding discussion of the sulfur
compost indicates how vigorous the biological oxidation with-
in the sulfur cycle may become under certain conditions. In
the soil, however, carbon dioxide is probably by far the most
important.1. Since the significance of carbon dioxide has
already been adequately discussed (pars. 17, 58 and 132), it is
sufficient at this point to state that this gas, because of its
large amounts and its intimate relationship to the mineral
material, is probably the most effective solvent agent in the soil.
1 Typical reactions involving tri-calcium phosphate, orthoclase and cal-
cium carbonate are as follows:
Ca,(PO,), + 2CO, + 2H,0 — Ca,H,(PO,), + Ca(HCO,)..
2K AISi,O, + CO, + 2H,0 — H,A1S8i,0, + K,CO, + 4Si0,.
CaCO, + H,O + CO, = Ca(HCO;)>.
CHAPTER XXI
SOIL ORGANISMS—THE NITROGEN CYCLE
OF THE various nutrient materials applied to the soil for
the use of plants nitrogen has the highest commercial value
and is absorbed in very large quantities. Moreover, nitro-
gen is lost from the soil in considerable amounts in drainage
water and possibly to some extent in gaseous form. The
ereat importance of this element and of its compounds in
agriculture and the possibility of it becoming a limiting factor
in crop production has lead to much study regarding its re-
actions and movements in the soil.
The original source of the world’s supply of combined nitro-
gen has been the atmosphere and, as the free gas is exceed-
ingly inert,’ the natural forces which facilitate its combina-
tion must be extremely powerful. The movement of nitrogen
from air to soil, from soil to plant, from plant back to soil or
to animal, and from animal to soil, with a return to air at
various stages, involves many forces, many factors, many or-
ganisms, and many reactions. These complicated changes
are spoken of as the nitrogen cycle.
226. The nitrogen cycle—In tracing the various trans-
formations through which the nitrogen passes, the conspicu-
ous feature is the great complexity of the cycle. Apparently
the nitrogen cycle is much more extended and intricate than
either the carbon or sulfur cycles. This complexity, however,
* Because nitrogen is such an inert gas, it must not be inferred that it
forms inactive compounds with other materials. In combination it is
extremely active, seemingly being the basis of all plant and animal life
processes,
409
410 NATURE AND PROPERTIES OF SOILS
is more apparent than real. The transformation of nitro-
gen has received so much attention and study that more
is known regarding the changes involved. The other cycles
are probably just as extended and complicated, the lack of
knowledge forcing a simpler presentation.
From the standpoint of soil fertility the compounds that
are produced in the nitrogen cycle and the relation of these
materials to plant growth are of major consideration. While
the organisms involved in the transformation should receive
as much attention as is practicable, the approach should be by
means of biological-chemistry rather than through bacteri-
ology.
It must not be inferred that the carbon, sulfur and nitro-
gen cycles are distinct or that transformations may proceed
in one with no activity in the others. As a matter of fact,
the cycles are interlocked in a hopelessly intricate manner.
The decomposition of proteid matter involves all of the cycles
already mentioned. The carbon, sulfur, and nitrogen un-
dergo distinctly different transformations, but the changes
are so closely related as to make definite lines of distinction
very difficult. Proteid matter may produce urea, carbon
dioxide, water, and sulfates. Certain of these products often
strongly influence the solubility of the soil minerals. Thus,
the four cycles already mentioned would be involved in the
decomposition of one original compound.
227. Decay and putrefaction.—The decomposition of
most nitrogenous matter is very rapid in a normal soil, the
putrefactive influences producing partially decayed sub-
stances of great variety.2, Some of these materials are very
complicated, while others are capable of being absorbed di-
*Decomposition and decay are general terms, referring to all types
of biological degradation. Fermentation refers to the decomposition of
carbohydrates, while putrefaction has to do with nitrogenous materials.
The two latter terms are generally very loosely used.
* Lathrop, E. C., Protein Decomposition in Soils; Soil Sci., Vol. I,
No. 6, pp. 509-532, 1916.
SOIL ORGANISMS 411
rectly by plants without further change. Carbon dioxide and
water are formed continuously as the process advances. The
sulfur of the proteid compounds produces hydrogen sulfide
or free sulfur and later sulfates.
Hutchinson and Miller,! as well as other investigators,
have studied the question of the assimilation of nitrogenous
organic compounds by higher plants. The general conclu-
sions indicate that such a source of nitrogen is quite impor-
tant and sometimes allows the plant to benefit markedly from
the assimilation of such materials. Maize, for example, seems
to be particularly stimulated by farm manure, which earries
large amounts of organic nitrogenous compounds such as
urea. Acetamide, urea, barbituric acid, creatinine, alloxan,
peptone, and a number of other organic compounds have
been shown to be available to certain higher plants.
Decay and putrefaction are carried on by a large number
of organisms, the higher fungi as well as such bacteria as
B. subtilis, B. mycoides, and similar micro-organisms engag-
ing in the decomposition processes. Some of the charac-
teristic, although not constant, products formed in the pu-
trefaction of albumin and proteins are albumoses, peptones,
and amino acids, followed by the formation of cadaverine,
putrescine, skatol, and indol. Where an abundant supply
of oxygen is present, or where a sufficient supply of carbo-
hydrates exists, the latter substances are not formed. There
are many other products of putrefaction, including a num-
ber of gases, as carbon dioxide, hydrogen sulfide, marsh gas,
phosphine, hydrogen, nitrogen, and the like.
Present-day knowledge of the subject does not make it pos-
sible to present a list of the organisms concerned in each step,
or to name all the intermediate products formed. For the
student of the soil the first consideration is a knowledge of
* Hutchinson, H. B., and Miller, N. H. J., The Direct Assimilation of
Inorganic and Organic Forms of Nitrogen by Higher Plants; Centrlb. f.
Bakt., IT, Band 30, Seite 513-547, 1911.
412 NATURE AND PROPERTIES OF SOILS
the circumstances under which the nitrogen is made avail-
able to plants, and the conditions that are likely to encourage
its loss from the soil.
228. Ammonification may be considered as the second step
in the simplification which nitrogenous compounds undergo
in the soil. As the name implies, it is the stage of the decay
process in which ammonia is one of the important products.
Like other processes of decomposition, there are many species
of organisms capable of producing ammonia, the higher fungi
Fig. 58.—Some soil organisms important in the nitrogen cycle. (a)
Azotobacter agilis; (b) nitrate bacteria. Urea bacteria, (c) Uro-
bacillus miguelii and (d) Urobacillus leubii.
and alge as well as bacteria participating in the changed in the
character of the nitrogen compounds.
Different soil organisms display diverse abilities in con-
verting the nitrogen of the same organic material into am-
monia, some acting more rapidly or more thoroughly than
others. In tests by certain investigators in which the same
bacteria were allowed to act on different substances, the order
of their efficiency was reversed with a change of substance.
This characteristic preference of a class of organisms for the
decomposition of certain substances is made evident by the
experiments of Sackett,! who found that in some soils dried
Sackett, W. G., The Ammonifying Efficiency of Certain Colorado
Soils; Colo. Agr. Exp. Sta., Bul. 184, 1912.
SOIL ORGANISMS 413
blood was ammonified more rapidly than was cottonseed meal,
while in other soils the reverse was true.
While the soil fungi have been but little studied, the litera-
ture available seems to indicate that they take an important
part in all soil processes, except possibly the fixation of at-
mospheric nitrogen and the formation of nitrates. Most soil
fungi produce ammonia readily. Waksman' found such
forms as Mucor racemosus, Pencillium lilacinum, and Rhiz-
opus sp. II compared favorably in capacity to produce am-
monia with Bacillus mycoides when grown in artificial cul-
ture, blood and cottonseed meal being the sources of nitrogen.
Kopeloft ? found that certain fungi seemed to prefer an acid
medium for their ammonifying activities. This suggests that
a natural provision is thus made for ammonification, no mat-
ter what the soil reaction may be.
Among the bacteria producing ammonification are B. my-
coides, B. subtilis, B. mesentericus vulgatus, B. janthinus,
and B. proteus vulgaris. Of these, B. mycoides has been very
carefully studied, and the findings of Marchal * may be taken
as representative of the process of ammonification. He found
that when this bacterium was seeded on a neutral solution of
albumin, ammonia and carbon dioxide were produced, to-
gether with small amounts of peptone, leucine, tyrosine, and
formic, butyric, and propionic acids. He concludes that in
the process atmospheric oxygen is used, and that the carbon
of the albumin is converted into carbon doxide, the sulfur
into sulfates, and the hydrogen partly into water, and partly
into ammonia by combining with the nitrogen of the organic
1Waksman, 8. A., Soil Fungi and Their Activities; Soil Scei., Vol.
II, No. 2, pp. 103-155, 1916. See also, McLean, H. C., and Wilson,
G. W., Ammonification Studies with Soil Fungi; N. J. Agr. Exp. Sta.,
Bul. 270, 1914.
2 Kopeloff, N., The Effect of Soil Reaction on Ammonification by
Certain Soil Fungi; Soil Sci., Vol. I, No. 6, pp. 541-573, 1916.
> Marchal, E., Sur la Production de l’Ammoniaque dans le Sol par
les Microbes; Bulletins de 1’Acad. Royale de Belg., 3 series, T. 25, pp.
727-776; 1893.
414 NATURE AND PROPERTIES OF SOILS
substance. Marchal found that B. mycoides was also capable
of ammonifying casein, fibrin, legumin, glutin, myosin, serin,
peptones, creatine, leucine, tyrosine, and asparagine, but
not urea.
The following reactions may be cited as indicating the
changes that probably occur when albumin and urea undergo
ammonification :
C,2H,,2.N,,80.. + 770, = 29H,0 + 72CO, + SO, + 18NH,
Albumin
CON.H, + 2H,0 = (NH,),CO,
Urea
While ammonification ' seems to proceed to the best advan-
tage in a well-drained and aérated soil with plenty of active
basic material present, it will take place to some extent under
almost any condition, due to the great number of different or-
ganisms capable of accomplishing the change. In certain
soils, as shown by Russell and Hutchinson? as well as by
other authors (see par. 211), protozoa may retard ammoni-
fication by feeding on the chief ammonia-producing organ-
isms. Such a condition is seldom serious in arable soils.
*The ammonifying efficiency of a soil is usually determined by treat-
ing a 200-gram sample of fresh soil with cottonseed meal or dried blood
carrying 120 milligrams of nitrogen. The mixture is then incubated,
usually for seven days, at optimum temperature and moisture. The in-
crease in ammonia is taken as a measure of the ammonifying efficiency.
The artificial nature of the test detracts largely from its value. See
Temple, J. C., The Value of Ammonification Tests; Ga. Agr. Exp. Sta.,
Bul. 126, 1919.
* Russell, E. J., and Darbishire, F. V., Oxidation in Soils and Its
Relation to Productiveness. Part 2. The Influence of Partial Steriliza-
tion; Jour. Agr. Sci., Vol. 2, pp. 305-326, 1907.
Russell, E. J., and Hutchinson, H. B., The Effect of Partial Steriliza-
tion of Soil on the Production of Plant Food; Jour. Agr. Sci., Vol. 3,
pp. 111-144, 1909.
Russell, E. J., and Hutchinson, H. B., The Limitation of Bacterial
Numbers in Normal Soils and Its Consequences; Jour. Agr. Sci., Vol.
5, pp. 152-221, 1903.
Buddin, W., Partial Sterilization of Soil by Volatile and Non-
volatile Antiseptics; Jour. Agr. Sci., Vol. 6, pp. 417-451, 1914.
SOIL ORGANISMS 415
229. Nitrification—Some agricultural plants can utilize
ammonium salts as a source of nitrogen.t This has been shown
to be true for rice, maize, peas, barley, and potatoes (see par.
248). Most plants, however, except for rice, show a decided
preference for nitrogen in the nitrate form. Whether these
common crops ean thrive as well on ammonium salts as on
nitrates has not been definitely demonstrated. In most arable
soils the transformation of nitrogen does not stop with its
conversion into ammonia, but goes on by an oxidation proc-
ess to the formation of nitrous acid. The nitrous acid, after
reaction with a base, is farther oxidized, a salt of nitric acid
resulting. This process of oxidation is generally spoken of
as nitrification. The reactions involved may be written as
follows:
2NH, + 30, = 2HNO, + 2H,0 ?
2HNO, + CaH,(CO,), = Ca(NO,), + 2H,O + 2CO, °
Ca(NO,). + O, = Ca(NO,),
Kach of these steps is brought about by a distinct bacteri-
um, but the groups are closely related. Collectively they are
called nitrobacteria. Nitrosomonas and Nitrosococeus are
the bacteria concerned in the conversion of ammonia into
nitrous acid or nitrites. The former are supposed to be char-
acteristic of European, and the latter of American, soils.
The organisms concerned in the oxidation of nitrites to ni-
* Kelley, W. P., The Assimilation of Nitrogen by Rice; Haw. Agr.
Exp. Sta., Bul. 24, 1911.
Hutchinson, H. B., and Miller, N. H. J., The Direct Assimilation of
Inorganic and Organic Forms of Nitrogen by Higher Plants; Centrlb.
f. Bakt., II, Band 30, Seite 513-547, 1911.
* Loew states that the reaction is as follows:
2NH, + 20, = 2HNO, + 4H
Loew, O., Die Chemischen Verhiltnisse des Bakterienlebens: II.
Centrlb. f. Bakt., II, Bd. 9, Seite 690-697, 1891.
*TIt has often been suggested that the acid produced by the nitrifying
process is of considerable importance in rendering mineral nutrients
available. While this may be true, the extent to which the solution
phenomenon takes place and its practical significance have never been
satisfactorily established by experimentation.
416 NATURE AND PROPERTIES OF SOILS
trates are generally designated as Nitrobacter. In practice
these bacteria are generally spoken of as nitrite and nitrate
organisms. The conditions favoring the two groups are
practically the same. As a consequence, nitrification is gen-
erally discussed as though the transformation was only one
step and depended on one group of organisms.?
Just as ammonification follows closely on putrefaction, so
nitrification closely accompanies the production of ammonia.
In fact, the processes are so well synchronized in a normal
soil that only traces of ammonia and nitrites are usually
found. The nitrates, however, may accumulate in large
amounts.
Marked differences have been noted in the nitrifying *
1While it was known from the middle of the nineteenth century that
nitrogenous compounds added to the soil quickly produced nitrates, it
was not until 1878 that Schloessing and Miintz demonstrated that the
process was biological. In 1890 Winogradsky succeeded in isolating
the organisms. As they do not develop on ordinary medium, as do
the decay and ammonifying bacteria, a special technique was necessary.
Winogradsky used silicic-acid-gel plates containing certain inorganic
salts, as he found that the presence of even small amounts of organic
matter prevented the development of the organisms. In the soil, how-
ever, well-decayed organic matter generally stimulates rather than de-
presses nitrification. For a review of literature and methods of isolat-
ing nitrifying organisms, see Gibbs, W. M., The Isolation and Study of
Nitrifying Bacteria; Soil Sci., Vol. VIII, No. 6, pp. 427-471, 1919.
2 Kaserer has isolated an organism, which he called B. Nitrator, that
can oxidize ammonia directly to nitrate. He writes the reaction as
follows:
NH, + H,CO, + 0, = HNO, + H,O + CH,O.
He thinks that the energy necessary for the completion of the reac-
tion is obtained from the formaldehyde (CH,O) as follows:
CH,O + O, = H,O + CO, + Energy
The correlation between carbon dioxide production and nitrate accumu-
lation lends probability to this theory.
Kaserer, H., On Some New Nitrogen Bacteria with Autotrophic Habits
of Life; Noted in Exp. Sta. Record, Vol. 18, p. 534, 1905-1906.
>The nitrifying efficiency of a soil is usually determined by treating
a 100-gram sample held in a tumbler with a suitable amount of ammonia
sulfate or some other readily nitrifiable material. After incubation for
a suitable period at optimum temperature and moisture, the increase of
nitrate nitrogen is determined. This method is merely comparative and
measures only the nitrate accumulation. Its value is limited as it does
not simulate field conditions.
SOIL ORGANISMS 417
power of different soils. Highly productive soils have gen-
erally been found to maintain a greater nitrifying efficiency
than less productive soils, but this is not always the case,
as factors other than available nitrogen may limit the pro-
ductiveness of a soil.
With the formation of nitrate nitrogen, the main portion
of the nitrogen cycle is completed, since plants absorb most
of their nitrogen as the nitrate ion. Of this cycle, from
pe ANIMAL
NITROGEN
OF AIR .
TRI STS LOSS ISS Wisp NOAA INTIRIRI
Fane CHER See
ORGANISMS MANERE
DECAY
PARTIALLY, DECAYED
CO NDS
Sen oe
(el EX
COMPOUNDS i * AMMONIFICATION
NITRIFICATION
REDUCTION (
FREE N NITRATES ~€NITRITES
Fic. 59.—Diagram representing the movements of nitrogen between
soil, plants, animals and the atmosphere. These transformations
are termed the ‘‘nitrogen cycle.’’
plant to soil, and from soil to plant again, the nitrification re-
action is the weakest point, since the other biological changes
proceed to a certain extent in spite of unfavorable soil con-
ditions. Nitrification is easily retarded and may even be
brought to a standstill. As a consequence, the factors affect-
ing this particular portion of the nitrogen cycle are of special
interest. A soil favorable to nitrification is generally wholly
favorable to the other desirable processes involving nitrogen
transformations.
418 NATURE AND PROPERTIES OF SOILS
230. Relation of soil conditions to nitrification.—<Al-
though a very great number of factors influence the process
of nitrification, the principal controls may be listed as fol-
lows: (1) presence of nitrifiable substance, (2) aération, (3)
temperature, (4) moisture, (5) soil reaction, and (6) the
presence of soluble salts.
A peculiarity in the artificial cultivation of nitrifying bac-
teria is that they cannot be grown in artificial media con-
taining organic matter. In the soil, however, organic matter,
when well decayed, stimulates nitrification, provided aéra-
tion and other conditions are favorable (see par. 313). The
application of twenty tons of farm manure to the acre to sod
on a clay loam soil for three consecutive years, at Cornell
University,” resulted in a larger accumulation and probably
a larger production of nitrates on the manured soils than
on a contiguous plat of similar soil left unmanured. This
was especially true during the third year of the application,
when the land was in sod, and also during the fourth year,
when no manure was applied to either plat and when both
plats were planted to maize, as may be seen from Table XC
(page 419).
These data indicate not only a marked influence of organic
matter on nitrification but also an effect from aération. Even
allowing for a direct and differential influence on nitrifica-
tion by the two crops, it is evident that tillage is a factor.
Further experimental data from Cornell University may be
quoted. Columns of soil eight inches in diameter and eight
inches in depth were removed from a field of clay loam on
the Cornell University farm and carried to the greenhouse
without disturbing the original structure of the soil. At
the same time, vessels of similar size were filled with soil dug
from a spot near by. These may be termed unaérated and
*The turning under of a green-manuring crop generally depresses
nitrification at first. Once the decay process is well under way, nitrifica-
tion activities seem to be stimulated.
? Unpublished data. Cornell Agr. Exp. Sta., Ithaca, N. Y.
SOIL ORGANISMS 419
TABLE XC
NITRATE ACCUMULATION ON HEAVILY MANURED AND ON UN-
MANURED SOIL.
NO, IN Parts To A MILLION OF
Dry Sor
CROP TWENTY Tons
UNMANURED MANURE TO THE
Soin ACRE FOR THREE
YEARS
Timothy (3rd year)
JCal 24s ee cee 8.2 21.0
fia Vey 14 eee eae a 8 ie
AME ust E4th. . Ss 5 ccs 1.8 3.0
Maize following timothy
VPA yen OGM ete os ahs 2 & 17.5 20.1
ATV BORNE sy sy Bod thc 50.0 105.0
Ationista LOtNs 86 cece. cee 151.0 184.0
aérated soils. Both were kept at the same temperature and
moisture content in the greenhouse, but no plants were grown
on them. The accumulation of nitrates was as follows:
TABLE XCI
NITRATES, PARTS PER MILLION Dry
TIME OF ANALYSIS Sor.
UNAERATED SorL AERATED SOIL
When taken from field.... 3.2 3.2
After standing one month. . 4.2 eG
After standing two months. 2:0 45.6
It has often been assumed that carbon dioxide is a detri-
mental factor in biological activity in two respects: by the
replacement of oxygen and by a toxic influence on the organ-
420 NATURE AND PROPERTIES OF SOILS
isms. Recent experimentation, however, indicates that car-
bon dioxide has little or no effect on nitrification and am-
monification as long as appreciable quantities of oxygen are
present. Aération, insofar as most biological activities are
concerned, has to do more with the presence of oxygen than
the elimination of the carbon dioxide which is always form-
ing. ‘
Since aération is such a factor in nitrification, the trans-
formation is very largely confined to the surface layers of
soil, except in the rich and porous subsoils of arid and semi-
arid regions. The lack of nitrate formation in the lower
depths is probably influenced by temperature as well as by
lack of oxygen and organic matter. At 5° C. nitrification is
very feeble. The optimum temperature seems to range from
25° to 30° C. The drainage of a soil probably promotes nitri-
fication quite as much by facilitating a rise of temperature
as by promoting the entrance of oxygen, especially in the
spring.
The speed with which nitrification proceeds in a soil is
governed to a marked extent by water content,? the process
being retarded by both low and high moisture conditions.
In practice, it is safe to assume that the optimum moisture
as recognized for higher plants is optimum for nitrification
1Plummer, J. K., Some Effects of Oxygen and Carbon Dioxide on
Nitrification and Ammonification in Soils; Cornell Agr. Exp. Sta., Bul.
Pee L. C., Untersuchungen iiber Nitrifikation; Centbl. f. Bakt.,
II, Bd. 20, Seite 401-420 and 484-513, 1908.
Fraps, G.S., The Production of Active Nitrogen in the Soil; Tex. Agr.
Exp. Sta., Bul. 106, 1908.
Patterson, J. W., and Scott, P. R., The Influence of Soil Moisture
upon Nitrification; Jour. Dept. Agr., Victoria, Vol. 10, pp. 275-282,
Taree eee R., and Greaves, J. E., The Production and Movement of
Nitric Nitrogen in Soil; Centbl. f. Bakt., II, Bd. 34, Seite 115-147,
1912.
Gainey, P. L., The Effect of Time and Depth of Cultwating a
Wheat Seed-bed Upon Bacterial Activity in the Soil; Soil Sci., Vol.
II, No. 2, pp. 193-204, 1916.
SOIL ORGANISMS 421
also. Greaves and Carter? found that a moisture content of
about 55 per cent. of the water-holding capacity, as determined
by the Hilgard method (see par. 90), was especially favorable
for nitrification.
It has generally been considered that nitrification was very
much retarded if not actually brought to a standstill in an
acid soil.2 Recent data,? however, seem to indicate that the
process will proceed in acid soil, although the addition of
lime in some form is usually beneficial. The marked stimula-
tion of liming to certain crops may be due partially to the in-
fluence of the lime on the nitrifying organisms. This rela-
tionship should be particularly noticeable if the crop in
question is unable to utilize organic or ammoniacal forms of
nitrogen.
The influence of certain mineral salts is quite significant.*
Small amounts of salts, even those of manganese, stimulate
the process. Sodium nitrate, unless applied in excessive
amounts, promotes the nitrification of dried blood and cotton-
seed meal. In general, the stimulation of soil bacteria by the
application of fertilizer salts is coordinate with the stimula-
tion ordinarily observed in higher plants. Rational fertilizer
practice, therefore, promotes nitrification, and no important
retarding influences may be expected on bacterial activity
unless the crop is itself directly injured.
1Greaves, J. H., and Carter, E. G., Influence of Moisture on the
Bacterial Activities of the Soil; Soil Sci., Vol. X, No. 5, pp. 361-387,
1920.
* Hall, A. D., Fertilizers and Manure, pp. 62-64, New York, 1909.
*Temple, J. C., Nitrification in Acid or Non-basic Soils; Ga. Agr.
Exp. Sta., Bul. 103, 1914.
White, G. W., Nitrification in Relation to the Reaction of the Soil;
Penn. Agr. Exp. Sta., Ann. Rep. 1913-14, pp. 70-84, 1916.
‘Kelley, W. P., Nitrification in Semiarid Soils; Jour. Agr. Res.,
Vol. VII, No. 10, pp. 417-437, 1916.
Brown, P. E., and Hitchcock, E. B., The Effect of Alkali Salts on
Nitrification ; Soil Sci., Vol. IV, No. 5, pp. 207-229, 1917.
Brown, P. E., and Minges, G. A., The Effect of Some Manganese
Salts on Ammonification and Nitrification; Soil Sei., Vol. II, No. 1,
pp. 67-85, 1916.
422 NATURE AND PROPERTIES OF SOILS
231. Influences of higher plants on nitrification —It has
been known for some time that the nitrate content of a soil
varies with the crop that occupies the land. King and Whit-
son! reported in 1901 that the accumulation of nitrates was
greatest under maize, with potatoes next and alfalfa and
clover much lower. Stewart and Greaves,” in an experiment
covering several years, also found that maize allowed the great-
est accumulation, with potatoes, oats, and alfalfa following
in the order named. Brown and MaclIntire* report forty
times more nitrates in a soil cropped to maize than when
planted to grass. As the moisture content was practically
the same in each ease, the difference cannot be ascribed to
this influence.
Perhaps the most extensive work along this line is that of
Lyon and Bizzell.t| They noted a characteristic relationship
between the crop at different stages of growth and the cor-
responding nitrate content of the soil. During the most ac-
tive growing period of maize, although the crop was absorb-
ing nitrogen in large amounts, the nitrates were frequently
higher under the maize than in a contiguous fallow plat. Oat
land contained less nitrates, while grass seemed to retard
markedly the accumulation of nitrates. Whether the nitrate
organisms are stimulated by certain plants or whether nitrate
formation is merely depressed more by some plants than by
others is not known. It is clear, however, that the relation-
ship of crop to nitrification must be reckoned with in practical
*King, F. H., and Whitson, A. R., Development and Distribution of
Nitrates and Other Soluble Salts in. Cultivated Soils; Wis. Agr. Exp.
Sta., Bul. 85, 1901.
*Stewart, R., and Greaves, J. E., The Production and Movement of
Nitric Nitrogen in Soil; Centbl. f. Bakt., II, Band 34, S. 115-147,
1912.
* Brown, B. E., and MacIntire, W. H., Seasonal Nitrification, Soil
Moisture and Lime Requirement in Four Plats Receiving Sulfate of
Ammonia; Penn. Agr. Exp. Sta., Rep. 1909-1910, pp. 57-63.
4Lyon, T. L., and Bizzell, J. A., Some Relations of Certain Higher
Plants to the Formation of Nitrates in Soils; Cornell Agr. Exp. Sta.,
Memoir 1, 1913.
SOIL ORGANISMS 423
soil management as well as the effect of nitrification on plant
growth.
The influence of plants on nitrification is not confined to
the period in which they are growing on the soil. Lyon and
Bizzell, in the investigation previously mentioned, found that
certain plants grew better when preceded by one species
rather than by another. These authors, as already explained,
have suggested that certain higher plants directly influence
nitrification with varying intensity. The question now arises
as to the possibility of such plants influencing the process of
nitrate formation after their removal.
The following data from Lyon and Bizzell suggest that,
while the effect is variable, plants seem definitely to influence
the production of nitrates during the season after they have
been removed. All of the plats were kept bare in 1911.
TABLE XCII
NITRATES IN Soi KEPT
SEASON 1910 BaRE IN 1911
Parts PER MILLION
Eee END NITRATES IN rh
ae Sort, Parts ee
aoe ee P OuNDS ree May 1 JUNE 28
AVERAGE CEE
Miaizeas nob e 167 3 52 Bi
anes seek 0-5: 186 — 50 35
POfAtoeS ss 3.52/34 104 43 28 26
AER. nes. oh se 108 — 43 32
Oats ei. rae kee 90 29 22 22
[5 che eam mpeets are 126 -— 36 33
These results indicate that maize exerts a stimulating influ-
ence during the following summer. Oats and potatoes seem
to depress nitrate accumulation.
232. Relation of nitrification to soil fertility——In spite
of the immense amount of work that has been done on the bio-
424 NATURE AND PROPERTIES OF SOILS
logical problems of the soil, no definite relationships have
been established between any given transformation and the
productivity of the soil. General correlations have been re-
peatedly observed! but specific relationships, when recorded,
are difficult to ascribe to other than chance concordance. Of
all of the biological transformations, nitrification seems most
likely to correlate with productivity, since most plants use
large amounts of nitrate nitrogen.
Available data seem to show that there is a general correla-
tion between the nitrifying capacity of soils and their crop-
producing power.? Such a statement, however, does not imply
that the productivity of soils, insofar as nitrogen is a limiting
factor, is especially controlled by nitrification. Arable soils
usually contain abundant nitrifying organisms, which seem
to oxidize ammonia to the nitrate form as fast as it is pro-
duced. It would appear that nitrification is only one of the
many factors that govern productivity, a high nitrate content
of a soil accompanying, rather than controlling, high crop
production.
233. Reduction of nitrates and allied compounds.—Ni-
trates may be removed from the soil in three ways: (1) by
drainage, (2) by plant absorption, and (3) by reduction to
free nitrogen. The loss of nitrogen by leaching and by crop-
ping has already been adequately treated. It has been shown,
for example (see par. 163), that as high a loss as 77 pounds of
nitrogen to the acre a year may be expected from a heavy
1 Ashby, S. F., The Comparative Nitrifying Power of Sotls; Jour.
Chem. Soc., London, Vol. 85, pp. 1158-1170, 1904.
Russell, E. J., and Hutchinson, H. B., The Effect of Partial Sterili-
zation of Soils on the Production of Plant Food; Jour. Agr. Sci., Vol.
III, pp. 111-144, 1909.
Kellerman, K. F., and Allen, E. R., Bacteriological Studies of the
Truckee-Carson Irrigation Project; U. S. Dept. Agr., Bur. Plant Ind.,
Bul id 19,
Brown, P. E., Relation Between Certain Bacterial Activities in Soils
and Their Crop Producing Power; Jour. Agr. Res., Vol. V, pp. 855-
869, 1916.
?Gainey, P. L., The Significance of Nitrification as a Factor in Soil
Fertility ; Soil Sci., Vol. III, No. 5, pp. 399-416, 1917.
SOIL ORGANISMS 425
soil through the combined influence of cropping and drainage.
This is equivalent to a removal of about 520 pounds of sodium
nitrate as far as the nitrogen contained is concerned.
While the removal of nitrogen from the soil is due very
largely to the phenomena just referred to, the loss of nitro-
gen through reduction demands a certain amount of atten-
tion. Reduction includes the change of nitrates to nitrites,
to ammonia and even to free nitrogen.' In the same way
nitrites may be reduced to ammonia and the latter to ele-
mental nitrogen. When the process is carried to completion
there is opportunity for an escape of some nitrogen to the at-
mospherie air. The loss of nitrogen is not the important con-
sideration, however. The interference with plant nutrition,
which naturally occurs, is much more serious and justifies
the attention which the phenomena have received from bac-
teriologists.
The number of organisms that are capable of accomplishing
one or more of the reduction processes is very large. This is
due to the facultative character of the soil flora, which is
able to alter its functions to suit the conditions. Thus B.
mycoides, which is a normal decay and ammonifying organ-
ism, may, under anaérobie conditions become a vigorous re-
ducing agent. Other specific reducing organisms are :—B
ramosus and B. pestifer, B. subtilis, B. mesenterious vul-
gatus, B. denitrificans, and many others. It is probable that
fungi also are able to effect the transformation.
Most of the reducing bacteria perform their functions only
in presence of a limited amount of oxygen, while others can
operate in the presence of a more liberal supply. In general,
thorough aération of the soil impedes the process to a consid-
erable degree. Straw apparently carries an abundant supply
of such organisms, and it is consequently possible to reach a
1The reaction may be illustrated empirically as follows:
2HNO; = 2HNO, + O,.
4HNO, — 2H,0 + 2N, + 30.
HNO, -- H,O= NH, + 20:.
426 NATURE AND PROPERTIES OF SOILS
point in manuring at which reduction takes place. When
fifty tons or more of farm manure, in addition to a nitrate
fertilizer, are added to the soil, unfavorable reactions may
occur. Plowing under heavy crops of green-manure may
produce the same result. In either case the best way to over-
come the difficulty is to allow the organic matter partly to de-
compose before adding the fertilizer. The removal of the
easily decomposable carbohydrates needed by the reducing
organisms decreases or precludes their activity in this
direction.
Under ordinary farm conditions conversion to free nitrogen
is of no significance in the soil where proper drainage and
good tillage are practiced. Warington! showed that if an
arable soil is kept saturated with water to the exclusion of air,
nitrates added to the soil are decomposed, with the evolution
of nitrogen gas. As lack of drainage is usually most pro-
nounced in early spring, when the soil is likely to be depleted
of nitrates, it is not likely that much loss occurs in this way
unless a nitrate fertilizer has been added. Among the many
difficulties arising from poor drainage the reduction of an
expensive fertilizer may be no inconsiderable item.
234. Assimilation of nitrates and allied compounds.?—
In addition to the nitrate-reducing organisms already men-
tioned, there are other bacteria and fungi that utilize nitrates,
nitrites, and ammonia. Like higher plants, they convert
the nitrogen into organic nitrogenous substances. The proc-
ess is therefore, one of synthesis, rather than of reduction al-
though reduction often occurs at the beginning of the proc-
ess. As such organisms operate in the dark, they must have
organic acids or carbohydrates as a source of energy. This
means of nitrate disappearance is probably of much more
*Warington, R., Investigations at Rothamsted Experimental Station ;
U.S. Dent. Agr., Office of Exp. Sta., Bul. 8, p. 64, 1892.
The term denitrification is often used in referring to the reduction
and assimilation of nitrates and allied compounds in the soil. The word
is so loosely used in soil literature that it has seemed best to ignore it,
at least for the present.
SOIL ORGANISMS 427
practical importance than nitrate reduction, yet even less is
known regarding the phenomena. Many different forms of
bacteria and fungi are probably capable of assimilating
nitrogen, but what conditions favor their activity in this re-
spect cannot be stated definitely.". To make the problem more
intricate higher plants seem to be a factor to a certain ex-
tent in this type of nitrate disappearance. Seasonal influ-
ences also have been noted, which suggest the possibility of a
special nitrate assimilating flora.
Nitrate accumulation always proceeds slowly on sod land,
especially if the soil is heavy. Lack of sufficient moisture or
unfavorable temperature relations do not always adequately
account for this phenomenon. An experiment at Cornell Uni-
versity ? is typical of the conditions mentioned above. In this
case, maize and grass were grown side by side, the nitrates
being determined at frequent intervals during the season.
The nitrates are expressed in parts per million of dry soil for
the various months.
TaBLE XCIIT
NITRATES IN PARTS PER MILLION UNDER MAIZE AND SOD.
CORNELL UNIVERSITY.
NITRATES, PARTS PER MILLION Dry
MontH Som
Sop LAND Maize LAND
ISS OETA OS I ea E 8.9 —
WGA ooe Ue ain ete ee 3.0 el
OD ees Ae ee 2.4 40.3
ATU seaceee sateen 4.0 194.0
NMOS mele ee cee ce ek ck 5.4 186.7
1 Murray has found at the Washington Agricultural Experiment Sta-
tion that the addition of straw to the soil markedly aided the bacterial
utilization of nitrates. The numbers of bacteria increased without
reference to the groups present.
Murray, T. J., The Effect of Straw on the Biological Soil Processes;
Soil Sei., Vol. XII, No. 3, pp. 233-259, 1921.
*Unpublished data. Cornell Agr. Exp. Sta., Ithaca, N. Y.
428 NATURE AND PROPERTIES OF SOILS
The high nitrate accumulation under the maize is probably
due to the tillage and aération which the soil received and
possibly to the direct stimulation of the crop on nitrification.
The low amounts of nitrate nitrogen in the grass land are
probably due, at least partially, to the influence of the sod in
encouraging nitrate assimilation by the soil organisms. The
nitrifying power of the sod soil is probably much greater
than the data just presented would lead one to suspect. Sodi-
um nitrate applied to grass at Cornell University was found
to be changed to other than the nitrate form very rapidly,
even when the amounts added were extremely large. This
rapid disappearance of the nitrate form of nitrogen is not
readily accounted for by cropping and drainage removal.
Such facts lend considerable plausibility to the suggestions
made above, regarding the encouragement which the synthetic
removal, especially of nitrates, receives from organisms when
the soil is under a grass crop.
The synthetic removal of nitrates, nitrites, and ammonia
assumes considerable importance at certain times of the year.
It seems to be a natural means of conserving an important
soil constituent, since nitrate nitrogen is extremely soluble
and easily lost by drainage. The nitrogen thus affected is
changed to a more or less stable form, from which nitrates
may be produced during the following year. The use of a
cover-crop in an orchard during the late summer and fall is
often practiced. A disappearance of nitrates but not a loss of
nitrogen thus oceurs and the trees are early forced into the
resting stage.
235. Natural acquisition of nitrogen by the soil—Since
all of the nitrogen now found in the soil was probably ac-
quired from the atmosphere, the natural forces which facili-
tate such a transfer assume considerable practical importance.
The more rapid the natural acquisition of nitrogen from the
air, the less serious will be the nitrogen problem in agricul-
tural practice.
SOIL ORGANISMS 429
Three modes of nitrogen fixation are usually recognized: (1)
rain-water additions, (2) the action of soil organisms fune-
tioning independently of living higher plants, and (3) the
influence of organisms functioning parasitically or symbi-
otically in the soil.
236. Additions of nitrogen in rainwater.—Nitrogen oc-
curring in rainwater is generally in the nitrate and ammoni-
eal forms and, consequently, is readily available to plants.
The amounts thus brought down are quite variable, usually
fluctuating markedly with season and location. The follow-
ing table gives some of the more important findings regarding
the amount of nitrogen thus added to the soil in various parts
of the world.
TABLE XCIV
Pounps TO ay
YEARS |RAINFALL AGE A UE
LOocATION OF IN
Recorp | IncHES eae NITRATE
NITROGEN NEO
Harpenden, England?.... 28 28.8 2.64 1.33
Gartiord, ‘Hmeland ?.: ..... 3 26.9 6.43 1.93
Plahult, Sweden*......... il 32.0 3.32 1.30
Groningen, Holland‘*..... — 27.6 4.54 1.46
Bloemfontein and Durban,
RSE PAUSE Sette eae ce css 2 — 4.02 1,39
Oitawan Canada: x... ye: 10 23.4 4.42 2.16
ithaca: New. York *....... 6 29.3 11.50 1.01
1Russell, E. J., and Richards, E. H., The Amount and Composition
of Rain Falling at Rothamsted; Jour. Agr. Sci., Vol. IX, pp. 309-337,
1919.
*Crowther, C., and Ruston, A. G., The Nature, Distribution and
Effects wpon Vegetation of Atmospheric Impurities In and Near an
Industrial Town; Jour. Agr, Sci., Vol. IV, pp. 25-55, 1911.
*Von Feilitzen, H., and Lugner, I., On the Quantity of Ammonia
and Nitrie Acid in Rainwater Collected Near Flahult, in Sweden; Jour.
Agr. Scei., Vol. III, pp. 311-313, 1910.
*Hudig, J.. The Amounts of Nitrogen as Ammonia and Nitric Acid
430 NATURE AND PROPERTIES OF SOILS
Apparently the ammoniacal nitrogen is always consider-
ably larger in amount than that in the nitrate form. It is
also noticeable that while the nitrate nitrogen is about the
same for every station, the nitrogen in the form of ammonia
shows wide variations. The quantities at Ithaca, New York,
are considerably larger than those from any other station.
Considering the figures as a whole, it seems fair to assume
that on the average about 414 pounds of ammoniacal and 114
pounds of nitrate nitrogen fall on every acre of soil yearly
in rainwater. Assuming that all of this nitrogen passes into
the soil, an average gain to the acre of 6 pounds of nitrogen
may be expected.
It is interesting at this point to compare such a gain with
the annual loss of nitrogen from the soil. The removal of
nitrogen from the Cornell lysimeter soils (see par. 163),
through drainage and cropping combined, amounted to 69.0,
77.8 and 56.9 pounds yearly to the acre, respectively, for a
bare soil, one carrying a standard rotation, and one continu-
ously in grass. While a gain of 6 pounds to the acre yearly
seems rather insignificant in comparison to these figures, such
an addition is of considerable importance over a period of
years, and has had much to do with the accumulation of the
nitrogen of our arable soils. Such a gain is equivalent in a
practical way to the addition of about 40 pounds of commer-
cial sodium nitrate to the acre yearly.
237. Acquisition of nitrogen by free-fixing organisms.—
While it has long been known that the soil contains a great
variety of organisms, it is only in recent years that it has been
in the Rainwater Collected at Uithwizer-Meeden, Gronigen; Jour. Agr.
Sci., Vol. IV, pp. 260-269, 1912.
5 Juritz, C. F., Chemical Composition of Rain in the Union of South
Africa; S. Africa Jour. Sci., Vol. 10, pp. 170-193, 1914.
®Shutt, F. T., and Dorrance, R., The Nitrogen Compounds of Rain
and Snow; Proc. and Trans. Roy. Soe. Canada, Vol. XI, No. 3, pp. 63-71,
1917.
7 Wilson, B. D., Nitrogen in the Rainwater at Ithaca, New York;
Soil Sci., Vol. XI, No. 2, pp. 101-110, 1921.
SOIL ORGANISMS 431
definitely shown that certain of these organisms have the
power of utilizing atmospheric nitrogen, which later becomes
a part of the nitrogenous matter of the soil. Boussingault *
in 1858 suggested the possibility of such a phenomenon, but
it was not until 1883 that Berthelot ? began experiments by
which he demonstrated that bare soils appreciably increase
in nitrogen on exposure under such conditions. Winograd-
ski* in 1894 was the first, however, to isolate an organism
eapable of affecting such a transformation. This bacterium
was an anaérobic, rod-shaped organism producing spores
and a boat-shaped mass (clostridium) ; hence the name, Clos-
tridium pastorianum. It is very widely distributed in soils.
The most important organism fixing nitrogen independently
in the soil was discovered by Beijerinck * in 1901. This or-
ganism was an aerobic bacillus to which he gave the name
Azotobacter. It was at first thought that this bacillus could
not fix nitrogen unless certain other organisms, sueh as Granu-
lobacter, Radiobacter and Aérobacter, were also present. Lip-
man ° has shown this idea to be erroneous, although the effi-
ciency of Azotobacter is much higher in mixed than in pure
cultures. A number of different species of Azotobacter have
been studied, the A. chrodcoccum apparently being the most
widespread.
Clostridium pastorianum and Azotobacter are by no means
the only soil organisms capable of fixing nitrogen. Among
*See Voorhees, E. B., and Lipman, J. G., 4 Review of Investigations
in Soil Bacteriology; U. S. Dept. Agr., Office of Exp. Sta., Bul. 194,
— Berthélot, M., Recherches nouvelles sur les microorganisms fixateurs
de l’azote; Compt. Rend. Acad. Sci. Paris, Tome 115, pp. 569-574 and
842-849, 1892-93.
* Winogradsky, S., Sur l’assimilation de l’azote gazeuxz de l’atmosphere
par les microbes; Compt. Rend. Acad. Sci. Paris, Tome 118, pp. 353-355,
Siar M. W., Uber Oligonitrophile Mikroben; Centrbl. Bakt.,
II, Ba. 7, S. 561-582, 1901.
‘Lipman, J. G., Experiments on the Transformation and Fixation of
Nitrogen by Bacteria; N. J. Agr. Exp. Sta., 24th Ann. Rep., pp. 217-285,
1903,
432 NATURE AND PROPERTIES OF SOILS
bacteria, B. mesentericus, B. pneumome, B. radiobacter, B.
amylobacter, B. prodigiosus, B. asterosporus, and B. lactis
viscusus have certain capacities in this direction. Duggar
and Davis? have shown that certain filamentous fungi, such
as Phoma beta, Aspergillus niger, Pencillium digitatum,
and others have the ability of utilizing atmospheric nitrogen.
The power of fixing nitrogen is, therefore, possessed by a
large number of different organisms, yet from the data now
at hand the Azotobacter group seems to be of the greatest
economic importance. The nitrogen fixed enters the nitrogen
eycle when the organisms die, undergoing decay, ammonifica-
tion and nitrification, thus becoming available to higher plants.
238. Conditions for azofication and the amount of nitro-
gen fixed.*—The term azofication relates to the fixation of
nitrogen by the Azotobacter group,.although it may be used
loosely in reference to all free-fixing activities. The soil con-
ditions favorable to this phenomenon are those which are opti-
mum for higher plants. This is especially true regarding
aeration, temperature, and moisture relations. The process
is encouraged by the application of lime when soils are acid
and seem to require considerable phosphorus. This element is
probably utilized in building up proteins within the bodies
of the organisms. Potassium, sulfur, iron, and magnesium
seem also to be essential to the phenomenon. The Azotobac-
ter themselves are influenced by catalytic agents such as
manganese.
Since considerable energy is required for nitrogen fixation
the presence of organic matter in the soil becomes very im-
portant in this regard. Almost any non-toxic organic ma-
terial may serve as a source of energy, even cellulose being
very effective. Farm manure seems especially to encourage
*Duggar, B. M., and Davis, A. R., Studies in the Physiology of the
Fungi; Ann. Mo. Bot. Garden, Vol. 35, pp. 413-437, 1916.
2A very excellent review of literature and discussion of Azofication:
Greaves, J. E., Azofication; Soil Sci., Vol. VI, No. 3, pp. 163-217,
1918.
SOIL ORGANISMS 433
nitrogen fixation. The maintenance of a fair supply of soil
organic matter is, therefore, as important as the regulation
of the temperature, the oxygen, the moisture, and the reac-
tion of the soil. While the presence of nitrates in small
amounts seems to stimulate azofication, large quantities of
nitric nitrogen tend to lessen nitrogen fixation.
The amount of nitrogen fixed in the soil by organisms fune-
tioning independently of higher plants is, as might be ex-
pected, a variable quantity. Hall‘ considers it to be on the
average about 25 pounds yearly to the acre, Greaves? 25
pounds, Lohnis* 36 pounds, and Lipman‘ from 15 to 40
pounds. As a basis for calculation 25 pounds is perhaps a
conservative and reasonable figure. A comparison of this
figure with the 6 pounds of nitrogen brought down yearly
in rain-water, indicates that the free-fixing organisms are
four or five times more important than rainfall as a source of
nitrogen.
239. Bacillus radicicola and its relationship to the host
plant.—lIt has long been recognized by farmers that certain
crops, as clover, alfalfa, peas, beans, and some others, im-
prove the soil, making it possible to grow larger crops of
cereals after these plants have occupied the land. Within
the last century the benefit has been traced to the fixation
of nitrogen through the agency of bacteria contained in nod-
ules on the roots. The specific plants so affecting the soil
were found to be, with a few exceptions, those belonging to
the family of legumes. It has furthermore been demonstrated
that the host plant is generally able to appropriate some of
the nitrogen so fixed and thus benefit by the relationship.
The phenomenon was fully explained in 1886 by Hellreigel
1 Hall, A. D., On the Accumulation of Fertility by Land Allowed to
Run Wild; Jour. Agr. Sci., Vol. I, pp. 241-249, 1905.
4Greaves, J. E., Azofication; Soil Sci., Vol. VI, No. 3, pp. 163-217,
1918.
’Lohnis, F., and Westermann, F., Uber Stickstoff fixierende Bakterien,
IV. Centrbl. f. Bakt., II, Bd. 22, S. 234-254, 1909.
‘Lipman, J. G., Marshall’s Microbiology, p. 343, 1917.
434 NATURE AND PROPERTIES OF SOILS
and Wilfarth. The organisms, of which there are a number
of strains, are called Bacillus radicicola.
The organisms living in the root nodules take free nitrogen
from the air in the soil, and the host plant secures it in some
form from the bacteria or their products. The presence of a
certain species of bacteria is necessary for the formation of
tubercles. Leguminous plants grown in cultures or in soil
not containing the necessary bacteria do not form nodules
and do not utilize atmospheric nitrogen, the result being that
the crop produced is less in amount and the percentage of
nitrogen in the crop is lower than if nodules were formed.
The nodules are not normally a part of leguminous plants,
but are evidently caused by an irritation of the root sur-
face, much as a gall is caused to develop on a leaf or a branch
of a tree by an insect. In a culture containing the proper
bacteria the prick of a needle on the root surface will cause a
nodule to form in the course of a few days. The entrance of
the organism is effected through a root-hair which it pene-
trates, and it may be seen as a filament extending the entire
length of the hair and into the cortex cells of the root, where
the growth of the tubercle starts.
Even where the causative bacteria occur in cultures or in
the soil, a leguminous plant may not secure any atmospheric
nitrogen, or perhaps only a small quantity, if there is an
abundant supply of readily available combined nitrogen on
which the plant may draw. The bacteria have the ability to
utilize combined as well as uncombined nitrogen, and prefer
to have it in the former condition. On soils rich in nitrogen,
legumes may, therefore, add little or no nitrogen to the soil,
if the above ground portion of the crop is not plowed under;
while in properly inoculated soils deficient in nitrogen an
important gain of nitrogen may result.
While B. radicicola is considered the organism common to
all leguminous plants, it is now known that the organisms
from one species of legume are not equally well adapted to
SOIL ORGANISMS 435
the production of tubercles on other leguminous species. Cer-
tain cross inoculations are, however, very successful. The
organisms seem to be interchangeable within the clovers, the
vetches and the bean family. The organisms from sweet
elover and burr clover will inoculate alfalfa, while the bac-
teria may be transferred from vetch to field pea or from cow-
pea to velvet bean.
It has been shown by several investigators that bacteria
from the nodules of legumes are able to fix atmospheric nitro-
gen even when not associated with leguminous plants. There
would seem to be no doubt, therefore, that the fixation of
nitrogen in the tubercles of legumes is accomplished directly
by this organism, not by the plant itself nor through any com-
bination of the plant and the organism. The relationship is,
therefore, parasitical rather than strictly symbiotic, although
the host plant benefits from the relation. The part played
by the plant is doubtless to furnish the carbohydrates which
are required in considerable quantities by all nitrogen-fixing
organisms and which the legumes are able to supply in large
amounts. The utilization of large quantities of carbohydrates
by the nitrogen-fixing bacteria in the tubercles may also ac-
count for the small proportion of non-nitrogenous organic
matter in the plants.
How the plant absorbs this nitrogen after it has been
secured by the bacteria is not well understood nor is it known
in exactly what form the nitrogen is at first fixed, although
amino and amide nitrogen very soon appear.’ Early in the
growth of the tubercle, a mucilaginous substance is produced,
which permeates the tissues of the plant in the form of long
slender threads containing the bacteria. These threads de-
velop by branching or budding, and form what have been
ealled Y and T forms, known as bacteroids, which are peculiar
to these bacteria. The threads finally disappear, and the
1Strowd, W. H., The Forms of Nitrogen in Soybean Nodules; Soil
Sci., Vol. XI, No. 2, pp. 123-130, 1921.
436 NATURE AND PROPERTIES OF SOILS
bacteria diffuse themselves more or less through the tissues of
the root. What part the bacteroids play in the transfer of
nitrogen is not known. It has been suggested that in this
form the nitrogen is absorbed by the tissues of the plant. It
seems quite likely that the nitrogen compounds produced
within the bacterial cells are diffused through the cell-wall and
absorbed by the plant.
240. The practical importance of B. radicicola.—The
nitrogen fixed by the nodule organisms may go in three di-
rections in the soil. It may be absorbed by the host plant,
the latter benefiting greatly by the association. This rela-
tionship has already been discussed. Secondly, the nitrogen
may pass in some way into the soil itself and benefit a crop
associated with the legume. Thirdly, the nodules may decay,
when the legume dies or is turned under, the nitrogen be-
coming available to the succeeding crop.
The relationship between associated legumes and non-
legumes has been particularly studied by Lyon and Bizzell *
and by Lipman.? It has been quite definitely proven that the
non-legume may be greatly benefited by the association under
some conditions. This accounts for the practice of growing
timothy with clover, which has been common for centuries.
Just how the transfer of nitrogen is facilitated yet remains
to be shown.
The beneficial influences of such legumes as clover, vetch,
and alfalfa on the succeeding crops has long been taken ad-
vantage of in practical agriculture. Until recently the stimu-
lation has been ascribed to an actual increase of nitrogen in
the soil, due to the growth of the legume and the activity of
its nodule organisms. This will not always account for the
phenomenon, since it has been shown by a number of investi-
tLyon, T. L., and Bizzell, J. A., Availability of Soil Nitrogen im
Relation to the Basicity of the Soil and to the Growth of Legumes;
Jour. Ind. and Eng. Chem., Vol. 2, No. 7, pp. 313-315, 1910.
* Lipman, J. G., The Associative Growth of Legumes and Non-Legumes.
N. J. Agr. Exp. Sta., Bul. 253, 1912. —
SOIL ORGANISMS 437
eators that the continuous growing of legumes, the tops being
removed as forage, does not always increase the nitrogen con-
tent of the soil to any greater extent than does a non-legumi-
nous crop.
The results of Swanson?’ are particularly striking in this
respect. This investigator sampled a number of fields in
Kansas that had grown alfalfa continuously for twenty or
thirty years, at the same time obtaining soil from contiguous
native sod. In most cases the alfalfa soil was lower in
nitrogen than the sod. Lyon and Bizzell* found practically
the same content of nitrogen in contiguous alfalfa and
timothy soils after the crops had been growing six years.
The maize crop following the alfalfa was nevertheless much
greater than that after the timothy. Since the soil on which
a legume has been growing generally has a rather high nitrify-
ing capacity,® the explanation seems to lie in the ready avail-
ability of the nitrogen in the soil which bore the legume,
rather than to the presence of an especially large amount.
The amount of nitrogen fixed by the nodule organisms of
a leguminous crop is very uncertain. If the soil is acid, if
it contains alkali salts above a certain amount, or if nitrates
develop rapidly, nitrogen fixation is markedly retarded. Much
also depends on the virulence of the organisms, the character
of the legume, the presence of organic matter, and other im-
portant conditions. Hopkins‘ estimates that about one-third
1Swanson, C. O., The Effect of Prolonged Growing of Alfalfa on
the Nitrogen Content of the Soil; Jour. Amer. Soc. Agron., Vol. 9,
No. 7, pn. 305-314, 1917.
Swanson, C. O., and Latshaw, W. L., Effect of Alfalfa on the Fer-
tility Elements of the Soil in Comparison with Grain Crops; Soil Sci.,
Vol. VIII, No. 1, pp. 1-39, 1919.
Lyon, T. L., and Bizzell, J. A., Hxuperiments Concerning the Top-
dressing of Timothy and Alfalfa; Cornell Agr. Exp. Sta., Bul. 339,
pp. 136-139, 1913.
Lyon, T. L., Bizzell, J. A., and Wilson, B. D., The Formation of
Nitrates in a Soil Following the Growth of Red Clover and of Timothy;
Soil Sci., Vol. IX, No. 1, pp. 53-64, 1920.
Hopkins, C. G., Soil Fertility and Permanent Agriculture, p. 223,
Boston, 1910.
438 NATURE AND PROPERTIES OF SOILS
of the nitrogen of a normal inoculated legume comes from
the soil and two-thirds from the air. He also assumes that
one-third of the nitrogen of the plant exists in the roots. Al-
though both of these assumptions are questionable, they sug-
gest the reason why the removal of the tops of legumes as
forage allows no accumulation of nitrogen in the soil.
According to Hopkins, the nitrogen in the tops of legumes
is a rough measure in general of the nitrogen fixed. On such
an assumption, the growth of red clover should facilitate the
fixation of about 40 pounds of nitrogen for every ton of air-
dry material. On the same basis, the figure should be about
50 pounds for alfalfa, 43 pounds for cowpeas, and 53 pounds
for soybeans. These figures, even though they are obviously
incorrect, give some idea of the importance of B. radicicola in
nitrogen fixation. The growth of an average leguminous
crop under proper conditions probably is accompanied by a
fixation of 80 to 100 pounds of nitrogen. Of the three nat-
ural methods by which atmospheric nitrogen may be fixed
by the soil that facilitated by the nodule organisms seems
at first thought to be considerably the most important. It
must be remembered, however, that with an average rotation
a legume occupies the land but one or two years in three to
six. Moreover, the gain of nitrogen in a fertile soil is but
slight unless the crop is turned under as a green-manure.
Unless so used the chief advantages of growing a legumi-
nous crop lie in the increase of soil organic matter, the
ready and favorable decay of the roots and stubble, and the
opportunity of growing a high protein crop without ma-
terially depleting the soil nitrogen.
241. Soil inoculation for legumes.—Although the inocu-
lation of the soil with free-fixing organisms has not proven
of value, since such organisms are always present and suffi-
ciently active if soil conditions are favorable, the inoculation
with nodule bacteria is of considerable practical importance.
Such organism may never have been present in a soil or may
SOIL ORGANISMS 439
have disappeared because of unfavorable conditions. If leg-
umes, especially of certain types, are to be grown most suc-
cessfully, the specific strains of B. radicicola for that crop
must be present.
Two general methods of inoculation are available: (1) the
use of soil from fields where the particular legume in ques-
tion is growing or has grown successfully ; and (2) the utiliz-
ation of artificial cultures of some form. Bacillus radicicola
is found in the soil as well as in the plant nodules. As a
matter of fact, this bacterium will live in the soil for long
periods, even if the host plant is not grown. Whether it fixes
nitrogen to any extent under such conditions is a question.
At least the organism does not lose its virulence. Such soil
may be spread on the land to be inoculated at the rate of
300 to 500 pounds to the acre. It should be applied in the
evening or on a cloudy day and harrowed in as soon as pos-
sible, as the organisms are injured by direct sunlight.
The soil carrying the organism may also be mixed after
air-drying with the seed, the latter having been moistened with
a dilute glue solution.t Enough of the dry earth sticks to
the seed to carry the organisms into the soil. The advantage
of this method is that the bacteria are in contact with the seed
and the plants become infected very soon after the seeds
germinate. The main objection to the soil method of inocu-
lation lies in the possibility of spreading plant diseases and
undesirable weeds.
1Dissolve ordinary furniture glue in boiling water, two handfuls of
glue to every gallon of water used, and allow the solution to cool. Put
the seed in a wash-tub, and then sprinkle enough of the solution on the
seed to moisten but not to wet it (one quart to a bushel is sufficient),
and stir the mixture thoroughly until all the seeds are moistened.
Dry the inoculating soil in the shade, preferably in the barn or base-
ment, and pulverize it thoroughly into a dust. Scatter this dust over the
moistened seed, using from one-half to one gallon of dirt for each
bushel of seed, mixing thoroughly until the seed no longer stick together.
The seed is then ready to sow.
See Vrooman, C., Grain Farming in the Corn Belt with Live Stock as
Side Line; Farmers’ Bul., No. 704, 1916.
440 NATURE AND PROPERTIES OF SOILS
Within recent years a number of cultures for soil mocula-
tion have been offered to the public. The first of these ntil-
ized absorbent cotton to transmit the bacteria in a dry state
from the pure culture in the laboratory to the user of the cul-
ture, who was to prepare therefrom another culture to be used
for inoculating the soil. Careful investigation of this method
showed that its weakness lay in drying the cultures on the ab-
sorbent cotton, which frequently resulted in the death of the
organisms. More recently liquid cultures have been placed
on the market in this country, and these have, in the main,
proved to be more successful, notably those sent out by the
United States Department of Agriculture.
Another very successful culture medium, now being used
by the Department of Plant Physiology at Cornel University,
is steamed soil. <A soil, favorable to the development of
nodule organisms and usually a sandy loam, is sterilized by
steaming. It is then brought up to optimum moisture and
later inoculated with a number of different strains of B.
radicicola. After incubation for several days at a favorable
temperature, the soil cultures are ready for distribution. The
soil is sent out in small air-tight cans by parcel post. The
advantage of such a culture is that the organisms are viru-
lent and there is no danger from plant diseases or undesir-
able weeds.
When a culture of this sort is received it may be used in a
number of different ways. It may be mixed with field soil
at the rate of 1 pound to 300 of the latter. This 300 pounds
of inoculated soil may then be spread on a acre of land in
the usual way. The culture may also be disposed of by the
glue method or it may be suspended in water and the extract
sprinkled on the seed and dried in the shade. In either case,
the seed should be sown as soon as possible.
242. Resume.—The biological phases of the soil are so nu-
merous and far-reaching that it is obviously impossible in
summarizing their practical relationships to do more than call
SOIL ORGANISMS 441
attention to certain significant facts. In the first place, the
soil fauna and flora, especially the latter, are exceedingly
complex. The number of plant forms are so numerous that
the discussion already presented serves as little more than an
introduction. In the second place, the transformations facili-
tated by soil organisms involve all of the normal constituents
of the soil, both organic and inorganic. Moreover, biological
activities determine to a large degree the efficacy of every
addition, natural or artificial, made to the land. While the
eyeles generally recognized are apparently clear cut, the
transformations themselves are actually involved in intrica-
cies, Which man will probably never entirely unravel.
A third phase of outstanding importance is the relationship
of the biological activities of the soil to the nitrogen prob-
lem. Not only are the complex nitrogenous compounds of the
soil readily made available to higher plants by soil organisms,
but means are provided whereby considerable nitrogen, in-
ert as it is, may be wrested from the atmosphere and forced
into activity within the soil. It is not impossible that in cer-
tain favored cases 150 pounds of nitrogen to the acre may
be yearly added to the soil by such processes. This phase
alone is worthy of the most careful practical study. Obvi-
ously no system of soil management can be wholly successful
unless full advantage is taken of this and other biological
possibilities of the land.
CHAPTER XXII
COMMERCIAL FERTILIZER MATERIALS *
WHILE the use of animal excrement on cultivated soils was
practiced as far back as systematic agriculture can definitely
be traced, the earliest record of the use of mineral salts for in-
creasing the yield of crops was published in 1669 by Sir
Kenelm Digby.? He says: ‘‘By the help of plain salt petre,
diluted in water, and mingled with some other fit earthly
substance, that may familiarize it a little with the corn into
which I endeavored to introduce it, I have made the barrenest
ground far outgo the richest in giving a prodigiously plentiful
harvest.’’? His dissertation does not however, show any true
conception of the reason for the increase in the crop through
the use of this fertilizer. In fact, the lack of any real knowl-
edge at that time of the composition of the plant would have
made this impossible.
In 1804, de Saussure,* a Frenchman, called attention, for
the first time to the significance of the ash ingredients of
plants not only showing that these mineral materials were
+The following general references may prove helpful:
Hall, A. D., Fertilizers and Manure; New York, 1921.
Halligan, J. E., Soil Fertility and Fertilizers; Kaston, Pa., 1912.
Van Slyke, L. L., Fertilizers and Crops; New York, 1912.
Fraps, G. 8., Principles of Agricultural Chemistry; Easton, Pa.,
1912.
Collins, S. H., Chemical Fertilizers and Parasiticides; New York,
1920.
* Digby, Kenelm, A Discourse Concerning the Vegetation of Plants;
London, 1669.
*Saussure, Theodore de, Recherches Chimiques sur la Vegetation;
Paris, 1804,
442
COMMERCIAL FERTILIZER MATERIALS 443
obtained from the soil but pointing out that they were ab-
solutely essential for plant growth. Liebig,t in Germany, at
about the middle of the nineteenth century, emphasized still
more strongly the importance of minerals to plants, refuting
the theory, at that time current, that plants obtained all of
their carbon from the soil organic matter. While he showed
the importance of potash and phosphoric acid in manures, he
failed to appreciate the value of nitrogenous materials, hold-
ing that the soil received sufficient ammonia in rain-water.
The true conception of the necessity of supplying nitrogen
in some form was definitely established in an experimental
way in 1857 by Lawes, Gilbert and Pugh? of the Rothamsted
Experiment Station, England. The extreme care used by
these investigators caused them to sterilize the soil with which
they were working. They thus failed to discover the utiliza-
tion of free atmospheric nitrogen by legumes. This phe-
nomenon, so important in practical agriculture, was explained
by Hellriegel and Wilforth in 1886.
Between 1840 and 1850 Sir John Lawes placed the manu-
facture of superphosphates on a commercial basis by treating
bones and coprolites with sulfuric acid. At about this time
the importation into Europe of Peruvian guano and sodium
nitrate began. The commercial fertilizers industry, which
has now attained such importance in practical agriculture,
may be considered as dating from this period.
243. Commercial fertilizers —Although the commercial
fertilizer industry is but little more than seventy years old,
the sale of fertilizers in this country at the present time
amounts to millions of dollars annually. Animal refuse and
1Liebig, J. Justus von, Principles of Agricultural Chemistry with
Special Reference to the Late Researches Made in England; London,
1855. Also, Chemistry in Its Applications to Agriculture and Physiology ;
New York, 1856.
?Lawes, J. B., Gilbert, J. H., and Pugh, E., On the Sources of the
Nitrogen of Vegetation, with Special Reference to the Question Whether
Plants Assimilate Free or Uncombined Nitrogen; Rothamsted Memoirs,
Vol. 1, No. 1, 1862.
444 NATURE AND PROPERTIES OF SOILS
phosphates are exported, while sodium nitrate and potash
salts are imported in large amounts. Fifty per cent. of the
fertilizers sold in the United States are applied in the south
Atlantic states within three or four hundred miles of the
seaboard. Nearly one-half of the remainder is purchased by
the New England and middle Atlantic states. West of the
Mississippi River, the use of fertilizers, especially those car-
rying phosphoric acid, is increasing rapidly.
The primary function of a commercial fertilizer is to supply
plant nutrients to the soil in such a form that the plant may
be directly influenced by such an application. The secondary
influences of fertilizers may be beneficial or detrimental. The
exact nature of the secondary influences depends on the par-
ticular fertilizer applied and especially on the type of soil
and the crop management in vogue.
Prepared fertilizers, as found on the market, are usually
composed of a number of ingredients. Since these ingredi-
ents are the carriers of the nutrient constituents, and since
it is on their composition and solubility that the value of a
fertilizer depends, a knowledge of the properties of these
materials is not only of interest to every one who uses fer-
tilizers but is also a valuable aid in their purchase.
FERTILIZERS USED FOR THEIR NITROGEN
Nitrogen is usually the most expensive constituent of ma-
nure and is of great importance, since it is very likely to be
deficient in soils. A commercial fertilizer may have its nitro-
gen in the form of soluble inorganic salts or in organic com-
bination. On the form depends to a certain extent the agri-
cultural value of the nitrogen, as the soluble inorganic salts
are very readily available to the plant, while the organic forms
must pass through the various biological processes before
the plant can use the nitrogen so contained. Only the best-
known fertilizer carriers need receive particular attention
bere.
COMMERCIAL FERTILIZER MATERIALS = 445
244. Dried blood and tankage.1—Both of these fertilizers
are packing-house products. The former is obtained by dry-
ing the blood from the slaughtering pens. It comes on the
market as a homogeneous blackish to dark greyish material,
often slightly moist and with a characteristic odor. Its con-
tent of ammonia (NH,) ranges from 10 to 16 per cent., de-
pending on the grade of the fertilizer. It often contains
traces of phosphoric acid (P,O;).?
Tankage is a mixture of various refuse materials from the
slaughter-houses, such as blood, hair, scraps of meat, and hide
and bone. It is generally steam-cooked and part of the gela-
tin and fat removed. It is variable in composition, carrying
from 5 to 10 per cent. of NH, and from 3 to 8 per cent. of
P,O,. The phosphoric acid is contained in the bone and is
in the form of tricalcium phosphate [Ca,(PO,),]. Tankage
is easily distinguished from blood meal by its heterogeneous
character.
When added to a soil, both blood and tankage undergo rapid
decomposition, ammonification, and finally nitrification. Such
fertilizers are, therefore, very effective in the late spring and
summer. For early application, however, a material such
as sodium nitrate is much better, since a biological transfor-
mation is unnecessary in order that it may be immediately
utilized by the plants.
245. Other organic nitrogenous fertilizers—Below will
be found the composition of a number of other organic ma-
terials that have been or are still used as fertilizers. Only two
need explanation. Guano consists of the excrement and ear-
easses of sea fowls, the composition depending on the climate
and position in which it is found. Guano from an arid region
contains ammonia, phosphoric acid, and potash. Under
humid conditions only the phosphoric acid remains in any
1Fry, W. H., Identification of Commercial Fertilizer Materials; U.S.
Dept. Agr., Bul. 97, 1914.
*The composition of commercial fertilizers is commonly expressed in
terms of ammonia (NH;), phosphoric acid (P,O;), and potash (K,O).
446 NATURE AND PROPERTIES OF SOILS
amount. Typical guano earries uric acid, urates, and am-
monium salts. The phosphorus occurs as calcium, potas-
sium, and ammonium phosphates. The potash is found in
the chloride, sulfate and phosphate forms. While guano
was once a very important fertilizer, the deposits are very
nearly exhausted and but little now appears on the market.
Process fertilizers are obtained by treating organic trade
wastes and refuse with acid or with steam under pressure.
Hydrolysis of the proteins occurs with the formation of pro-
teoses, peptones, and simple amino acids. The water soluble
nitrogen of such materials has been shown by Lathrop of the
United States Bureau of Soils to be as readily available as
that of dried blood or tankage.
TABLE XCV
FERTILIZER NH, iP-Or K,O
Giang sion: Bae Cee Aarne 10-14 6— 2—5
Process, COOdS haa. eee: 1l- 3 —
Fook meal.c8 os sees eae Leis (G3 =
RUSH SCrAD S25 Kaien eee ee 8-11 6— 7 ——
Weather smeales pigs eee S12 oe oe
Wool and hair waste... /: : 10-16 —
Cottonseed. meal......... 8-10 Se 2-3
Tamseed samedleriee ae ieee 4-6 1- 2 1-2
Castor pomtaceviale 4 sccm ad. b- 7 1— 1% 1-1%
These compounds vary greatly in their values as fertilizers.
Guano, process goods, and fish scrap when in the soil decom-
pose rapidly and are as effective ordinarily as blood or tank-
age. Untreated leather meal and wool and hair waste decay
very slowly and are of little value as fertilizing materials.
246. Utilization of nitrogenous organic compounds by
plants.—One of the early beliefs in regard to plant nutrition
was that organic matter as such is directly absorbed by higher
plants. This opinion was afterwards entirely replaced by the
COMMERCIAL FERTILIZER MATERIALS = 447
mineral theory propounded by Liebig; and still later the dis-
covery of the nitrifying process almost disposed completely of
the belief that organic matter is used directly by higher
plants. It is quite certain, however, that some organic nitrog-
enous compounds furnished suitable material for some higher
plants without undergoing bacterial change and producing
a nitrate form of nitrogen.
The following compounds have been shown by Hutchinson
and Miller? to be readily assimilated by peas: acetamide,
urea, barbituric acid, and alloxan. Formamide, glycerine,
eyanurie acid, oxamine, peptone, and sodium aspartate were
assimilated but less easily. Creatinine has been shown by
Skinner * to be used directly by plants as a source of nitro-
gen. Histidine, arginine, and creatine have also been found
in soils and it has been demonstrated that they have a direct
influence on wheat seedlings.
These and numerous other investigations of this subject
show that amine as well as amide nitrogen is assimilated by
at least some agricultural plants, but to what extent most
of these compounds may successfully replace the inorganic
forms of nitrogen, such as the nitrates, has not been definitely
established. Certain organic nitrogenous fertilizers—as, for
example, dried blood—have a high commercial value, the
nitrogen in this form selling for more a pound than the nitro-
gen in any of the inorganic salts. Many crops, especially cer-
tain vegetables, are most successfully grown only when
supplied with organic nitrogenous material. Some ni-
trate nitrogen is always present under natural soil condi-
tions, so that crops are never limited to organic nitrogen
alone; and it may be that the latter form of nitrogen is most
useful when it supplements the nitrate form.
* Hutchinson, H. B., and Miller, N. H. J., The Direct Assimilation
of Inorganic and Organic Forms of Nitrogen by Higher Plants; Centrlb.
f, Bakt., II, Band 30, Seite 513-547, 1911.
*Skinner, J. J., II. Effects of Creatinine on Plant Growth; U. S.
Dept. Agr., Bur. Soils, Bul. 83, pp. 33-44, 1911.
448 NATURE AND PROPERTIES OF SOILS
247. Sodium nitrate (NaNO, +).1—Sodium nitrate is
mined in Chile, occurring as a crude salt (caliche) in the
semiarid regions along the coast. It is found near the sur-
face under an over burden of varying thickness. The eal-
iche contains, besides sodium nitrate, such salts as NaCl,
K,SO,, Na,SO,, and MgSO, besides traces of Na,CO,, K,COsg,
and boron. The refined salt, which is shipped to this country,
carries from 2 to 3 per cent..of NaCl and KNO,. Its am-
monium content is generally rated at about 18 per cent.
The fertilizer appears on the market in clouded crystals of
a yellowish cast, extremely soluble in water and quite de-
liquesecent. The fertilizer is generally alkaline to litmus.
In the soil it diffuses rapidly and is immediately avail-
able to plants. For this reason it, is extremely valuable early
in the spring before nitrification is active.
The long-continued use of sodium nitrate will tend to pro-
duce an alkaline residue of sodium carbonate in the soil.?
This is due to the absorptive power of the soil for sodium and
the ease with which the nitrate ions are lost in drainage. The
plant, by using large amounts of nitrates, intensifies this se-
lective absorption.
The origin of the caliche deposits is problematical. The
theory has been advanced that the origin is due to the de-
composition of great deposits of seaweed on an uplifted con-
tinental shelf. Another hypothesis would have the deposits
originate from wind-carried guano dust. As rational a the-
ory as any is proposed by Singewald and Miller,* who believe
the nitrates were leached from the Andes Mountains and
1 Fertilizer materials are never pure salts. The plus after the formula
indicates the presence of impurities.
*Hall, A. D., The Effect of the Long Continued Use of Sodium Nitrate
on the Constitution of the Soil; Trans. Chem. Soc. (London), Vol. 85,
pp. 950-971, 1904, Also, Brown, B. E., Concerning Some Effects of Long-
Continued Use of Sodium Nitrate and Ammonium Sulfate on the Soil;
Ann. Rep. Pa. State Coll., 1908-1909, pp. 85-104.
*Singewald, J. N., and Miller, B. L., Genesis of the Chilean Nitrate
Deposits; Econ. Geol., Vol. II, pp. 103-113, 1916.
COMMERCIAL FERTILIZER MATERIALS 449
earried by ground water to their present location. The con-
centration of the salts is considered by these authors as due
to surface evaporation and consequent upward capillary
movement of the highly charged ground water.
248. Ammonium sulfate ((NH,),SO, +).—This fertil-
izer is a by-product from coke ovens and from the distilla-
tion of coal in gas manufacture... About one-fifth of the
nitrogen of the coal is thus driven off as ammonia, which is
caught in special washing devices. The mother liquid is then
distilled, the NH, being driven into sulfuric acid. The prod-
uct is later concentrated and the salt crystallized out. An-
other and simpler process provides for a direct union of the
gas and the acid, thus eliminating the washers.
This fertilizer usually carries about 25 per cent. of am-
monia. It usually has a greyish or greenish color due to
coal-tar products. This commercial ammonium sulfate is
very soluble in water and has a characteristic taste. When
heated, it readily breaks up, giving off ammonia gas. It
is very acid to litmus paper, due to the union of a weak
base with a strong acid radical. The ammonia is very strongly
absorbed by the soil and also is used to a greater extent by
the plant than are the sulfate ions. It thus leaves in the
soil an acid residue? which should be alleviated by lime if
the soil is not already supplied with plenty of active calcium
and magnesium. In a warm soil the ammonia is quickly
nitrified to the nitrate form. This transformation is general-
* By-Product Coke and Gas Plants; The Koppers Company, Pitts-
burgh.
Sulfate of Ammonia. Its Source, Production and Use; The Barrett
Company, New York.
* Hall, A. D., and Gimingham, C. T., The Interaction of Ammonium
Salts and the Constitution of the Soil; Jour. Chem. Soe. (London),
Molod ptt: Gli. 1907.
White, dle W., The Results of Long Continued Use of Ammonium
Sulfate Upon a Residual Limestone Soil of the Hagerstown Series; Ann.
Rep. Pa. State Coll., 1912-1913, pp. 55-104.
Ruprecht, R. W., and Morse, F. W., The Effect of Sulfate of Ammonia
on Soil; Mass. Agr. Exp. Sta., Bul. 165, 1915.
450 NATURE AND PROPERTIES OF SOILS
ly so rapid as to make this fertilizer almost as quickly effec-
tive as sodium nitrate.
While the nitrogen of ammonium salts is quickly changed
to the nitrate combination in a well-drained soil, some plants
seem to prefer ammoniacal nitrogen to the nitrate form. Kell-
ner * in 1884 and later Kelley ? demonstrated that rice plants
growing on lowland soils use ammoniacal nitrogen rather
than other forms. On upland soils, however, it is presumable
that rice plants utilize nitrate nitrogen, which would indi-
eate that some plants, at least, may adapt themselves to the
use of a more abundant form of nitrogen.
Hutchinson and Miller * found that peas obtained nitrogen
from ammonium salts as readily as from sodium nitrate, but
that wheat plants, although able to obtain nitrogen directly
from ammonium salts, grew much better in a solution con-
taining nitrates. One feature brought out by the numerous
experiments with ammonium salts is the difference between
plants of various kinds in respect to their ability to absorb
nitrogen in this form.
249. The artificial fixation of nitrogen.t—The vast store
of atmospheric nitrogen, chemically uncombined and very
inert, will furnish an inexhaustible supply for plants when it
ean with reasonable economy be combined in some manner to
give a product that can be commercially transported and
that will, when placed in the soil, become available without
liberating substances toxic to plants. The importance of the
1Kellner, O., Agrikulturchemische Studien tiber die Retskultur ;
Landw. Vers. Stat., Band 30, Seite 18-41, 1884.
? Kelley, W. P., The Assimilation of Nitrogen by Rice; Haw. Agr. Exp.
Sta., Bul. 24, pp. 5-20, 1911.
’ Hutchinson, H. B., and Miller, N. H. J., The Direct Assimilation of
Inorganic and Organic Forms of Nitrogen by Higher Plants; Centrlb.
f. Bakt., II, Band 30, Seite 513-547, 1911.
*Norton, T. H., Utilization of Atmospheric Nitrogen; U.S. Dept. of
Comm. and Labor, Special Agents Ser., No. 52, 1912.
Knox, J., Fixation of Atmospheric Nitrogen; New York.
Slosson, E. E., Creative Chemistry, Chaps. Il and III; New York,
1920.
COMMERCIAL FERTILIZER MATERIALS 451
nitrogen supply for agriculture may be appreciated when it
is considered that nitrates are being carried off in the drain-
age water of all cultivated lands at a surprisingly rapid rate.
A Dunkirk silty clay loam at Cornell University, carrying
a rotation of maize, oats, wheat, and hay, lost in crop and
drainage water in a period of ten years over 77 pounds to the
acre of nitrogen annually. This is equivalent to 520 pounds
of commercial sodium nitrate or to about 380 pounds of com-
mercial ammonium sulfate.
The exhaustion of the supply of nitrogen in most soils may
be accomplished within one or two generations, unless a re-
newal of the supply is brought about in some way. Natural
processes provide for an annual accretion through the wash-
ing-down of ammonia and nitrates by rain-water from the
atmosphere, and through the fixation of free atmospheric
nitrogen by bacteria. Farm practice of the present day re-
quires the application of nitrogen in some form of manure,
and, as the end of the commercial supply of combined nitro-
gen is easily in sight, there is urgent need of discovering a
new source. The world war has given great impetus to the
study of the artificial fixation of nitrogen and a number of
compounds thus produced are on the market or will appear
shortly.
250. Calcium cyanimid (CaCN, + ).2—The manufacture
of this fertilizer begins with calcium carbide (CaC,) which
is produced by heating lime and coke together.
CaO + 38C = CaC, + CO
This impure carbide is then powdered and heated elec-
trically in special ovens. At the proper temperature nitro-
gen gas is passed through the carbide with the following re-
sult :
CaC, + N, = CaCN, + C
*For complete data, see par. 163, this text.
?Pranke, E. J., Cyanamid; Easton, Pa., 1913.
452 NATURE AND PROPERTIES OF SOILS
The product is a black dry erystalline powder of rather
light weight, containing about 20 per cent. of NH,. It is very
impure as shown by the following analysis:
CaGNae ohc0 ce Soe 45.9 VE MME Pere ams SA's > 13.1
Cat Oe ais. cee 4.0 FeO, and AlOg se 1.9
CaS iad conkers i TArS SIO; 2G. eu aoe 1.6
OF 5 Ege Me meted caren ta ail Mie)? rah. a ali
CacOlhj fic Uses 26.6 BGO 338 hao eee 3
Its odor and the presence of carbon are characteristic. It
is intensively alkaline to litmus. In the soil it undergoes a
number of very complex changes, urea ultimately being pro-
duced. Toxic compounds are present as the reactions pro-
ceed. It should, therefore, be placed in the soil some time be-
fore the crop is seeded. The carbon seems to aid in the trans-
formation as a catalytic agent. The urea quickly breaks
down biologically to ammonia:
CON.H, + 2H,0 = (NH,), CO,
This ammonia is then oxidized to the nitrate form.
251. Basic calcium nitrate (Ca(NO,),-+-)—This fertil-
izer, like calerum cyanimid, is produced by the artificial fixa-
tion of nitrogen. Air is passed through an electric are of high
temperature. Under such conditions a part of the oxygen and
the nitrogen are forced together forming nitric oxide. This
gas is then oxidized in suitable chambers to the peroxide,
which is passed into water, producing nitric acid. The nitric
oxide which also results is led back to the oxidizing chambers.
The reactions are as follows:
N, -+ 0, = 2NO
ONO + O, = 2NO,
3NO, + H,0 = 2HNO, + NO
The nitric acid is passed into lime-water, giving calcium
nitrate. This fertilizer contains from 13 to 16 per cent. of
ammonia and is intensely alkaline to litmus. Due to its high
COMMERCIAL FERTILIZER MATERIALS 453
deliquescence, it must either be treated in some way, which
raises the cost of manufacture, or must be shipped in sealed
casks. It is very soluble in water and is immediately available
to plants. It leaves no harmful residue in the soil.
252. Other methods of nitrogen fixation.—Calcium ni-
trate, because of its cost, cannot compete either with sodium
nitrate or ammonium sulfate and is not manufactured in this
country. Calcium cyanamid is produced only in amounts
sufficient to satisfy the demands of mixed fertilizer manu-
facture. Its dry character makes it valuable in such com-
pounding.
At the present time a number of more efficient methods of
artificially fixing nitrogen are known. The Haber process
proved extremely successful in Germany, especially when
supplemented by the Oswald method of converting ammonia
-into nitric acid. In the Haber method a mixture of nitrogen
and hydrogen are placed under pressure and moderately
heated in the presence of a catalyst. A good yield of ammonia
results.
N, + 3H, = 2NH,
In the Oswald method this ammonia is passed over a cata-
lytic agent in the presence of oxygen.
NH, + 20, = HNO, + H,0
The advantage of producing both ammonia and nitric acid
is obvious, as ammoniun nitrate (NH,NO,), ammonium phos-
phate ((NH,),P0,), and potassium nitrate (KNO,) may be
produced at one plant.
During the war Professor Bucher of Brown University per-
fected a simple and inexpensive method of producing sodium
cyanide synthetically. Producers gas, formed by passing air
over hot coal, is forced through a heated revolving drum con-
taining soda ash, iron, and coke. The reaction is as follows:
Na,CO, + 4C + N, = 2NaCN + 300
454 NATURE AND PROPERTIES OF SOILS
Ammonia may be produced very easily from the sodium
cyanide and used as such or changed to nitric acid by the
Oswald method.
253. Relative availability of nitrogen fertilizers..—It is
very difficult to rank nitrogenous fertilizers on the basis of
their rate of availability, since the conditions within the soil
so markedly influence the transformations, especially those
of a biological nature. Dried blood and ammonium sulfate,
for example, will give almost as quick results in a warm, well
aérated soil, as far as higher plants are concerned, as sodium
nitrate. In general, however, the nitrate fertilizers should be
rated as most readily available, followed in order by ammo-
nium salts, dried blood, tankage, and similar materials. Such
substances as wool, hair, and untreated leather waste should
rank last.
FERTILIZERS USED FOR THEIR PHOSPHORUS
Phosphorus is generally present in nature in combination
with calcium, iron, or aluminum. Some phosphates carry or-
ganic matter and when thus associated are generally consid-
ered to decompose more readily when added to the soil.
254. Bone phosphate (Ca,(PO,),+).—Bones were for-
merly applied to the soil in the raw condition, either ground
or unground. Most bone as now sold is merely steamed or
boiled to remove the fat and nitrogenous matter, which is
used in other ways. Bone-meal comes on the market as a dusty
powder of characteristic odor. It contains about 27 per cent.
of phosphoric acid as tricalcium phosphate. Tankage, which
has already been spoken of as a nitrogenous fertilizer, con-
tains from 3 to 8 per cent. of phosphoric acid, largely in the
form of tricalcium phosphate. All bone phosphates are slow-
acting manures, and should be used in a finely ground form
and for the permanent benefit of the soil rather than as an
1Thorne, C. E., Carriers of Nitrogen in Fertilizers; Soil Sci., Vol.
IX, No. 6, pp. 487-494, 1920.
COMMERCIAL FERTILIZER MATERIALS = 455
immediate source of phosphorus. In the soil, water charged
with carbon dioxide slowly converts the insoluble tricalcium
phosphate into the soluble mono-calcium form:
Ca, (PO,).-+ 4C0, + 4H,0 = CaH,(PO,), + 2CaH,(CO,),
255. Rock phosphate’ (Ca,(Po,),-++-).—There are many
natural deposits of mineral phosphates in different parts of
the world, some of the most important of which are in North
America. The phosphorus in all of these is in the form of
tricalcium phosphate, but the materials associated with it
vary greatly. Rock phosphate may occur in nature as soft
phosphate, pebble phosphate, boulder phosphate, and hard
rock phosphate.
South Carolina phosphate contains from 26 to 28 per cent.
of phosphoric acid and a very small amount of iron and
aluminum. As these latter substances interfere with the man-
ufacture of acid phosphate from rock, their presence is very
undesirable, rock containing more than from 3 to 6 per cent.
being unsuitable for that purpose.
Florida phosphates exist in the form of soft phosphate,
pebble phosphate, and boulder phosphate. Such phosphate
contains from 18 to 30 per cent. of phosphoric acid, and be-
cause of its being softer than most of these rocks it is often
applied to the land without being first converted into a soluble
form. The other two forms, pebble phosphate and boulder
phosphate, are highly variable in composition, ranging from
20 to 40 per cent. in phosphoric acid content. Tennessee
phosphate, which is now very important, contains from 25 to
35 per cent. of phosphoric acid.
Rock phosphate, or floats as it is often called, appears on
the market as a heavy finely ground powder of light gray
eolor. It generally carried about 27 per cent. of phosphoric
acid as Ca,(PO,),. A typical analysis is as follows:
1Waggaman, W. H., and Fry, W. H., Phosphate Rock and Methods
Proposed for Its Utilization as a Fertilizer; U. S. Dept. Agr., Bul. 312,
1915.
456 NATURE AND PROPERTIES OF SOILS
Moisture,’ organic (matter ebony iim eal nel) Seb eee 5.06
Ca,(PO, ‘5 Deseo ae Hu RLS ARUBA Ss usr ey hus ok Sa a Oe 77.76
KePO, and ALIPOSMU veer ag) oh el eee 1.50
CaCO, ditt bachelor Hat MPR ce te it Ny ER a 4.43
IND CO oO tes i eae ROR cl OEE re eae ne Sa a 0
CaP, a CaO Paaeeyceer ic Gtoeres eae at oon Mee Oa ee onal
aS Jee aicneh sao Reno eels hee dm Oe US nated eee 7G
He. OF and: “Al Ores 2 oa. elancn ateietelte Sea meets a ee 3.87
Rock phosphate undergoes the same change in the soil as
bone-meal but generally much more slowly, unless the soil is
very high in organic matter. Mixing the rock with manure
seems to hasten its availability to plants.
256. Acid phosphate’ (CaH,(PO,).+).—Acid phosphate
is a dry material of a browning gray color, partially soluble in
water, and has a characteristic acrid odor. It is intensely
acid to litmus, as it contains certain acid salts. It carries
from 14 to 16 per cent. of available P,O, and small amounts
of insoluble P,O,. It is made by treating raw rock with sul-
furic acid under the proper conditions.”
Ca,(PO,), + 2H,SO, = CaH,(PO,),. + 2Ca SO,
(insoluble) (water soluble)
The acid is never added in amounts capable of quite com-
pleting this reaction. Some di-calecium phosphate [Ca,H,
(PO,).|, spoken of as citrate soluble or reverted phosphoric
acid, is thus produced.
Ca,(PO,), + H,SO, = Ca,H,(PO,), + CaSO,
(insoluble) (reverted)
Acid phosphate consists mostly of gypsum and mono-eal-
cium phosphate with some di-calecium phosphate and impuri-
1Chemically, three forms of phosphoric acid are recognized by the
fertilizer industry: (1) insoluble (Ca,(PO;,).), (2) reverted or citrate
soluble (Ca,H,(PO,).), and (3) water soluble (CaH,(PO,).). The
water soluble and citrate soluble phosphates are rated as available to
plants. The insoluble form is considered as unavailable.
?Waggaman, W. H., The Manufacture of Acid Phosphate; U.S. Dept.
Agr., Bul. 144, 1914.
COMMERCIAL FERTILIZER MATERIALS 457
ties. The water soluble and reverted phosphoric acid are both
rated as available.
The phosphates of acid phosphate when added to the soil
quickly revert to an insoluble form:
Call) (PO)), -- 2CaH,(CO,), = Ca,(P0,), 4-4C0, + 4H,0
Ca,H, (PO,), ++ CaH,(CO,), = Ca,(PO,). + 2CO, 4+ 2H,0
Plenty of active calcium should be present when acid phos-
phate is used to insure this reaction instead of the formation
of the very insoluble ferric phosphate (KePO,) and aluminum
phosphate (AIPO,). Acid phosphate does not seem to make
the soil acid. In fact, it is considered by some investigators
to decrease the acidity by rendering aluminum and iron in-
soluble.
257. Basic slag ((CaO),.P,0,.S10,-+-).—Iron or steel con-
taining over 2 per cent. of phosphorus is too brittle to be
useful and, as a consequence, ores of this character were little
used until methods of removing this phosphoric acid were
discovered. The use of wood in smelting provided a basic ash,
thus removing phosphorus from the pig iron. With coal, how-
ever, the slag is acid and the phosphorus remains with the
ore. In the open-hearth method of smelting the furnaces are
lined with a specially prepared dolomitic limestone. Lime is
later added as the smelting proceeds. The calcium of the
slag unites with the phosphorus of the iron, thus reducing
the percentage of that element in the steel. The most prob-
able formula for the phosphorus compound in basic slag is
(CaO)..P,0,.SiO,. Basie slag contains a large amount of
iron and calcium hydroxide. Below is a typical analysis:
BAO Mt enc eres Oe ee 45.0 0 hs 0 ee a Pe OW 2 a beef
111 (Fn @ acai ae AiR 6.2 PSKOS cn ee ian ON Gat. 2 6.9
BeEOi-E HesOs 2.5. 2... 17.6 1 EAS G a cts Me a sect ee Ae 18.1
WEAWE Ieee Seer 6 Ok Ie oD Other constituents... 1.0
*Conner, S. D., Acid Soils and the Effect of Acid Phosphate and
Other Fertilizers Upon Them; Jour. Ind. and Eng, Chem., Vol. 8, No.
1, pp. 35-40, 1916.
458 NATURE AND PROPERTIES OF SOILS
Basic slag comes on the market as a heavy dark gray pow-
der, extremely alkaline to litmus, and contains from 14 to
20 per cent. of P,O,. The phosphorus of basic slag is almost
all soluble in citric acid and, therefore, is rated as available
phosphoric acid. It does not revert in the soil as does acid
phosphate, but is immediately attacked by carbon dioxide and
rendered rather quickly available. A possible reaction is as
below:
(CaO),.P,0,.Si0, + 8CO, + 6H,O = CaH,(PO,). +
4CaH,(CO,). + Si0,
258. Relative availability of phosphate fertilizers—
Acid phosphate carries most of its phosphoric acid in a water-
soluble form and although the phosphates revert to the tri-
calcium form immediately when added to the soil, they are
rather readily available to plants. This is due to the charac-
ter of the freshly precipitated salt and the surface exposed
for solution activities. To insure a good distribution in the
soil of the phosphoric acid and a rapid influence on crops, acid
phosphate should be well mixed with the soil.
Basie slag, since its phosphoric acid is largely citrate sol-
uble, is generally considered as next to acid phosphate in
availability. Steamed bone-meal usually gives better results
than raw rock phosphate and rates third, with rock phos-
phate fourth in availability. The degree of fineness makes a
great difference in the availability of the less soluble phos-
phate fertilizers, especially the ground bone and raw rock
phosphate. The latter material should be ground fine enough
to pass through a sieve having at least one hundred meshes to
the inch.
259. Raw rock phosphate versus acid phosphate.—Con-
siderable discussion as well as controversy has of late arisen
regarding the relative merits of acid phosphate and raw rock
phosphate not only when applied on the basis of equal amounts
of phosphoric acid but also when compared on the basis of
COMMERCIAL FERTILIZER MATERIALS = 459
equal money values. If rock phosphate could be made to
equal or nearly equal the availability of acid phosphate, ob-
vious advantages would accrue, since raw rock costs much less
than acid phosphate and carries about twice as much phos-
phorie acid.
The availability of the phosphorus of raw rock phosphate
varies considerably with conditions. At least four major in-
fluences have been recognized: (1) the character of the crop
grown, (2) reaction of the soil, (3) the character of accom-
panying salts, and (4) the decomposition of organic matter.
It is to be expected that the various kinds of plants should
not be equally influenced by the phosphorus of tri-calcium
phosphate. Prianischnikov! found that lupines, mustard,
peas, buckwheat, and vetch responded to fertilization with
raw rock phosphate in the order named, while the cereals
did not respond at all. He did not include maize in his ex-
periments, but that crop is said to respond well to difficultly
soluble phosphates. It is generally considered that those
plants which have a long growing season are better able to
utilize tri-caleium phosphate than are more rapidly growing
plants.
A number of investigators have stated, as a result of their
experimentation, that the availability of raw rock phosphate
is greater in acid soils than in those strongly basic. If acidity
of the soil is due to the presence of an actual acid, it is con-
ceivable that the availability may be due to the solvent action
of the soil acid on the calcium of the tri-calecium phosphate,
producing the di-calcium salt which appears to be fairly read-
ily available to plants. When, however, soil acidity is due
to a lack of certain active bases, the case is different. Gedroiz?
1Prianischnikov, D., Bericht iiber Verschiedene Versuche mit Rohphos-
phaten unter Reduction; Moscow, 1910.
*Gedroiz, K. K., Soils to which Rock Phosphates May Be Applied
with Advantage; Jour. Exp. Agron. (Russian), Vol. 12, pp. 529-539,
811-816, 1911. The authors are indebted to Dr. J. Davidson for the
translation.
460 NATURE AND PROPERTIES OF SOILS
explains this on the basis of the absorptive properties of the
so-called acid soil. He regards rock phosphate, not as a chemi-
cal compound, but as a solid solution of di-caleium phosphate
with lime. According to Gedroiz it is this excessive basicity
of the phosphate which is responsible for its unavailability.
Absorption of the excess calcium would leave the phosphate
in a more readily available condition by forming the di-
calcium salt.
The presence of certain salts has been found to influence the
availability of difficultly soluble phosphates. The subject has
been investigated by a large number of experimenters, and it
will be possible to summarize their results only in part and
very briefly. It has been found, for example, that calcium
carbonate decreases the availability of raw rock phosphate
and bone-meal. Sodium nitrate reduces the availability of
the tri-caleium phosphates, while the ammonium salts increase
their availability. Iron and aluminum salts decrease avail-
ability. The influence of other salts has not been so well
worked out. Prianischnikov,! as the result of his extended
experiments on the subject, holds that salts from which plants
absorb acid radicals in larger amounts than they do bases
decrease availability, or at least do not affect it, while salts
from which plants absorb the bases in the greater quantity
have a tendency to render the phosphate more available be-
cause of the hydrogen ion concentration.
There has been great differences of opinion among investi-
gators as to the effect of the decomposition of organic matter
on the availability of the phosphorus of tri-calcium phosphate.
The contention that the availability is increased probably
originated with Stoklasa,t whose experiments with bone-meal
*Prianischnikov, D., Uber den Einfluss von Kohlensiuren Kalk auf die
Wirkung von Verschiedenen Phosphaten; Landw. Vers. Stat., Band 75,
Seite 357-376, 1911.
?Stoklasa, J., Duchacek, F., and Pitra, J., Uber den Einfluss der Bak-
terien auf die Knochenzersetzung; Centrlb. f. Bakt., Il, Band 6, Seite
526-535, 554-558, 1900.
COMMERCIAL FERTILIZER MATERIALS 461
indicate that the availability is increased by decay. A large
number of experiments have been conducted with raw rock
phosphate composted with stable manure, among which may
be mentioned those by Hartwell and Pember' and also by
Tottingham and Hoffman,’ who, in carefully conducted experi-
ments, failed to find that the availability of the raw phos-
phate, as indicated by chemical methods, was increased by
fermentation with stable manure. Opposing results have also
been obtained, however, and the evidence is somewhat con-
flicting.
With so many factors active in varying the results, espe-
cially those from raw rock phosphate, it is not surprising that
satisfactory field data where acid phosphate and raw rock
are compared are difficult to obtain. Thorne,® after a critical
review of the field experiments where acid phosphate and raw
rock were used, comes to the conclusion that, while raw rock
phosphate is an excellent fertilizer, acid phosphate is gener-
ally superior. He finds that, while raw rock may be used
with profit on land materially deficient in phosphorus, acid
phosphate has generally proven to be the more effective and
the more economical carrier of phosphoric acid for crops.
These conclusions, which are corroborated by other in-
vestigators,* do not imply that raw rock phosphate is never
equal or superior to acid phosphate, nor that raw rock does
not have a place as a fertilizer on the average farm. On a
+ Hartwell, B. L., and Pember, F. R., The Effect of Cow Dung on the
Availability of Rock Phosphate; R. I. Agr. Exp. Sta., Bul. 151, 1912.
?Tottingham, W. E., and Hoffman, C., The Nature of the Changes in
Solubility and Availability of Phosphorus in Fermenting Mixtures; Wis.
Agr. Exp. Sta., Res. Bul. 29, 1913.
®*Thorne, C. E., Raw Phosphate Rock as a Fertilizer; Ohio Agr. Exp.
Sta., Bul. 305, 1916.
4 Wiancko, A. T., and Conner, 8S. D., Acid Phosphate versus Raw Rock
Phosphate as Fertilizer; Purdue Univ. Agr. Exp. Sta., Bull. 187, 1916.
Brooks, W. P., Phosphates in Massachusetts Agriculture; Mass. Agr.
Exp. Sta., Bull. 162, 1915.
Waggaman, W. H., and Wagner, C. R., Analysis of Experimental
Work with Ground Raw Rock Phosphate as a Fertilizer; U. S. Dept.
Agr., Bul. 699, 1918.
462 NATURE AND PROPERTIES OF SOILS
soil rich in organic matter it may be added to advantage. It
is especially useful in reinforcing farm manure, seemingly be-
ing about as effective under such conditions as is acid phos-
phate. Its higher phosphorus content and lower cost a ton
gives it an added advantage. The figures from Ohio,! cover-
ing a period of fourteen years in a rotation of maize, wheat,
and hay may be taken as evidence regarding these points.
The manure, reinforced to the ton with 40 pounds of acid
phosphate and raw rock phosphate, respectively, was applied
to the corn at the rate of eight tons to the acre.
TABLE XCVI
A COMPARISON OF ACID PHOSPHATE AND RAW ROCK IN EQUAL
WEIGHTS WHEN ADDED TO THE SOIL WITH MANURE.
AVERAGE ANNUAL INCREASE TO THE
ACRE
MANURE
MAIZE WHEAT Hay
14 Crops 14 Crops 11 Crops
With raw rock............ 25.0 bu. | 12.9 bu. | 1578 Ibs.
With acid phosphate....... 30.6 bu. | 15.1 bu. | 1853 Ibs.
FERTILIZERS USED FOR THEIR POTASSIUM
The production of potassium fertilizers is largely confined
to Germany, where there are extensive beds varying from
50 to 150 feet in thickness, lying under an area extending
from the Harz Mountains to the Elbe River and known as
the Stassfurt deposits. Large deposits of crude potash salts
occur in other sections of Germany, and also in France.
While small deposits occur in other parts of the world the
French and German mines are at present the only ones of
any great commercial importance. The World War stimu-
lated considerable investigation regarding possible sources of
*Thorne, C. E., et al., Plans and Summary Tables of the Experiments
at the Central Farm; Ohio. Agr. Exp. Sta., Cire. 120, p. 112, 1912.
COMMERCIAL FERTILIZER MATERIALS = 463
potash, especially in the United States. Kelp, saline brines,
deposits in old lake beds, and flue dust yielded considerable
potassium. Most of these sources, however, are too expensive
to compete with European potash in normal times.
260. Stassfurt salts and their refined equivalents.—The
Stassfurt salts contain their potassium either as a chloride
or as a Sulfate. The chloride has the advantage of being more
diffusible in the soil, but in most respects the sulfate is pref-
erable. Potassium chloride in large applications has an in-
jurious effect on certain crops, among which are tobacco,
sugar-beets, and potatoes. On cereals, legumes, and grasses
the muriate appears to have no injurious effect.
Kainit is the most common of the crude products of the
Stassfurt mines and is imported into this country in large
amounts. It is generally a greyish vari-colored salt, soluble
in water and alkaline to litmus. It carries from 12 to 14
per cent. of K,O, largely as potassium sulfate. Its potash
is immediately available to the crop. Below is a typical
analysis :
ESO Ta Sacer as ak 21.3 Wallis esac et 34.6
LC OU SS ee ae ear 2.0 CasOs Wertoe ver sen sleg/
VTi Svea epee ciao aleasete 14.5 Inisoluibler sean ceotels ee 8
INIA CS At ee ee 12.4 PASO Arter neuen iciersivas 12.7
Silvinit contains its potassium both as a chloride and as a
sulfate. It also contains sodium and magnesium chlorides.
Potash constitutes about 16 per cent. of the material. Owing
to the presence of chlorides, it has the same effect on plants
as has kainit. There are a number of other Stassfurt salts,
consisting of mixtures of potassium, sodium, and magnesium
in the form of chlorides and sulfates. They are not so widely
used for fertilizers as are those mentioned above.
A great proportion of the crude salts are refined for ex-
port purposes, appearing on the market as either the chloride
or the sulfate. They usually contain from 48 to 50 per cent.
464 NATURE AND PROPERTIES OF SOILS
of potash. The chief impurity is common salt. Some of the
potash salts produced in this country carry boron, which is
extremely toxic to plants. Such is not generally true of the
German and French products.
Potassium chloride and potassium sulfate when added to
the soil are immediately soluble, being held in the soil solu-
tion or absorbed either physically or chemically by the eol-
loidal complexes. Due to the selective absorption of the soil
for the potassium ion and the fact that plants absorb more of
this ion than of the acid radical, an acid residue tends to re-
sult from the use of such fertilizers. Some means, such as the
use of lime, should be employed to counteract this tendency.
261. Other sources of potash..—For some time after the
use of fertilizers became an important farm practice, wood-
ashes were the source of most of the potash. They also con-
tain a considerable quantity of lime and a small amount of
phosphorus. The product known as unleached wood-ashes
contains from 5 to 6 per cent. of potash, 2 per cent. of phos-
phorie acid, and 30 per cent. of caleium oxide. Leached wood-
ashes contain about 1 per cent. of potash, 114 per cent. of phos-
phorie acid, and from 28 to 29 per cent. of lime in the form
of the hydroxide and carbonate. Unleached ashes carry the
oxide, hydroxide, and carbonate forms of calcium. Ashes
contain the potassium in the form of a carbonate, (K,CO,),
which is alkaline in its reaction and in large amounts may be
injurious to seeds. Otherwise this form of potash is very de-
sirable, since no acid residue is left in the soil by its use.
*Young, G. J., Potash Salts and Other Salines in the Great Basin;
U. 8S. Dept. Agr., Bul. 61, 1914.
Waggaman, W. H., and Cullen, J. A., The Recovery of Potash from
Alunite; U. 8. Dept. Agr., Bul. 415, 1916.
Hirst, C. T., and Carter, E. G., Some Sources of Potassium; Utah
Agr, Exp. Sta., Cire. 22, 1916.
Waggaman, W. H., The Production and Fertilizer Value of Citric-
poe Phosphoric Acid and Potash; U. S. Dept. Agr., Bul. 143,
Ross, W. H., et al., The Recovery of Potash as a By-Product in the
Cement Industry; U.S. Dept. Agr., Bul. 572, 1917.
COMMERCIAL FERTILIZER MATERIALS = 465
Ashes are beneficial to acid soils through the action of both
the potassium and calcium salts.
Insoluble forms of potassium, existing in many rocks
usually in the form of a silicate, are not regarded as having
any manurial value. Experiments with finely ground feld-
spar have been conducted by a number of investigators, but
have, in the main, offered little encouragement for the suc-
cessful use of this material. Leucite and alunite have given
but little better results. An insoluble form of potassium is
not recognized as of value when a fertilizer is rated on the
basis of chemical analysis.
During the World War, since the German importation of
potash salts ceased, potassium was sought commercially from
a number of sources in this country. Alunite, a hydrous sul-
fate of aluminum and potassium, has been experimented with
to some extent as have also the green-sand marls which carry
glauconite. In a number of cases the recovery of potash
from fiue dust has proven commercially profitable. It is esti-
mated that 87,000 tons of potash are lost yearly from cement
kilns alone in the United States and Canada. During the war
considerable progress was made in harvesting and drying the
kelp which grows off the coast of southern California. The
kelp was later extracted for its potash. This source of potas-
sium is rather expensive, however, when brought into com-
petition with European products.
Perhaps the most reliable sources of domestic potash are
the brines of certain alkali lakes of western United States and
from the deposits in old lake beds in the same region.1. The
exploitation of such sources will, of course, depend upon the
price at which German potash can be laid down in this
country.
*Such salts unless properly prepared are likely to contain borax
which is usually toxic when applied at a greater rate than five pounds
to the acre, the influence being more intense at low soil moisture.
Neller, J. R., and Morse, W. J., Effects upon the Growth of Potatoes,
Corn and Beans, Resulting from the Addition of Borax to the Fertilizer
used; Soil Sci., Vol. XII, No. 2, pp. 79-105, 1921.
466 NATURE AND PROPERTIES OF SOILS
SULFUR AND SULFATES AS FERTILIZERS *
The use of these substances as a means of increasing plant
growth when applied to soils has recently received much at-
tention. While sulfates have been used for centuries as a
soil amendment, it is only within the last few years that sulfur
itself has been applied to soil. The question of the effect of
the latter has received considerable study, not only in France
and Germany but in this country as well. The influence of
both sulfur and sulfates may be a direct nutrient relationship
or the action may be that of a soil amendment. Only in case
the former influence occurs could these materials be rated as
fertilizers.
262. The use of free sulfur.—Boullanger ” in 1912 added
1 Another group of fertilizers may be mentioned—the so-called catalytic
fertilizers. Such materials are supposed to aid plant growth by accelerat-
ing natural soil processes. The catalytic action of any material is very
difficult to establish when it is added to the soil, since the soil itself
carries many substances of a catalytic nature. Manganese has been most
seriously considered as a catalytic fertilizer.
Konig, J., Hasenbaumer, J., and Coppenrath, E., Einige Neue Eigen-
schaften des Ackerbodens; Landw. Vers. Stat., Band 63, Seite 471-478,
1905-1906.
May, D. W., and Gile, P. L., The Catalase of Soils; Porto Rico Agr.
Exp. Sta., Cire. 9, 1909.
Sullivan, M. X., and Reid, F. R., Studies in Soil Catalysis; U. S.
Dept. Agr., Bur. Soils, Bul. 86, 1912.
Konig, J., Hasenbaumer, J., and Coppenrath, E., Beziehungen zwischen
den HKigenschaften des Bodens und der Nahrstoffaufnahme durch die
pflanzen; Landw. Vers. Stat., Band 66, Seite 401-461, 1907.
Kelly, M. P., The Influence of Manganese on the Growth of Pine-
apples; Jour. Ind. and Eng. Chem., Vol. I, p. 533, 1909.
Sullivan, M. X., and Robinson, W. O., Manganese as a Fertilizer;
U. S. Dept. Agr., Bur. Soils, Cire. 75, 1912.
Skinner, J. J., and Sullivan, M. X., The Action of Manganese in Soils;
U.S. Dept. Agr., Bul. 42, 1914.
Skinner, J. J., and Reid, F. R., The Action of Manganese Under Acid
and Neutral Soil Conditions; U.S. Dept. Agr., Bul. 441, 1916.
Bertrand, G., The Action of Chemical Infinitesimals in Agriculture ;
Address before 8th Inter. Cong. App. Chem., New York, 1912.
Ross, W. H., The Use of Radioactive Substances as Fertilizers; U.S.
Dept. Agr., Bul. 149, 1914.
Hopkins, C. G., and Sachs, W. H., Radiwm as a Fertilizer; Ill. Agr.
Exp. Sta., Bul. 177, 1915.
?Boullanger, E., Action du soufre en fleur sur la végétation; Compt.
Rend. Acad. Sci. Paris, T. 154, pp. 369-370, 1912.
COMMERCIAL FERTILIZER MATERIALS = 467
flowers of sulfur to a soil at the rate of 23 parts per million
of soil. He obtained increased growth in all treated soils on
which carrots, beans, celery, lettuce, sorrel, chicory, potatoes,
onions, and spinach were grown, the weights of the crops on
the treated soil being from 10 to 40 per cent. greater than those
on the untreated soil. On soils that had been sterilized before
applying sulfur, the effect was less marked, from which he
concludes that the beneficial effects were due to the influence
of the sulfur on the micro-organisms of the soil. There may
be some question, however, whether this conclusion is justi-
fiable. Sulfur was found by Boullanger and Dugardin' to
favor ammonification in soils. Beneficial effects from the use
of free sulfur have also been obtained by Demelon,? and by
Bernhard,*? while von Feilitzen * found it to be ineffective as
a fertilizer.
In this country, Shedd ® of Kentucky obtained increases in
tobacco yield with sulfur. Perhaps the most marked results
with sulfur are reported by Reimer and Tartar ° from Oregon.
Alfalfa and clover yields were increased from 50 to 100 per
cent.
That free sulfur may, under certain conditions, exert a ben-
eficial influence on plant growth must be conceded, but that
the action is a direct nutritive one remains to be proven.
Free sulfur is insoluble and cannot be absorbed as such by
plants. It readily undergoes oxidation, however, producing
the sulfate, as already explained under sulfofication. As such
*Boullanger, E., and Dugardin, M., Mecanisme de l’action fertilisante
du soufre; Compt. Rend. Acad. Sci. Paris, T. 155, pp. 327-329, 1912.
?Demelon, A., Sur l’action fertilisante du soufre; Compt. Rend. Acad.
Sci. Paris, T. 154, pp. 524-526, 1912.
* Bernhard, A., Versuche iiber dis Wirkung des Schwefels als Dung im
Jahre 1911; Deutsche Landw. Presse., Band 39, S. 275, 1912.
*von Feilitzen, H., Uber die Verwendung der Schwefelblute zur Be-
kampfung des Kartoffelschorfes und als indirktes Dungemittel; Fuhling’s
Landw. Zeit., Band 62, Seite 7, 1913.
* Shedd, O. M., The Relation of Sulfur to Soil Fertility; Ky. Agr. Exp.
Sta., Bul. 188, 1914.
*Reimer, F. C., and Tartar, H. V., Sulfur as a Fertilizer for Alfalfa
in Southern Oregon; Ore. Agr. Exp. Sta., Bul. 163, 1919.
468 NATURE AND PROPERTIES OF SOILS
a reaction tends to encourage soil acidity, injurious influ-
ences may easily occur on soils already acid or possessing only
small quantities of active calcium and magnesium. If sulfur
functions as a fertilizer, it is by a change to the sulfate, in
which form it is absorbed by plants.
263. The use of sulfate sulfur——The experimental evi-
dence regarding the direct fertilizer influence of sulfate sulfur
is much more difficult to interpret than that regarding flowers
of sulfur. Gypsum has been applied to soils for centuries
and marked influences on crop growth are of common observa-
tion. Whether this stimulation is due to the sulfate or to the
base which accompanies it cannot be determined. Even if the
sulfate influence could definitely be proved, there would still
remain the question as to whether the action was direct or
indirect.
264. Relation of sulfur to soil fertility—The possible
deficiency of sulfur in arable soils was first established by
Hart and Peterson.t They point out that crops remove more
TABLE XCVII
POUNDS SULFUR TRIOXIDE AND PHOSPHORUS PENTOXIDE
REMOVED TO THE ACRE BY AVERAGE CROPS.
POUNDS TO THE ACRE
CROP AND YIELD TO THE ACRE
SO, ZO:
Wihedts(3 Oebiis) Mu bl inp tey alestttiavastenerara: Bye Pal a |
‘Barley (40vbu))\o secures ae oe ee 14.3 20.7
Carts 94D MOU) ar cet ere eae at rauere cient aes 197 Bat
Corns (BO wu) iniesas Be Ae esate 12.0 18.0
Altalta(S000Tbs air diny)t &-eeatws ae 64.8 39.9
Turnips (4657 Vbsvamdiy ). 22) cre oe: 92.2 33.1
Cabbage (4800 lbs. air dry)........... 98.0 61.0
Potatoes (@GabOilbssairdiny )ieacer. en: 11.5 21.5
Meadow hay (2822 lbs. airdry)...... i113 PAS
* Hart, E. B., and Peterson, W. H., Sulfur Requirements of Farm Crops
in Relation to the Soil and Air Supply; Wis. Agr. Exp. Sta., Res. Bul.
ich ale
COMMERCIAL FERTILIZER MATERIALS — 469
sulfur from the soil than is indicated by the earlier analyses
of plant ash, since considerable sulfur was lost by volatization
in the former determination. On the basis of their own
methods, they present the data given as to the removal of
sulfur trioxide and phosphoric acid from the soil by average
crops. (See Table XCVII, page 468.)
It is to be noted that the amount of sulfur removed by crops
is generally about equal to and in some cases much in excess
of the phosphorie acid taken from the soil. The fact that
soils are generally as low in sulfur as in phosphoric acid lends
weight to the argument, that if the latter is a limiting factor
in productivity the former should be also.
To ascertain whether the supply of sulfur in the soil is
really depleted by cropping, Hart and Peterson made parallel
determinations of sulfur in five virgin soils and in five soils of
the same respective types that had been cropped for sixty
years. In each type the cropped soil contained less sulfur
than the virgin soil, the average for the former being .053
per cent. SO, and for the latter .085 per cent. SO,.
Considerable sulfur is added to the soil every year in the
rain-water, largely in the sulfate form, although near cities
appreciable amounts of hydrogen sulfide and sulfur di-oxide
are formed. The amount of such sulfur is variable. Miller,!
at the Rothamsted Experiment Station, reports 17.4 pounds
of SO, to the acre, while Crowther and Ruston? near Leeds,
England, found 161 pounds of SO, to the acre. Peck * found
the addition of SO, to be at the rate of 1 pound to the acre a
month at Mt. Vernon, Iowa, while Trieschmann,* over a
* Miller, N. H. J.. The Amount of Nitrogen, as Ammonia and as
Nitric Acid, and of Chlorine in the Rain-Water Collected at Rotham-
sted; Jour. Agr. Sci., Vol. I, pp. 280-303, 1905.
* Crowther, C., and Ruston, A. C., The Nature, Distribution and
(Effact Upon Vegetation of Atmospheric Impurities In and Near an
Industrial Town; Jour. Agr. Sci., Vol. 4, pp. 25-55, 1911.
* Peck, E. L., Nitrogen, Chlorine and Sulfates in Rain and Snow;
Chem. News., Vol. 116, p. 283, 1917.
*Trieschmann, J. E., Nitrogen and other Compounds in Rain and
Snow; Chem, News, Vol. 119, p. 49, 1919.
470 NATURE AND PROPERTIES OF SOILS
different period at the same place, determined the addition to
be less than .2 pound a month. Stewart,! at the University
of Illinois, reports the addition of sulfur as SO, over a period
of seven years aS amounting to 9.4 pounds of SO, monthly to
the acre or 113 pounds yearly.
The loss of sulfur expressed as SO, from the Cornell lysi-
meters,” due to cropping and drainage combined, amounted,
over a period of ten years, to 149.5 pounds from an acre
yearly from the rotation tanks. The addition of sulfur in the
rain-water at Ithaca amounts to about 65.4 pounds of SO,
each year. It is, therefore, safe to assume that rain-water will
not replace the sulfur removed by normal cropping and
leaching. It must be remembered, however, that in rational
soil management, sulfur is returned to the soil in green-
manures, crop residues and farm manures. Commercial fer-
tilizers are now very commonly used, especially acid phos-
phate, which is about one-half gypsum. At the Ohio Experi-
ment Station,® plats treated with sulfate bearing fertilizers
were found over a period of years to contain considerably
more sulfur than soils not so fertilized but cropped in a
similar manner.
In the light of such data it seems that the sulfur problem
is not comparable with or as serious as the phosphorus prob-
lem of soil fertility. By the careful utilization of the normal
residues produced on the farm there seems little reason for
sulfur being a limiting factor in soil productivity, especially
if fertilizers carrying sulfur are used in connection with a
rational system of soil management.
*Stewart, R., Sulfur in Relation to Soil Fertility; Ill. Agr. Exp. Sta.,
Bul. 227, 1920.
Wee ias aag data on these lysimeters will be found in par. 163 of this
> Ames, J. W., and Boltz, G. E., Sulfur in Relation to Soils and Crops;
Ohio Agr. Exp. Sta., Bul. 292, 1916.
CHAPTER XXIII
THE PRINCIPLES OF FERTILIZER PRACTICE ?
THE USE of commercial fertilizers has increased so rapidly
within the last decade that specific knowledge is needed re-
garding the various materials offered for sale in order that
the most economical results may be attained. The greater
the general knowledge, both practical and theoretical, that a
person possesses as to the effects of the different nutrient con-
stituents on plant growth, the more rational will be the fer-
tilizer use. Fertilizer inspection and control, principles of
buying and home-mixing, methods of application, mixtures for
special crops, are a few of the many phases of economical
fertilizer practice. The final and vital consideration is re-
garding the financial return from fertilizer application. A
fertilizer should always pay.
As all fertilizers exert, either directly or indirectly, a resid-
ual effect, the problem necessarily broadens into a study of
the systems of applying them to a series of crops or to a rota-
tion, rather than a study of the effects of one particular fer-
tilizer application on one particular crop.
265. Influence of nitrogen on plant growth.2—Of the
three elements carried in an ordinary complete fertilizer,
*Hall, A. D., Fertilizers and Manures; New York, 1921.
Halligan, J. E., Soil Fertility and Fertilizers; Easton, Pa., 1912.
Van Slyke, L. L., Fertilizers and Crops; New York, 1912.
Fraps, G. S., Principles of Agricultural Chemistry ; Easton, Pa., 1913.
? Discussions of the effects of the various elements on plants may be
found as follows: Russell, E. J., Soil Conditions and Plant Growth,
Chapter II, pp. 19-50; London, 1912. Also, Hall, A. D., Fertilizers and
Manures, Chapters III, IV and VI; New York, 1921.
471
472 NATURE AND PROPERTIES OF SOILS
nitrogen! seems to have the quickest and most pronounced
effect, not only when present in excess of other constituents,
but also when moderately used. It tends primarily to encour-
age above ground vegetative growth and to impart to the
leaves a deep green color, a lack of which is usually due to
insufficient nitrogen. It tends in cereals to increase the
plumpness of the grain, and with all plants it is a regulator
in that it governs to a certain extent the utilization of potash
and phosphoric acid. Its application tends to produce succu-
lence, a quality particularly desirable in certain crops. In its
general effects it is very similar to moisture, especially when
supplied in excessive quantities.
The peculiarity of nitrogen lies not only in its absolute ne-
cessity for plant growth, its stimulation of the vegetative
parts, and its close relationship to the general tone and vigor
of the crop, but also in the fact that it was not one of the
original elements of the earth’s crust. During the formation
of the soil it slowly and gradually became present, brought
down by rains and fixed naturally in the soil through the
agency of bacterial action. Now it exists in complex nitrog-
enous compounds of the more or less decayed organic matter,
and becomes available to plants largely through bacterial
activity.
It may be stated with certainty that one of the possible
limiting factors to crop growth is a lack of water-soluble nitro-
gen at critical periods in amounts necessary for normal devel-
opment. Since soluble nitrogen may be very readily lost
from the soil by leaching, the problem of proper plant nutri-
tion becomes a serious one. Not only must the farmer be able
so to regulate the addition of nitrogen in fertilizers as to obtain
the highest efficiency, but he must understand the control and
1 For a discussion of nitrogen in relation to crop yield, see Hunt, T. F.,
.The Importance of Nitrogen in the Growth of Plants; Cornell Agr.
Exp. Sta., Bul. 247, 1907.
THE PRINCIPLES OF FERTILIZER PRACTICE 473
encouragement of the natural fixation as well. Due to the
practical possibility of keeping up the nitrogen supply of the
soil by the proper use of farm manure, crop residues, green-
manures, and the utilization of legumes in the rotation, the
quantity of nitrogen purchased in commercial fertilizers
should be as small as possible if its use is to be profitable.
When so purchased it should function more or less as a crop
starter rather than as a source of any large amount of the
plants’ supply of nutrient. The emphasis placed on all phases
of the nitrogen problem serves to reveal its great importance
in fertility practices.
Because of the immediately visible effect from the applica-
tion of soluble nitrogen, the average farmer is prone to ascribe
too much importance to its influence in proper crop develop-
ment. This attitude is unfortunate, since nitrogen is the
highest priced constituent of ordinary. fertilizers and should
usually be purchased to a less extent than potash and espe-
cially than phosphoric acid. Moreover, of the three common
fertilizer elements, it is the only one which, added in excess,
will result in harmful after-effects on the crop. These pos-
sible and important detrimental effects of nitrogen may be
listed as follows:
1. Tt may delay maturity by encouraging vegetative
erowth. This oftentimes endangers the crop to frost, or may
cause trees to winter badly.
2. It may weaken the straw and cause lodging in grain.
This is due to an extreme lengthening of the internodes, and
as the head fills the stem is no longer able to support the in-
creased weight.
3. It may lower quality. This is especially noticeable in
certain grains and fruits, as barley and peaches. The ship-
ping qualities of fruits and vegetables are also impaired.
4. It may decrease resistance to disease. This is probably
due to a change in the physiological resistance within the
474 NATURE AND PROPERTIES OF SOILS
plant, and also to a thinning of the cell-wall, allowing a more
ready infection from without.
While certain plants, as the grasses, lettuce, radishes, and
the like, depend for their usefulness on plenty of nitrogen, it
is generally better to limit the amount of nitrogen for the
average crop so that growth may be normal. This results in
a better utilization of the nitrogen and in a marked reduction
of the fertilizer cost for a unit of crop growth. This is a
vital factor in all fertilizer practice, and shows immediately
whether nitrogen fertilization is or is not an economic success.
266. Influence of phosphorus on plant growth.—lIt is
difficult to determine exactly the functions of phosphoric acid
in the economy of even the simplest plants. Neither cell divi-
sion nor the formation of fat and albumen go on to a suffi-
cient extent without it. Starch may be produced when it is
lacking, but will not change to sugar. As grain does not form
without its presence, it very probably is concerned in the pro-
duction of nucleoproteid materials. Its close relationship to
cell division may account for its presence in seeds in compara-
tively large amounts.
Phosphoric acid hastens the maturity of the crop by its
ripening influences. This effect is especially valuable in wet
years and in cold climates where the season is short. The use
of acid phosphate is being advocated in the Middle West, espe-
cially for maize, as an insurance against frost-injury and a
means of avoiding soft corn. Phosphorie acid also encourages
root development, especially of lateral and fibrous rootlets.
This renders it valuable in such soils as do not encourage root
extension and to such crops as naturally have a restricted root
development. Phosphoric acid is especially valuable for fall-
sown crops, such as wheat. A sturdy root growth is developed
which tends to prevent winter injury and prepares the plant
for a rapid spring development.
Phosphoric acid decreases the ratio of straw to grain in
cereals. It also strengthens the straw, thus decreasing the
THE PRINCIPLES OF FERTILIZER PRACTICE 475
tendency to lodge, which is likely to occur especially with
oats if too much available nitrogen is present. In certain
eases, phosphoric acid decidedly improves the quality of the
erop. This has been recognized in the handling of pastures
in England and France. The effect on vegetables is also
marked. Phosphorus is also known to increase the resistance
of some plants to disease, due possibly to a more normal cell
development. In this respect phosphoric acid counteracts the
influence of a heavy nitrogen ration.
Excessive quantities of phosphoric acid ordinarily have no
bad effect, as phosphorus does not stimulate any part unduly,
nor does it lead to a development which is detrimental. The
lack of phosphoric acid is not apparent in the color of the
plants as in the case of nitrogen, and as a consequence phos-
phoric acid starvation may occur without any suspicion there-
of being entertained by the farmer.
One of the most important phases to be noted from this
comparison of the effects of nitrogen and phosphorus is the
balancing powers of the latter on the unfavorable influences
generated by the presence of an undue quantity of the former.
The possible detrimental effects of too much nitrogen have
already been noted. This relationship between the phosphorus
and nitrogen in plant nutrition is very important in fertilizer
practice, since normal fertilizer stimulation generally results
in the most economical gains.
267. Effects of potassium on plant growth.—The pres-
ence of plenty of available potash in the soil has much to do
with the general tone and vigor of the plant. By increasing
resistance to certain diseases it tends to counteract the ill
effects of too much nitrogen, while in delaying maturity it
works against the ripening influences of phosphoric acid. In
a general way, it exerts a balancing effect on both nitrogen
and phosphate fertilizer materials, and consequently is espe-
cially important in a mixed fertilizer, if the potash of the
soil is lacking or unavailable.
476 NATURE AND PROPERTIES OF SOILS
Potash is essential to starch formation, either in photo-
synthesis or in translocation, and is necessary in the develop-
ment of chlorophyll. It is important to cereals in grain for-
mation, giving plump heavy kernels. As with phosphorus, it
may be present in large quantities in the soil and yet exert
no harmful effect on the crop. While potassium and sodium
are similar in a chemical way, sodium cannot take the place
of potash in plant nutrition. Where there is an insufficiency
of potash, however, sodium seems in some way, either directly
or indirectly, to be useful.*
268. The element in the ‘‘minimum.’’—In connection
with the obvious importance of utilizing, for any particular
soil and crop, a fertilizer well balanced as to the three primary
elements, two queries naturally arise. These are: (1) What
are the proper proportions of nitrogen, phosphoric acid, and
potash to apply under given conditions? (2) What would
be the effect if any one of these should not be present in suffi-
cient quantity as to make it equal in function to the others?
The first query cannot be disposed of until the question of
fertilizer mixtures has been considered. The second, how-
ever, is not affected by so many factors, and is more clearly
a question of the function of the elements concerned and is
logically discussed at this point.
Any element that exists in relatively small amounts as com-
pared with the other important nutrient constituents natur-
ally becomes the controlling factor in plant development.
Any reduction or increase in this element will cause a corre-
sponding reduction or increase in the crop yield. This ele-
ment, then, is said to be ‘‘in the minimum.”’ In fertilizer
practice, ideal conditions would exist if no constituent func-
tioned as a decided minimum and the entire influence of each
single element was fully utilized. In other words, the fertil-
izer would be balanced as to its relationship to normal plant
1 Hartwell, B. L., and Damon, S. C., The Value of Sodiwm when
Potassium is Insufficient; R. I. Agr. Exp. Sta., Bul. 177, 1919.
THE PRINCIPLES OF FERTILIZER PRACTICE 477
growth. That such a condition is more or less ideal and is
seldom realized is obvious, from the fact that the various fer-
tilizer carriers undergo more or less radical changes after
being applied to the soil. The composition of the soil itself
is also a disturbing factor. Nevertheless, the nearer an ap-
proach can be made to such conditions, the greater will be the
economy in fertilizer practice.
Numerous persons have investigated the question as to what
effect an increase of an element in the minimum may have on
erop yield, and various ideas have been advanced to explain
the effect. The idea of a definite law governing the increase
of plant growth according as the element in the minimum is
increased, was first suggested by Liebig. Wagner? later
stated definitely that up to a certain point the increase yield
was proportional to the increase in the application. This,
however, evidently cannot apply except over a very limited
field, since it is a matter of common observation that increased
crop yield becomes lower as the lacking element is continu-
ously supplied.
Mitscherlich ? has formulated a law which is a logarithmic,
rather than a direct, function of the increase in the element
occupying the position of the minimum. Mitscherlich’s law
may be stated concisely as follows: the increased growth pro-
duced by a unit increase of the element in the minimum is
proportional to the decrement from the maximum. In other
words, the increase is proportional to the difference between
the actual yield and the possible yield at which the element
ceases to be a limiting factor.
Mitscherlich has proposed a definite formula for such a
*Wagner, H., Bettrige zur Dungerlehre; Landw. Jahr., Band 12,
Seite 691 ff., 1883.
* Mitscherlich, E. A., Das Gesetz des Minimums und das Gesetz des
Abnehmen den Bodenertrages; Landw. Jahr., Band 38, Seite 537-552,
Hr Ein Beitrage zur Erforschung der Ausnutzung des im Minimum
Vorhandenen NdGhrstoffes durch die Pflanze; Landw. Jahr., Band 39,
Seite 133-156, 1910.
478 NATURE AND PROPERTIES OF SOILS
growth curve. This formula has been questioned by several
investigators,” who have shown that a number of conditions,
such as light, heat, and moisture, tend to disturb the applica-
tion of such a law. The fact that crop yield is the summation
of so many varying factors seems to argue in favor of no hard
and fast rule regarding the increased growth due to the added
increments of an element in the minimum. It is enough, in
the practical utilization of fertilizers, to remember that in
order to obtain the best results from fertilizers a mixture
should be used that is approximately balanced so far as the
effects of the nutrients are concerned, the crop as well as the
chemical constitution of the soil being considered.
269. Fertilizer brands.—In an attempt to meet the ae!
mands for well-balanced fertilizers suited to various crops and
soils, manufacturers have placed on the market a large num-
ber of brands of materials containing usually at least two of
the important nutrient elements, and nearly always the three;
the former being designated as incomplete fertilizers, while
the latter are spoken of as complete. These various brands
usually have a significant name,* which frequently implies the
usefulness of the material for some special crop growing on a
particular soil. Oftener, however, the brand name bears no
relation either to crop or soil. The name should always be
ignored in fertilizer purchase, the availability and composi-
tion being the important considerations.
bs = (a—y)k. Integrating, log (a—y) = c—kx.
y = total yield from any number of increments.
x—amount of any particular fertilizer constituent utilized.
a= maximum yield and is a constant.
k—a constant depending on y and x, variables.
2Pfeiffer, Th., Blanck, E., and Flugel, M., Wasser und Licht als Vege-
tationsfaktoren "und ihre "Beziehungen zum Gesetze vom Minimum ;
Landw. Ver. Stat., Band 76. Seite 211-223, 1912.
Also, Mazé, P., Recherches sue les Relations de la Plante avec les
Elements Nutritifs der Sol; Compt. Rend., Tome 154, pp. 1711-1714,
1912.
Potato and Corn Fertilizer, Golden Harvest, Ureka Corn Special,
Blood and Bone, Harvest King, Soil Builder and ‘the like.
THE PRINCIPLES OF FERTILIZER PRACTICE 479
A brand of fertilizer is usually made up of a number of
materials containing the important nutrient ingredients.
These materials, already described, are called carriers. The
making-up of a commercial fertilizer consists in mixing the
various carriers together so that the required percentages of
ammonia, potash, and phosphoric acid are obtained, care being
taken that no detrimental reaction shall occur and that a
physical condition consistent with easy distribution shall be
maintained. Brands of fertilizer put out by reputable com-
panies carry a large proportion of their nutrients in a readily
available form. A fertilizer made up principally of dried
blood, tankage, acid phosphate, and kainit or muriate of pot-
ash is a good example of the ordinary composition of ready
mixed goods.
The various brands on the market, besides being complete
or incomplete, may be designated as high-grade or low-grade
as to availability, or high-grade or low-grade as to amount of
plant nutrients carried. In the fertilizer trade the terms
generally refer to the latter condition. A low-grade fertilizer
in the latter sense is always encumbered with a large amount
of inert material, called filler, which adds to the cost of mix-
ing, transportation and handling. A low-grade fertilizer is
generally more expensive a unit of nutrient obtained than
are higher grade goods, and consequently should be avoided.
Fertilizer concerns have always found it more profitable to
sell ready mixed fertilizers than to deal in the separate car-
riers, such as dried blood, muriate of potash, and the like. Of
late years, however, it has been possible to buy the separate
materials. The conditions during the World War greatly
encouraged the application directly to the soil of separate
carriers, especially acid phosphate, since potash was almost
unobtainable and nitrogen fertilizers were very high in price.
The use of phosphoric acid alone is often much more eco-
nomical and rational than the use of a complete mixture, since
the nitrogen removed from the soil by normal cropping and
480 NATURE AND PROPERTIES OF SOILS
drainage may be replaced in other and more practical ways.
By maintaining the soil organic matter the natural supply of
potash may in a loamy or clayey soil often be so influenced
as to render a potash fertilizer unnecessary. At least there
may be enough soil potash available so that the use of a com-
mercial form will not be profitable.
270. Fertilizer inspection and control—From the fact
that so many opportunities are open for fraud either as to
availability or as to the actual quantities of ingredients pres-
ent, laws have been necessary for controlling the sale of fer-
tilizers. These laws apply not only to the ready mixed goods
but to the separate carriers as well. Most states have such
laws, the western laws generally being superior to those in
force in eastern states, where the fertilizer sale is heavier.
This is because the western regulations are more recent and
the legislators have had the advantage of the experience gained
where fertilizers have long been used. Such laws are a pro-
tection not only to the public but to the honest fertilizer com-
pany as well, since spurious goods are kept off the market.
Certain provisions are more or less common to most fer-
tilizer laws. In general, all fertilizers selling for a certain
price or over must pay a state license fee or a tonnage tax and
print the following data on the bag or on an authorized tag:
1. Number of net pounds of fertilizer to a package.
2. Name, brand, or trade-mark.
3. Name and address of manufacturer.
4. Chemical composition or guarantee.
For the enforcement of such laws the states usually pro-
vide adequate machinery. The inspection and analyses may
be in the hands of the state department of agriculture, of the
director of the state agricultural experiment station, of a
state chemist, or under the control of any two of these. In
any case, a corps of inspectors is provided, the members of
which take samples of the fertilizers on the market throughout
the state. These samples are analyzed in laboratories provided
THE PRINCIPLES OF FERTILIZER PRACTICE 481
for the purpose, in order to ascertain whether the mixture is
up to guarantee. The expense of the inspection and control of
fertilizers is usually defrayed by the license fee or the ton-
nage tax.
If the fertilizer falls below the guarantee,—allowing, of
course, for the variation permitted by law,—the manufacturer
is subject to prosecution in the state courts. A more effective
check on fraudulent guarantees, however, is found in pub-
licity. The state law usually provides for the publication
each year of the guaranteed and found analyses of all brands
inspected. Not only has this proved effective in preventing
fraud, but it is really a great advantage to the honest manu-
facturer, as his guarantees receive an official sanction. The
found analysis of most fertilizers is generally above the
guarantee.
271. The fertilizer guarantee—Every fertilizing mate-
rial, whether it is a single carrier or a complete ready-to-apply
mixture, must carry a guarantee. The exact form is gener-
ally determined by the state in which the fertilizer is offered
for sale. The content of nitrogen is almost invariably ex-
pressed in terms of ammonia (NH,), although the amount of
total nitrogen is sometimes required in addition. The phos-
phorus is quoted in terms of phosphoric acid (P,0,). In
some cases, a bone-phosphate of lime (B. P. L. or Ca,(PO,)2)
equivalent is included. The guarantee of a simple fertilizer
material is easy to interpret, since the name of the material is
printed on the bag or tag. When the amount of the nutrient
element carried is noted, the availability and general value
of the goods is immediately known. If the material is sodium
nitrate at 18 per cent. ammonia, it is apparent that the fer-
tilizer is high-grade and should give immediate and definite
results when properly applied to a growing crop.
The interpretation of a complete fertilizer analysis is not
as easy, however, since the names of the carriers are seldom
included in the guarantees. The simplest form of guarantee
482 NATURE AND PROPERTIES OF SOILS
is a mere statement of the percentages of NH,, P,O, and K,0,
as, for example, a 2—8—2.1 This, however, is too brief for a
guaranteed analysis on goods exposed for sale, as it gives no
idea whatsoever regarding the solubility of the materials. As
might be expected, there is a wide range in the character of
the guarantees required by the various states. For example,
some states insist on the statement of the percentage of both
nitrogen and ammonia, while others insist only on the percent-
age of nitrogen. Some require the soluble, the reverted, and
the total phosphoric acid, while others require only the soluble
and the reverted. As to potash, in some cases the soluble
must be stated, while in other cases the total must be given.?
In general, a guarantee should show not only the amount
of the various constituents but also their form or availability.
The following outline analysis is excellent in this respect:
Percentage of NH, as nitrate. Percentage of P,O,; soluble
Percentage of NH, as ammonia. in water.
Percentage of NH, total. Percentage of P,O, reverted.
Percentage of K,O water soluble. Percentage of P,O, as
Percentage of K,O as chloride. insoluble.
272. The buying of mixed goods.—The successful buying
of mixed fertilizers on the retail market depends on two
things: (1) the selection of a composition suitable to soil and
crop with carriers of known value; and (2) the purchase of
high-grade goods. The farmer who observes these points will
at least have purchased successfully. Whether he obtains a
1In the South, the order is different. An 8-3-2 means 8 per cent. of
P,O,, 3 per cent. of NH, and 2 per cent. of K,O.
? Below is the guarantee of a complete fertilizer:
INDtTO GEM hase tte chin renee reece evolewetaekt teterspciere tokens 4.2%
Higa! to vammoniaiere ceteris ieee rote clevonetentae 5.0
Soluble: SPsORecke acperee vate areterPevetiens ola ciaeiereerersel 4.0
Reverted: PeOen en cexccat oye ste iv ene ere sie el oreees 2.0
Available PsOy rats. tielaete nets ererer eee hotretecva cist 6.0
Tnsoluble | Ps@ es cca s ses ec cashes Coens on see euete tegen ees 1.0
Total PaO ee ed oe artes tesa orclen yee e eta encton toren te 7.0
THE PRINCIPLES OF FERTILIZER PRACTICE 483
profit from the use of the fertilizer depends on the interrela-
tion of a number of factors more or less variable from season
to season.
The selection of a suitable fertilizer, as to carriers and com-
position, entails, after the need of the crop and soil are de-
cided, a careful study of the guarantee. Should the guarantee
be such as that just cited, a large amount of information is
at hand concerning the forms of the carriers and the availa-
bility of the important constituents. This knowledge, prop-
erly correlated with the probable needs of the crop and the
soil, will determine whether a particular brand should be pur-
chased or not. The real question here is not so much the
actual quantities of the elements in a ton of the fertilizer,
as it is their balance among themselves. The actual pounds of
nitrogen, phosphoric acid, or potash applied to the acre can
be governed by the rate at which the mixture is added.
The purchase of high-grade goods is the second important
point to be considered. Data collected from practically every
State show that the higher the grade of the fertilizer, both as
to availability and as to the percentage of the constituents
earried, the greater is the amount of nutrients obtained for
every dollar expended. Avoiding the abnormal war
prices, the following data from Vermont! for 1909 seem
representative :
TABLE XCVIII
Cost (IN CENTS) OF ONE PouUND OF| CENTS’ WoRTH
oF NUTRIENTS
MIXED FERTILIZER RECEIVED FOR
NH, E207 K,O EvEerRY DOLLAR
EXPENDED
Iie (HEIs bob oooDe 32 7.6 8.5 50
Medium grade....... 26 6.3 7.0 60
15 Gife) 1 209246 Gis leo choi = 23 5.7 6.3 67
1 Hills, J. L., Jones, C. H., and Miner, H. L., Commercial Fertilizers ;
Vt. Agr. Exp. Sta., Bul. 143, pp. 147-149, 1909.
484 NATURE AND PROPERTIES OF SOILS
It is always true that the lower the grade of a fertilizer the
higher is the proportional cost of placing the goods on the
market. In other words, it costs just as much a ton to market
a low-grade material as a high-grade one. This accounts for
the fact that the nutrients are cheaper a pound in a high-
gerade mixture, and that the value received for every dollar
expended is greater.
273. The purchase of unmixed fertilizers——There has
always been a tendency among fertilizer manufacturers to
discourage the purchase by the farmer of the separate car-
riers of fertilizer nutrients. When this was possible the fer-
tilizer manufacturer was able absolutely to control the mar-
ket. By selling only mixed goods the manufacturer could
not only realize a profit on the ingredients themselves but a
profit on the mixing in addition. In order to escape these
costs many farmers have begun the practice of buying the
separate carriers, thus avoiding the extra charges. In many
eases, the mixing on the farm costs nothing, as it can be done
in winter when the farm work is not pressing. Home-mixing
has been greatly encouraged by post-war conditions. In 1920
_ from ten to twenty dollars a ton was often saved on a high-
grade mixture by purchasing the carriers separately.
In many instances the fertilizing materials purchased sepa-
rately need not be mixed at all, thus effecting a considerable
saving in time and labor. Acid phosphate is generally added
separately, especially to fall wheat. Bone-meal, basic slag,
and raw rock give excellent results when applhed with farm
manure. Sodium nitrate and ammonium sulfate give good
returns as a top dressing on meadows, pastures, and small
cereals, especially if phosphates have been added at some
other point in the rotation. When farm manure is available,
the use of acid phosphate with lime and manure in a legume
rotation is generally desirable. Even where little manure
is available, the application of sodium nitrate or ammonium
sulfate as a top dressing for meadows, with acid phosphate in
THE PRINCIPLES OF FERTILIZER PRACTICE 485
its proper place, is feasible. The purchase of expensive ready-
mixed fertilizers may thus be avoided without necessitating
home-mixing.
For vegetable crops, however, especially potatoes, a com-
plete fertilizer is generally advisable. Home-mixing is in such
cases necessary. Special soils often demand a complete mix-
ture. Muck soils generally require both potash and phos-
phorie acid, while sandy soils, especially if the organic matter
is low, respond to a mixture carrying all three of the fer-
tilizer elements.
As might be expected, this practice of home-mixing has met
with much opposition from manufacturers. In general, it is
claimed that the factory goods are more finely ground than
those mixed by the farmer, and consequently the ready-mixed
goods are not only more uniform but also in better physical
condition. Also, the manufacturer is able to treat certain
materials with acids, and thus increase their availability.
While these reasons are more or less valid, good results may
be expected from a fertilizer even though it may not be quite
uniform, as the soil tends to equalize this deficiency. More-
over, by screening and by using a proper filler, a farmer can
obtain a physical condition which will in no way interfere
with the drilling of the material. While, obviously, one farm-
er alone cannot afford to buy small lots direct from the whole-.
sale dealer because of the high freight charges, this objection
is being met by organizations of various kinds whereby the
single carriers may be purchased in carload lots and shipped
directly to the association.
It is evident that by purchasing the separate carriers, a
farmer is able to obtain pure high-grade material at a reason-
able price. Even if the fertilizers are not home-mixed, an
educational value enters. The farmer is forced to study the
influence of the materials on his crops more closely and is thus
placed in a position to make changes that will tend to a higher
efficiency of the constituents. The chances are that he will
486 NATURE AND PROPERTIES OF SOILS
advantageously alter his fertilizer practice as the rotation
progresses and his soil changes in fertility.
Such arguments do not always mean, however, that it pays
to buy the separate materials. As a matter of fact, in many
cases it does not pay, especially where only a small amount of
fertilizer is needed and it is impossible to codperate with
other farmers. As a general rule, fertilizers should be bought
by the method that will give the greatest value for every dollar
expended, providing, of course, that the proper material is
purchased. Farmers can often avail themselves of the advan-
tage of both systems by asking for bids from various manu-
facturers on carload lots of mixed goods having a certain
composition. The farmers in this case designate the carriers
as well as the formula. All the advantages of machinery mix-
ing may thus be gained.
274. How to mix fertilizers..—The first step in the buy-
ing of the separate fertilizer carriers is to obtain quotations
which should state the price a ton, the composition, and the
freight rate. With this information, the most desirable car-
riers are selected and the amount of each is calculated.? If
*Certain materials should not be mixed, especially in large amounts.
Thus lime, especially the oxide and hydroxide forms or fertilizers earry-
ing lime in considerable amount, should not be mixed with ammonium
sulfate and animal manures, since ammonia is likely to be freed. Such
materials should be kept away from acid phosphate or the reversion of
the latter will occur. Calcium carbonate in small amounts, however, is
often mixed with fertilizers carrying acid phosphate. It is not wise to
allow moist acid phosphate to lie in contact with sodium nitrate, as nitric
acid may be liberated by free sulfuric acid.
* Below are three satisfactory mixtures:
2-12-0
400 pounds of tankage.
100 pounds of sodium nitrate.
1500 pounds of acid phosphate (16%P.0;).
2-12-2
320 pounds of tankage.
100 pounds of ammonium sulfate.
1500 pounds of acid phosphate (16%P,0,).
80 pounds of potassium chloride.
4-10-4
150 pounds of sodium nitrate.
100 pounds of ammonium sulfate.
THE PRINCIPLES OF FERTILIZER PRACTICE 487
the materials are to be applied separately, the rate to the acre
and the number of acres must be known. If a mixture is to be
made, the formula of this mixture must be decided on in addi-
tion. The pounds of the various carriers necessary to produce
a given amount of a certain mixture can now be calculated.
All of this is a matter of good judgement and careful arith-
metic.*
With the separate carriers at hand, the mixing, if necessary,
is quickly accomplished. All that is needed may be lsted
as follows: (1) a tight floor, (2) a coarse sand screen, (3) a
tamper or grinder, and (4) shovels, a rake, and like tools.
Since the pounds of fertilizer are quoted on each bag, weigh-
ing is unnecessary in making up a given amount of a mixture
having a certain formula. Bags may be divided into half or
quartered with sufficient accuracy.
The bulkiest material is spread on the floor first and leveled
uniformly by raking. The remaining ingredients are then
spread in thin layers above the first, in the order of their bulk.
Beginning at one side, the material is next shoveled over, care
being taken that the shovel reaches the bottom of the pile each
time. The pile is then again leveled, and the process is re-
peated a sufficient number of times to insure thorough mixing.
Sometimes a mixing machine may be used for this operation.
For storage and general convenience, the fertilizer may be
weighed into sacks of 100 to 150 pounds capacity and put in a
240 pounds of tankage.
100 pounds of dried blood.
1250 pounds of acid phosphate (16%P.0,).
160 pounds of muriate of potash.
1A 2-8-2 fertilizer is to be compounded from dried blood containing
12% NH;, acid phosphate carrying 14% P.O, and kainit containing
12% K,O. In one ton of the mixture there should be 40 pounds of NH,,
160 pounds of P ae and 40 pounds of K,O.
== ooo lbs: of dried blood.
iy ae 14= 1142 lbs. of acid phosphate.
40 — .12— 333 lbs. of kainit.
192 lbs. of filler.
2000 ibs. total.
488 NATURE AND PROPERTIES OF SOILS
dry place until needed. Each sack should be labeled, especi-
ally if different mixtures are made.
A word of caution should be inserted here regarding the
concentration of the mixture. Some farmers, in order to les-
sen the work of mixing and application in the field, raise the
percentage of the elements exceedingly high—a condition very
likely to occur when high-grade materials are used. This
sometimes is bad practice, in that it may interfere with ger-
mination after the fertilizer is applied and may also injure
the young plants. Also, it is likely to result in a poor physi-
eal condition, which may clog the drill, and in uneven distribu-
tion, which will bring about a lowered efficiency of the fertil-
izer. The use of sufficient dry finely divided filler will obviate
such dangers.’
275. The choice of a fertilizer—Two primary considera-
tions must be observed in the actual utilization of fertilizers.
The first of these has to do with the composition of the fer-
tilizer and its suitability to soil and to crop. A careful study
should be made not only of the percentages of ammonia, phos-
phorie acid, and potash but also the availability of these con-
stituents. The second consideration in the rational use of
fertilizing materials is in regard to the amounts to be applied.
As much eare and good judgment are necessary in handling
a single carrier as a complete ready-mixed material, especially
if the rotation as a whole is considered.
It is evident, due to many factors that cannot be controlled,
that fertilizer formule for different crops on particular soils
are difficult to determine. In fact, such data can never be
more than merely suggestive. Further, the best quantity of a
mixture to apply, even though it is perfectly balanced, is a
figure that can only be approximated. Probably the largest
percentage of the fertilizer waste that occurs annually can
1Sand, dry soil, saw dust, dry muck, and even ground limestone, if in
small amounts, may be used as fillers.
THE PRINCIPLES OF FERTILIZER PRACTICE 489
be charged to this factor. Many farmers make the mistake of
applying too much fertilizer. Any information along such
lines, however, can only be suggestive, rather than literal,
it being understood that the general formule suitable to vari-
ous crops, and the quantities ordinarily applied, are subject
to wide variations.
276. Fertilizer formulae.'—In the popular mind, the nu-
trition of a plant is considered as similar to and as easy as
the proper feeding of an animal. With animals, the food is
compounded with the correct balance of nutrients and if other
conditions are favorable, normal results should be obtained.
The nutrition of a plant is by no means as simple as the proper
feeding of an animal. In the first place, the plant receives
most of its nutrients from the soil and air and not from the
fertilizer, since the latter usually merely supplements the nu-
trients already present in the soil. Again, the food for the
animal remains balanced as it is utilized. In the case of plants,
the fertilizer nutrients undergo great changes on addition to
the soil, the soil influencing the availability of the fertilizer
as well as the fertilizer influencing the soil in a great number
of different ways. Moreover, the question of fertilizer resi-
dues, especially those of an acid nature, is always paramount
when fertilizers are used over long periods. The proper for-
mula for a given crop and a given soil under a probable series
of weather conditions is thus more or less of a guess and will
always remain so.
*The following example of fertilizers similarly named but carrying
strikingly different guarantees are taken from Bull. 206 of the Vt.
Agr. Exp. Sta.
Potatoes and Maize Potatoes and Tobacco
4-7-8 2- 6-7
4-8-4 2- 6-4
4-8-0 2-12-0
Vegetables Top Dressings
3- 7-10 7-6-5
4- 8- 4 7-6-2
5-10- 0 7-6-0
490 NATURE AND PROPERTIES OF SOILS
In spite of the intangible nature of the question, certain gen-
eral rules seem to govern the compounding and use of fertiliz-
ers. In the first place, the ratio of the nutrients removed by
the average crop bears no relation to the composition of the
fertilizer usually added. This is to be expected because of
the complex changes that the fertilizer undergoes in the soil
and because the different nutrients influence the plant di-
versely.
TABLE XCIX
RATIO OF THE | RATIO OF THE
CONSTITUENTS | CONSTITUENTS
CONSTITUENTS AS THEY OccuR|CARRIED BY THE
IN THE AVERAGE AVERAGE
CROP FERTILIZER
VANUNIOMTA. 05.5 Secs soe eae ae 4 0-2
Phosphorie(acid: G27. eee nae be 2 16-8
Potashts 2743. Pe OE Oe 3 O-2
It is immediately noticeable that the ratios of the ammonia
and potash in fertilizers are low. The ammonia ratio is low
because of the ready response of plants to nitrogen and the
ease with which this constituent is lost from the soil. The
potash ratio is likewise small because potassium is a rather
expensive constituent and it is generally better if possible to
render available by suitable means that which is already in
the soil than to buy it commercially. The phosphoric acid
is high in comparison with the ammonia and potash because
of its complex reversion in the soil and the tendency of much
of it to remain unavailable for long periods due to the high
absorptive power of the soil.
The following data may now be presented. These for-
mule are tentative and suggestive only, being a modification
and curtailment of certain analyses standardized for the use
of fertilizer manufacturers in the United States.
THE PRINCIPLES OF FERTILIZER PRACTICE 491
TABLE C
GROUP I: FODDER AND STAPLE CROPS.
Wheat (fall) Maize Millet
Oats Barley Beans (field)
Rye (fall) Buckwheat Peas (field)
Som WITHOUT WITH
FarM MANURE FARM MANURE
RNPIDEL Wy SOMME vey che 4 evo cia, aie mae 2-10-6 0-12-4 / or Acid
pany SOUL eyes caress 0s eet 2-10-4 0-12-2 {| Phos.
Clay SOM 0s o's ess tinr ons Sai Acid Phosphate
TABLE CI
GROUP Il: ‘TOP DRESSINGS.
WHEAT, RYE
TIMOTHY y
? AND OATS PASTURES*
Soin Sees Sop FoR Hay = AND
oe SPRING EGUMES
BOS eee €
Sandy sil, ..-.... 7-8-6 fee ee s|p0710-6), OF 8
WWoamy soil... <5. 7-8-3 7-8-0 0-12-4 Bae
Clavey soil... 5.’ 7-8-0 7-8-0 0-12-2 Sine :
* Note.—Sodium nitrate or ammonium sulfate may be used alone as
a top-dressing on all of these crops except legumes.
TaBLE CII
GROUP III: VEGETABLES.
1. Extensively — Tomatoes, | 2. Intensively—Cabbage, let-
sweet corn, beets, cab- tuce, celery, asparagus,
bage, ete. ete.
Sandynr SOW. cio. 0% +2 3-10-6 ANGy "SOU. ome: 4-10-6
hoamy sows. .5.6< 3-10-4 Loamy soil......... 4-10-4
Glee coil... a Clayey ‘soils isanes. 4-10-2
All root-crops should re-
ceive at least 2 per cent.
of K,0.
The ammonia should be re-
duced if farm manure is
used.
492 NATURE AND PROPERTIES OF SOILS
3. Miscellaneous.
Nandy ‘sell 223)...
a. Early potatoes * a2 2.
i
Loamvy, soil: patie eee 5-
Clayey soil.))..Gn eee 4
b. Late potatoes*........
e. General trucking * on sandy soils of Atlantic
Seaboard ee 2) i0.)..0 caus ¢ ote eee eee 5-8-7
* Note.—Reduce ammonia if farm manure is used.
In this table of suggested formule, it is noticeable that
wherever manure is used, the ammonia is reduced or even
eliminated. Ammonia is also unnecessary on leguminous
crops. With vegetables, the ammonia is usually high. Top
dressings for pastures, meadows, and cereals in the spring
should always carry large quantities of readily available nitro-
gen.
In a mixed fertilizer, the phosphoric acid is generally high,
for reasons already explained. Due to the absorptive power
of a clay, the mixture applied to such a soil should generally
carry more phosphorus than that added to a sandy soil. Pot-
ash is usually lower in a fertilizer for clayey soils, due to the
possibility of liberating potassium from the soil itself by good
soil management.
277. Amounts of fertilizers to apply.—The agricultural
value of a fertilizer is necessarily a variable quantity, since,
in applying fertilizers, a material subject to change is placed
in contact with two wide variables, the soil and the crop.
Moreover, soil conditions are constantly changing, thus fore-
ing a modification of the fertilizer applied to the same soil
bearing the same erop at different times. The factors influ-
encing the efficiency of a fertilizer application may be listed
as follows: (1) seed, crop, and adaptation of crop, (2) weather
conditions, (3) physical condition of the soil, including drain-
THE PRINCIPLES OF FERTILIZER PRACTICE 493
age, (4) organic content of the soil, and (5) chemical constitu-
tion of the soil and its reaction.
Although the conditions affecting fertilizer efficiency have
thus been so briefly disposed of, it is evident that they are of
vital importance in the economical utilization of fertilizing
materials. One point of broader scope stands out particularly
in this connection—the necessity of putting a soil in any
given climate in the best possible condition for plant growth.
This means that drainage, lime, organic matter, and tillage,
in the order named, must be raised to their highest perfection
in order to realize the best results from fertilizers.
Such considerations indicate that the decision as to the
amount of a single carrier or of a mixed fertilizer that should
be applied will be difficult and probably more indefinite than
formula selection. In fact, the amount of a fertilizer applied
to the acre is more vital than the actual chemical composition,
as far as money returns are concerned.
With all the groups considered above, except garden and
root-crops, the applications are generally relatively light, rang-
ing from 150 to 350 pounds to an acre. Where excessive vege-
tative growth is required, as in silage, the rate may be in-
creased to 500 pounds. In the top dressings of meadows or
grains, the rate varies from 100 to 200 pounds an acre. Very
often this dressing is sodium nitrate or ammonium sulfate
alone. With garden and root-crops, the amount of fertilizer
applied is very large, ranging from 800 to sometimes as high
as 2000 pounds. The cropping here is intensive, and the ex-
penditure for fertilization may be large and yet yield substan-
tial profits.
278. The law of diminishing returns.—It must always
be remembered that in fertilizer practice the very high yields
obtained under fertilizer stimulation are not always the ones
that give the best returns on the money invested. In other
words, the law of diminishing returns is a factor in the in-
fluence of fertilization on crop yield. After a certain point
494 NATURE AND PROPERTIES OF SOILS
is reached, the return for each added increment of fertilizer
becomes less and less. It is evident, therefore, that with an
excessive application of any mixture, the returns to an in-
crement will at last become so small that the increased crop
fails entirely to pay for even the fertilizer, not to mention
Cy
~
@USHELS OF GRAIL
Te)
POUNDS oF “FLOATS “APPLIED "PER ACRE
2000 2400
Fic. 60.—In the upper diagram the heavy line indicates the increase
in the yield of maize due to graduated applications of floats. The
lower diagram shows how the cost of the fertilizer approaches and
finally exceeds the value of the crop as the applications increase
in size.
such charges as cost of application, harvesting of increased
crop, storage, and the like. The application of moderate
amounts of fertilizer is to be urged for all soils until the maxi-
mum paying quantity that may be applied to any given crop
is ascertained by careful experimentation. Over-fertilization
probably accounts for the fact that such a large proportion of
THE PRINCIPLES OF FERTILIZER PRACTICE 495
the fertilizer sold to farmers each year not only is entirely
wasted, but probably in some cases even becomes detrimental
to crop yield.
The law of diminishing returns may be illustrated by data
from the Cornell University Agricultural Experiment?! Sta-
tion. Floats were applied at different rates to plats receiv-
ing a uniform dressing of farm manure at the rate of 15
tons to the acre. Table CIII shows the increased yields of
maize due to the treatment with the rock phosphate. Pre-
war prices were used in the calculations. (See Fig. 60.)
TABLE CIII
PouNDS OF FLOATS MAIZE MAIZE FLOATS
TO THE ACRE (BUS.) (VALUE) (CcOsT) DIBSERENCE
20 ee 7.0 $4.62 $ .90 aes 72
ee tees ss 8.3 5.48 1.80 + 3.68
0S SAS eee 10.2 6.73 3.60 + 3.13
DANO REY hace OS: 12.7
8.38 10.80 — 2.42
279. Method and time of applying fertilizers —
Although considerable emphasis has been placed on the selec-
tion of the correct fertilizer formulae and on the adequate and
economical amounts to use, the method of application must
not be lost sight of. A fertilizer is never effective unless uni-
formly distributed. It should also be placed in the soil in
such a position that it will stimulate the plant to the best
advantage.
The distribution of the fertilizer by means of machinery
is much more satisfactory than is broadcasting by hand,
as the former method gives a more uniform distribution.
Cereals and other crops are now usually planted with a drill
or a planter provided with an attachment for dropping the
fertilizer at the same time that the seed is sown, the fertilizer
*Lyon, T. L., Soils and Fertilizers; p. 216; New York, 1917.
496 NATURE AND PROPERTIES OF SOILS
being by this method placed under the surface of the soil.
Broadcasting machines are also used, which leave the fer-
tilizer uniformly distributed on the surface of the ground,
permitting it to be harrowed in sufficiently before the seed is
planted, thus preventing injury to the seed by the chemical
activity of the fertilizing material.
Corn-planters with fertilizer attachments deposit the fer-
tilizer beneath the seed, thus avoiding a possible detrimental
contact. Grain-drills do not do this, and, where the amount
of fertilizer used exceeds 300 or 400 pounds an aere, it is
better to apply it before seeding. Grass and other small seeds
should be planted only after the fertilizer has been mixed
with the soil for several days. For crops to which large quan-
tities of fertilizers are to be added, especially potatoes and
garden crops, it is desirable to drop only a portion of the
fertilizer with the seed, the remainder having been broad-
casted by machinery and harrowed in earlier.
280. Systems of fertilization—During the evolution of
fertilizer practice since the middle of the nineteenth century,
a number of systems of applying fertilizers have been advo-
cated and in many eases actually followed. Perhaps the first
plan to be suggested was the single element system. At that
time, each crop was supposed to respond largely to one par-
ticular element. Thus, nitrogen was supposed to dominate
wheat, rye, and oats; phosphoric acid, to dominate maize,
turnips, and sorghum; and potash to dominate potatoes,
clover, and beans. Present knowledge of plant nutrition and
the balancing effects of fertilizer nutrients show this idea to
be fallacious.
The supplying of abundant minerals as a fertilizer system
had its origin from the fact that potash and phosphorie acid
are relatively cheap and are rather slowly leached from the
soil, while nitrogen is expensive and easily lost in this way.
Such a plan, therefore, always provides plenty of potash and
phosphorie acid, which are to be balanced each season with
THE PRINCIPLES OF FERTILIZER PRACTICE 497
sufficient nitrogen to give paying yields. While this system
is not feasible in its entirety at the present time, the prin-
ciple involved is worthy of incorporation with more economi-
eal plans.
A system based on the amount of nutrients removed by
crops has received from time to time considerable support.
According to this plan, as much plant-food material is added
each year as will probably be taken out by the plant, this
being determined by chemical analyses of the crop. The
system not only overlooks the fact that diverse plants feed
differently on the same soil, but that the same crop exhibits
marked variability with change of season and change of soil.
Moreover, no allowance is made for losses by leaching, which
are known to equal at times the losses due to plant absorption.
In trucking or in general farming operations, one crop is
often the money crop. Naturally its stimulation by heavy
fertilization will pay better than applications to crops that
bring less on the market. The general plan in this system
is to allow the crops following the money erop to utilize
the residuum. When this residual influence works out fa-
vorably, the system is likely to be a profitable one; but when
the following crops fail to respond, the method becomes
wasteful in the extreme.
281. Rational fertilizer practice——In the selection of a
system that will result in an effective utilization of fertilizers,
only two of the plans described above need be considered. In
any fertilizer, phosphoric acid and usually potash should
always be present in amounts sufficient more than to balance
the nitrogen, since the activity of nitrogen is so pronounced.
Therefore, a scheme that calls for an abundance of minerals
is a sound one. This, coupled with the heavy fertilization
of the money crop, does not, however, constitute what might
be considered a rational system, since the crops that follow
may or may not be adequately supplied with nutrients.
Not only must the soil, the crop and the fertilizer formula
498 NATURE AND PROPERTIES OF SOILS
and amount receive careful study, but the rotation should
be considered in addition. This is a fundamental principle
not only with the application of commercial fertilizers but
with liming and the use of farm manure as well. The care-
ful fertilization of the rotation, with special reference to the
money crop, is the only rational system that should ordi-
narily be employed, since it not only cares for the crop on the
land but also looks to those that are to follow. The atten-
tion that must necessarily be paid to the fertility of the soil
in such a system insures the establishment of a soil manage-
ment which will result in an economical use of the plant
nutrients, while at the same time the yields will be raised and
a continuous productivity will be provided for.
CHAPTER XXIV
FARM MANURE *
Or all the by-products of the farm, barnyard manure is
probably the most important, since it affords a means where-
by the unused portion of the crop may become a part of
the soil. Its use not only makes possible a return to the
land of a part of the nutrients previously removed by the
crop but also permits an actual gain of carbohydrate ma-
terials, the elements of which the plant obtains not from
the soil but from air and water.
This country has already entered an era in which the pre-
vention of agricultural waste is becoming necessary and a
nearer approach to a self-sustaining system of soil manage-
ment more and more essential. For the maintenance of fertil-
ity, a careful handling and a wise utilization of all the manure
*The following publications will be valuable:
Ames, J. W., and Gaither, E. W., Barnyard Manure; Ohio Agr. Exp.
Sta., Bul. 246, June 1912.
Hart, E. B., Getting the Most Profit from Farm Manure; Wis. Agr.
Exp. Sta., Bul. 221, June 1912.
Thorne, C. E., Farm Manures; New York, 1914.
Beavers, J. C., Farm Manures; Purdue Uniy. Agr. Exp. Sta., Cire. 49,
Mar. 1915.
Burdick, R. T., Concerning Farm Manures; Vt. Agr. Exp. Sta., Bul.
206, June 1917.
Fippin, E. O., Farm Manure; Cornell Reading Course for the Farm,
Lesson 127, Aug. 1917.
Weaver, F. P., Farm Manure; Pa. State Coll., Ext. Cire. No. 67, Oct.
1917.
Brodie, D. A., Handling Barnyard Manure in Eastern Pennsylvania;
U.S. Dept. Agr., Farmers’ Bul. 978, July, 1918.
Wiancko, A. T., and Jones, 8. C., The Value of Manure on Indiana
Soils; Purdue Univ. Agr. Exp. Sta., Bul. 222, Sept. 1918.
Duley, F. L., Handling of Farm Manure; Mo. Agr. Exp, Sta., Bul.
166, Sept. 1919.
499
500 NATURE AND PROPERTIES OF SOILS
produced on the farm are vital. Obviously an understanding
is necessary regarding the character and composition of farm
manure, its fermentative and putrefactive changes, its losses
in handling and storage, and above all its rational use as an
amendment and a fertilizer. This need appeals not only to
the wide-awake farmer but to the technical man as well, since
in the use of farm manures theory and practice widely over-
lap.
282. Composition and general characteristics of farm
manures.—The term farm manure may be employed in ref-
erence to the refuse from all animals of the farm, although,
as a general rule, the bulk of the ordinary manure which
ultimately finds its way back to the land is produced by
cattle and horses. This arises because these animals consume
the greater part of the grain and roughage on the average
farm, and because the methods of handling such live-stock
make it easier and more practicable to conserve their excreta.
Yard manure generally refers to mixed manures. The mixing
usually occurs during storage, either for convenience in han-
dling or for the purpose of checking losses and facilitating
fermentation. Thus, horse and cow manures are commonly
mixed, since the too rapid putrefaction and consequent loss
of ammonia in the former is checked, while at the same time
a more rapid and much more complete decomposition is en-
couraged in the latter.
Ordinary manure consists of two original components,
the solid, or dung, and the urine in about the rate of three
to one. As these constituents differ greatly, not only in com-
position but also in physical properties, their proportions
must appreciably affect the quality of the excreta and its agri-
cultural value. Litter added for bedding or for absorptive
purposes is almost always an important factor, for while it
prevents losses of the soluble constituents, it may at the same
time lower the value of the product for a unit amount.
While compiiations of available data on the composition of
FARM MANURE 501
farm manures demand liberal interpretations, they afford
considerable light regarding the differences to be expected be-
tween excrement from various animals.
TABLE CIV
THE COMPOSITION OF FRESH MANURE.?
PERCENTAGE OF
EXCREMENT ~
H,0 NH, EOF K,O
Ae eee BUG ak eS. 75 .66 30 40
Horse Urine, DA ote ees 6 aaa 90 1.63 |Trace 1.25
Whole manure.... 78 84 BAS, 5
olide 10%). f oak ors 85 48 .20 10
Cow + Urine, 30%./..... 92 1.21 |Trace 1.35
Whole manure.... 86 12 15) 45
Sold eGo... fas 60 90 50 5
Sheep, Urine, 38%....... 85 1.63 05 2.10
Whole manure..... 68 1.14 BE 1.00
OlidemON Vo Hse ea: 80 .66 .50 40
Swine, Urine, 40%....... oF A8 10 45
Whole manure..... 87 .60 a0. 40
Since the horse does not ruminate its food, the manure is
likely to be of an open character. It is also fairly dry, as is
that from sheep, the urine in these two manures making up
20 and 33 per cent., respectively, of the whole product. The
complete manure from these two animals contains 78 and
68 per cent., respectively, of water—a considerable contrast
to the cattle and swine increments. Cattle and swine ma-
nures, being very wet, are rather solid and compact. The air,
therefore, is likely to be excluded to a large degree and de-
composition is relatively slow. They are usually spoken of
as cold inert manures as compared with the dry, open, rapidly
heating excrements obtained from the horse and the sheep.
*Van Slyke, L. L., Fertilizers and Crops, p. 291; New York, 1912.
502 NATURE AND PROPERTIES OF SOILS
In every case except that of swine, the urine is much the
richer than the dung in ammonia, containing on an average
more than twice as much when compared on the percentage
basis. The urine is also richer in potash than the solid, aver-
aging for the four classes of animals 1.29 per cent. as com-
pared to 0.34 per cent. contained in the solid manure. Most
of the phosphoric acid, however, is contained in the solid ex-
TOTAL TOTAL. TOTAL
AULUIONA FHIOSPHOR!/C POTAS/T
0.6% AIC/D OF %.
O25
55% 65%
OUNG, VKINE. DUNG. URINE. DUNG, URINE.
Fig. 61.—Diagram showing the distribution of ammonia, phosphoric
acid and potash between the dung and urine of average farm
manure.
erement, only traces being found in the urine except in the
ease of swine. It is, therefore, evident that the urine, pound
for pound, is more valuable insofar as the nutrient elements
are concerned. The advantage leans heavily toward the
urine also in that the constituents therein contained are im-
mediately available; this cannot be said of the solid manure.
283. Liquid versus solid manure.—While the urine car-
ries more nutrients to an equal weight than the dung, it yet
remains to be seen whether in the total excreta voided by an
animal there are more nutrients in the urine than in the dung.
FARM MANURE 503
In general, more solid manure is excreted than liquid, tend-
ing to throw the advantage toward the former as a carrier
of plant nutrients. The following table, adopted from Van
Slyke,’ bears on this point:
TABLE CV
DISTRIBUTION OF NUTRIENT CONSTITUENTS BETWEEN THE LIQUID
AND THE SOLID OF WHOLE MANURE.
PERCENTAGE | PERCENTAGE | PERCENTAGE
or TOTAL oF TOTAL oF TOTAL
ANIMAL NH; PO; K,0
SOLID ‘LIQUID SOLID | LIQUID moun LIQUID
EUGESE ist eng chads Gis uetet 62 | 38 | 100 0 56 | 44
OLONAR eee ie en 49 | 51 | 100 Oma tas 85
STIS) Dis enone, CRN ar ae 52 | 48 95 Dela 10
SN VALI ON Ben Re Gian ierc So. ee owen! 4e
PNUERAUE a. 20 Wattal | ieee he 3 a7 | 43 95 a 1 40a" 60
Average for horse and cow | 55 | 45 ; 100 Ov} 35% 4 65
|
It is seen here that a little more than one-half the am-
monia, almost all the phosphoric acid, and about two-fifths
of the potash, are found in the solid manure. Nevertheless,
this apparent advantage of the solid manure is balanced by
the ready availability of the constituents carried by the urine,
giving it in total about an equal commercial and agricultural
value with the solid excrement. Such figures are suggestive
of the care that should be taken of the liquid manure. Its
ready loss of ammonia by fermentation and putrefaction, and
the ease with which all its valuable constituents may escape
by leaching, should make it an object of especial regard in
handling. (See Fig. 61.)
284. Poultry manure.—While poultry manure is often
produced on the farm in large quantities, it is not included
under the term farm manure, which, as generally used, refers
*Van Slyke, L. L., Fertilizers and Crops, p. 295; New York, 1912.
504 NATURE AND PROPERTIES OF SOILS
to the excrement of the larger animals. Its general composi-
tion is as below, the data being averages from Thorne.*
TABLE CVI
COMPOSITION OF POULTRY MANURE.
PERCENTAGE OF
‘ CONDITION
H,O INE |e Or KO
Whole manure, fresh.......... 57 1.31 40 00
Whole manure, air dry........ a 2.84 | .86 1.08
It is to be seen that poultry manure in the air-dry state,
the condition in which it is applied, has over twice the
amounts of nutrients carried by the other classes. It should
be applied to the soil at at least one-half the rate commonly
recommended for ordinary farm manure. Notwithstanding
its ease in handling and its great value, poultry manure re-
ceives less care and attention than any other produced on the
farm.
285. Farm manure—a direct and indirect fertilizer.—
Farm manure, when applied to the land, ordinarily fulfills
two functions which are usually not so distinctly developed in
one material—that of a direct and indirect fertilizer. Mixed
farm manure ready to apply to the land contains on the aver-
age .6 per cent. of ammonia, .25 per cent. of phosphoric acid
and .5 per cent. potash.? It is obviously a low-grade fertilizer
1Thorne, C. E., Farm Manures, p. 90; New York, 1914. Also,
Storer, F. H., Agriculture, Vol. I, p. 613; New York, 1910.
Vorhees, E. B., Ground Bone and Miscellaneous Samples; N. J. Agr.
Exp. Sta., Bul. 84, 1891.
Goessman, C. A., Mass. Agr. Exp. Sta., Bul. 37, 1890, and Bul. 63,
1896.
?See Analyses, Storer, F. H., Agriculture, pp. 237-248; New York,
1910.
Thorne, C. E., Farm Manures, pp. 89-93; New York, 1914.
Aikman, C. M., Manure and Manuring, pp. 279-292; Edinburgh and
London, 1910.
ary I. P., The Fertility of the Land, pp. 159-182; New York,
1904,
FARM MANURE 505
both as to the amounts of nutrients carried and as to their
availability. Because of the large acre applications of ma-
nure commonly made, the fertilizer constituents added in ma-
nure are considerable. Ten tons of farm manure, even if only
one-half its ammonia, one-sixth of its phosphoric acid and one-
half of its potash were readily available, are equal in fertil-
izing value to 833 pounds of sodium nitrate, 52 pounds of
acid phosphate, and 416 pounds of kainit. This equiva-
lent to the addition of 801 pounds of a readily available mix-
ture of fertilizer salts. This calculation, however, ignores
an equal quantity of nutrients which remain in the soil as
a residuum and may be used by succeeding crops. This resi-
dual effect of manure is generally a paying one during the
period of an ordinary rotation.
Farm manure acts as an indirect fertilizer in that it adds
to the soil organic matter and thus improves the physical
condition of the land. While it may not increase the organic
matter of the soil, because of the loss of carbon by exhalation
and leaching during the period of crop growth, its use materi-
ally influences the rate of reduction. Better aération, drain-
age and bacterial activity ' of necessity result from such an
addition. The influence of manure on the availability of
the mineral constituents of the soil is not the least of its
indirect actions. The fact that rock phosphate when mixed
with manure seems to have a higher availability bespeaks
a considerable solvent activity. The tendency of farm
manure to alleviate toxic conditions, such as alkali and acid-
ity, deserves attention.
286. Outstanding characteristics of farm manure.—As
farm manure is essentially a fertilizer, whether it is pro-
duced on the farm or purchased outright, it is logical to con-
trast it with the ready-mixed materials on the market. In
*Conn, H. J., and Bright, J. W., Ammonification of Manure in
Soil; Jour. Agr. Res., Vol. XVI, No. 12, pp. 313-350, March, 1919.
Fulmer, H. L., and Fred, E. B., Nitrogen Assimulating Organisms in
Manure; Jour Bact., Vol. II, No. 4, pp. 423-434, 1917.
506 NATURE AND PROPERTIES OF SOILS
such a comparison, five characteristics are outstanding: (1)
the moist condition of manure, (2) its low grade, (3) its
unbalanced nutrient condition, (4) its variability, and (5)
its rapid fermentative and putrefactive processes. These
characteristics, neither present nor desirable in ordinary fer-
tilizers, place farm manure in a class by itself as to its hand-
ling, storage, and field utilization.
Of the above points, the first three may be disposed of
quickly. Average farm manure, whether fresh or well-rotted,
contains from 70 to 85 per cent. water. <A ton of average
mixed manure when applied to the land carries but 12 pounds
of ammonia, 5 pounds of phosphoric acid, and 10 pounds of
potash to the ton. Approximately one-half, one-sixth, and
one-half, respectively, of these constituents are readily avail-
able. Farm manure is, therefore, low-grade on two distinct
counts. Moreover, its readily available nutrients approximate
a ratio of about 6-1-6, a marked contrast to the 2-8-2 often
given for the average ready-mixed fertilizers on the market.
Obviously, manure is much too low in phosphoric acid for its
content of active ammonia and potash. The variability and
decomposition of farm manure will be considered separately.
287. Variability of farm manure.—The manure pro-
duced on the average farm will obviously vary in its char-
acter and composition from time to time. The factors re-
sponsible may be listed as follows: (1) class of animal, (2)
age, condition, and individuality of animal, (3) food, and
(4) the handling and storage which the manure receives be-
for it is placed on the soil.
The differences in composition due to class of animal have
been adequately disposed of in previous paragraphs. In ad-
dition, it is obvious that the age and condition of any
animal within a class will influence the character of the ex-
ecrement produced. A young animal gaining in bone and
muscle will retain large amounts of nutrients, and the manure
will be correspondingly poorer in dry matter, nitrogen, lime,
FARM MANURE 507
phosphoric acid, and potash. A fattened animal on a main-
tenance ration will return almost all of the nutrient value of
the original food.
Sinee the animal will retain only a certain quantity of
the important food elements, it is only reasonable to assume
that the richer the food, the richer will be the corresponding
excrement. The following data from Ohio’ obtained with
western lambs substantiate this assumption:
TABLE CVII
EFFECT OF RATION ON MANURIAL COMPOSITION.
PERCENTAGE OF
RATION
NH, POF KO
Conte ang (erhay es 05. cae ee Se oe 180s) 25h |) 1.33
Gorm ouimmeal and Way 20.) 2:0. shee 3 AS feos Noe
58 | 1.25
Corn: oil meal and clover..........'... | 2.03
While the factors just disposed of cause some variation in
farm manure, the character of the product as it goes on to
the land is determined in large degree by the handling. Tight
floors and proper bedding hold the liquid manure in contact
with the solid and thus maintain the proportion of valuable
constituents. A neglect of these two conditions means a grave
loss in value. The storage of manure, when it is not taken
directly to the field, always results in loss not only of organic
matter, but of ammonia and minerals as well. As more than
one-half of the ammonia and potash are water-soluble, seri-
ous loss is unavoidable. Such losses over-ride other causes of
variation. The influence of storage is clearly shown by the
following figures from Schutt? on mixed horse and cow
*Thorne, C. E., and others. The Maintenance of Fertility; Ohio Agr.
Exp. Sta., Bul. 183, 1907.
“Schutt, M. A., Barnyard Manure; Canadian Dept. Agr., Centr. Exp.
Farm, Bul. 31, 1898.
508 NATURE AND PROPERTIES OF SOILS
manure. The protected manure was stored in a bin under
a shed. The exposed sample was in a similar bin but unpro-
tected.
Taste CVIII
LOSS OF CONSTITUENTS FROM PROTECTED AND UNPROTECTED
MANURE.
PERCENTAGE LOSS AT| PERCENTAGE LOSS AT
END oF Six MontTHS END OF ONE YEAR
CONSTITUENTS
PROTECTED | EXPOSED | PROTECTED] EXPOSED
Loss of organic matter 58 65 60 69
oss ore NIE eee 19 30 23 40
fiussvot (O01 see 0 12 4 16
Loss: ot dks Ok ee ec 3 29 3 36
288. The fermentation and putrefaction of manure.'—
In the process of digestion, the food of animals becomes more
or less decomposed. This condition comes about partly be-
cause of the digestive process and partly from the bacterial
action that takes place. Of these two influences within the
animal, bacterial activities are probably of the greater im-
portance as far as the breaking-up of the complicated food-
stuffs is concerned. The fresh excrement, then, as it comes
from the stable, consists of decayed or partially decayed
plant materials, with a certain amount of broken-down animal
tissue and mucus. This is more or less intimately mixed with
litter and the whole mass is moistened with the liquid exere-
ment carrying considerable quantities of soluble nitrogen and
potash. This mass of material, ranging from the most com-
*Good general discussions may be found as follows: Lipman, J. G.,
Bacteria in Relation to Country Life, pp. 303-356; New York, 1911.
Hall, A. D., Manures and Fertilizers, pp. 184-210; New York, 1921.
For a technical discussion see Russell, E. J., and Richards, E. H., The
Changes Taking Place During the Storage of Farm Manure; Jour. Agr.
Scei., Vol. VIII, Part 4, pp. 495-563, Dec., 1917.
FARM MANURE 509
plex compounds to the most simple, is teeming with bacteria,*
especially those that function in fermentation and putrefac-
tion. The number very often runs into billions to a gram
of excrement. In such an environment, it is little wonder
that biological changes go on rapidly. These changes may be
grouped for convenience of discussion under two heads—
aérobie and anaérobie.
When manure is first produced, it is likely to be rather
loose, and if allowed to dry at once it becomes well aérated.
The first bacterial action is, therefore, likely to be rather
largely aérobic in nature. Transformations are very rapid
and are accompanied by considerable heat, ranging from 100°
to 150° F. and sometimes higher. This action falls largely
on the simple nitrogenous compounds, although the more
complicated nitrogenous and non-nitrogenous constituents are
by no means unaffected. Urea is particularly influenced by
aérobic activities and quickly disappears from well-aérated
manure.
CON,H, + 2H,0 = NH,),CO,
NH,),CO; = NH, + CO, + H,O
Thus nitrogen may be rapidly lost from manure by allow-
ing excessive aérobic decay and decomposition to proceed.
This loss, however, is often somewhat checked by the oxidiz-
ing influence of nitrifying bacteria, especially in the outer
portions of the manure pile. The evolution of carbon dioxide
which goes on continuously indicates how extensively the
organic matter of the manure is suffering through biological
activity.
As the manure becomes compacted, especially if it is left
moist, oxygen is gradually excluded from the heap and its
place is taken by carbon dioxide, which is given off during
the progress of any form of bacterial activity. The decay
now changes from aérobie to anaérobic, it becomes slower, and
*Murray, T. J., Study of the Bacteria of Fresh and Decomposing
Manure; Va. Agr. Exp. Sta., Bul, 15, Part II, 1917.
510 NATURE AND PROPERTIES OF SOILS
the temperature falls to as low as 80° or 90° F. New organ-
isms may now function, although many of those active under
aérobie conditions may continue to be effective. The prod-
ucts become changed to a considerable degree. Carbon diox-
ide, of course, continues to be evolved in large amounts, but
instead of ammonia being formed, the nitrogenous matter is
converted into the usual putrefactive products, such as indol,
skatol, and the like. If sufficient reduction occurs, free nitro-
gen may escape.
The carbonaceous matter is resolved into numerous hydro-
carbons, of which methane (CH,) is prominent; and as a by-
product of the breaking-down of the proteins, hydrogen sul-
fide (H,S) and sulfur dioxide (SO,) are evolved. The com-
plex nitrogenous and carbohydrate bodies are attacked with
the splitting-off, not only of simpler materials, but often of
those more complex. Such compounds may be listed in gen-
eral as organic acids and humous bodies. They, of course, ul-
timately succumb to simplification.
The general changes' in any manure pile can readily be
recapitulated. First is the aérobic action, with the escape of
ammonia and carbon dioxide. Next the manure is wetted,
it compacts, and the slow, deep-seated decay sets in with a
simplification of some compounds, with the production of
acids, and with a gradual formation of humous materials.
As the manure becomes alternately wet and dry, the two gen-
eral processes may follow each other in rapid succession, the
anaérobie bacteria attacking the complex materials, the
aérobice affecting both the complex and the simpler com-
1The proteid compounds, which are the most important group in farm
manures, split up in the soil or compost heap into amino-acids. These
amino-acids undergo deaminisation and decarboxylation. The former
takes place either under aérobie or anaérobic conditions producing am-
monia and a complex acid. The decarboxylation occurs only when oxygen
is excluded giving either ammonia and an organic acid as in deaminisa-
tion, or carbon dioxide and a complex amine, which may be rather stable.
Deaminisation and decarboxylation go on together, the former generally
predominating.
FARM MANURE 511
pounds. Carbon dioxide is given off continuously during the
process. Some gaseous nitrogen as well as ammonia is prob-
ably lost because of the rapid alternations of conditions.
289. Effect of decomposition on the value of manure.—
Because of the great loss of carbon dioxide and water dur-
ing the decay processes, there is considerable change in bulk
of the manure. Fresh excrement loses from 20 to 40 per cent.
in bulk by partial rotting and 50 per cent. by becoming more
thoroughly decomposed. This means that 1000 pounds of
fresh manure may be reduced to 800, 600, or 500 pounds,
according to the degree of change it has undergone.
It is often argued that if the manure is properly stored,
this rapid loss of carbon dioxide and water will raise the
percentage amounts of the fertilizer elements. The simplify-
ing action of the anaérobic fermentation and putrefaction
is an additional reason for expecting better results from well-
rotted manure when it is compared, ton for ton, with the
fresh material. In practice, however, the losses in handling
due to leaching and fermentation are so dominant as to place
well-rotted manure at a disadvantage except on sandy land or
for garden and trucking purposes. At the Ohio Experiment
Station,? yard and stall manure were compared in equal
amounts in a three-year rotation of maize, oats, and hay. The
yard manure was exposed for some months in the open, while
the stall manure came directly from the stable. The increase
due to yard manure is taken as 100 in each ease. (Table CLIX,
p. 512.)
A change of a biological nature which sometimes takes
place in loose and rather dry manure is fire-fanging. Many
farmers consider this to be due to actual combustion, as the
* Under the alternating aérobic and anaérobie conditions found in the
average manure pile, gaseous nitrogen seems to be lost in considerable
amounts. This loss probably occurs through the oxidation of ammonia
to nitrites or nitrates with a later reduction of the nitrogen so carried
to a free state.
*Thorne, C. E., The Maintenance of Fertility; Ohio Agr. Exp. Sta.,
Bul. 183, p. 209, 1907.
kK
512 NATURE AND PROPERTIES OF SOILS
TABLE CIX
COMPARATIVE YIELDS FROM YARD AND STALL MANURE.
AVERAGE INCREASE TO THE ACRE
MANURE Corn, 10 YEARS | WHEAT, 10 YEARS Hay
crain | stover | erarw | stover || ® YEARS
tale sos. ly de keen Oo 100 100 100 100
Nard? 24, 2ccs eee 72 68 85 87 54
manure is very ight in weight and has every appearance of
being burned. This condition, however, is produced by fungi
instead of bacteria, and the dry and dusty appearance of the
manure is due to the mycelium, which penetrates in all di-
rections and uses up the valuable constituents. Manure thus
affected is of little value either as a fertilizer or as a soil
amendment.
290. Evaluation of farm manure.—F or purposes of com-
parison, experimentation, and sale, farm manures are often
evaluated in a way similar to that used with commercial fer-
tilizers. The great difficulty here lies in arriving at prices
for the important constituents which are at all comparable
with the value of the manure in the field. If the value of the
ammonia in manure is arbitrarily placed at 15 cents a pound,
phosphoric acid at 5 cents, and potash at 8 cents, certain
tentative calculations may be made. While such assumptions
do not establish the commercial value either of fresh or
stored manure, they are of some use in comparisons and gen-
eralizations. The average manure, as it goes on the land, car-
ries about 12 pounds of ammonia, 5 pounds of phosphoric
acid, and 10 pounds of potash. Using the prices above, such
manure is worth commercially about $3.00 a ton.
The commercial evaluation must be applied with care be-
cause of the many factors tending to vary the composition of
FARM MANURE 513
the excrement. Litter, particularly, will exert a great influ-
ence in this direction. Moreover, this mode of evaluation
must never be confused with the much more important figure
known as the agricultural value of a manure. The former
is based on composition and assumed values of doubtful char-
acter. The latter arises from the effect of the manure on crop
yield. Obviously, a rational utilization of farm manure, as
with any fertilizer, should strive for the highest return to
an increment applied. A very good comparison between
commercial and agricultural values may be cited from the
Ohio experiments! with manure. The manure was treated in
various ways and applied to maize in a three-year rotation
of maize, wheat, and hay. Twenty-six crops were grown.
The commercial evaluation is taken as 100 in every case.
TABLE CX
COMMERCIAL AND AGRICULTURAL EVALUATION OF FARM MANURE.
MANURE COMMERCIAL | AGRICULTURAL
VALUE _ VALUE
Nard manure, untreated... os. tc. 100 152
Yara manure, plus floats.......... 100 162
Yard manure, plus acid phosphate. . 100 222
Yard manure, plus kainit......... 100 192
Yard manure, plus gypsum....... 100 186
291. Amount of manure produced by farm animals.—A
well-fed moderately worked horse will produce daily from
45 to 55 pounds of manure, of which 10 to 12 pounds is
urine. A dairy cow, having a greater food capacity, will ex-
erete from 70 to 90 pounds during the same period, of which
20 to 30 pounds is liquid. Farm animals, especially sheep
and swine, vary so much in size that a thousand pound
*Thorne, C. E., and others, The Maintenance of Fertility; Ohio Agr.
Exp. Sta., Bul. 183, pp. 206-209, 1907.
514 NATURE AND PROPERTIES OF SOILS
weight of animal is the only fair and logical basis of caleu-
lation.
TaBLE CXI
MANURE EXCRETED BY VARIOUS FARM ANIMALS TO THE 1000
POUNDS LIVE WEIGHT.
Axia renee | aa
FlOrse Ail eek Ree br ee er 50 Oak
(OTE gtr Punee rsh” ta), aren Wel SUB iter 70 | BAT
SHO. aoa oe aos ta cess eee 40 f(a)
SWING? ©) Herc eke ee Ws 2 ote Soaeusne 85 Lay
foil dV 22) eee cud hh ae ae ARI 34 6.2
Powlieryy 2 ', P een ee 2, «ae ee 23 | 4.2
It is to be noted that these figures do not include Litter,
which, in cases of horses and cattle, will range from 15 to 20
per cent. of the weight of the pure excrement. A working
horse would be expected to produce from 10 to 11 tons of
average manure a year, while a dairy cow on the same basis
would produce 14 or 15 tons.
Rough calculations as to manurial production from horses
and cattle may be made from the food consumed by these
animals.® It is assumed that 50 per cent. of the dry matter of
the food appears in the excrement and that the necessary
bedding equals one-half of the dry matter of the excrement.
+ Roberts, I. P., and Wing, H. H., On the Deterioration of Farmyard
Manure by Leaching and Fermentation; Cornell Agr. Exp. Sta., Bul. 13,
1889. Also, Roberts, I. P., The Production and Care of Farm Manure ;
Cornell Agr. Exp. Sta., Bul. 27, 1891. Also, Watson, G. C., The Produc-
tion of Manure; Cornell Agr. Exp. Sta., Bul. 56, 1893.
*Thorne, C. E., Farm Manures, p. 97; New York, 1914.
* Thorne, C. E., and others, The Maintenance of Fertility; Ohio Agr.
Exp. Sta., Bul. 183, 1907.
*Watson, G. C., The Production cf Manure; Cornell Agr. Exp. Sta.,
Bul. 56, 1893.
5 Van Slyke, L. L., Fertilizers and Crops, p. 294; New York, 1912.
° Hart, E. B., and Tottingham, W. E., General Agricultural Chemistry,
p. 125; Madison, Wis., 1913.
FARM MANURE 515
Average manure (bedding plus excrement) is about 75 per
cent. water. This means that from 100 pounds of mixed food
there results 50 pounds of manurial dry matter, 25 pounds
of litter, and 225 pounds of water or 300 pounds in all. The
weight of the food consumed multiphed by three should give
in a rough way the weight of the fresh excrement plus its
litter.
292. Loss of crop constituents in the production and
handling of manure.—Any system of agriculture, whether it
be grain farming, animal husbandry, or some specialized type
such as trucking, must ultimately arrange for the addition
of certain nutrients to replace those lost in the crop, in drain-
age and through biological activity. It is evident, however,
that even if all of the crop constituents were returned to the
soil, a constant degree of fertility would not be maintained,
although the organic matter and possibly the nitrogen, if
legumes were included in the rotation, might not greatly de-
erease. The large loss of certain nutrients in the drainage
water must always be considered in any rational system of
soil fertility.
Since farm manure lessens or even eliminates the need of a
green-manure and at the same time offers a means of lower-
ing the fertilizer bill, it is worth while to inquire what pro-
portion of the nutrients contained in the crop may be re-
turned to the soil in the resulting manure. The losses en-
tailed are three: (1) those that occur in the handling and
feeding of the crop, (2) those incurred as the food passes
through the animal, and (3) those due to the handling and
storage of the manure produced.
293. Losses during manurial production—A_ certain
amount of every crop is lost before it is finally consumed by
the animal. Such loss, while important, is usually small on
every farm, especially when compared to the nutrients re-
tained by the animal. Attention is, therefore, particularly
directed towards those losses sustained by the food as it un-
516 NATURE AND PROPERTIES OF SOILS
dergoes normal digestion. Some of the data available in this
respect are quoted below:
TABLE CXII
PERCENTAGE OF ORIGINAL FOOD CONSTITUENTS RECOVERED
IN FRESH MANURE.
ANIMAL NH, EOF K,0O
Dbeere) ONO ie ape or co acne ole 61.0 86.8 82.4
Steers. Perini mpeeie atic. nee: 69.4 79.1 81.2
Steers: Bnelamdiera ss .). oa trsahee 95.5 93.0 98.5
Milking cows; Wilmois'=3..2.22..).25. 80.3 73.3 76.0
Malkano cows; semme seis. 40045 aor 84.6 70.7 91.0
Milking cows, England® .......... 71.8 15.0 90.0
Heifers, Hnelandi 222 3062. oa. acces 77.8 78.4 86.4
Dheepy Ohio he we teteewn: ars cre 68.0 87.0 91.5
As might be expected, the data are quite variable, depend-
ing on the age, condition, individuality and class of animal,
and the character of the food. As a generalization and for
purposes of calculation, it may be considered that three-
fourths of the ammonia, four-fifths of the phosphorus, nine-
tenths of the potash, and one-half of the organic matter are
recovered in the manure.® This means losses of about 25, 20,
1Thorne, C. E., Maintenance of Fertility; Ohio Agr. Exp. Sta., Bul.
183, p. 200, 1907.
2¥Frear, W., Losses of Manure; Pa. Agr. Exp. Sta., Bul. 63; Apr.
1903.
3 Hall, A. D., Fertilizers and Manures, p. 180; New York, 1921.
*Hopkins, C. G., Soil Fertility and Permanent Agriculture, p. 201,
Boston, 1910.
°>Sweetser, W. S., The Manurial Value of the Excreta of Milch Cows;
Pa. State Coll., Ann. Rep., 1899-1900, pp. 321-351.
® Hall, A. D., Fertilizers and Manures, p. 180; New York, 1921.
™Wood, T. B., Losses in Making and Storing Farm Yard Manure ;
Jour. Agr. Sci., Vol. II, pp. 207-215, 1907-08.
®’Thorne, C. E., Maintenance of Fertility; Ohio Agr. Exp. Sta., Bul.
183, p. 202, 1907.
®See Hopkins, C. G., Soil Fertility and Permanent Agriculture, p. 206;
Boston, 1910.
Also, Fippin, E. O., Live Stock and the Maintenance of Organic
FARM MANURE 517
10 and 50 per cent., respectively, for these constituents. While
such losses are necessary and are usually compensated by the
animal products, their magnitude must be considered in esti-
mating the value of manure in the ordinary rotation.
294. Losses due to handling and storage.—<As about one-
half of the ammonia and three-fifths of the potash of average
farm manure are in a soluble condition, the possibility of loss
by leaching is usually great, even though the manure is not
exposed to especially heavy rainfall. The loss of phosphorus
is also of some consequence. In addition, decomposition, espe-
cially that of an aérobic nature, will cause a rapid waste of
ammonia, one-half of that present being especially susceptible.
Packing and moistening the manure will change the decay
from aérobie to anaérobic, thus reducing the waste of am-
monia while encouraging the simplification of the manurial
constituents. Tight floors in the stables and impervious bot-
toms in the manure pit or under the manure pile will con-
siderably diminish leaching losses.
It is impossible, in quoting figures for waste of manure,
to separate the losses due to fermentation and putrefaction
from those due to leaching. The two processes go on simul-
taneously, the loss from one source being dependent, to a cer-
tain extent, on the other. It is only the nitrogen, however,
that may be lost by both decomposition and leaching, the min-
erals being wasted only through the latter avenue.
While the figures are variable (Table CXIII), it is easily
seen that one-half of the ammonia and potash and one-third of
the phosphoric acid are readily lost under fairly careful meth-
ods of storage. On the average farm where manure very often
remains outside for several months, the losses will run much
higher, easily amounting to 50 per cent. of the organic mat-
ter, 60 per cent. of the ammonia, 40 per cent. of the phos-
Matter in the Soil; Jour. Amer. Soc, Agron., Vol. 9, No. 3, pp. 97-105,
Mar. 1917.
Also Armsby, H. P., and Fries, J. A., Net Energy Values of Feeding
Stuffs for Cattle; Jour. Agr. Res., Vol. III, pp. 435-491, 1915.
518 NATURE AND PROPERTIES OF SOILS
phorie acid, and 65 per cent. of the potash. This means a loss
of at least one-half of the nutrient constituents of the ma-
nure and considerably over one-half of the fertilizing value,
since the elements wasted are those most readily available to
plants. Considering the losses which the food sustains during
digestion and the waste of the manure in handling and stor-
age, it cannot be expected that more than 25 per cent. of the
TABLE CXIII
LOSSES FROM MANURE THROUGH LEACHING AND
FERMENTATION.
KIND oF MANURE |HorSE'|HorSE1|HorsE?|} Cow? | Cow? | STEER *
Days exposed....| 183 183 274 183 fal 91
Percentage loss of
ammonia, ..j.%.5- 36 60 40 41 31 30
Percentage loss of
phosphoric acid) 50 47 16 19 ig) 23
Percentage loss of
WOLASHS «vi .agaeies 60 76 | 34 8 43 58
organie matter, 30 per cent. of the ammonia, 50 per cent. of
the phosphoric acid, and 30 per cent. of the potash of the
original crop will reach the land.° Even if leaching losses
1 Roberts, I. P., and Wing, H. H., On the Deterioration of Farmyard
Manure by Leaching and Fermentation; Cornell Agr. Exp. Sta., Bul. 13,
1889.
*Schutt, M. A., Barnyard Manure. Canadian Dept. Agr., Centr. Exp.
Farms, Bul. 31, 1898.
Thorne, C. E., Farm Manures, p. 146; New York, 1914.
*Thorne, C. E., and others, The Maintenance of Fertility; Ohio Agr.
Exp. Sta., Bul. 183, 1907.
° Voeleker and Hall have drawn up recommendations for the compen-
sation of the out-going English tenant for manure produced on the farm
but not realized on. They suggest that he receive pay at fertilizer prices
for one-half of the nitrogen, three-fourths of the phosphoric acid, and
all of the potash contained in the food consumed during the last year
of tenancy. For the second, third, and fourth years previous, the com-
pensation value shall be one-half that of the year immediately preced-
ing. Voelcker, A., and Hall, A. D., The Valuation of Unexhausted
Manures; Jour. Roy. Agr. Soc. Eng., Vol. 63, pp. 76-114, 1902.
FARM MANURE 519
ORGAWN/C
SIATTER
RETAINED BY ANIMAL
LOS7 IN HANOLING
ALND STORAGE
AIODED 70 THE SO/L
Fic. 62.—Diagram showing the proportion of the important constituents
of the food retained by the animal, lost in the handling and the
storage of the manure and applied to the soil under ordinary
conditions.
were not important, a self-sustaining system of agriculture
could not be established by the use of farm manure alone, as
organic matter is the only constituent that would be added
to the soil in amounts that approach the magnitude of the
loss.!
1Fippin, E. O., Live Stock and the Maintenance of Organic Mat-
ter in the Soil; Jour. Amer. Soc. Agron., Vol. 9, No. 3, pp. 97-105,
Mar. 1917.
520 NATURE AND PROPERTIES OF SOILS
295. Two phases of manurial practice.—A commercial
fertilizer, if made properly, may be kept for long periods
unimpaired and is always in a condition for instant applica-
tion to the soil. The only problem confronting the farmer is
the profitable application of such material. Storage is a
minor factor. Farm manure, on the other hand, although a
true fertilizer, presents, because of its peculiar characteris-
tics, serious complications. As it is subject to tremendous
losses by leaching, putrefaction, and fermentation, its han-
dling and storage, if the latter becomes necessary, is as im-
portant as its rational utilization on the land. Manurial prac-
tice, therefore, is logically discussed under two headings:
(1) handling and storage, and (2) utilization of the manure
in the field.
296. Care of manure in the stalls——Considerable loss to
manure occurs in the stable, due to decomposition and leach-
ing. Before the urine can be absorbed by the litter, it is
likely to decay and leach away in considerable amounts.
Therefore, the first care is to the bedding, which should be
chosen for its absorptive properties, its cost, and its cleanli-
ness. The following table + shows the approximate absorptive
capacity of some common litters. (Table CXIV, page 521.)
The amount of litter to be used is determined by the char-
acter of the food. If the food is watery, the bedding should
be increased. In general, the litter amounts to about one-
fourth of the dry matter of the food consumed. Sheep re-
quire about a pound of bedding a head, cattle from eight to
ten pounds, and horses from ten to fifteen pounds. No more
litter than is necessary to keep the animal clean and to ab-
sorb the liquid manure should be used, as the excrement is
*Beal, W. H., Barnyard Manure; U. S. Dept. Agr., Farmers’ Bul.
192, 1904,
Whisenand, J. W., Water-holding Capacities of Bedding Materials
for Live Stock, Amounts Required to Bed Animals, and Amounts of
Manure Saved by Their Use; Jour. Agr. Res., Vol. XIV, No. 4, pp.
187-190, July 1918,
FARM MANURE 021
PAsin CX1'V
ABSORPTIVE POWER OF BEDDING FOR WATER.
PERCENTAGE OF
MaTERIAL WATER RETAINED
J CISR2S76 MAS) C11 Tun) a Ree 124
NERC Oe SEMAOUIST Sich cssic wctcioss wna eee aaa 160
Re S DMO US MAYAN GS 5) oo. sche ws Acie edi nes 185
LU TLC ge Sl Nee ope ee a Oe 200
AAI OSU RE one a 0 a gO 210
IO AUNSStVeRr ELT ae = hie ey ee PA ee 250
eal Meer Sn feet he As Cee watts Ahaha s 600
| PASSE RLTTAVO ISIS ie eh 1300
thus diluted unnecessarily with material which often does
not carry large quantities of available fertilizing ingredients.
The next care is that floors should be tight, so that the
free liquid cannot drain away but will be held in contact with
the absorbing materials. The preserving of manures in stalls
with tight floors has been for years a common method of han-
dling dung in England. The trampling of the animals, and
the continued addition of litter as the manure accumulates,
explain the reason for the success of the method. The follow-
ing data, from Ohio, show the relative recovery of food ele-
ments in manure produced on a cement floor and on an earth
floor, respectively. The experiment was conducted with steers
over a period of six months. Even with a good dirt floor, the
leaching losses are considerable. (Table CXV, page 522.
297. Hauling directly to the field.-—Where it is possible
*Thorne, C. E., Maintenance of Fertility; Ohio Agr. Exp. Sta., Bul.
183; p: 199, 1907.
* Good discussions of handling farm manure are as follows:
Hart, E. B., Getting the Most Profit from Farm Manure; Wis. Agr.
Exp. Sta., Bul. 221, 1912.
Beal, W. H., Barnyard Manure; U. 8. Dept. Agr., Farmers’ Bul. 192,
1904,
Roberts, I. P., The Fertility of the Land, Chapter IX, pp. 188-213;
New York, 1904.
522 NATURE AND PROPERTIES OF SOILS
TABLE CXV
RECOVERY OF FOOD ELEMENTS IN MANURE PRODUCED ON CEMENT
FLOOR; ON EARTH FLOOR.
PERCENTAGE RECOVERY
CONSTITUENTS
CEMENT FLooR| EARTH FLOOR
ATA TIOTUIG HE © cccce eee erates oe sania (44 62.4
Phosphori¢sacid: sary se eran ot (ORD 78.9
Potash. icib eee oe oi ye 87.8 78.4
INVGNAC EG se Pn Core oe saute 80.0 73.2
to haul directly to the field, this practice is to be advised,
since opportunities for excessive losses by leaching and fer-
mentation are thereby prevented. Manure may even be
spread on frozen ground or on the top of snow, provided the
land is fairly level and the snow is not too deep. This sys-
tem saves time and labor, and when leaching does occur the
soluble portions of the manure are carried directly into the
soil. The practice of allowing the manure so spread to le
on the surface of the land all winter is sometimes questioned,
especially in New England.‘ On sandy soils it may some-
times be better practice to store the manure until spring.
298. Piles outside.—Very often it is necessary to store
manure outside, fully exposed to the weather. When this is
the case, certain precautions must be observed. In the first
place, the pile should be located on level ground far enough
from any building that it receives no extra water in times
of storm. The sides of the heap should be steep enough to
shed water readily, while the depth of the pile should be such
as to allow little leaching even after heavy storms. The earth
under the manure may be slightly dished in order to prevent
* Brooks, W. P., Methods of Applying Manure; Mass. Agr. Exp. Sta.,
Bul. 196, Sept. 1920.
FARM MANURE 523
loss of excess water. If possible, the soil of the depression
should be puddled, or, better, lined with cement.
The manure should be kept moist in dry weather in order
to decrease aérobie action. Each addition of manure should
be packed in place, the fresh on and above the older. This
allows the gases from the well-rotted dung to pervade the
fresher and looser portions, thus quickly establishing the
anaérobie conditions so essential to economic and favorable
fermentation.
Placing fresh manure in small heaps in the field to be
spread later, is, in the first place, poor economy of labor.
Moreover, it encourages loss by decay, while at the same time
the soluble portions of the pile escape into the soil imme-
diately underneath. There is thus a poor distribution of the
essential elements of the dung, and when the manure is finally
spread, an over-feeding of plants at one point and an under-
feeding at another results. A low efficiency of the manure
is thus realized. This method of handling manure is not to
be recommended.
299. Manure pits—Some farmers, especially if the
amount of manure produced is large, find it profitable to con-
struct manure pits of concrete. These pits are usually rec-
tangular in shape with a shed covering. Often one or even
both ends are open to facilitate the removal of the manure.
In such a structure, leaching is prevented by the solid bottom
while the roof allows a better control of moisture conditions.
By keeping the manure carefully spread and well moistened,
putrefaction may proceed with a minimum loss of nitrogen.
Some European dairymen even go so far as to utilize a cis-
tern, into which is shoveled both the liquid and the solid
manure. Later when decomposition has proceeded suffi-
ciently, the material is pumped out and applied to the land.
This method is not to be advocated in this country except
under special conditions, owing to the cost of handling.
300. Covered yards.—Another method of storage is by
524 NATURE AND PROPERTIES OF SOILS
means of a covered barnyard. Such a yard should have a
more or less impervious floor. The manure is spread out in
the yard and is kept thoroughly packed as well as damp by
the animals. This is a common method of handling the ma-
nure in the fattening of steers in the Middle West and pro-
duces manure at a minimum loss, providing hogs are not al-
lowed to follow the steers. The storage of manure in deep
stalls, a favorite method in England, is similar to this system
and has been shown to be very economical. It also affords an
opportunity for the mixing of the manure from different
classes of animals. The desirability of this has already been
shown in the case of horse and cow excrements. The advan-
tages of trampling, so far as the keeping qualities of manure
are concerned, are clearly shown by the following figures
taken from the work of Frear: *
TABLE CXVI
LOSS OF MANURE IN COVERED SHEDS.
PERCENTAGE LOSS OF
CONDITION oo eee
NH, K,O EOF
Covered and tramped.).22...5...:. oe 5.0 8.5
Covered and untramped........... 34.1 19.8 14.2
Throwing manure in heaps under a shed and allowing hogs
to work the mass over, is a desirable practice so far as food
utilization is concerned. It interferes, however, with a proper
and economical packing of the manure. The question to be
decided is whether the added food value of the manure over-
balances the extra losses by decomposition incurred by the
rooting of the swine.
301. Increased value of protected manure.—From the
previous discussion, it is evident that a well-protected and
1Frear, W., Losses of Manure; Pa. Agr. Exp. Sta., Bul. 63, 1903.
FARM MANURE 525
carefully preserved manure will be higher in available plant
constituents than one not so handled. Moreover, the agricul-
tural value of such manure will be higher. This is shown
by actual tests from Ohio.t Over a period of fourteen years,
in a three-years’ rotation of maize, wheat, and hay, a stall
manure gave a yield 38 per cent. higher than that with a yard
manure.
TABLE CX VII
INCREASE YIELDS FROM YARD AND STALL MANURE.
AVERAGE ANNUAL INCREASE TO
THE ACRE
MANURE
MAIZE WHEAT CLOVER
14 Crops 14 Crops 11 Crops
Yard, 8 tons to the rota-
UGE eee eet i a 18.6 bus. 9.5 bus. 801 lbs.
Stall, 8 tons to the rota-
LEGS Ne ae ee a 23.6 bus. | 10.9 bus. 1395 lbs.
Increase, stall over yard
MIVA TNITE Ce. fan ais Sane eye =, o « 26.8% 14.7% 74.1%
In New Jersey, fresh manure showed a gain in crop yield
53 per cent. higher than leached manure over the three years
immediately following the application. Such figures are
worthy of careful consideration.
302. Application of manure.—In the application of ma-
nure to the land, the same general principles observed in the
use of any fertilizer should be kept in mind. Of these, fine-
ness of division and evenness of distribution are of prime im-
portance. The efficiency of the manure may be raised con-
siderably thereby. Moreover, it is generally better, since the
*Thorne, C. E., and others, Plans and Summary Tables of the Experi-
ments at the Central Farm; Ohio Agr. Exp. Sta., Cire. 120, p. 112,
1912.
526 NATURE AND PROPERTIES OF SOILS
supply of manure is usually limited in diversified farming, to
decrease the amounts at each spreading and cover a greater
acreage. Thus, instead of adding 20 tons to the acre, 10 tons
may be applied and twice the area covered. Applications
could then be made oftener and a larger and quicker net
return realized for each ton of manure. With manure, as
with any fertilizer, the yield to the acre is not so important
as the crop increase for a given increment of manure added.
The influence of rate of application on increased yield to a
ton of manure is shown by the Ohio! experiments over eight-
een years in a three-year rotation of wheat, clover and pota-
toes, the manure being placed on the wheat.
TABLE CX VIII
INCREASED YIELD TO THE TON WHEN MANURE IS APPLIED IN
DIFFERENT AMOUNTS. OHIO EXPERIMENT STATION.
WHEAT CLOVER | Porators
nat (BUS.) (LBS.) (BUS.)
4 tons-to, theeacre. eee 1.34 wry) 3.81
8) tons, to the acreci... 6 94 150 2.79
6; tonssto the acres. 70 99 2.76
Not only is the increased efficiency from the smaller appli-
cation apparent, but a greater recovery of the manurial fer-
tility in the crops also results. The Ohio experiments show
that in the first rotation after the manure is applied, a 25 to
30 per cent. higher recovery may be expected from the 8 tons
treatment than from the 16 tons.
Evenness of application and fineness of division are greatly
facilitated by the use of a manure-spreader. This also makes
possible the uniform application of small amounts of manure,
*Thorne, C. E., and others, Plans and Summary Tables of the Experi-
ments at the Central Farm; Ohio Agr. Exp. Sta., Cire. 120, p. 108,
1912.
FARM MANURE D27
even as low as 5 or 6 tons to the acre. It is impossible to
spread so small an amount by hand and obtain an even dis-
tribution. Moreover, a spreader lessens the labor and more
than doubles the amount of manure one man can apply a day.
When any considerable quantity of manure is to be handled,
a manure-spreader will pay for itself in a season or two at the
most.
Whether manure should be plowed under or not depends
largely on the crop on which it is used. On timothy it is
spread as a top dressing. Ordinarily, however, it is plowed
under. This is particularly necessary if the manure is long,
coarse, and not well-rotted. It should not be turned under
so deep, however, as to prevent ready decay. If manure is
fine and well decomposed, it may be harrowed into the surface
soil. The method employed depends on the crop, the soil, and
the condition of the manure. The amount to be applied va-
ries considerably. Eight tons to the acre would be a lght
dressing, 15 tons a medium dressing, and 25 tons heavy for
an ordinary soil. In trucking land, however, as high as 50
or 100 tons are often used.
303. Reinforcement of manure.—The reinforcement of
farm manure is designed to accomplish two things in the han-
dling of this product: (1) checking loss due to leaching and
decomposition, and (2) balancing the manure and rendering
its agricultural value higher. Four chemicals may be used
in this reinforcement: gypsum (CaSO,), kainit (mostly
K,SO,), acid phosphate (CaH,(PO,), + CaSO,), and floats
(raw rock phosphate, Ca,(PO,),).
Gypsum and kainit are supposed to react with the ammonia
of the manure, changing it to ammonium sulfate, a stable
compound. As gypsum is rather insoluble, its action is prob-
ably slow. It may be applied either in the stable or on the
manure pile, usually at the rate of 100 pounds to the ton.
It has no balancing effect. Kainit is soluble and because of
its caustic tendencies should not come into contact with the
528 NATURE AND PROPERTIES OF SOILS
feet of the animals. It must not be spread on the manure
until the stock are out of the way. Since manure is unbal-
anced as to phosphorus, the agricultural value of kainit is
slight. When applied, it is generally used at the rate of 50
pounds to the ton of manure.
Acid phosphate is partially soluble and will not only react
readily with the ammonia but will tend to raise the phos-
phorus content to the proper point. From 40 to 80 pounds
of acid phosphate are generally recommended to a ton of
average farm manure. It should not be allowed to come into
contact with the feet of farm animals.
Raw rock phosphate, or floats, is a very insoluble compound,
and consequently reacts but slowly with the soluble constitu-
ents of manure. Carrying such a large percentage of phos-
phorus, it tends to balance the manure and to raise its agri-
cultural value. It is supposed that the intimate relationship
between the phosphate and the decaying manure increases the
availability of the former to plants when the mixture is added
to the soil. The reinforcement is usually at the rate of 75
to 100 pounds to a ton of manure.
Experimental data have shown that these various rein-
foreements have no particular effect on the nature, function,
and number of the bacterial flora. Their conserving influ-
ence, if any, when the manure is exposed, might be in check-
ing leaching and in preventing loss of ammonia. The follow-
ing figures from Ohio experiments ? show how slight this con-
serving effect is. The reinforcement was at the rate of 40
pounds to the ton. (See Table CXIX, page 529.)
It is immediately evident that kainit and gypsum do not
conserve the manure, and, although acid phosphate and floats
show some influence, it is sight and evidently well within the
experimental error. The principal benefit from reinforcing
manure, if any, must, therefore, be as a balancing agent. The
*Thorne, C. E., and others, The Maintenance of Fertility; Ohio Agr.
Exp. Sta., Bul. 183, p. 206, 1907.
FARM MANURE 929
TABLE CXIX
CONSERVING EFFECT OF REINFORCING AGENTS ON MANURE
EXPOSED FOR THREE MONTHS.
RATIO VALUES OF A
TRC GRLERIS Ton oF MANURE PERCENTAGE
——— Loss
IN JANUARY] IN APRIL
No remforcement......... 100 64 36
WAG) SV PSU. ike os oo 93 67 38
WY THEM eo. se ae oe 102 66 a0
SG gel elena} Uc oe) he 128 93 27
With acid phosphate....... 106 15 29
figures from Ohio' over a period of fourteen years in a rota-
tion of maize, wheat, and hay may be taken as evidence re-
garding this point. The manure treated and handled as above
was added to the maize at the rate of 8 tons to the acre.
It is evident that the principal benefit of reinforcing ma-
nure lies in the balancing influence and that acid phosphate
and floats are the most desirable agents. It is also evident
AWG hope Op. @.4
INFLUENCE OF REINFORCING ON THE EFFECTIVENESS
OF MANURE.
AVERAGE ANNUAL INCREASE TO THE ACRE|RATIO VALUE
or INCREASE
EAT
EN Corn WHEAT Hay PER TON OF
14 Crops 14 Crops 11 Crops MANURE
No reinforcement..| 18.6 bus. 9.5 bus. 801 Ibs. 100
With gypsum...... 23.6 bus. 11.6 bus. 916 lbs. 119
Wath kaart... ance. 23.7 bus. 11.3 bus. 1156 lbs. 135
Wath toate asa. 25.0 bus. 12.9 bus. 1578 lbs. 138
With acid phosphate} 30.6 bus. 15.1 bus. 1853 Ibs. 161
*Thorne, C. E., and others, Plans and Summary Tables of the Experi-
ments at the Central Farm; Ohio Agr. Exp. Sta., Cire. 120, p. 112,
1912,
530 NATURE AND PROPERTIES OF SOILS
that floats, if added in money values equal to acid phosphate,
should be about as satisfactory as a reinforcing material.
304. Lime and manure.—Very often it would be a say-
ing of labor to apply lime and manure to the soil at the same
time. This can readily be done with the carbonated forms.
Such lime may be mixed with the manure, either in the stable
or in the pile, without any danger of detrimental results. The
close union of the lime and manure may increase the effective-
ness of the former and at the same time promote a better type
of decomposition in the latter. If the soil is really in need of
calcium, however, a separate application of lime is much bet-
ter, as the amount of calcium added with the manure is never
large. Caustic compounds of lime such as calcium oxide
(CaO) and calcium hydroxide (Ca(OH),) must be kept from
manure. These forms readily react with the ammonium ear-
bonate coming from the urea, and cause the lheration of
ammonia, which may be readily lost to the air:
CON,H, + 2H,0 = (NH,).CO,
(NH,),.CO, + Ca(OH), = CaCO, + 2NH,OH
A stable or shed containing manure may be at once deodor-
ized by the use of quicklime, but with the loss of much nitro-
gen. If the manure is to be worked into the surface soil, the
caustic lime may be applied some days before and if it is in
thorough contact with the soil, it will change to the carbonate
before the manure is added. When the manure is plowed
under, the lime is best added after the plowing and thor-
oughly harrowed in as the seed-bed is prepared.
305. Manure and composting.—A compost is usually
made up of alternate layers of manure and some vegetable
matter that is to be decayed. Layers of sod or of soil high in
organic matter are often introduced. The manure supplies
the decay organisms and starts biological activities. The
foundation of such a compost is usually soil, and the pile is
preferably capped with earth. The mass should be kept
FARM MANURE 531
moist in order to prevent loss of ammonia and to encourage
vigorous bacterial action. Acid phosphate or raw rock phos-
phate and a potash fertilizer are often added, to balance up
the mixture and make it a more effective fertilizer. Lime is
also introduced, to react with such organic acids as may tend
to interfere with proper decay. Undecayed plant tissue,
such as sod, leaves, weeds, grass, sticks, or organic refuse of
any kind, may thus be changed slowly to a form which will be
valuable in building up the soil and in nourishing plants.
Even garbage may be disposed of in such a manner.
306. Residual effects of manure—No other fertilizer
exerts such a marked residual effect as does farm manure.
As it is applied in large amounts, its physical and biological
influences are of necessity very great and persist for a con-
siderable time. As only about one-half the nutrients of farm
manure are readily available, the residual effect of its fertiliz-
ing elements carry over into succeeding years. Hall? pre-
sents the following comparative data regarding the recovery
of nitrogen from various fertilizers. The crop used was man-
golds. The low recovery of the nitrogen from the manure is
of especial note. There is no reason to believe that the pot-
ash of the manure would be any more readily available and
the phosphoric acid would certainly show a lower recovery.
TABLE CX XI
RECOVERY OF NITROGEN IN A CROP OF MANGOLDS.
PERCENTAGE
RATE TO YIELD IN
THE ACRE TONS ee een
Sodium nitrate.... 550 Ibs. 17.95 78.1
Ammonium salts... 400 lbs. i eya hey Sie
Fuapeyeakes x x6 5.5-...': 2000 Ibs. 20:95 70.9
Farm manure... .-. 14 tons 17.44 31.6
* Hall, A. D., Fertilizers and Manures, p. 210; New York, 1921.
532 NATURE AND PROPERTIES OF SOILS
The length of time through which the effects of an appli-
cation of farm manure may be detected in crop growth is
very great. Hall’ cites data from the Rothamsted Experi-
ments in which the effects of eight yearly applications of 14
tons each were apparent forty years after the last treatment.
This is an extreme case. Ordinarily, profitable increases may
be obtained from manure only from two to five years after
the treatment.2, The fact remains, nevertheless, that of all
fertilizers, farm manure is the most lasting and lends the most
stability to the soil.
307. The place of manure in the rotation.*—With
trucking, garden, and greenhouse crops, the applications of
large amounts of manure year after year have proven advis-
able. Asa matter of fact, manure has shown itself, especially
if balanced with phosphoric acid, to be the best fertilizer for
intensive operations. This is due not only to the nutrients
carried by the manure, but to the large amounts of easily
decomposed organic matter that are at the same time intro-
duced. In a rotation involving the staple crops, such as maize,
oats, wheat, hay, and the like, less intensive applications are
advisable, not only because of a lack of manure but because
the return to a ton of manure applied must be raised as high
as possible. On the average farm, there is less than one ton
of manure produced to an acre of arable land. Moreover, the
return from manure will vary according to its place in the
rotation. This has proved to be the case with commercial
fertilizers and the fact is becoming more and more apparent
with farm manure.
In general, meadows and pastures derive more benefit from
manure, either residually or directly, than any other crop.
1Hall, A. D., Fertilizers and Manures, p. 213; New York, 1921.
*Voeleker, A., and Hall, A. D., The Valuation of Unexhausted
Manure Obtained by the Consumption of Foods by Stock; London,
1903.
*See Thorne, C. E., Farm Manures, Chaps. XI and XIII, New York,
1914,
FARM MANURE 533
The long tests conducted by the Pennsylvania and Ohio ex-
periment stations ' have established this fact. The following
data from Illinois? may be cited, comparing the response of
maize and oats when manured to the increased yield of clover
receiving the same treatment. (See Table CX XII, page 534.)
CROP
FOOD LOSSES
MANURIAL LOSSES
0
MANURE —>| dis ~20%
ee -40 »
-65»
PERCENTAGE OF THE CONS-
TITUENTS OF CROP
ADDED TO SOIL
SOIL Stace aS)
oe 2
Bue
LEACHING
Fig. 63.—Diagram showing the proportion of the harvested crop added to
the soil in farm manure under average conditions.
It is easy to see that a liberal dressing of manure on the
hay and pasture will markedly increase the crop. Neverthe-
less, aS manure is available in limited amounts on the average
farm and as commercial fertilizers will give almost as good
returns on hay, it is generally considered judicious, except in
1Hunt, T. F., General Fertilizer Experiments; Ann. Rep. Penn. hee
Exp. Sta,, 1907- 1908, pp. 68-93.
Thorne, C. E., and others, Plans and Summary Tables of the gee
ments at the Central Farm; Ohio Agr. Exp. Sta., Cire. 120, np. 101-
105, 1912.
* Hopkins, C. G., Thirty Years of Crop Rotation in Illinois; Ill. Agr.
Exp. Sta., Bul. 125, p. 337, 1908.
534 NATURE AND PROPERTIES OF SOILS
TABLE CX XII
INFLUENCE OF MANURE ON MAIZE, OATS, AND CLOVER.
AVERAGE PERCENTAGE RaTIo VALUE OF
INCREASE INCREASE
TREATMENT
MAIzE AND : MAIZE AND CLOVER
OATS CEOS OATS
Manure alone.. Hak 92 100 134
Manure, lime
and phosphate 30 141 162 206
certain cases, to reserve most of the manure for other crops.
The top dressing of meadows is, however, always an allowable
practice, especially on new seeding or on hay land that is
soon to be plowed for maize.
As a food producer, maize has no close rival. Where the
climate is favorable, a 75-bushel crop of maize is as easily
secured as 40 bushels of wheat or 300 bushels of potatoes to
the acre. Moreover, the maize stover may be made more valu-
able as roughage than the straw of oats, wheat, or rye. The
maize plant must have, however, for its successful growth
plenty of available nitrogen. In addition, its response to
abundant organic matter indicates the utilization of certain
organic compounds. These considerations argue for the use
of most of the farm manure on the maize when this crop is
important, especially if the supply of manure is limited.
Again the maize crop is ready for the manure in the spring
and is generally grown on land where the excreta may be
distributed during the previous winter and fall.
Potatoes are a spring crop and where they are prominent
in the rotation may receive liberal applications of manure.
If potatoes are the money crop, this should by all means be
the practice. Oats, because of the tendency to lodge, gener-
ally follow maize or potatoes as a residual feeder, receiving, if
necessary, a dressing of commercial fertilizer. If manure is
FARM MANURE 539
used on fall wheat, a great loss of manurial value is incurred,
due to the necessity of storage during the summer months.
Moreover, commercial fertilizers high in phosphorus are so
convenient and effective on wheat that the use of manure on
this crop is becoming rather uncommon, although manure
may be used to advantage as a fall and winter dressing, since
it not only stimulates the wheat but is of great value to the
new seeding as well. Where cotton and tobacco are the staple
erops, they should receive at least a part of the manure pro-
duced. The value of manure in orchards should not be over-
looked, especially on sandy soils. The up-keep of organic
matter, the conservation of moisture, and the nutrients sup-
plied are as important here as in any phase of soil manage-
ment.
308. Resume.—Barnyard manure, from the standpoint
of soil fertility, is the most valuable by-product of the farm.
A careful farmer will, therefore, attempt to utilize it in the
most economical way. The handling of manure in such a
manner that only a minimum waste occurs from the time
the manure is voided until it has reached the land is not an
easy problem. Manure is so susceptible to the loss of valuable
ingredients, both by leaching and by decay, that careful
methods must be employed. Tight floors in the stable and
covered sheds or manure pits are always advisable. Hauling
immediately to the field is the wisest procedure, yet even with
the best of care more than 50 per cent. of the fertilizing value
is usually lost. The problem of rational manurial utilization
is not solved, however, by careful handling and storage alone.
Manure must be applied in such a condition, in such amounts
and at such a point in the rotation as to realize a reasonable
return for every increment applied. The reinforcement of
farm manure with phosphoric acid is by no means an unim-
portant feature. In fact, all of the principles which are ob-
served in the profitable utilization of commercial fertilizers
should be adhered to in the use of farm manures.
536 NATURE AND PROPERTIES OF SOILS
A permanent system of agriculture evidently cannot be
established by merely returning all the manure possible to
the land, as approximately only 25 per cent. of the organic
matter, 380 per cent. of the ammonia, 50 per cent. of the phos-
phorie acid, and 30 per cent. of the potash of the food con-
sumed on the farm ever reach the land in the manure. Never-
theless, it is certainly worth the while of a farmer to use
some eare in handling this product and some thought as to
its rational utilization in the field. Even if the manure
should aid only in the up-keep of organic matter, the effort
would be worth while. Reasonable care in the handling of
farm manure will save this country thousands of pounds of
manurial fertility which are now utterly lost and at the same
time increase by thousands of dollars the food production.
CHAPTER XXV
GREEN-MANURES
From time immemorial the turning-under of a green-crop
to supply organic matter to the soil has been a common agri-
eultural practice. Records show that the use of beans, vetches,
and lupines for such a purpose was well understood by the
Romans, who probably borrowed the practice from nations
of greater originality. The art was lost to a great extent dur-
ing the Middle Ages, but was revived again as the modern
era was approached. At the present time, green-manuring
is considered a part of a well-established system of soil man-
agement, and is given a place, when possible, in every ra-
tional plan for permanent soil improvement.
309. Importance of green-manures.—The plowing under
of some succulent rapid-growing crop, such as oats, rye, or
clover, tends to bring about three desirable soil conditions;
additional organic matter, a betterment of the physical con-
dition of the soil, and a rise in the nitrogen content of the
land, if the crop is an inoculated legume. If conditions are
*Penny, C. L., Clover Crops as Green Manures; Del. Agr. Exp. Sta.,
Bul. 60, 1903.
Storer, F. H., Agriculture, pp. 137-175; New York, 1910.
Lipman, J. G., Bacteria in Relation to Country Life, Chapter XXIV,
pp. 237-263; New York, 1911.
Piper, C. V., Leguminous Crops for Green Manuring; U.S. Dept. Agr.,
Farmers’ Bul. 278, 1907.
Spillman, W. J., Renovation of Worn-out Soils; U. S. Dept. Agr.,
Farmers’ Bul. 245, 1906.
Pieters, A. J., Green Manuring: A Review of the American Experi-
ment Station Literature; Jour. Amer. Soc. Agron., Vol. 9, No. 2, pp.
62-82, Feb. 1917; Vol. 9, No. 3, pp. 109-126, Mar. 1917; Vol. 9, No. 4
pp. 162-190, Apr. 1917.
I
537
938 NATURE AND PROPERTIES OF SOILS
favorable, an increase in crop production should result.
Where there is a shortage of farm manure, the practice be-
comes of special importance since roots and crop residues are
usually insufficient to maintain the organic content of the
soll. Even where manure is available, a green-manuring
erop now and then in the rotation does much towards sus-
taining normal production.
The effects of turning under green plants are both direct
and indirect—direct as to the influence on the succeeding crop,
and indirect as to the soil so treated. In the first place, cer-
tain ingredients are actually added to the soil by such a
procedure. The carbon, oxygen, and hydrogen of plants come
largely from the air and water, and the plowing-under of a
crop, therefore, increases the store of such constituents in the
soil. The compounds that result from crop decay increase
the absorptive power of the soil, and promote aération, drain-
age, and granulation—conditions that are extremely impor-
tant in successful plant growth. If the crop turned under is
a legume and the nodule organisms are active, the store of soil
nitrogen is markedly augmented, a point of extreme impor-
tance in fertilizer practice.
Green-manures may function also as cover-crops, insofar as
they take up the extremely soluble plant nutrients and pre-
vent them from being lost in the drainage water. The nitrates
of the soil are of particular importance in this regard as they
are very soluble and are absorbed only shghtly by the soil
complexes. Besides this, green-manures, especially those with
long roots, tend to carry nutrients upward from the subsoil
and when the crop is turned under this material is deposited
within the root zone. Again, the added organic material acts
as a food for soil organisms, and tends to stimulate biological
changes to a marked degree. This biological action is espe-
cially important in the production of carbon dioxide, am-
monia, nitrates, and organic compounds of various kinds,
which are necessary in plant nutrition.
GREEN-MANURES 539
310. Gain of constituents by green-manuring.—In an
average crop of green-manure, from five to ten tons of mate-
rial are turned under. Of this, from one to two tons are dry
matter, and from four to eight tons water. Of this dry matter,
a great proportion is carbon, hydrogen, and oxygen. It might
seem at first thought that such an addition is pure gain as
far as carbon and carbonaceous matter are concerned. Such
is not the case. Large amounts of carbon are lost continu-
ously in drainage, to say nothing of that removed by crops or
that which is respired by the soil as carbon dioxide. It has
already been shown, from results obtained with the Cornell
lysimeters, that a heavy soil will yearly lose over 250 pounds
of carbon, in drainage alone (see par. 220). This is approxi-
mately equivalent to a 2-ton application of green-manure.
Although the loss of carbonaceous material is considerable,
even during the period that the green-manuring crop is being
grown, nevertheless the practice offers a rapid as well as a
natural means of increasing the soil organic matter.
The mineral parts of the turned-under crop came from the
soil originally and they are merely turned back to it again
and represent no gain. As they return, however, they are in
intimate union with organic materials, and are thus readily
available as the decay processes go on. Indeed they are prob-
ably more readily available than they previously were, when
the green-manuring crop acquired them.
The amount of nitrogen added to a soil if the green-manure
is a legume‘ is an uncertain quantity. Much depends on the
virulence of the organisms occupying the nodules. These bac-
*Smith, C. D., and Robinson, F. W., Influence of Nodules on the Roots
upon the Composition of Soybean and Cowpea; Mich. Agr. Exp. Sta.,
Bul. 224, 1905.
Hopkins, C. G., Alfalfa on Illinois Soil; Il. Agr. Exp. Sta., Bul. 76,
1902.
Hopkins, C. G., Nitrogen Bacteria and Legumes; Tl. Agr. Exp. Sta.,
Bul. 94, 1904.
Shutt, F. T., The Nitrogen Enrichment of Soils through the Growth
of Legumes; Canadian Dept. Agr., Rept. Centr. Exp. Farms, 1905, pp.
127-132.
540 NATURE AND PROPERTIES OF SOILS
teria are in turn much influenced by plant and soil conditions,
such as amount of organic matter, presence of nitrates, acidity
and the like. Hopkins' estimates that about one-third of the
nitrogen in a normal innoculated legume comes from the soil
and two-thirds from the air. He also considers that one-third
of the nitrogen exists in the roots.
Both of these assumptions are questionable and at best
tentative. The amount of nitrogen fixed by legume organisms
is extremely variable, probably more so than that assimilated
by the azotobacter and allied groups. Again the percentage
of the nitrogen held in the roots of legumes is by no means
the same for all species. The amount varies within the species
with age, degree of maturity and, season. The Delaware in-
vestigations ° show that the proportion of the total nitrogen
of the plant occurring in the roots may be as low as 6 per cent.
in case of cowpeas and as high in the roots of alfalfa as 42
per cent. A range from 6 to 28 per cent. of the total nitrogen
of crimson clover was noted in the roots under different condi-
tions.
According to Hopkins, the nitrogen found in the tops of
legumes will be a rough measure of the nitrogen fixed by the
nodule organisms. When the crop is turned under, this will
represent the gain to the soil. If the preceding assumption
is correct, red clover turned under would actually add about
50 pounds of nitrogen for every ton of air-dry substance util-
ized, alfalfa about 50, cowpeas 48, and soybeans 53 pounds.
These figures, even though they may be far from correct, at
least give some idea of the possible addition of nitrogen by
green-manuring practices, and show how the soil may be en-
riched by such management. As in the case of farm manures,
the indirect effects of such a procedure on the physical and
bacteriological properties of the soil may over-ride the direct
1 Hopkins, C. G., Soil Fertility and Permanent Agriculture, p. 223;
Boston, 1910.
?Penny, C. L., The Growth of Crimson Clover; Del. Agr. Exp. Sta.,
Bul. 67, 1905.
GREEN-MANURES 541
influences, lessening the advantage that lezumes as green-
manures are supposed to have over non-legumes, due to their
ability to use atmospheric nitrogen.
311. Green-manures as cover-crops.—When green-ma-
nures are seeded in the late summer or early fall, they func-
tion as cover-crops and may have rather important influences
aside from their effects when turned under. Their greatest
influence seems to be on the nitrate content of the soil. Nitri-
fication is usually checked, a disappearance of nitrates gen-
erally following. This reduction in the amount of nitrates
probably occurs because of a retardation of nitrification ac-
companied by a stimulation of biological utilization of the
nitrates. Such an effect is important in conserving the soil
nitrogen and is of particular value in orchards,” as it hastens
the maturity of the new growth. At Cornell University,
green-manures were seeded in July and plowed under in the
following spring. Nitrate determinations were made on the
soil in July and in October. The figures are five-year aver-
ages. (See Table CXXITI, page 542.)
312. The decay of green-manure.—When a green-crop
is turned under, the process of its decay is the same as that
of any plant tissue that becomes a part of the soil body. The
organisms that are active are those common to the soil, to-
evether with such bacteria as are carried into the soil on the
turned-under crop. The decomposition that results is prob-
ably both aérobiec and anaérobic in nature, carbon dioxide be-
ing given off continuously. When proper decay has occurred,
end products should result which can be utilized as nutrients.
*Wright, R. C., The Influence of Certain Organic Materials upon the
Transformation of Soil Nitrogen; Amer. Soe. Agron., Vol. 7, pp. 193-
208, 1915.
Martin, T. L., The Decomposition of Green Manures at Different Stages
of Growth; Thesis for degree of Doctor of Philosophy, Cornell University,
1919.
*Lyon, T. L., The Formation of Nitrates in Soil Under Grass;
Proce. West. N. Y. Hort. Soc., pp. 82-87, Jan., 1915.
Lyon, T. L., Relation of Certain Cover Crops to the Formation of
Nitrates in Soil; Proce West. N. Y. Hort. Soc., pp. 32-34, Jan., 1917.
4
i)
NATURE AND PROPERTIES OF SOILS
On
TABLE CX XIII
EFFECT OF VARIOUS CROPS ON THE NITRATE NITROGEN OF THE
SOIL DURING OCTOBER, 1916-1920."
PERCENTAGE RE-
DUCTION OF
NITRATES IN
OcTOBER COMPARED
NITRATES IN THE
Sor. IN OCTOBER.
1
GREEN-MANURING CROP fecay IDM AS
100
WITH JULY
Uys h e S ss rece ERE Te 100 37
Oatsins coo aces oe 73 44
Wretelia tcc. hariee: teen es 73 57
PCa ated acter aes ies 83 10
Raye ang. Vetch are eeger. 74 58
Rivevatid ease. « ooh teers ee: 75 58
Oye tein ence tet RRO yg hae 6 0
The intermediate compounds that are formed should yield
an organic matter carrying a black pigment, should readily
split up into simple compounds, and should be in general
beneficial, both directly and indirectly, to plant growth.
Plenty of moisture is essential when green-manures are de-
caying, not only to hasten the transformation itself but that
the normal soil processes may not be interrupted by a lack
of water. The caution with which green-manures must be
utilized in semi-arid regions arises because of the drying influ-
ences of rapid decay and the danger of filling the soil with
undecomposed plant residues. Even in humid regions, green-
manures may be detrimental if dry weather sets in before a
major portion of the decay processes is completed.
As plant tissue decays in the soil, there seem to be two
general groups of forces at work which produce three distinct
stages of organic destruction.? In the first stage, humus pro-
*Unpublished data. Dept. Soils. Cornell University.
* Martin, T. L., The Decomposition of Green-Manures at Different
Stages of Growth; Thesis for degree of Doctor of Philosophy, Cornell
University, 1919.
GREEN-MANURES 543
duction is dominant and the amount of the humous materials
increases. In the second stage, humus production and humus
destruction are more or less balanced, while in the third stage
humus destruction is in the ascendant. The amount of humus
is on the decrease in the latter stage. The length of these
stages will vary with the season, with soil conditions,! and
with the character of the crop turned under. Obviously, the
influence of decomposing green-manure on the chemical and
biological activities of the soil will vary as the decay cycle
progresses. In general, over one-half of the organic matter
of the average green-manure disappears during the first nine
months after application.
313. Influence of decaying green-manure.—In the first
stage of decay, which should be a rapid one, many complex
compounds are generated along with carbon dioxide and other
simple products. The complex materials, which result partly
from protein decomposition and partly from the breaking
down of easily attacked carbohydrates, may be harmful to
ordinary crops. Germinating seeds and young plants are
especially susceptible, and detrimental influences are some-
times noticed immediately after the turning under of a green-
manure. Fred? found that the germination of oily seeds,
such as cotton and soybean, was much reduced. Starchy
seeds, such as maize, oats, and wheat, were little affected. The
germination of flax, hemp, mustard, and clover was some-
what reduced. An actual contact of the seed with the de-
caying material was usually necessary for serious damage.
The detrimental influence always occurred during the first
two or three weeks after the green-crop was turned under.
Obviously the more succulent the crop, the shorter will this
period be.
+ Russell, E. J.. and Appleyard, A., The Influence of Soil Conditions
on the Decomposition of Organic Matter in the Soil; Jour. Agr. Sci.,
Vol. VIII, Part 3, pp. 385-417, 1917.
? Fred, E. B., Relation of Green Manure to the Failure of Certain
Seedlings; Jour. Agr. Res., Vol. V, No. 25, pp. 1161-1176, Mar., 1916.
544 NATURE AND PROPERTIES OF SOILS
Not only do the products of the first stage of decay influ-
ence the crop growing on the soil, but they affect the biological
activities as well.t Nitrification in particular seems to be in-
fluenced, as nitrates do not begin to appear until the process
of humification is well advanced. Nitrification, however, is
probably not entirely suppressed as it is possible for soil or-
ganisms to use up the nitrates as rapidly as they are formed.
Zz
w ro)
5% wtf
vr Fel
a [man
n= Ee
> Zz
=n VU
wy <
Le
J
TIME AFTER APPLICATION
Fic. 64.—Diagram illustrating the three stages in the decay of a
green-manure. I, humus production dominant; II, a balance be-
tween humus production and destruction; III, humus destruction
dominant. A depression in nitrate accumulation generally occurs
in stage I followed by an increase. (After Martin.)
As the humus destruction gradually dominates over humus
production, the end products of the decay become prominent.
The complex proteid decomposition is practically completed
and cellulose destruction is slowly progressing. Of the sim-
ple nutritive products, the nitrates are of particular impor-
tance. In fact, they have been chosen by a number of in-
1 Briscoe, C. F., and Harned, H. H., Bacterial Effects of Green
Manures; Miss. Agr. Exp. Sta., Bul. 168, Jan. 1915.
Hutchinson, H. B., The Influence of Plant Residues on Nitrification
and on Losses of Nitrates in Soil; Jour. Agr. Sci. Vol. IX, Part 1,
pp. 92-111, Aug. 1918.
GREEN-MANURES 545
vestigators+ as a measure of humification, since a favorable
environment for nitrification probably does not occur until
the more rapid decomposition processes are completed. In
general, the more rapid the decay of the green-manure, the
sooner will nitrification be active again.
Besides affecting the bacterial activity of the soil, the de-
ecaying green-crop influences the solubility of the soil min-
erals. Jensen* found that the addition of 3 per cent. of
ereen-manure raised the solubility of lime and phosphoric
acid 30 to 100 per cent. This was over and above the mineral
constituents which came directly from the decomposing green-
crop. Magnesium and iron were also markedly influenced.
314. Crops suitable for green-manures.—An ideal green-
manuring crop should possess three characteristics: rapid
growth, abundant and succulent tops, and the ability to grow
well on poor soils. The more rapid the growth, the greater
the chance of economically using such a crop as a means of
soil improvement. The higher the moisture content of the
crop, the more rapid the decay and the more quickly are bene-
fits obtained. As the need of organic matter is especially
urgent on poor land, a hardy crop has great advantages.
The crops that may be utilized as green-manures are usually
* Hutchinson, C. M., and Milligan, S8., Green-Manuring Experiments,
1912 and 1913. India Agr. Res. Inst. Bul. 40, Pusa, India, 1914.
Maynard, L. A., The Decomposition of Sweet Clover as a Green-
Manure under Greenhouse Conditions; Cornell Agr. Exp. Sta., Bul. No.
394, 1917.
Martin, T. L., The Decomposition of Green-Manures at Different
Stages of Growth; Thesis for degree of Doctor of Philosophy, Cornell
University, 1919.
? Jensen, C. A., Effect of Decomposing Organic Matter on the Solu-
bility of Certain Inorganic Constituents of the Soil; Jour. Agr. Res.,
Vol. IX, No. 8, pp. 253-268, May 1917.
See also, Snyder, H., Humus as a Factor in Soil Fertility; Minn. Agr.
Exp. Sta., Bul. 41, 1895; and Production of Humus from Manures;
Minn. Agr. Exp. Sta., Bul. 53, 1897.
Hopkins, C. G., and Aumer, J. P., Potassium from the Soil; Tl. Agr.
Exp. Sta., Bul. 182, 1915.
Hopkins, C. G., and Whiting, A. L., Soil Bacteriology and Phosphates ;
Ill. Agr. Exp. Sta., Bul. 190, 1916.
546 NATURE AND PROPERTIES OF SOILS
grouped under two heads, legumes and non-legumes. Some
of the common green-manures are as follows:
LEGUMES NON-LEGUMES
Annual Biennial
Cowpea ‘Red clover Rye
Soybean White clover Oats
Peanut Alsike clover Mustard
Vetch Alfalfa Mangels
Canada field pea Sweet clover Rape
Velvet bean Buckwheat
Crimson clover
Hairy vetch
When other conditions are equal, it is of course always bet-
ter to choose a leguminous green-manure in preference to a
non-leguminous one, because of the nitrogen that may be
added to the soil. However, it is so often difficult to obtain
a catch of some of the legumes that it is poor management to
turn the stand under until after a number of years. Again,
the seed of many legumes is very expensive, almost prohibit-
ing their use as green-manures. Among the legumes most
commonly grown as green-manures, cowpeas, soybeans, and
peanuts may be named. Many of the other legumes do not so
fit into the common rotations as to be turned under conven-
iently as a green-manure.
For the reasons already cited, the non-legumes have, in
many eases, proved the more popular and economic as green-
manures. Rye and oats are much used because of their rapid,
abundant, and succulent growth and because they may be
accommodated to almost any rotation. They are hardy and
will start in almost any kind of a seed-bed. They are thus
extremely valuable on poor soils. Often the value of such a
ereen-manure as oats is greatly increased by sowing peas with
it. The advantages of a legume and a non-legume are thus
combined.
It has already been shown that the nitrate production in a
GREEN-MANURES 547
soil may be used as a rough measure of the rate of decay of
ereen-manures. Admitting such a criterion, certain data from
Cornell University become particularly interesting. In a
five-year continuous test, green-manuring crops were seeded
in July and plowed under in the early part of the succeeding
May. The nitrate content of the soil was determined at a
number of times during the spring, summer, and fall. A de-
crease in nitrates always occurred in the autumn, while an
increase began soon after the crops were turned under in the
spring. In the following table the rye crop is taken as 100 in
both October and July:
TABLE CX XIV
RELATIVE INFLUENCE OF GREEN-MANURES ON THE
ACCUMULATION OF SOIL NITRATES.!
NITRATES IN JULY, NITRATES IN OcT.,
Som FALLOow SINCE) Soin UNDER Crop
GREEN-MANURE May 1. SINCE JULY.
RYE TAKEN AS 100)/RYE TAKEN As 100
Ryd, ek ee nee 100 100
(CANS 5 se aera at, ee ae 78 73
TEE GL ages ee A 120 13
LEE) a AO bea, ek a ee 99 83
nyerand Vetch fis. ola 136 74
ye sand peas... 4. ooo ak os 102 75
It is immediately apparent that the succulent rye and vetch
that survive the winter give better results, as far as nitrate
production is concerned, than the dry and dead oats and peas.
This shows clearly the value of succulence and the necessity
of turning under a crop partially matured.2, The advantage
of the legumes over the non-legumes is not hard to explain.
*Unpublished data. Dept. Soils, Cornell University.
7Martin, T. L., The Decomposition of Green Manures at Different
Stages of Growth; Thesis for the Degree of Doctor of Philosophy,
Cornell University, 1919.
548 NATURE AND PROPERTIES OF SOILS
The combination of rye and vetch, both of course in a sucev-
lent condition, seems especially efficacious. Sod as a green-
manure always appears more or less at a disadvantage.
315. The use of green-manures.—The indiscriminate
use of green-manures is of course never to be advised, as the
soil may be injured thereby and the normal rotation much
interfered with. When soils are poor in nitrogen and organic
matter, they are very often in poor tilth. This is true whether
the texture of the soil be fine or coarse. The turning-under
of green-crops must be judicious, however, in order that the
soil may not be clogged with undecayed matter. Once or twice
in a rotation is usually enough for such treatments. Proper
drainage must always be provided. In regions where the rain-
fall is seanty, great caution must be observed in the handling
of green-manures. The available moisture that should go to
the succeeding crop may be used in the process of decay, and
the soil left light and open, due to an excess of undecomposed
plant tissue. In western United States, it is still a question
whether green-manures have any advantage over summer
fallowing.
It is generally best to turn under green-crops when their
sueculence is near the maximum and yet at a time when
abundant tops have been produced. This occurs at about the
half mature stage. A large quantity of water is carried into
the soil when the crop is at this stage, and the draft on the
original soil-moisture is less. Again, the succulence encour-
ages a rapid and more or less complete decay, with the maxi-
mum production of humus and other products. The plowing
should be done, if possible, at a season when a plentiful supply
of rain occurs. The effectiveness of the manuring is thereby
much enhanced. At Cornell University various green-manures
were seeded in the summer and plowed under that fall or the
next spring. The experiment was continuous for three years,
the nitrates being determined in the soil each year in April
and in June. The results are as given on the next page.
GREEN-MANURES 549
TABLE CX XV
INFLUENCE OF THE TIME OF TURNING-UNDER OF GREEN-MANURES
ON THE NITRATE ACCUMULATION IN THE SOIL.+
PARTS PER MILLION oF NITRATES
Crop In Apris Just | In June, Som
BEFORE THE FALLOWED SINCE
SPRING PLOWING PLOWING
Rye, fall plowed.......... 58 57
Rye, spring plowed........ 53 67
Oats, fall plowed... ..4.2.. 0. 61 42
Oats, spring plowed....... 36 50
Vetch, fall plowed. f. 2.0.0.6. 719 45
Vetch, spring plowed...... 41 67
Average, fall plowed...... 66 48
Average, spring plowed.... 43 61
It is apparent that the decay of the green-manuring crop
is hastened by fall plowing, as the nitrates in every case are
higher in April on land so handled. In June, however, the
nitrate accumulation has passed its highest point in the fall-
plowed soil, leaving the spring-plowed plats, where the decay
was initiated later, in the ascendancy. The table also shows
the advantage that a legume has over a non-legume in causing
nitrate accumulation. Oats fall-plowed appear about on an
equality with rye. Spring plowing, since the oats are then
dry and dead, gives the rye a marked advantage. All of the
points above noted have a very practical field application.
In turning under green-manures, the furrow slice should
not be thrown over flat, since the green-crop is then deposited
as a continuous layer between the surface soil and the sub-
soil. Capillary movement is thus impeded until a more or
* Unpublished data. Dept. Soils, Cornell University.
590 NATURE AND PROPERTIES OF SOILS
less complete delay has occurred, and the succeeding crop
may suffer from lack of moisture. The furrow ordinarily
should be turned only partly over, and thrown against and
on its neighbor. The green-manure is then distributed evenly
from the surface downward to the bottom of the furrow.
When decomposition occurs, the resulting materials are evenly
mixed with the whole furrow slice. Moreover, this method of
plowing does not interfere with the capillary movements of
water, and in actual practice is a great aid in drainage and
aération.
316. Green-manure and lime.—The decay of organic
matter in the soil is always accompanied by the production of
organic acids of various kinds. The greater the succulence
of the material, the more rapid is the accumulation of such
products. In spite of this, however, the effect of a green-
manure is to decrease the acidity rather than increase * it and
later greatly to stimulate nitrification even if the soil origi-
nally was quite acid. The decrease in lime requirement may
be due to the liberation of mineral constituents from the de-
caying organic matter and to the effect of the decomposition
on the inorganic constituents of the soil.
The ultimate influence of green-manure on acidity is some-
what in doubt. The bulk of the evidence available seems to
indicate that decaying organic matter, if it has any effect, ulti-
mately tends to decrease rather than increase the lime re-
quirement of the soil.2 Nevertheless, plenty of active calcium
should be in the soil, since it promotes the decay of the plant
tissue added and seems to control to a certain extent the pres-
ence of toxic materials. Lime may be added to the green-
manure seeding and be turned under with that crop. The
* White, J. W., Soil Acidity as Influenced by Green Manures; Jour.
Agr. Res., Vol. XIII, No. 3, pp. 171-197, April, 1918.
* Hill, H. H., A Comparison of Methods for Determining Soil Acidity
and a Study of the Effects of Green Manures on Soil Acidity; Va.
Poly. Inst., Tech. Bul. 19, April 1919.
Ames, J. W., and Schollenberger, C. J., Liming and Lime Require-
ment of Soils; Ohio Agr, Exp. Sta., Bul. 306, pp. 381-383, Dee. 1916.
GREEN-MANURES 551
amendment would thus be in very close contact with the de-
caying vegetable tissue. Ordinarily, however, the application
of lime at some point in the rotation is sufficient.
Lime, besides its capacity to alleviate toxic residues, tends
to hasten organic decay.’ This is a very important function
as the first stage of decomposition, during which soil and plant
activities may under certain conditions be detrimentally af:
fected, is markedly shortened. Such a promotion is indicated
in a green-manuring experiment at Cornell University. The
ereen-manures were seeded in the fall under two treatments,
limed and unlimed. The parts per million of nitrates in the
soil are given for two dates on the year succeeding, the green-
manures having been plowed under either in the fall or early
spring. The data are averages of three years.
TABLE CX XVI
INFLUENCE OF LIME ON THE NITRATE ACCUMULATION IN A SOIL
RECEIVING VARIOUS GREEN-MANURES.”
Parts PER MILLION oF NITRATES
Crop AND TREATMENT
APRIL JUNE
yen NOM MMe ye sc. bes 6h: 66 53
Fever IMEC ate esc cweuhnatoss cvs, t 45 fal
Gatsnno) Mme sce kia ees 53 43
CALS ewIIMOG Sle). sy sara sicatse 45 50
Weteh no! messi. 5 S02: rah 52
Neteh slimmed iect. ok 43 63
Average, no lime........ oe 65 49
wverdge., MEM... ss. 5.5 ss 44 61
*Lemmermann, O., et al., Untersuchung iiber die zerzetzung der Kohlen-
stoff Verbindungen Verscheidener Organischen Substanzen im Boden
Spezielle unter dem einfluss der Kalk; Landw. Jahrb., Bd. 41, S. 216-
257, 1911.
? Unpublished data. Dept. Soils, Cornell University.
552 NATURE AND PROPERTIES OF SOILS
The effect of lime on nitrification is very noticeable in June.
In April the no-lime plats are higher in accumulated nitrates,
due to the lesser growth of the green-manuring crop.
317. Practical utilization of green-manures.—Green-
manures seem to have their greatest value where a permanent
instead of a rotation pasture is used, where a long cycle rota-
tion of grain is practiced, or where little or no manure is
available. The experimental data bearing on the use of green-
manures seems to indicate that such a practice is productive
of larger crop yields. The following data from Nappan, Nova
Scotia, is from one of the more reliable and conclusive experi-
ments. <A ecatch-crop of clover in the grain was turned under
for grain the following year. The figures are for 1905, the
third year of the test.
TABLE CXXVII
YIELD OF WHEAT, OATS AND BARLEY IN BUSHELS TO THE ACRE
ON THE NAPPAN FARM IN 1905 ON PLATS CROPPED
CONTINUOUSLY TO GRAIN.!
TREATMENT WHEAT OaTS BARLEY
No green-manure......... 34.3 41.2 One
Clover catch-crop......... | 40.0 59.3 37.9
The use of a green-manure is often determined by the char-
acter of the rotation. Very often it is somewhat of a problem
as to when, in an ordinary rotation, a green-manure may be
introduced so that it may fit in well with the crops. In a
rotation of maize or potatoes, oats, wheat, and two years of
hay, a green-manure might be introduced after the corn or
potatoes. This would not be a very good practice, however, as
a cultivated crop usually should follow a green-manure in
order to facilitate decomposition and decay. In such a rota-
tion, the plowing-under of the hay stubble is really a form
*Ottawa Exp. Farms Rept., 1905, p. 284.
GREEN-MANURES 593
of green-manuring, there being a considerable accumulation
of stubble and aftermath on the soil. When a rotation of
this kind is used, it is better either to supply organic matter
in other ways, or to alter or break the rotation in such a man-
ner as to admit of a more advantageous use of green-crops.
Where trucking crops are raised and no very definite rota-
tice is adhered to, green-manuring is easier. It is especially
facilitated when cover-crops are grown, as in orchards. Soil-
ing operations also favor the easy and profitable use of green-
manures. In general, it may be said that the organic matter
obtained from such a source should be supplemented by farm-
yard manures where possible. A better balanced and richer
soil organic matter is more likely to result,
CHAPTER XXVI
THE MAINTENANCE OF SOIL FERTILITY 1
THE maintenance of a profitable and continuous soil pro-
ductivity is an intricate problem, since many variable factors
are involved. Weather conditions, moisture relations, soil or-
ganic matter and tilth, plant diseases, soil reaction, and avail-
able nutrients are only a few of the influences that function
continuously throughout the growing season. No scheme of
soil management and crop production is perfect, even though
it is fairly profitable. Except in special cases, every system is
open to improvement and modification as soil and plant
knowledge increases.
The sources of knowledge regarding the profitable growing
of plants are numerous. Much data have arisen from expe-
rience and observation, much are empirical, while some are
confessedly conjectural. In spite of the large amount of
scientific information available regarding the soil and its
plant relationships, practical experience has contributed more
towards a profitable and continuous soil productivity. Soil
survey classification and mapping have contributed some-
thing. Field tests, both practical and technical, have added
to such information, while laboratory and greenhouse experi-
ments, although often arbitrary and artificial, are by no
means unimportant. These latter contributions, however,
always need practical confirmation under typical field con-
ditions over a period of years.
318. Loss of plant nutrients from the soii—A consid-
eration of the principles governing the rational management
* Fertility is here used in the sense of continuous productivity.
554
THE MAINTENANCE OF SOIL FERTILITY 555
of a soil is obviously impossible unless some knowledge is at
hand regarding the losses and additions which a soil sustains
in the course of a definite rotation. Fortunately, some fairly
reliable data have already been presented regarding the re-
moval of soil constituents under controlled conditions. The
Cornell lysimeter tanks, bearing a rotation of maize, oats,
wheat, and two years of hay, offer very satisfactory informa-
tion (paragraphs 95 and 163). The losses covering a ten-year
period are expressed in pounds to the acre a year. The soil is
a Dunkirk silty clay loam.
While such figures are probably open to considerable error
and obviously would not apply with any degree of accuracy
to a light soil, they indicate in a general way the magnitude
and order of the losses that may be expected from such a soil
under the conditions specified.
TABLE CXXVIII
LOSSES FROM A DUNKIRK SILTY CLAY LOAM SOIL EXPRESSED IN
POUNDS TO THE ACRE A YEAR OVER A TEN-YEAR PERIOD.
ROTATION: MAIZE, OATS, WHEAT AND TWO YEARS
HAY. CORNELL LYSIMETER TANKS.
SourcE or Loss N P.O; K,O CaO SO,
Drainage (par. 163).... 7.3 | trace | 68.7] 345.9 | 108.5
Cropping (par. 163)....| 70.5 | 43.5 | 105.4] 24.3) 41.0
Atmosphere (pars.
eeUrand 293) 25% 2.22 ids 2 | —— | ——} ——]} ——
TRO UOIA AAs eam Se 77.8 | 438.5 | 174.1] 370.2 | 149.5
|
The organic carbon in this soil over the ten-year period was
reduced at the rate of approximately 1 per cent. a year.” This
is equivalent to a reduction in organic matter of about 1200
*The largest loss of carbon is probably to the atmosphere as carbon
dioxide. The other avenue of loss is in the drainage water.
*Lipman and Blair report a reduction of organic carbon of .74 per
cent. a year over a period of ten years on Sassafrass loam in New
596 NATURE AND PROPERTIES OF SOILS
pounds each year to the acre-four feet. It is evident, there-
fore, that the losses sustained by the average soil fall most
heavily on the organic constituents, a condition often ignored
in practical soil management. The removal of calcium oxide is
also very large, being equivalent to a loss of 661 pounds of
calcium carbonate an acre a year. Although losses of sulfur
trioxide and phosphoric acid are smaller than that of the
potash, they are far more important, since there is very com-
monly one hundred times more potash in a soil than of the
other two constituents combined. The magnitude of the loss
of a soil constituent is never a safe measure of its importance.
The removal of nitrogen is equivalent to over 500 pounds of
commercial sodium nitrate and consequently is also a loss of no
small consideration.
319. Additions of nutrients to the soil—tThe figures
presented above are based on reliable experimental data. Un-
fortunately the information regarding the additions which
normally occur to a soil under any particular rotation are by
no means so exact. Certain assumptions and estimates, often
of questionable validity, must be: admitted in order that a
complete survey may be possible. Table CX XIX sets forth
the additions which the Dunkirk clay loam of the Cornell lysi-
meters may reasonably be expected to receive each year when
cropped to a five-year rotation of maize, oats, wheat, and two
years hay. The data are expressed in pounds to the acre a
year. (See Table CX XIX, page 557.)
The additions listed above are not the only avenues open
for important acquisitions. The crops removed may be fed to
animals and the manure returned to the land. Moreover, the
utilization of a green-manure is also possible. Below will be
found the additions that may reasonably be expected from the
Jersey. The rotation was maize, oats, wheat, and two years hay. No
lime was added.
Lipman, J. G., and Blair, A. W., The Lime Factor in Permanent
Soil Improvement. I. Rotations Without Legumes; Soil Sci., Vol.
IX, No. 2, p. 87, 1921.
THE MAINTENANCE OF SOIL FERTILITY 6557
TABLE CX XIX
ESTIMATED ADDITIONS THAT MIGHT OCCUR TO A SOIL UNDER A
ROTATION OF MAIZE, OATS, WHEAT, AND TWO YEARS HAY.
EXPRESSED IN POUNDS TO THE ACRE A YEAR.
Source oF ADDITION N EZOF Keo) CaO: SO;
Rain-water (pars. 236 and 264) | 12.5; ——| ——| ——| 65.0
Free fixation by soil organisms
Ia ON) te Ne a wae kien als a 5 25.0} ——-| ——-}| ——-| —
Crop-roots and residues?....... —| —] —| —] —
LTTE tice ca eR ese 37.5| ——| —J|— | 65.0
use of farm manure and a green-manure on the soil in question.
The green-manure is leguminous and is applied once during
the five-year rotation.
TABLE CX XX
FURTHER ADDITIONS THAT MIGHT BE MADE TO THE FIVE-YEAR
ROTATION ON DUNKIRK SILTY CLAY LOAM, EXPRESSED IN
POUNDS TO THE ACRE A YEAR.
Appirtons wn | p,o,| K,0| cao! so, Gere
Farm manure?........| 21.1| 21.7] 31.6| 7.3] 12.4| 1000
Leguminous green-
TLTE TA 7 ot eee a 2080) 5 ——— | 600
{SID la er ee 41.1 | 21.7) 31.6) 7.3/12.4| 1600
‘Important because of the additions of organic matter that occurs
thereby.
* It is estimated that of the crops removed and fed or used as bedding,
only 30 per cent. of the N, K,0, CaO and SO,, 50 per cent. of the P,O,;
and 25 per cent. of the organic matter reach the soil as farm manure (par.
294). The crops removed carried about 4000 pounds of organic matter
to the acre.
°*The green-manure is estimated as 4000 pounds of air-dry matter
carrying 100 pounds of nitrogen, which is considered as fixed from the
air, This should yield 3000 pounds of soil organic matter.
508 NATURE AND PROPERTIES OF SOILS
320. The balance sheet.—For convenience of compari-
son, the data previously presented are drawn together in a
single table and presented below as pounds to the acre an-
nually. These figures are considered as relating to the Dun-
kirk silty clay loam carrying a five-year rotation of maize,
oats, wheat, and two years hay. It must always be remem-
bered that such data are specifically applicable to only one
soil. Nevertheless the practical deductions that may be drawn
are of wider scope.
TABLE CXXXI
SUMMARY TABLE OF LOSSES AND ADDITIONS THAT MIGHT OCCUR
TO DUNKIRK SILTY CLAY LOAM UNDER A FIVE-YEAR ROTA-
TION. EXPRESSED IN POUNDS TO AN ACRE A YEAR.
CoNDITIONS N P,O;| K,O CaO | SO, ee
Reductions when farm
manure and green ma-
nure are not used?....| 40.3 | 438.5 | 174.1 | 370.2 | 84.5 1200
Additions from farm ma-
TUT Oy La eietteteree eee Pall || Palaty 31.6 Wo | W2e4 1000
Additions from farm ma-
nure and green-manure| 41.1 | 21.7 31.6 (eas) |) Wee: 1600
Additions using green-
MAMUTC! 2 tyne che senor 20.0 — — — — 600
It is immediately apparent that when farm manure and
green-crops are not utilized, a notable decrease occurs in every
constituent cited. Such a system of soil management must
reduce the productivity of the soil very quickly and
certainly is not a rational scheme of soil and crop adjustment.
Nevertheless, it is the condition under which much of the
arable land is producing crops today.
When farm manure is utilized, even allowing for a large
*Obtained by subtracting the natural additions from the rormal
losses.
THE MAINTENANCE OF SOIL FERTILITY 539
waste in its production and handling, the organic matter is
almost maintained and the loss of nitrogen is met to some ex-
tent. Under such a system, the addition of nitrogen and of
mineral constituents is a problem, although some attention
should be paid to the soil organic matter. Liming will be
necessary ultimately if not immediately, while the addition
of phosphoric acid obviously will some day be profitable.
If acid phosphate is utilized at a normal rate, the sulfur
losses that occur should be very nearly counterbalanced.
Potash, especially as the soil under consideration is a clay
loam, will no doubt be available for a long period if the
organic matter is adequately maintained.
The use of a green-manure once in the rotation in addition
to the farm manure will adequately care for the soil or-
ganic matter and reduce the nitrogen problem to a minor
position.
When animal products are relatively high in price and
crop values are low, stock farming will be advisable and a sys-
tem whereby considerable farm manure will be available may
be followed. It has already been indicated that under such
conditions the organic matter, and to a lesser degree the nitro-
gen content of the soil, may adequately be maintained espe-
cially if a green-manure is used once in the rotation. Where
grain farming is necessary, reliance must be placed almost
wholly on green-manures for the upkeep of the soil organic
matter, especial care being given to the full utilization of crop
residues. According to the data presented in Table CX XXI,
such a system, as far as the nitrogen and organic matter are
concerned, could be made about as satisfactory as where farm
manure is available and has the possibility and advantage of
considerable expansion. Grain farming makes necessary,
however, a more intensive and careful use of mineral constitu-
ents. Liming and commercial fertilizers will, therefore, fig-
ure somewhat more prominently in grain-growing than where
dairying or stock-raising are practiced.
560 NATURE AND PROPERTIES OF SOILS
321. The maintenance of soil fertility—The practical
management of a soil, whereby profitable crops may be grown
without materially reducing the fertility of the land rests
on five fundamental principles. The basic factors are: (1)
drainage, (2) tillage, (3) organic matter, (4) lime, and (5)
fertilizers. Obviously, the removal of excess water depends
on adequate drainage, while aération and all of the activities
that attend it rests both on drainage and tillage. The upkeep
of the soil organic matter by the use of crop roots and resi-
dues, by farm manure, and by the turning under of green-
crops has already been emphasized as fundamental to con-
tinuous productivity.
These factors are by no means the whole program of ra-
tional soil management. Artificial additions must be made.
Of these lime is of vital importance. Calcium and magnesium
are lost from the soil in such large amounts that outside
sources must be drawn on. Every arable soil will ultimately
come to the point where liming will be profitable. Finally, the
judicious use of commercial fertilizers must receive attention.
The addition of phosphoric acid will probably be the first
fertilizer element to be considered seriously, especially in gen-
eral farming. Under special conditions of soil and crop, nitro-
gen and potash will also be a part of the program. The adap-
tation of crops in suitable rotation to climate and soil, with
adequate attention to the factors emphasized above, are the
prime essentials of a paying system of permanent soil pro-
ductivity.
1 Hartwell, B. L., and Damon, S. C., Six Years’ Experience in Im-
proving a Light Unproductive Soil; Jour. Amer. Soc. Agron., Vol. 13,
No. 1, pp. 37-41, 1921.
Lipman, J. G., and Blair, A. W., The Lime Factor in Permanent
Soil Improvement. I. Rotations without Legumes. II. Rotations with
Legumes; Soil Sci., Vol. LX, No. 2, pp. 83-114, 1921.
INDEX OF AUTHORS
Aarnio, B., 134.
Abbott, J. B., 347.
Aberson, J. H., 252.
Agee, A., 362.
Ageton, C. U., 376.
Aikman, C. M., 504.
Allen, E. R., 424.
Allison, F. E., 387.
Alway, F. J., 43, 44, 68, 115, 118, 119,
120, 155, 168, 166, 195, 198,
199, 221.
Ames, J. W., 58, 406, 470, 499, 550.
Ammon, Georg, 156.
Appiani, G., 73.
Appleyard, A., 158, 248, 252, 253, 257,
273, 543.
Ashby, S. F., 424.
Ashley, H. E., 132, 184, 137.
Atterburg, A., 68, 140, 141, 187.
Averitt, S. D., 118.
Aumer, J. P., 545.
Bancroft, W. D., 127, 129.
Barker) PB 22.
Barlow, J. vl, oo.
Barrett Company, The, 449.
Baumann, A., 106.
Beattie, J. H., 351, 520, 521.
Beaumont, A. B., 134, 157.
Beavers, J. C., 499.
Bennett, H. H., 38, 50, 63, 118.
Bernard, A., 467.
Bertholot, M., 431.
Bertrand, G., 466.
Bishop, E. S., 120.
Bizzell, J. A., 179, 207, 251, 252, 284,
422, 436, 437.
Blair, A. W., 307, 354, 356, 381, 556,
560. j
Blanck, E., 478.
Bogue, R. H., 267.
Boliey, H. L., 397.
Boltz, G. E., 406, 470.
Boullanger, E., 466, 467.
Bouyoucos, G. J.,
NEON Ava Wit,
228, 232, 235,
280, 281, 286, 287, 291, 356.
Bradley, C. E., 380.
Breazeale, J. F., 113, 331, 381.
Brenchley, W. E., 284, 287.
Briggs, L. J.,
172, 188,
277, 278, 380.
Bright, J. W., 505.
Briscoe, C. F., 544.
Brodie, D. A., 499.
Bronet, G., 267.
Brooks, W. P., 461, 522.
Broughton, L. B., 377.
Brown, B. E., 111, 422.
Brown, C. F., 211, 340.
182, 196,
Brown, P. E., 44, 362, 388, 392, 405,
406, 421, 424.
Bryan, H., 71.
Buckingham, E., 182, 260.
Buckman, H. O., 29.
Buddin, W., 414.
Bunger, H., 186.
Burd, J. S., 280, 322, 325.
Burdick, R. T., 499.
Burr, W. W., 194, 221.
Burton, E. F., 127, 129.
Caldwell, J. S., 195.
Call, L. E., 220, 221.
Cameron, F. K., 118, 141, 283.
Carr eho nonnl aoe
Carrero, P. L., 299.
Carter, E. G., 392, 398, 421, 464.
Cates, J. S., 221.
Chamberlain, T. C., 57.
Chase, L. W., 144.
Christensen, H. R., 354.
Clarke, F. W., 4, 13.
Clarke, V. L., 155, 198.
561
153, 154, 155, 159,
223,
239, 259, 277,
67, 113, 156, 168, 171,
190, 195, 196, 197,
562
Coffman, W. B., 190.
Coleman, D. A., 387, 388.
Coleman, L. C., 420.
Collins, 8S. H., 442.
Comber, N. M., 360.
Conn, H. J., 388, 389, 505.
Conn, H. W., 384.
Conner, S. D., 295, 328, 347, 349, 351,
457, 461.
Cook, R. C., 273.
Coppenrath, E., 466.
@ox, He Re 2215
Cowles, A. H., 380.
Crosby, W. A., 36.
Crowther, C., 429, 469.
Cullen, J. A., 464.
Cummins, A. B., 267.
Curry, B. E., 267, 380.
Curtis, R. E., 389.
Cushman, A. S., 73, 132.
Czermak, W., 1438, 296.
Damon, S. C., 381, 476, 560.
Darbishire, F. V., 414.
Davidson, G., 109.
Davidson, J. B., 144.
Davis, A. R., 4382.
Davis, N. B., 137.
Davis, Ra O. He, Lil 204;
Davis, W. M., 46.
Davy, J. B., 340.
Demolon, A., 267, 467.
Digby, Kenelm, 442.
Diller, J. S., 33.
Dobeneck, A. F., 156.
Dorrance, R. L., 430.
Dorsey, C. W., 330, 334, 337, 340.
Doryland, C. J. T., 249.
Duchacek, F., 460.
Dugardin, M., 467.
Duggar, B. M., 432.
Duley, F. L., 499.
Dupré, H. A., 169.
Dyer, Bernard, 318.
Eastman, KE. E., 204.
Ehrenberg, P., 134, 143.
Ellett, W. B., 362.
Elliott, C. G., 210, 213.
Emerson, H. L., 17, 40, 46.
Ernest, A., 110, 252.
INDEX OF AUTHORS
Hailyer) Gay H.) wisezoss 2eonnozle
Faure, L., 210.
Feilitzen, H. von, 429, 467.
Fellers, C. R., 387.
Fippins Bev O}, 122;
519.
Fisher, M. L., 204.
Fleischer, M., 44.
Fletcher, C. C., 71.
Floess, R., 134.
Floyd, B. F., 363.
Flugel, M., 478.
Fraps, G. S., 208, 319, 420, 443, 471.
Frear, W., 362, 376, 377, 516, 524.
Freckmann, W., 186.
Fred, E. B., 505, 543.
Fry, W. H., 6, 76, 133, 445, 455.
Fulmer, H. L., 505.
Funchess, M. J., 347.
143, 211, 499, 516,
Gaither, E. W., 58, 499.
Gainey, P. L., 249, 356, 392, 420, 424.
Gallagher, F. E., 141, 1438, 273.
Gans, R., 265.
Gedroiz, K. K., 459.
Gee; ES C@:, 211.
Georgeson, C. C., 239.
Gerlach, U., 272, 306.
Gilbert, J. H., 180, 448.
Gile, P. L., 299, 376, 466.
Gillespie, L. J., 281, 350, 356.
Glass, J. S., 204.
Goessman, C. A., 504.
Gortner, R. A., 116.
Grandeau, L., 115.
Greaves, J. E., 392, 393, 420, 421, 422,
432, 433.
Gustafson, A. F., 124, 220, 242.
Guthrie, F. B., 336.
Haberlandt, H., 140, 224.
Hall, A. D., 10, 68, 78, 206, 217,
287, 294, 305, 421, 433)
448, 449, 471, 508, 516,
531, 532:
Halligan, J. E., 442, 471.
Harned, H. H., 544.
Harris, F. S., 328, 334, 836, 340.
Hart, E. B., 303, 315, 468, 499,
O2is
Hart, Re Ane 2e e340.
Harter, L. L., 337.
284,
442,
519,
514,
INDEX OF AUTHORS 56:
Hartwell, B. L., 347, 349, 354, 381, 461,
476, 560.
Hasenbaiumer, J., 466.
Headden, W. P., 330, 332.
Heinrich, R., 197.
Hellriegel, H., 189, 191, 192.
Helms, R., 336.
Hendrick, J., 78.
Hibbard, P. L., 342.
Hildebrandt, F. M., 267.
Hilgard, E. W., 31, 68, 73, 116, 120,
155, 162, 330, 340.
Hill, H. H., 550.
Hills, J. L., 483.
Hiltner, L., 389.
Hirst, C. T., 464.
Hitchcock, E. B., 421.
Hoagland, D. R., 279, 280, 281, 284,
285, 323, 350.
Hoffman, C., 461.
Hopkins, C. G., 122, 355, 362, 437, 466,
516, 533, 539, 540, 545.
Houston, H. A., 116.
Howard, L. P., 358, 354.
Hubbard, P., 73.
Hudelson, R. R., 362.
Hudig, J., 429.
Humphreys, W. J., 53.
Bunt, es 4725533:
Hurst, L. A., 350, 356.
Hutchinson, C. M., 545.
Hutchinson, H. B., 108, 355, 387, 402,
411, 414, 415, 424, 447, 450,
544,
Ingle, Herbert, 100.
Isham, R. M., 332.
Israelsen, O. W., 92, 93, 163.
Jaffrey, J. A., 211.
Jensen, C. A., 545.
Jodidi, S. L., 106, 248.
Joffe, J. S., 351, 356.
Johnson, H. W., 405.
Johnson, 8S. W., 249.
Jones, C. H., 355, 483.
Jones, S. C., 499.
Juritz, C. F., 430.
Karraker, P. E., 163, 171, 358.
Kaserer, H., 416.
Kearney, T. H., 337.
Keen, B. A., 151.
Kellerman, K. F., 424.
Kellner, O., 450.
Kellogg, E. H., 405.
Kellogg, J. W., 365, 379.
Kelley, N. P., 107, 267, 347, 415, 421,
450.
Kelly, M. P., 466.
Kiesselbach, T. A., 188.
King; He Hy (94, 145, 16ssn72) 176:
189, 210, 230, 241, 242, 282,
284, 422.
Kinnison, C. S., 140.
Klippart, J. H., 210.
Knox, J., 450.
Knox, W. H., 355.
Knudson, L., 402.
Koch, G. P., 388.
Konig, J., 466.
Kopecky, J., 179.
Kopeloff, N., 377, 387, 388, 413.
Koppers Company, The, 449.
Kratzman, E., 347.
Krusekopf, H. H., 362.
Krzymowski, R., 187.
Lang, C., 228, 232.
Lapham, M. H., 171.
Lathrop, E. C., 107, 410.
Latshaw, W. L., 437.
Lau, E., 248.
Lawes, J. B., 180, 189, 443.
Leather, J. W., 190.
Leidigh, A. H., 211.
Lemmermann, 0O., 551.
Liebig, J. Justus von, 443.
Lipman, C. B., 32, 158, 278, 376.
Lipman, J. G., 307, 342, 381, 384, 403,
406, 431, 433, 436, 508, 537,
556, 560.
Loew, O., 376, 415.
Lohnis, F., 433.
Loughridge, R. H.,
337.
Lugner, I., 429.
Lyon; UT.) i, 279, 18i5 207s 251s 252)
284, 297, 422, 436, 437, 495,
541, 542.
Lynde, ©. J., 169.
Lynde, H. M., 211.
78, 122, 156, 198,
564
MacIntire, W. H., 181, 250, 345, 370,
371,422.
MacLennan, K., 355.
Martin, J. C., 280, 285.
Martin, L. M., 46.
Martin, T. L., 541, 545, 547.
Martin, W. H., 351.
Marchal, E., 335, 413.
Marshall, C. E., 384.
Massey, A. B., 109.
May, D. W., 466.
Mayer, A., 200.
Maynard, L. A., 545.
Mazé, P., 402, 478.
McBeth, I. G., 267, 389.
McBride, F. W., 116.
McCall, A. G., 267, 278.
McCaughey, W. G., 5, 36, 76.
McCool, M. M., 362.
McDole, G. R., 118, 166.
McGeorge, W. T., 78, 79, 273.
McLane, J. W., 168, 277.
McLean, H. C., 388.
MeMillar, P. R., 380.
Merrill; (G. B:, 3; 1725232; 36, 138; 265.
Middleton, H. E., 133.
Miles, M., 210.
Millar, C. E., 362.
Miller, B. L., 448.
Miller, E. C., 190, 194.
Miller, M. F., 362.
Miller, N. H. J., 10, 108, 402, 411, 415,
447, 450, 469.
Milligan, S., 545.
Miner, H. L., 483.
Minges, G. A., 421.
Mirasol, J. J., 347, 349.
Mitscherlich, E. A., 134, 140, 186, 284,
477.
Miyake, K., 347.
Molisch, H., 296.
Montgomery, E. G., 188.
192.
Mooers, C. A., 181, 362.
Moore, C. J., 133.
Morgan, J. F., 278, 281, 282.
Morrow, C. A., 99, 105.
Morse, F. W., 122, 267, 380, 449.
Morse, W. J., 465.
Mosier, J. G., 124, 204, 219, 220, 242.
Murray, T. J., 427, 509.
Mulder, T. J., 105.
190, 191,
INDEX OF AUTHORS
Neller, J. R., 256, 465.
Niklas, H., 127.
Norton, T. H., 450.
Ogg, W. J., 78.
Oliver Plow Book, 144.
Olsen, C., 351.
Osborne, T. B., 68, 70.
Osugi, S8., 346, 349.
Owen, W. L., 256.
Pantanelli, E., 284.
Parker, E. G., 267, 269, 271.
Parker, F. W., 278.
Parks, J., 242.
Parsons, L. J., 210.
Patten, H. E., 154, 232, (2355) 237,268.
23s
Patterson, J. W., 420.
Peake, W. A., 113.
Peck, E. L., 469.
Pember, F. R., 347, 349, 354, 381, 461.
Penny, C. L., 587, 540.
Peters, E., 266, 271.
Peterson, W. H., 303, 315, 331, 3382,
468.
Pettit, J. H., 855.
Pfeiffer, Th., 478.
Pick, H., 134.
Pickel, G. M., 44.
Pieters, A. J., 537.
Piper, C. V., 537.
Pirsson, L. V., 3, 46.
Pitman, D. W., 336.
Pitra, J., 460.
Plummer, J. K., 5, 6, 76, 251, 256, 356,
873, 392, 420.
Potter; R. \S:; 251, (315;
Pranke, E. J., 451.
Prescott, J. A., 263.
Prianischnikoy, D., 459, 460.
Prince, A. L., 354, 356.
Puchner, H., 78, 141.
Pugh, E., 443.
Rahn, Otto, 392.
Ramann, E., 127, 259.
Ramser, C. E., 204.
Ramsower, H. C., 145.
Rather, J. B., 113.
Ravin, P., 402.
Reed, H. S., 109, 297.
INDEX OF AUTHORS 56
Reid, F. R., 347, 466.
Reimer, F. C., 467.
Rice, F. E., 346, 349.
Richards, E. H., 429.
Richmond, T. E., 406.
Roberts, I. P., 504, 514, 519, 521.
Robbins, W. J., 109.
Robbins, W. W., 386.
Robinson, C. S., 44.
Robinson, F. W., 539.
Robinson, G. W., 78.
Robinson, W. O., 5, 18, 14, 86, 41, 52,
63, 77, 118, 466.
Rodewald, H., 134.
Ross, W. H., 464, 466.
Rost, ©: 0;, 63; 118; 119; 315.
Ruprecht, R. W., 347, 449.
Russell, E. J., 9, 68, 78, 158, 248, 252,
2585) 2ots Qlos OS, Alas 404
429, 471, 543.
Russell, I. C., 46.
Ruston, A. G., 429, 469.
Sachs, J., 296.
Sachs, W. H., 466.
Sackett, W. G., 331, 412.
Salisbury, R. D., 52, 57.
Salter, R. M., 116.
Saussure, Theodore de, 442.
Schantz, H. L., 156, 188, 190, 195, 196,
197.
Schollenberger, C. J., 315, 354.
' Schone, E., 73.
Schreiner, O., 105, 107, 108, 109, 111,
268, 279, 297, 321.
Schulze, F., 322.
Schutt, M. A., 507, 519.
Seelhorst, C., von, 186, 187, 192.
Sewell, M. C., 144, 220, 221.
Sharp, L. T., 281, 350.
Shaw, C. F., 92.
Shedd, O. M., 325, 406, 467.
Sherman, J. M., 387.
Shorey, F. C., 76, 105, 107, 362.
Shutt, F. T., 430, 539.
Singewald, J. N., 448.
Skinner, J. J., 108, 109, 347, 351, 447,
466.
Slosson, E. E., 450.
Smalley, H. R., 44, 347.
Smith, Alfred, 89.
Smith, C. D., 539.
On
Smith, O. C., 116.
Snyder, H., 122, 284, 317, 545.
Snyder, R. S., 251, 313, 315.
Spillman, W. J., 537.
Spurway, C. H., 287.
Stephenson, R. E., 353, 354.
Stevenson, W. H., 44.
Stewart, C. F., 45.
Stewart, G. R., 279, 280, 284, 323.
Stewart, R., 331, 332, 376, 381,
420, 422, 470.
Stoddard, C. W., 100.
Stoklasa, J., 110, 252, 255, 256, 460.
Storer, F. H., 504, 537.
Stérmer, K., 389.
Stremme, H., 134.
Strowd, W. H., 435.
Sullivan, E. C., 267, 270.
Sullivan, M. X., 107, 466.
Swanson, C. O., 437.
Sweetser, W. S., 511.
Swezey, G. D., 242, 260.
Tacke, Br., 355.
Tartar HH; V., 467.
Tarr, R. S., 46.
Taylor, W. W., 127.
Tempany, H. A., 134.
Temple, J. C., 421.
Thatcher, R. W., 100, 122, 127.
Thomas, W., 376, 377.
Thompson, H. C., 44.
Thorne, O. E., 375, 382, 454, 461, 462,
499, 504, 507, 511, 518, 514,
516, 519, 521, 525, 526, 528,
529; 532, 533.
Tottingham, W. E., 461, 514.
Trieschmann, J. E., 469.
Trnka, R., 92.
True, R. H., 300, 346, 348.
Truog, E., 348, 359.
Turpin, H. W., 252.
404,
Ulrich, R., 232, 233.
Underwood, T. M., 284, 287.
Vageler, P., 134.
Van Bemmelen, J. M., 36, 106, 132, 265,
266, 270.
Van Slyke, L. L., 442, 471, 501, 503,
514,
Van Suchtelen, F. H. H., 278.
Veitch, F. P., 317, 355.
566
Voelcker, A., 519, 532.
Von Englen, 0. D., 58.
Voorhees, E. B., 431, 504.
Vrooman, C., 439.
Waggaman, W. H., 263, 455, 456, 461,
464.
Wagner, F., 239.
Wagner, H., 477.
Waksman, S. A.,
413.
Walker, S. S., 51, 118.
Walters, E. H., 107.
Warington, R., 113, 132, 144, 180, 182,
265, 303, 426.
Warner, H. W., 406.
Warren, G. M., 210.
Watson, G. C., 514.
Way, J. T., 132, 264.
Waynick, D. D., 113.
Weaver, F. P., 499.
Weir, W. W., 362.
Welitschkowsky, D., von, 176.
Wells, A. A., 248.
Wills, C. F., 116.
Westerman, F., 433.
Whitbeck, R. H., 58.
Whitney, M., 81, 83, 85, 89.
Whisenand, J. W., 520.
387, 388, 389, 392,
INDEX OF AUTHORS
White, J. W., 351, 353, 365, 377, 421,
449, 550.
Whiting, A. L., 545.
Whitson, A. R., 44, 204, 362, 422.
Wiancko, A. T., 365, 381, 461, 499.
Widtsoe, J. A., 172, 186, 187, 190, 192.
Wiegner, G., 127, 265, 270.
Wiley, H. W., 78, 112, 114, 115, 314.
Williams, C. B., 49, 52, 118.
Williams, H. F., 5.
Wilson, B. D., 11, 374, 404, 430, 437.
Wilson, G. W., 388.
Wilson, J. K., 297.
Wing, H. H., 514.
Winogradsky, S., 431.
Wolkoff, M. I., 1381.
Wollny; Hey) 210) 1635 L776;
200, 228, 230, 245.
Wood, T. B., 516.
Woodward, S. M., 210.
Wright, R. C., 541.
Wyatt, F. A., 368, 376, 381.
Wyckoff, M. I., 267.
Yarnell, D. L., 211.
Woder: (Pa Ag was
Young, G. J., 464.
Young, H. J., 221.
Zzigmondy, R., 127.
189,
INDEX OF SUBJECT MATTER
Ability of plants to grow on poor soils,
299.
Abrasion defined, 18.
Absorption by litter, 521.
Absorption, by soils explained, 263.
capacity of soils to retain nitrates,
321.
due to soil colloids, 265.
effect of on soil acidity, 352.
effect of texture on, 267.
importance of in soils, 273.
of litter in stable, 521.
selective by soils, nature of, 269.
selective by soils, types of, 269.
Absorption by soils, capacity for, 266.
causes of, 264.
defined, 263.
importance of, 273.
influence of time on, 269.
law of, 269.
relation to acidity, 274.
relation to the soil solution, 276.
selective, 269.
types of, 263.
Absorption of solar insolation, as influ-
enced by atmosphere, 226.
as influenced by color, 228.
as influenced by slope, 229.
as influenced by soil, 226.
Absorptive capacity of different crops,
301.
Acid phosphate, 456.
changes in soil, 457.
character, 456.
compared with rock phosphate, 458.
composition, 456.
manufacture, 456.
reinforcement of manure with, 528.
Acidity, as influenced by absorption, 274.
development of by hydrolysis, 348.
production of by selective absorp-
tion, 270.
soil, nature of, 345.
Acids, production of by plant roots, 296.
Actinomyces in soils, character of, 389.
Actinomyces in soils, importance of, 389.
number of, 289.
Addition of nutrients to soil, 556.
Additions to and losses from soil under
various types of farming, 558.
Adobe, inportance of, 64.
origin of, 64.
wind formation of, 21.
fEolian soils, adobe, 64.
loess, 61.
sand dunes, 64.
volcanic dust, 65.
Aération of soil, effect on nitrification,
418.
importance in soil, 256.
influence on bacteria in soils, 393.
Agglutination of colloids, 131.
Agricultural lime, defined, 363.
forms of, 363.
Agricultural value of farm manure, 513.
Air of the soil, carbon dioxide of, 250.
composition of, 247, 248.
composition data, 248, 250.
effect of oxidation on, 254.
general characteristics of, 247.
importance of oxygen in, 256.
practical modification of, 261.
movement of, 258.
types of, 249.
volume of, 257.
Alkali, black, 329.
composition of, 329.
conditions affecting influence of, 338.
control of, 343.
control of by means of gypsum, 342.
effect of concentration of on crops,
337.
effect on crops, 334.
effect on soil organisms, 335.
eradication of, 341.
eradication of by means of drainage,
341.
influence on nitrification, 421.
in river water, 332.
in irrigation water, 334.
567
568
Alkali, origin of, 331.
resistance of crops to, data on, 338.
rise of as influenced by irrigation,
339.
white, 329.
Alkali lands, handling of, 340.
Alkali salts, listed, 330.
Alkali soils, defined, 328.
importance of, 328.
Alkali spots, nature of, 332.
Alkali tolerance by plants,
336.
Alkali vegetation, 340.
Alluvial fans, 47.
Alluvial soils, chemical composition, 49.
classified, 46.
deltas, 47.
fans, 47.
flood plain, 47.
importance of, 49.
origin of, 46.
Aluminum, hydrolysis of in soil, 348.
relation of to soil acidity, 347.
relation to the reversion of acid
phosphate, 457.
Alunite as a fertilizer, 465.
Amino acids defined, 106.
in farm manure, 510.
Amides defined, 106.
Ammonia in rain water, data on, 429.
Ammonification, conditions for, 414.
influence of protozoa on, 387.
nature of, 412.
organisms of, 413.
products of, 413.
reactions of, 414.
Ammonifying efficiency of soil, determi-
nation of, 414.
Ammonium salts, utilization by higher
plants, 415, 450.
Ammonium sulfate, changes in soil, 449.
character of, 449.
composition of, 449.
source of, 449.
Amounts of fertilizer to apply, 492.
Amounts of lime to apply, 368.
Analysis of plant tissue, method of, 102.
Analysis of soil, bulk, 311, 314.
carbon in, 1138, 114.
extraction, dilute acids, 317.
extraction, strong acids, 316.
extraction, with water, 319.
factors of,
INDEX OF SUBJECT MATTER
Analysis of soil, humus, 115.
lime requirement of, 355.
minerological, 76.
nitrogen in, 311.
organic matter of, 115.
value of, 323, 326.
Apatite in soil, 6.
Application of farm manure,
526.
evenness, 526.
incorporation in soil, 526.
Arid soils, biological activity in, 32.
chemical analysis of, 31.
humus content of, 120.
Assimilation of nitrates by soil organ-
isms, 426.
importance of, 428.
Available water in soil, 198.
Availability of nitrogen fertilizers, 454.
of phosphate fertilizers, 458.
Azofication, amount of nitrogen fixed,
433.
energy for, 432.
organisms of, 432.
Azotobacter ehrodcoceum in soil, 431.
amounts,
B. Radicicola, amount of nitrogen fixed
by, 437.
availability of nitrogen fixed by, 437.
function of, 434.
importance of, 436.
inoculation of the soil, methods of,
439.
nature of organism, 435.
nodules of, 434.
relation to host plant, 435. -
strains of, 434.
Bacteria, decomposition of organic mat-
ter by, 103.
increase of in frozen soil, 394.
influence on aération in soils, 393.
injurious to higher plants, 396.
method of counting in soil, 392.
multiplication of, 391.
production of carbon dioxide by, 252.
relation of to alkali, 332.
relation to liming, 395.
relation of moisture to, 393.
relation to organic matter in soil,
394.
relation to soil acidity, 395.
relation to soil temperature, 394.
INDEX OF SUBJECT MATTER
Bacteria, shape of, 391.
seasonal flora, 394.
spore formation by, 391.
Bacteria in soils, character of, 390.
determination of numbers of, 392.
factors affecting growth of, 393.
influence of green manures on, 544.
numbers of, 392.
position in soil, 391.
production of enzymes by, 390.
size of, 391.
Bacterial activity, measured by carbon
dioxide produced, 256.
growth, conditions affecting,
393.
Bases, substitution of in soils, 271.
those used to correct soil acidity,
362.
toxic nature of in acid soils, 346.
Basic exchange, 270.
influence on drainage water, 305.
Basic slag, changes in soil, 458.
character of, 458.
composition of, 457.
source of, 457.
Beaker method of mechanical soil analy-
sis, 69.
Biological cycles of the soil, importance
of, 398.
names of, 399.
nature of, 398.
Biological effects of lime on soil, 371.
Bog lime, nature of, 45.
Bomb method for determining soil or-
ganic matter, 114.
Bone phosphate, changes in soil, 455.
character, 454.
composition, 454.
source, 454.
Brands of fertilizers, 478.
Bromberg soil tanks, data from, 306.
Brownian movement, explained, 128.
Bucher method of fixing nitrogen, 453.
Bulk analysis of soils, carbon and nitro-
gen, 311.
mineral constituents, 314.
Burned lime, 364.
Bacterial
Calcium, amount in soils, 13.
forms of in soil, 11.
importance of in fertility evalua-
tions, 324.
569
Calcium, in soil minerals, 6.
lack of in relation to soil acidity,
348.
loss of from soil, 307, 370, 555.
of di-silicate as an amendment, 380.
relation to reversion of acid phos-
phate, 457.
use of as lime, 363.
Calcium cyanamid, change in soil, 452.
character of, 452.
composition of, 452.
manufacture of, 451.
Calcium and magnesium ratio in soils,
375.
in gypsum as an amendment,
379.
Calcium losses, Bromberg lysimeters, 306.
from Cornell soils, 307.
Calcium nitrate, character of, 452.
composition of, 452.
manufacture of, 452.
Capillary-absorbed water, defined, 196.
Capillary capacity of soils, factors affect-
ing, 163.
Capillary film, thickness of and effect on
capillary movement, 171.
Capillary movement of soil water, data
on rate, 174.
effect of structure on, 174.
effect of texture on, 173.
factors affecting, 170.
explained, 168.
influence of film thickness, 171.
relation to soil mulch, 175.
role in supplying plants with water,
193.
Capillary pull of soils, data on, 169.
determination of, 168.
Capillary water of soil, amounts in soil
columns, 165.
colloidal control of, 159.
defined, 159.
determination of amount, 161.
kinds of, 159.
position of inter film, 160.
surface tension control, 159.
Carbide method of fixing nitrogen, 451.
Carbon, cycle of in soil, 399.
determination of in soil, 113.
gain of by green manures, 539.
in Cornell drainage water, 402.
in organic matter, 113.
Calcium
570
Carbon, loss from the soil, data of, 402.
loss of from soil, 555.
use of organic carbon by higher
plants, 402.
Carbon cycle of the soil, loss of carbon
from, 400.
nature of, 399.
organisms of, 399.
products of, 400.
Carbon dioxide, a measure of bacterial
activity, 256.
from decaying manure, 509.
from lime, 369.
function in soil, 255.
in atmospheric air, data, 110.
in soil air, data, 110.
influence on nitrification, 256, 419.
relation to mineral cycle of soil, 408.
of soil air, 250.
of soil air, influence of farm manure
on, 254.
of soil air, influence of organic mat-
ter on, 253.
production of, 110.
produced by bacteria in soil, 252.
produced by plant roots, 252, 295.
source of in soil air, 251, 400.
Carbonated lime, 365.
Carbonation, influence in soil formation,
26.
Carbonized materials in soil, importance
of, 112.
nature of, 111.
Castor pomace, composition of, 446.
Catalytic fertilizers, 466.
Catalyst defined, 103, 135.
Cell sap, nature of in relation to plant
absorption, 300.
Centrifugal mechanical analysis of soils,
Tile
Character of soil particles, 69.
Chemical absorption by soils, 263.
Chemical analysis, alluvial and upland
soils, 49.
arid and humid soils, 31.
bulk and extraction methods, 311.
by digestion with strong acids, 316.
by water extraction, 319.
glacial soils, 57.
granite soil, 33.
importance in fertility evaluation,
323.
INDEX OF SUBJECT MATTER
Chemical analysis, limestone soil, 33.
loess soils, 63.
marine soils, 52.
of alkaline river water, 334.
of Cornell soils, 325.
of good and poor Ohio soils, 326.
of Minnesota soils, 316.
of Minnesota and Maryland
Shas
of soil, popular conception of, 311.
of soil separates, 78, 79.
peat and muck, 44.
residual soils, 41, 52, 57.
resumé as to value of, 326.
value as shown by actual data, 326.
with weak acids, 317.
Chemical composition of soils, compared
to lithosphere, 13.
Chemical composition of soil separates,
hs Ce
Chemical effects of lime on soil, 371.
Chromic acid method for determination
of soil organic matter, 113.
Chile salt petre, source and character of,
448,
Classification of methods of mechanical
analysis, 72.
Classification of soils, geological, 38.
for soil survey, 85.
Classification of soil particles, Bureau of
Soils, 67.
Classification of soil particles other than
Bureau of Soils, 68.
Climate, effect on transpiration, 191.
relation of to soil formation, 30.
Clostridium pastorianum in soil, 431.
Coastal plain soils, chemical composition
of, 52.
Cohesion, cause of in soils, 136.
defined, 136.
Colloidal materials, properties of, 130.
in soils, 265.
Colloidal matter, absorptive power for
water, 153.
Colloidal matter, influence on soil prop-
erties, 135.
Colloidal matter in soils,
structure, 137.
estimation of, 134.
generation of, 132.
resumé of, 138.
Colloidal particles, size of, 128.
soils,
influence on
INDEX OF SUBJECT MATTER
Colloidal state, defined, 127.
defined briefly, 75.
electrical condition of, 131.
examples of, 130.
phases of, 129.
practical importance of, 135.
relation of to granulation, 142.
Colloids and crystalloids, 129.
Color of soil, compounds of, 36, 37.
influence on absorption of insulation,
228.
nature of, 36.
Colluvial soils, origin and nature, 45.
Commercial fertilizer, amounts to apply,
492.
development of use, 442.
used for their nitrogen, 444.
used for their phosphorus, 454.
used for their potash, 462.
used in United States, 444.
Commercial value of farm manure, 512.
Composition of average soil, 12.
of cow manure, 501.
of drainage water, 304.
of farm manure, average, 504.
of horse manure, 501.
of muck and peat, 44.
of plant tissue, 100.
of sheep manure, 501.
of swine manure, 501.
Composts, use of manure in, 530.
Composts of sulfur, 406.
Conductivity of heat,
230.
formula for, 236.
Conductivity coefficients of various soils,
236.
Conductivity of various soils, 235.
Conduction, loss of heat from soil by,
240.
Conduction of heat in soils, factors af-
fecting, 235.
nature of, 234.
Constituents of soil,
ganic, 2.
Control of alkali in soils, 343.
of evaporation, 218.
of soil air, 261.
of soil temperature, 244.
Conservation of soil moisture, 219.
Conversion factors for lime, 367.
Convection of heat in soil, 238.
measurement of,
organic and inor-
571
Correction of soil acidity,
for, 363.
Corrosion defined, 18.
Cotton and tobacco, influence of manure
on, 535.
Cotton seed meal, composition of, 446.
Cover crops, influence on nitrates of soil,
541.
resistance to alkali,
table of, 338.
in pounds per acre, 338.
Crop residues, to maintain organic mat-
ter, 124.
Crop rotation, relation of to green ma-
nuring, 552.
Crops, absorptive capacity of, 301.
amounts of fertilizers for, 493.
bacteria injurious to, 396.
detrimental influence of nitrogen on,
473.
eftect of calcium
ratio on, 376.
effect of concentration of salts on,
337.
effect of on conservation of plant
nutriants, 308.
fertilizer formule for, 491.
for green manures, 546.
fungi injurious to, 396.
influence of green manures on, 547.
influence of manure on, 532.
influence of nitrogen on, 472.
influence of phosphorus on, 474.
influence of potassium on, 475.
injurious effect of soil organisms on,
396.
quantities of nutrients removed by,
308.
removal of nutrients by, 555.
removal of sulfur by, 404.
removal of sulfur and_ prohphorus
by, 468.
response to lime, 372.
systems of fertilizing, 496.
Crushers, action of, 148.
Cultivation, implements for, 147.
importance of, 219.
Cultivators, action of, 147.
Cumulose soils, agricultural
43.
location of, 42.
origin, 42.
bases useful
Crop generalized
and magnesium
importance,
o72
Decay and decomposition defined, 103,
410.
and putrefaction, in nitrogen cycle,
410.
and putrefaction, organisms of, 411.
effect on soil temperature, 239.
of farm manure, importance of, 511.
of green manure, influence on lime
and phosphorus, 545.
of green manure, influence on nitrate
accumulation, 543.
of green manure, influence on nitri-
fication, 544,
of green manure, stages of, 542.
of organic matter in soil, products
of, 110.
Decomposition, defined, 17.
of organic matter in soil, 103.
Delta soils, 47.
Denitrification, use of term, 426.
Deoxidation, influence in soil formation,
24,
Deposition, its relation to soil formation,
16.
relation to lime requirement, 356.
Depression of the freezing point, a
method of studying soil solu-
tions, 280.
Determination of soil humus, 115.
Determination of soil organic matter,
bomb method, 114.
chromic acid method, 113.
loss on ignition, 112.
Di-calcium silicate as a soil amendment,
380.
Diffusion, differential into plants, 292.
of nutrients into plants, 291.
of soil air, 260.
Diminishing returns, law of, 493.
Disc plow, influence on soil, 146.
Disintegration, defined, 17.
Dissociation, defined, 270.
Drainage and evaporation at Rotham-
sted, 217.
Drainage, importance of, 210.
influence of, 210.
loss of sulfur by, 404.
nutrient losses from soil, 555.
qualitative composition of water of,
304.
quantitative
of, 304.
composition of water
INDEX OF SUBJECT MATTER
Drainage, use of in eradication of alkali,
341.
usual type of, 212.
Drainage water, carbon in, 402.
composition data of, 305.
composition of, at Bromberg, 272.
importance of study, 178.
qualitative composition of, 304.
quantitative composition of, 304.
Dried blood, changes in soil, 445.
character, 445.
composition, 445.
source, 445.
Earth worms, importance of, 385.
Earth’s crust, minerals in, 4.
Electric arc method of fixing nitrogen,
452.
Electrolyte, defined, 130.
effect on colloids, 131.
Element in the minimum, 476.
Energy necessary for evaporation of
water, 241.
Energy, wave length of, 225.
Enzymes, action of, 390.
defined, 103, 390.
importance in soils, 103.
Eradication of alkali from soils, 341.
types of, 341.
Erosion defined, 18.
relation to soil movement, 16.
Erosion of soil, control of, 204.
types of, 205.
Evaluation of farm manure, 512.
Evaporation and drainage at Rotham-
sted, 217.
Evaporation of soil moisture, control of,
218.
energy necessary for, 241.
influence of on soil heat, 241.
loss of soil water by, 216.
water influenced by, 182.
Exfoliation in soil formation, 21.
Exhaustion of soil, discussion of, 309.
possibility of, 308.
Exosmosis, nature of, 290.
Extraction of soils, with concentrated
acids, 316.
with dilute acids, 317.
with water, 319.
with water, successive extractions, 322.
Exudates, excretion of by plant roots,
296.
INDEX OF SUBJECT MATTER 573
Factors influencing rise of soil tempera-
ture, 231.
Farm manure, a direct and indirect fer-
tilizer, 504.
agricultural value of, 513.
agricultural value of protected ma-
nure, 525.
amounts applied, 527.
amount produced by cows, 514.
amounts produced by farm animals,
513.
amount produced by horses, 514.
amount produced by poultry, 514.
amount produced by sheep, 514.
amount produced by steers, 514.
amount produced by swine, 514.
average composition of, 504.
care of in stalls, 520.
characteristics of, 500.
commercial eyaluation of, 512.
composition of from various animals,
501.
covered yards for, 523.
effect on carbon dioxide of soil air,
254.
efficient application of, 525.
evaluation of, 512.
factors influencing composition of,
506.
fermentation and _ putrefaction of,
508.
fresh and well rotted compared, 511.
fresh and yard, crop effects, 512.
hauling directly to field, 521.
importance of, 499.
importance of its decay, 511.
importance of protection, 524.
importance of tight floors, 521.
influence of handling on, 507.
influence of tramping on, 524.
influence on cotton, 535.
influence on maize, 534.
influence on meadows, 532.
influence on potatoes, 534.
influence on tobacco, 535.
liquid and solid compared, 502.
loss of constituents from, 508, 515.
losses during handling and storage,
519.
Maintenance of soil organic matter
by, 124, 519, 559.
modern manurial practice, 520.
Farm manure, nutrient losses during pro-
duction, 516.
outstanding characteristics of, 505.
piles outside, 522.
pits for, 523.
place in rotation, 532.
produced by animals, calculation of,
514,
products of decay, 510.
reinforcement of, 527.
residual effects of, 53
resumé of use, 535.
use of in sulfur composts, 406.
use of lime with, 530.
use of litter with, 521.
use in composting, 530.
variability of, 506.
Feldspar as a fertilizer, 465.
Fermentation, defined, 103, 410.
of farm manure, 508,
Fertility, maintenance of as influenced by
different types of farming, 558.
Fertility of soil, defined, 554.
effect on transpiration ratio, 192.
possible exhaustion of, 308.
Fertility evaluations by means of a
chemical analysis, 323.
Fertilization, systems of, 496.
Fertilizers, advantages of home mixing,
485,
amounts to apply, 492.
brands of, 478.
calculations of for home-mixing, 487.
carrying free sulfur, 467.
catalytic, 466.
containing nitrogen, 444.
containing phosphorus, 454.
containing potash, 463.
development of their use, 442.
early use of, 442.
effect of on soil acidity, 353.
element in the minimum, 476.
factors which determine the choice
of, 488.
farm manure, 504.
formulz, for different soils and crops,
491.
formule, nature of, 489.
formule, theory of, 490.
function of, 444,
guarantees of, 481.
how to buy, 483.
574
Fertilizer, how to home mix, 487.
importance of high grade, 483.
importance of residues from, 295.
inspection and control, 480.
interpretation of guarantee, 481.
laws of, 480.
law of diminishing returns, 493.
low grade and high grade, 479.
method and time of application of,
495.
purchase of unmixed, 484.
rational utilization of, 497.
systems of applying, 496.
use in United States, 444.
which should not be mixed, 486.
Fertilizer mixtures, those of value, 487.
Fertilizer practice, principles of, 471.
rational system, 497.
Fertilizer residues, cause of, 294.
nature of from different salts, 294.
Fillers, use of in fertilizers, 488.
Fineness of limestone, data as to impor-
tance, 377.
importance of in liming, 377.
influence of on decomposition, 378.
Fish scrap, composition of, 446.
Fixation of: nitrogen artificially, 450.
Bucher method, 453.
carbide method, 451.
electric are method, 452.
Haber method, 453.
Fixation of nitrogen by free-living soil
organisms, 430.
by nodule bacteria, 433.
Floats, see rock phosphate, 455.
Flocculation, cause of, 131.
defined, 130.
relation of to granulation, 144.
Flood plain soils, 47.
Floors, importance in care of manure,
520.
Flue dust, a source of potash, 465.
Food for plants, defined, 8.
Forms of water in soil, diagram of, 199.
Forms of soil water, 151.
Forms of lime to apply, 367.
Formule of fertilizers for different soils
and crops, 491.
examples of, 489.
theory of, 490.
Freezing and thawing,
23.
effect on soils,
INDEX OF SUBJECT MATTER
Frost, importance in soil formation, 23.
Fungi and alge, smaller forms in soil,
388.
fixation of nitrogen by, 432.
injurious to higher plants, 396.
in soil, number of, 388.
large forms in soil, 386.
Germination of seeds,
224,
Geological classification of soils, 38.
resumé of, 65.
Glacial lakes, origin of, 59.
soils of, 58.
Glacial soils, chemical composition of,
bile
compared with residual, 57, 58.
fertility of, 57.
general character, 54.
importance of, 57.
origin, 54.
Glaciation, American ice sheet, 53.
effect of, 54.
influence on agriculture, 58.
in North America, 54.
Glaciers in soil formation, 18.
Grading of ground limestone, 377.
Grandeau method, nature of, 312.
Granite, chemical composition of, 33.
weathering of, 33.
Grass, influence on nitrate accumulation,
427.
influence on nitrification, 422.
Granulation of soil, as influenced by
lime, 143.
beneficial effects, 141.
defined, 139, 141.
forces producing, 143.
influence of plowing on, 146.
influence of tillage on, 144.
production of, 142.
Gravity water, amount soil will hold,
Wee
calculation of, 178.
factors affecting movement, 175.
importance of study, 178.
Green manures, ancient use of, 537.
as cover crops, 538, 541.
constituents gained by use of, 539.
erops for, 545.
decay of in soil, 541.
general influence of, 538.
temperature of,
INDEX OF SUBJECT MATTER
Green manures, importance of, 537.
influence of decay of, 543.
influence of decay on lime and phos-
phorus, 545.
influence of decay on nitrate accu-
mulation, 544.
influence on crops, 552.
influence on nitrate reduction, 426.
manner of turning under, 549.
practical utilization of, 552.
relation of to the rotation, 552.
relation to humus formation, 548.
relative value of different crops for,
547.
time for plowing under, 548.
to maintain organic matter, 123.
use of, 548.
use of lime with, 550.
Ground limestone, 365.
Guano, nature of, 445.
Guarantees on fertilizers,
481.
Gullying and its control, 206.
Gypsum as a soil amendment, 379.
effect of on soils, 379.
reinforcement of manure with, 527
use of in alkali control, 342.
statement of,
Haber method of fixing nitrogen, 453.
Handling of manure, covered yards, 523.
hauling directly to field, 521.
influence on composition, 507.
manure pits, 523.
piles outside, 522.
care of in stalls, 520.
Hematite, as a soil color, 37.
change of to limonite, 27.
formation of in soil, 25.
source of in soil, 7.
Heat, conduction of, 240.
conduction of in soil, 234.
conductivity of various soils for, 235.
convection transfer of, 238.
eycle between soil and atmosphere,
225:
factors affecting conduction of, 235,
236.
evaporation loss by, 241.
importance in soil formation, 21.
loss of from soil, 240.
movement in soil, 234.
radiation of, 240.
575
Heat of wetting of soils, amount of, 153.
data of, 154.
effect of texture on, 154.
significance of, 158.
High grade fertilizers, importance of,
4°3.
Higher plants, influence on nitrification,
422.
Home-mixing of fertilizers, calculation
of, 487.
advantages, 485.
good mixtures for, 487.
how performed, 486.
Hoof meal, composition of, 446.
Humid soil, biological activity in, 32.
chemical analysis of, 31.
humus content of, 120.
Humidity, influence of on the hygro-
scopic coefficient, 158.
Humus, amount in California soils, 120.
amount in Nebraska loess, 120.
defined, 115.
determination of, 115, 312.
formation of from green manures,
543.
Hydration, influence of in soil formation,
26.
Hydrogen-ion concentration, a
of soil acidity, 356.
method of expression, 350.
relation to soil acidity, 346.
Hydrolysis, explanation of, 348.
production of by enzymes, 390.
Hygroscopic capacity of soils, data on,
156.
Hygroscopie coefficient, data as to spe-
cific soils, 157.
defined, 152.
determination of, 154.
factors affecting, 157.
range of in soils, 158.
Hygroscopic water of soils, specific char-
acter of, 153.
measure
Ice, disintegration of rocks by, 23.
glacial, in soil formation, 18.
Ice action, glaciation, 53.°
Ice age, 53.
Ignition method for determining soil or-
ganic matter, 112.
Influence of alkali, condition affecting,
338.
576
Inoculation of soil with B. Radicicola,
methods of, 439.
Insulation, absorbed by earth’s atmos-
phere, 226.
absorbed by soil, 227.
absorption of as influenced by color,
228.
absorption of as influenced by slope,
229.
received by soil, 225.
Insoluble phosphoric acid, defined, 456.
Inspection and control of fertilizers, 480.
Ions, absorption of by soils, 270.
differential diffusion of, 293.
diffusion of into plants, 291.
Ionization, defined, 270.
of water, 270.
Irrigation, relation to rise of alkali, 339.
Irrigation water, alkali content of, 333.
Iron, in soil minerals, 7.
relation to the reversion of acid
phosphate, 457.
relation of to soil acidity, 347.
reinforcement of manure with,
SPAT (=
Kaolinite, importance in soils, 7.
source of in soil, 6.
Kelp, a source of potash, 465.
Kjeldahl method for determination of
nitrogen, 312.
Kainit,
Lacustrine soils, character of, 60.
glacial lake, 58.
importance of, 60.
location in U. §., 60.
recent lake, 60.
Lake salines, a source of potash, 465.
Law of diminishing return, 493.
Leaching, effect of on soil acidity, 352
loss of lime thereby, 370.
use of in alkali eradication, 341.
Leather meal, composition of, 446.
Legumes, inoculation of, 438.
Leguminous crops, amounts of nitrogen
fixed by, 438.
eross inoculation of, 434.
effect on soil nitrogen, 437.
nitrogen fixation by, 433.
Leucite as a fertilizer, 465.
Lime, agricultural terminology of, 364.
agricultural use of, 3638.
INDEX OF SUBJECT MATTER
Lime, amounts to apply, 368.
biological effects in soil, 371.
burned, 364.
earbonated, 365.
cause of crop response to, 372.
changes in soil, 369.
chemical effects of on soil, 871.
composition of as sold in Pennsylva-
nia, 366.
contact action of, 374.
conversion factors of, 367.
crop response to, 372.
effect of caustic forms on manure,
530.
forms of, 363.
forms to apply, 367.
importance of in soil improvement,
381.
influence of green manures on, 545.
influence on availability of nutrients,
373.
influence on decay of green manures,
551,
influence on granulation, 143.
influence on nitrification, 373.
influence on soil bacteria, 395.
influence on sulfofication, 405.
losses from Cornell soils, 307, 370.
methods of applying, 374.
need of determinations, 365.
physical effects on soil, 371.
problem showing form to buy, 368.
proper utilization of, 382.
relation of to fertilizer mixtures,
486.
relation to reversion of monocalcium
phosphate in soil, 457.
relation to the use of manure and
fertilizers, 382.
time to apply, 374.
use of manure with, 530.
use of with green manure, 551.
water slaked, 364.
Lime requirement determinations, on
soils, 355.
types of, 355.
Lime requirement of soils, Veitch method,
356.
Limestone, amounts to apply, 368.
burning of, 364.
changes in soil, 370.
chemical composition of, 33.
INDEX OF SUBJECT MATTER
Limestone, conversion factors, 367.
fineness of average product, 378.
fineness of for agricultural use, 367.
grading of as to fineness, 377.
importance of fineness, 377.
mechanical composition as
Pennsylvania, 379.
ratio of calcium and magnesium, 375.
Liming, amounts of lime to apply, 368.
calcium and magnesium ratio of,
Bidap
cause of crop response to, 372.
crop response to, 372.
forms of lime to apply, 367.
importance of in soil improvement,
381.
method and time of applying lime,
374.
reasons for, 362.
Limonite, source of in soil, 7.
production of from hematite, 27.
weathering of, 33.
Limonite group, as soil color, 37.
Linseed meal, composition of, 446.
Lithosphere, composition of compared to
soils, 13.
Litmus paper test, criticism of, 360.
procedure, 358.
use of potassium nitrate with, 358.
Litter, absorptive power of, 521.
influence on character of manure,
521.
Loam, defined, 82.
Loess, a wind laid soil, 21.
character of, 62.
chemical composition of, 63.
importance of, 63.
location of, 62.
minerals of, 62.
origin of, 61.
Loss of nutrients from soil, 554.
types of, 289.
Loss of soil heat, by conduction, 240.
by evaporation, 240.
by radiation, 240.
Loss of soil water by run off, 203.
Losses during the production and han-
dling of manure, 515.
Losses from and addition to soils under
various types of farming, 558.
Lysimeter experiments, at Bromberg, 272.
306.
sold in
977
Lysimeter experiments, at Cornell Uni-
versity, 307.
at Rothamsted Experiment Farm,
180, 217, 288.
Lysimeters, nature of, 180.
of Cornell University, 181.
of Rothamsted Experiment Station,
180.
Macro-organisms of the soil, 384.
Maintenance of soil fertility, 554.
influence of different types of farm-
ing on, 558.
program of, 560.
Maintenance of soil organic matter, 122.
Maize, influence of farm manure on, 534.
influence on nitrate accumulation,
428.
influence on nitrification, 422.
Manganese, relation of to soil acidity, 347.
Mangum terrace, 205.
Manurial practices, phases of, 520.
Marine soils, character of, 51.
chemical composition of, 52.
importance of, 51.
origin of, 50.
Marl, origin and nature of, 45.
term defined, 45.
use of, 45.
Maximum retentive power of soil for
water, 162.
determination of, 162.
Maximum water capacity of soils, data
on, 166.
Meadows, influence of manure on, 532.
Mechanical analysis of soils, 67.
beaker method, 69.
Bureau of Soils method, 71.
determination of soil class from, 84.
value of, 79.
Mechanical analyses of typical soils, 83.
of various soils, 81.
Methods of applying fertilizers, 495.
Methods of studying drainage losses, 180.
Micro-organisms of the soil, 386.
Micron, magnitude of, 128.
Millimicron, magnitude of, 128.
Mineral constituents of soils, bulk analy-
sis of, 314.
extraction of with dilute acids, 317.
extraction of with strong acids, 316.
extraction of with water, 319.
578
Mineral cycles in soils,
408.
nature of, 407.
organisms of, 408.
types of, 407.
Minerals in earth’s crust, 4.
Minerals of the soil, 77.
importance of, 6.
Tistsofaio:
source of, 4.
specific gravity of, 89.
Minerological analysis of soils, 76.
Minerological character of soils, 77.
of soil particles, 75.
Minimum, element in the, 476.
law of Mitscherlich, 477.
Modification of soil air, 261.
Moisture of soil, conservation by mulch,
221,
conservation, weed control, 220.
control, summary of, 221.
data for sandy and clayey soils,
179, 200.
determination on soil, method of,
161.
effect on heat conductivity, 236.
effect on movement of soil air, 258.
effect on nitrification, 420.
effect on specific heat of soils, 2338.
influence on nitrification, 420.
influence on bacteria, 393.
Moisture equivalent of soils, defined, 167.
for various soils, 168.
method of determination, 167.
Molecules, absorption of by soil, 269.
Moraines, agricultural value, 54.
ground, 54.
terminal, 54.
Moyement of soil air, factors affecting,
258.
Muck, agricultural value of, 43.
capacity for water, 164.
character of, 438.
chemical analysis of, 44.
term defined, 438.
Mulch, artificial, 218.
soil, use of, 218.
Muscovite, change of to kaolinite, 26.
present in soils, 5, 77.
Nitrates in alkali spots, 332.
Nitrates in rain water, data, 429.
INDEX OF SUBJECT MATTER
importance of,
Nitrates in soils, accumulation, 419.
accumulation as influenced by green
manure, 544, 549.
accumulation, influence of grass on,
427.
accumulation, influence of maize on,
428.
as a source of nitrogen for higher
plants, 415.
assimilation of by
426, 428.
influence of green manures on, 543.
production of, 111.
reduction of, 424.
Nitrate reduction, cause of, 425.
control of, 426.
influence of green manures on, 426.
influence of straw on, 425.
nature of, 425.
organisms of, 425.
Nitrification in soil, as affected by soil
conditions, 418.
as influenced by carbon dioxide, 256.
effect of aération on, 418.
effect of alkali on, 421.
effect of carbon dioxide on, 419.
effect of farm manure on, 418.
effect of moisture on, 420.
effect of soil acidity on, 421.
effect of temperature on, 420.
efficiency of, 417.
influence of higher plants on, 422.
influence of lime on, 373.
influence of previous crops on, 4238.
influence on carbon dioxide produc-
tion, 255. ;
nature of, 415.
organisms of, 415.
products of, 415.
reactions, 415.
relation to ammonification, 416.
relation of to carbon cycle, 408.
relation of to mineral cycle, 408.
relation to soil fertility, 423.
Nitrifying organisms, types of, 415.
Nitrites, production of in soils, 111.
Nitrobacter in soil, 415.
Nitrogen, additions to soil, by free-fixing
organisms, 4380.
additions to soil, in manure, 557.
additions to soil, in rain water, 429.
additions to soil, modes of, 429.
soil organisms,
INDEX OF SUBJECT MATTER
Nitrogen, additions to soil, nature of, 429.
amount fixed by B. Radicicola, 437.
amount in ammonium sulfate, 449.
amount in calcium cyanamid, 452.
amount in calcium nitrate, 452.
amount in California soils, 120.
amount in dried blood, 445.
amount in Nebraska loess, 120.
amount in sodium nitrate, 448.
amount in soils, 12.
amount in soils of United States, 118.
amount in tankage, 445.
artificial fixation of, 450.
availability of in fertilizers, 454.
contained in rocks, 10.
determination of in soils, 312.
fixation by B. Radicicola, 438.
fixed in soil by azofication, 433.
forms of in:soil, 10.
from B. Radicicola, availability of,
437.
gain due to green manures, 539.
gain due to natural causes, 429.
importance in biological processes,
409.
importance of in fertility evaluation,
323.
importance of in soils, 409.
in farm manure, 501.
in liquid and solid manure, 503.
in rain water, data on, 429.
inert character of, 409.
influence on plant growth, 471.
losses from Bromberg lysimeters,
306.
losses from Cornell soils, 307.
losses from decaying manure, 511.
losses from farm manure, 519.
losses from soil, 555.
natural addition to soil, 557.
of food recovered in farm manure,
516.
organic forms used by plants, 411.
possible detrimental influences of,
473.
relation of to life, 409.
removed by crops from Cornell soils,
325.
utilization of
plants, 447.
Nitrogen cycle, addition of nitrogen to
soil by free-fixing bacteria, 430.
organic forms by
579
Nitrogen cycle, addition of nitrogen to
soil in rain water, 429.
ammonification, 412.
assimilation of nitrates by soil or-
ganisms, 426.
complexity of, 409.
decay and putrefaction, 410.
fixation of nitrogen by Azotobacter,
432.
fixation of nitrogen by B. Radici-
cola, 433.
nitrification, 415.
reduction of nitrates, 424.
relation of to other cycles, 410.
Nitrogenous fertilizers, ammonium sul-
fate, 449.
ealeium ecyanimid, 451.
calcium nitrate, 452.
castor pomace, 446.
cotton seed meal, 446.
dried blood, 445.
fish scrap, 446.
guano, 446.
hoof meal, 446.
leather meal, 446.
linseed meal, 446.
process goods, 446.
relative availability, 454.
sodium nitrate, 448.
tankage, 445.
utilized by higher plants, 411, 447.
wool and hair waste, 446.
Nitrosomonas in soils, 415.
Nitrous acid, relation to mineral cycle,
408.
Nodules on the roots of leguminous plants,
nature of, 434.
Number of particles in soil, 96.
Number of soil particles, calculation of,
96.
elements used by
amounts in soil, 12.
defined and explained, 8:
listed, 9.
primary, 10.
source of, 10.
Nutrients in soils, addition by leguminous
green manures, 557.
addition of in farm manure, 557.
differential diffusion into plants,
293.
diffusion into plants, 291.
Nutrient plants,
580
Nutrients in soils, direct influence of
plants on solubility of, 295.
how lost from the soil, 289.
influence of lime on solubility of,
Silos
lost by drainage and cropping, 307.
lost by leaching, Cornell data, 210.
lost by plant influence, 303.
lost during manurial production,
cows, 516.
lost during manurial production,
heifers, 516.
lost during manurial production,
sheep, 516.
Jost during manurial production,
steers, 516.
lost from Cornell soil, 554.
lost from soil, relative losses, 308.
lost in handling and storage of ma-
nure, 517.
natural additions of to soil, 556.
quantities removed by crops, data of,
303.
recovery of in farm manure, 516.
solubility as influenced by carbon
dioxide, 255.
Nutrient losses from and addition to soil
under various types of farming,
558.
Ocean, soils found in, 50.
Ohio results with raw rock phosphate,
462.
Optimum soil moisture,
structure on, 201.
for plant growth, 200.
Organic carbon, determination of, 311.
use of by higher plants, 402.
Organic compounds of soil, character of,
105.
classification of, 107.
nitrogenous, 106.
relation to plants, 108.
Organic decay, effect on soil tempera-
influence of
ture, 239.
Organic decomposition, simple products
of, 110.
Organic matter, amount in Nebraska
loess, 120.
amount in soil of United*states, lal
decay of, 103.
compounds isolated from, 108.
INDEX OF SUBJECT MATTER
Organic matter, defined, 99.
determination of in soils, 112.
effect of on soil acidity, 353.
effect on capillary capacity of soil,
164.
effect on carbon dioxide of soil air,
253.
effect on specific heat, 233.
influence in soil, 8.
influence of soil conditions on decay
of, 124.
influence on availability of
phosphate, 460.
influence on the soil, 121.
in Minnesota soils, 119.
maintenance of in soil, 122.
Organic matter of soil, effect on heat
conductivity, 236.
general nature, 7.
influence on bacteria, 394.
portion alive, 100.
sources of, 7, 99.
Organic nitrogenous compounds, utiliza-
tion by higher plants, 411, 446.
Organie nitrogenous fertilizers of secon-
dary importance, 445.
Organic toxins, elimination of, 109.
of soil, 108.
Organisms, benefits of in soil, 397.
pounds of in soil, 384.
Orthoclase, change of to koalinite, 26.
importance in soil, 6.
Osmosis, defined, 289.
how demonstrated, 290.
pressure developed by, 290.
Osmosis of water into plants, 290.
Osmotic pressure, nature of, 290.
Oswald method of converting ammonia
into nitrie acid, 453.
Outlets for tile drains, construction of,
214.
Oxidation, effect of on composition of soil
air, 254.
importance of in soil formation, 24.
of sulfur in soil, 403.
Oxidases, production of by plant roots,
297.
Oxygen, importance in soil air, 256.
rock
Packers, action of, 148.
Partial analysis of soils, 315.
digestion with dilute acids, 317.
INDEX OF SUBJECT MATTER
Partial analysis of soils, digestion with
dilute acids, objections, 318.
digestion with dilute acids, value,
318.
digestion with strong acids, 316.
digestion with strong acids, objec-
tions, 316.
extraction with water, 319.
extraction with water, method of,
Ay Als
extraction with water, value, 322.
of Minnesota soils, 316.
of Minnesota and Maryland
317.
Partially decomposed matter of soils, 105.
Particles of soil, number to a gram, 96,
Peat, agricultural value of, 43.
capillary capacity of, 164.
character of, 43.
chemical analysis of, 44.
term defined, 43.
Percolation, control of, 208.
Cornell data, 209.
effects of crops on, 210.
loss of nutrients by, 208.
in arid regions, 208.
in humid regions, 208.
Rothamsted data, 207.
Ph values of acidity explained, 350.
Phosphate fertilizers, acid phosphate,
456.
basic slag, 457.
bone phosphate, 454.
relative availability of, 458.
reck phosphate, 455.
Phosphoric acid, amount of in acid phos-
phate, 456.
amount of in apatite, 6.
amount of in basic slag, 457.
amount of in igneous rocks, 6.
amount of in manure, 501.
amount of in bone, 454.
amount of in rock phosphate, 455.
amount of in soils, 12.
forms of in fertilizers, 456.
forms of in soil, 11.
influence of green manures on, 545.
influence of lime on reversion of,
373.
influence on plant growth, 474.
in liquid and solid manure, 508.
loss of from farm manure, 519.
soils,
581
Phosphoric acid, loss of from soil, 555.
losses from Cornell soils, 307.
of food recovered in farm manure,
516.
of soil, 140.
organic and inorganic in soils, 315.
organic nature of, 11, 314.
pounds removed by various crops,
468.
relative availability of in fertilizers,
458.
Phosphorus, see phosphoric acid.
Physical absorption by soils, 263.
Physiological character of plants in re-
lation to alkali toxicity, 336.
Piconometer, for determination of specific
gravity, 90.
action of, 148.
absorptive activity of as deter-
mined by certain factors, 299.
acquisition of nutrients by, 291.
alkali vegetation, 340.
capacity of to grow on poor soils,
299.
cause of drought resistance by, 195.
cause of wilting, 194.
detrimental influence of nitrogen on,
473.
differential diffusion into, 292.
different absorptive capacity for soil
nutrients, 301.
direct influence of upon soil nu-
nutrients, 296.
effect of alkali on, 334.
effect of calcium and magnesium
ratio on, 376.
effects of on percolation, 208.
factors affecting transpiration from,
188.
function of water in, 184.
growth of in acid medium, 350.
influence of on the soil solution,
284.
influence of phosphorus on, 474.
influence of potassium on, 475.
influence of roots on soil colloids,
297.
influence of soil water on, 186.
production of acids by, 296.
productions of oxidases by, 297.
reduction produced by roots of, 297.
resistance of to alkali, 335.
Plankers,
Plants,
582
Plants, response of to lime, 372.
soil organisms injurious to, 396.
tolerance of to soil acidity, 353.
used for green manures, 546.
utilization of ammonia by, 415, 450.
utilization of organic carbon by, 402.
utilization of organic nitrogen by,
411, 447.
water requirements of, 187.
Plants and animals, relation to soil
formation, 23.
Piant diseases, control of in soil, 397.
Plant food, defined, 8.
Plant growth, factors for, 8.
influence of nitrogen on, 472.
optimum moisture for, 200.
temperature for, 224.
Plant nutrients, amounts in soil, 12.
contained in minerals, 5.
defined, 8.
derived from air, 9.
derived from soil, 9.
listed, 9.
primary, 10.
Plant roots, production of carbon dioxide
by, 252.
prying effect on rocks, 23.
Plant tissue, composition of, 100.
method of analysis, 102.
Plasmolysis, defined, 290.
Plowing, influence of on the soil, 146.
Pore space of soils, calculation of, 94,
178.
data on, 95.
importance of, 95.
nature of, 93.
Potash, amount in soils, 12.
fertilizers carrying, 463.
forms of in soil, 11.
in farm manure, 501.
influence on plant growth, 475.
in liquid and solid manure, 503.
in minerals, 6.
loss of from soil, 555.
loss of from farm manure, 519.
losses from Cornell soils, 307.
miscellaneous fertilizers of, 464.
of food recovered in farm manure,
516.
Potash fertilizers, alunite, 465.
feldspar, 465.
flue dust, 465.
INDEX OF SUBJECT MATTER
Potash fertilizer, kelp, 465.
lake salines, 465.
leucite, 465.
Stassfurt salts, 463.
wood ashes, 464.
Potassium, see potash.
Potassium chloride as a fertilizer, 463.
Potassium nitrate, use of in litmus test,
358.
Potassium sulfate as a fertilizer, 464.
Poultry manure, character and composi-
tion of, 503.
Potatoes, influence of manure on, 534.
Practical soil management, factors of,
560.
Precipitation, addition of sulfur by, 469.
Pressure, effect on gravity water, 175.
effect on movement of soil air, 260.
Process fertilizers, nature of, 446.
Productivity, as influenced by soil solu-
tion, 287.
equation of, 327.
Protection, influence of on farm manure,
525. :
Proteid compounds, changes of in de-
caying manure, 510.
Protozoa, importance of in soil, 387.
number of in soil, 387.
relation of to ammonification,
types of in soil, 387.
Puddling of soils, 141.
Purchase of commercial fertilizers, 483.
Purchase of unmixed fertilizers, 484.
Putrefaction, defined, 103, 410.
of farm manure, 508.
387.
products of, 411.
Qualitative composition of drainage
water, 304.
of the soil solution, 280.
Quantitative composition of drainage
water, 304.
of soil solution, 282.
Qualitative tests for soil acidity, 358.
compared and criticized, 359.
Quantitative tests for soil acidity, nature
OLD.
value of, 357.
Radiation, loss of heat from soil by, 240.
Rain-water, analysis of, 429.
suifur in, 404.
INDEX OF SUBJECT MATTER 583
Rational fertilizer practice, 497.
Recovery of nutrients in farm manure,
516.
Reduction, as affected by plant roots,
297.
Reduction of nitrates in soil, 424.
Reinforcement of farm manure, 527.
agricultural value of, 529.
balancing influence, 529.
conserving effects, 529.
Residual influence of manure, 531.
Residual soils, age of, 39.
analysis of, 33, 41.
chemical composition of, 52, 57.
compared with glacial soils, 57.
colors of, 32, 39.
formation of, 38.
from specific rocks, 39.
location of in U. S., 41.
organic content, 41.
Residues in soil from differential dif-
fusion, 294.
Resistance of plants to alkali, generalized
table of, 338.
Resistance to alkali by various plants,
data on, 338.
Reversion of mono-calcium phosphate in
soil, 457.
Reverted phosphoric acid, defined, 456.
Rock phosphate, as a reinforcement for
manure, 528.
changes in soil, 456.
compared with acid phosphate, 458.
composition, 456.
composted with manure, 462.
influence of organic matter on, 460.
Ohio results on, 462.
source, 455.
use of in sulfur composts, 406.
Rocks, igneous, sedimentary and meta-
morphic, 4.
soil forming, 3.
Rodents, macro, soil organisms, 384.
Rollers, actions of, 148.
Roots of higher plants, a type of macro-
organism, 386.
production of carbon dioxide by,
295.
production of exudates by, 296.
Rooting habit of plants, in relation to
alkali toxicity, 336.
Rotation, farm manure and the, 532.
Sampling of soil, method of, 311.
Sand dunes, nature of, 64.
Season, influence on soil solution, 283.
Sedentary soil, explanation of term, 28.
Sediment carried into ocean, 46.
Selective absorption by soils, nature of,
269.
types of, 269.
Selection of a commercial fertilizer, fac-
tors to consider, 482.
Sheet erosion and its control, 205.
Size of colloidal particles, 128.
Slope, influence on soil temperature, 229.
influence upon absorption of solar
insolation, 229.
Sod, influence on nitrate accumulation,
427.
Sodium chloride as a soil amendment,
380.
presence of in alkali, 333.
Sodium nitrate, changes in soil, 448.
character of, 448.
composition of, 448.
retention of by soils, 321.
origin of, 448.
source of, 448.
Soils, absorption by, 263.
absorptive capacity of, 266.
acid nature of, 345.
acquisition of nitrogen by, 428.
addition of sulfur to by precipita-
tion, 469.
zolian, 61.
alkali, 328.
alluvial, 46.
amendments used on, 363.
ammonification in, 412.
amounts of capillary water in, 166.
amount of gravity water in, 177.
available water of, 198.
average composition of, 12.
bulk analysis of, 311.
capacity of to retain nitrates, 321.
capillary capacity for water, 163.
capillary movement of water in, 168.
capillary water of, 159.
cause of acid condition of, 351.
changes of lime in, 369.
chemical analysis of water extract
from, 320.
eolluvial, 45.
eolor of, 36.
584
conductivity coefficients of, 236.
conditions, effect on _ nitrification,
418.
control of air in, 261.
control of alkali in, 348.
control of erosion, 205.
cumulose, 42.
defined, 2.
diseases, control of, 397.
diseases, nature of, 396.
dynamic nature of, 3.
eradication of alkali from, 341.
erosion of by water, 204.
fertility evaluation of by chemical
analysis, 323.
formation of, 16.
forms of water in, 152.
functions of water in, 184.
general composition of, 2.
geological classification of, 38.
glacial, 54.
granulation of, defined, 139.
handling of alkali soils, 340.
heat conduction in, 234.
heat convection in, 238.
hygroscopic water of, 152.
importance of absorption by, 273.
influence of earth worms on, 385.
insolation received by, 225.
lacustrine, 58.
losses of water from, 202.
management, practical factors
560.
marine, 50.
method of moisture determination
on, 161. ,
moisture data of, 200.
. movement of air in, 258.
movement of gravity water in, 175.
mulch on, 218.
names in common use, 82.
names, origin and meaning, 80.
nitrification in, 416.
nitrogen content of, 118.
partial analysis of, 315.
of,
partial analysis with strong acids,
316.
partial analysis with weak acids,
317.
particles of, 67.
plasticity of, 140.
INDEX OF SUBJECT MATTER
Soils, composition of air in, 247.
Soils, pore space of, 93.
Soil
practical management of, 560.
productivity of as related to soil
solution, 287.
puddling of, 141.
reaction, importance of, 345.
reaction, types of, 345.
reduction of nitrates in, 424.
residual, 38.
sampling of, 311.
series defined, 86.
specific gravity of, 88.
specific heat data, 2382.
sulfofying power of, 405.
survey classification of, 85.
tests for acidity in, 354.
thermal movement of moisture in,
182.
the solution of, 275.
tilth, defined, 149.
toxins of organic nature, 108.
type defined. 86.
weathering, importance of,
weight of, data, 93.
wilting coefficient, 197.
acidity, active toxic bases, 346.
as influenced by absorption, 274.
causes of development, 352.
causes of harmful effects, 346.
expression of by ph values, 350.
general nature of, 345.
influence of absorption on, 352.
influence of fertilizers on, 353.
influence of leaching on, 352.
influence on bacteria, 395.
influence on nitrification, 421.
lack of calcium in relation to, 348.
lack of nutrients theory, 348.
lime requirements, determination of,
355.
litmus paper test for, 358.
present status of question, 349.
relation of iron to, 347.
relation of manganese to, 347.
resumé of, 360.
37.
tests for, 354.
theory, aluminum, 347.
theory, hydrogen ion, 346.
tolerance of plants to, 353.
Truog test for, 358.
types of tests, 355.
zine sulfide test for, 358.
Soil air,
Soil amendments, forms of lime,
INDEX OF
carbon dioxide of, 250.
general characteristics, 247.
composition data, 248, 250.
eontrol of, 261.
general composition of, 247,
movement of, 258.
resumé of, 262.
types of, 249.
volume of, 257.
363.
organic matter important as, 124.
Soil analysis, alluvial and upland, 49.
Soil
Soil
arid and humid soils, 31.
determination of organic matter,
112.
glacial soils, 57.
granite soil, 33.
good and poor soils, 326.
humus determination of, 115.
humus in California soils, 120.
humus in Nebraska soils, 120.
lime requirement of soil, 355.
limestone soil, 33.
loess soils, 63.
marine soils, 52.
mechanical, 67.
nitrogen in California soils, 120.
nitrogen in Nebraska soils, 120.
nitrogen in soils of United States,
118.
organic matter in Nebraska loess,
120.
organic matter in Minnesota soils,
119.
organic matter in soils of United
States, 117.
peat and muck, 44.
residual soils, 41, 52, 57.
class, discussion of, 79.
determination from a
analysis, 84.
practical determination of, 83.
colloids, absorption by, 265.
as influenced by plant roots, 297.
generation of, 132.
importance of, 135.
influence of, 135.
resumé of, 138.
mechanical]
Soil color, cause of, 36.
significance of, 386.
Soil erosion and its control, 204.
types of, 205.
SUBJECT MATTER
Soil
Soil
Soil
Soil
Soil
Soil
Soil
Soil
Soil
585
exhaustion, discussion 309.
possibility of, 308.
time for, 309.
extraction, a method of studying the
soil solution, 279.
fertility, defined, 554.
effect on transpiration, 192.
factors involved in maintenance, 554.
importance of nitrification to, 423.
influence of plants and animals on,
23.
maintenance program of, 560.
relation of sulfur to, 468.
sources of knowledge, 554.
formation, forces of, 16.
general statement of, 29.
glacial action, 18.
influence of carbonation, 26.
influence of climate, 30.
influence of hydration, 26.
influence of solution, 27.
oxidation and deoxidation, 24.
processes classified, 16.
special cases of, 32.
temperature changes, 21.
water action, 17, 19.
heat, importance of, 223.
influence of on the soil, 224.
loss of by conduction, 240.
loss of by evaporation, 240.
loss of by radiation, 240.
transfer of, 238.
humus, determination of, 115.
of,
minerals, importance of, 6.
list: of, 5.
moisture, conservation of, 219.
data of, 179.
effect on conductivity of heat, 236.
effect on heat capacity, 233.
effect on transpiration, 191.
importance of amount in plowing,
146.
influence of on the soil
286.
optimum for efficient tillage, 150.
optimum for plants, 200.
relation of to granulation,
solution,
142.
mulch and moisture conservation,
ry ai ls
relation of to capillary movement,
V5.
use of, 218.
586
Soil organic matter, amount of in
Minnesota soils, 119.
amount of in soils of United States,
117.
general nature, 7.
importance of, 121.
maintenance of, 122.
resumé of, 126.
source and character of, 99.
Soil organisms, and the free-fixation of
nitrogen, 431.
benefits of, 397.
general methods of study, 399.
groups of, 384.
influence in nitrate assimilation, 426.
influence of alkali on, 335.
injurious to higher plants, 396.
macro-animal forms, 384.
macro-plant forms, 385.
micro-animal forms, 386.
micro-plant forms, 388.
resumé of, 440.
Soil particles, character as determined by
size, 69.
classification of, 67.
minerological character, 75.
number of, 95.
surface of, 97.
Soil separates, chemical and minerological
characters, 75.
chemical composition of, 78, 79.
physical characters of, 73.
sizes of, 67.
specific gravity of, 89.
Soil solution, as studied by aqueous ex-
traction, 279.
as studied by depression of freezing
point, 280.
composition data of, 283, 288.
concentration data of, 282,
286.
general character of, 275.
influence of crop on, 284.
influence of miscellaneous factors on
286.
influence of season on, 283.
methods of study, 277.
qualitative composition of, 280.
quantitative composition of, 282.
relation to absorption, 276.
relation to productivity, 287.
summary of, 288.
285,
INDEX OF SUBJECT MATTER
Soil structure, ideal, 88.
nature of, 87.
types of, 139.
Soil temperature,
data of, 243.
influence of slope,
variations of, 242.
Soil water, availability of, 198.
diagram of forms, 199.
effect on air movement, 258.
effect on specific heat of soils, 233.
form of molecule, 28.
forms of, 151.
function to plants, 184.
general characteristics of, 152.
influence on plants, 186.
loss by evaporation, 216
loss by percolation, 206.
loss by percolation at Cornell, 209.
loss by percolation at Rothamsted,
207.
modes of loss, 202.
methods of expressing, 156
run-off losses, 203.
summary of control, 221.
thermal movement of, 182.
Soluble matter carried into ocean, 46.
Soluble salts in soil, influence on nitri-
fication, 421.
Solubility of nutrients as influenced by
earbon dioxide, 255.
Solution, loss of nutrients because of, 28.
importance of in soil formation, 27.
relation of to soil productivity, 28.
Specific gravity of minerals, 89.
Specific gravity of soils, defined, 88.
determination of, 90.
Specific gravity of soil separates, 89.
Specific heat, data on soils, 232.
defined, 231.
Specific heat of soil, 251.
control of, 244.
229.
factors affecting, 232.
Stages in the decay of green manures,
542.
Stassfurt salts, chlorides and _ sulfates,
463.
kainit, 463.
silvinit, 463.
Stone drains, construction of, 212.
Straw, influence on nitrate reduction,
425.
Streams, soil formation by, 46.
INDEX OF SUBJECT MATTER
Structure of soil, effect on capillary
capacity, 164.
effect on capillary movement, 174.
effect on gravity water, 176.
effect on heat conductivity, 236.
ideal condition, 88.
influence on optimum water, 201.
nature of, 87.
summary of, 149.
types of, 139.
Substitutions of bases in soils, 270.
Sulfate sulfur as a fertilizer, 468.
Sulfofication, effect of lime on,
factors influencing, 405.
influence on carbon dioxide produc-
tion, 255.
determination of, 405,
reactions of, 403.
relation of to mineral cycle, 408.
Sulfur, amount added to soil in precipi-
tation, 469.
amount in soils, 13.
405.
as a fertilizer, 467.
experiments with as a fertilizer,
467.
forms of in soil, 11.
how lost from soil, 404.
importance of in soil fertility, 470.
loss of from Cornell soils, 307, 404.
loss of from soil, 555.
natural addition to soil, 557.
oxidation of in soils, 403.
possible deficiency in arable soils,
468.
pounds removed by various crops,
468.
sources of in soils, 403.
use in composting, 406.
use of as a sulfate, 468.
Sulfur composts, 406.
Sulfur cycle of soil, losses of sulfur from,
404,
sources of sulfur, 403.
sulfofication, 403.
Sulfurous acid, relation to mineral cycle,
408.
Superfluous water, 198.
Surface of soil particles, calculation of,
97.
importance of, 97.
Surface tension, defined, 160.
effect on capillarity, 170.
\
587
Surface tension, force of, 160.
relation to capillary movement, 169.
Synergism, relation of to plant absorp-
tion, 300.
relation of to soil acidity, 349.
nature of, 349.
Systems of applying fertilizers, 496.
Tankage changes in soil, 445.
character of, 445.
composition of, 445.
source of, 445.
Temperature of soil, control of, 244.
data of, 243.
effect of change on soil air, 259.
effect on capillary capacity, 163.
effect on gravity water, 176.
importance in soil formation, 21.
influence of decay on, 239.
influence of slope, 230.
influence on bacteria, 394.
influence on hygroscopic coefficient,
158.
influence on nitrification, 420.
variations of, 242.
Temperatures for crop growth, 224.
for germination of seeds, 224.
Terracing, 205.
Texture of soil, definition of, 66.
effect on absorption, 267.
effect on capillary capacity, 164.
effect on capillary movement, 173.
effect on gravity water, 176.
effect on heat conduction, 236.
effect on specific heat, 232.
influence on moisture equivalent,
168.
Thermal movement of soil water, na-
ture of, 182.
relation to evaporation, 182.
Tile drains, depth and interval of, 214.
effective grade for, 214.
functions of, 212.
outlets of, 214.
size of tile, 213.
study of drainage water from, 180.
systems, 212.
table for determination of size, 214.
Tillage, influence on granulation, 144.
influence on soil solution, 286.
killing of weeds by, 219.
Tilth of the soil, defined, 149.
588
Time, influence on absorption by soils,
269.
Time of applying fertilizers, 495.
Tolerance of plants to soil acidity, 353.
Tramping, influence on farm manure,
524.
Transpiration, factors affecting, 188.
Transpiration ratio, defined, 187.
determination of, 187.
of different crops, data, 189.
Transported soil, explanation of term, 28.
Truog test for soil acidity, 358.
Types of farming, influence on the main-
tenance of fertility, 558.
Urea, ammonification of, 414.
decomposition of in manure, 509.
production of from calcium cyana-
mid, 250.
Unavailable water in soil, 198.
Unmixed fertilizers, purchase of, 484.
use of, 484.
Utilization of ammonium
higher plants, 450.
of organic compounds
446.
in salts by
by plants,
Variability of farm manure, 506.
Value of farm manure, agricultural, 513.
commercial, 512.
Vegetables, fertilizer formule for, 491.
Vegetation, resistant to alkali, 340.
Veitch method of determining the lime
requirement of soils, 356.
procedure, 356.
value of, 357.
Viscosity, effect on capillarity, 170.
Voleanic dust, as soil, 65.
Volume of soil air, 257.
calculation of, 258.
Volume weight, determination of, 91.
relation to specific gravity, 94.
Volume weight of soils, data, 93.
explanation of, 91.
Water, alkali in river water, 332.
availability of to plants, 198.
deposition of sediment by, 46.
diagrams of forms in soil, 199.
effect on rocks by freezing, 23.
erosive effects of, 204.
function of to plants, 184.
in farm manure, 501.
INDEX OF SUBJECT MATTER
Water, influence on concentration of soil
solution, 286.
influence on plants, 186.
intake of by plants, 289.
loss of from soil, 202.
loss of from soil by percolation,
206.
loss of from soil by evaporation,
216.
mechanical action of, 17.
methods of expression in soil, 156.
movement in soil, 168, 175, 182.
movement in soil in relation to
plants, 193.
production of hydration by in soil,
27.
relation of to granulation, 142.
required to mature a crop, 193.
use of alkali water in irrigation,
333.
Water requirements of plants, factors
affecting, 188.
investigations of, 189.
nature of, 187.
Water slaked lime, 364.
Water soluble phosphoric acid, defined,
456.
Weathering, character of in arid regions,
30.
character of in humid regions, 30.
defined, 16.
losses due to, 33.
of granite, 33.
of limestone, 33.
of soil, practical relations of, 37.
relation of to alkali, 331.
Weeds, killing of, 219.
Weight of soils, data of, 93.
Wilting, cause of, 194.
explanation of, 194.
Wilting coefficient, calculation of, 198.
determination of, 196.
effect of texture on, 196.
explained, 195.
for different soils, 197.
Wind in soil formation, 19.
Wool and hair waste, composition of,
446.
Zine-sulfide test, criticism of, 360.
for soil acidity, 358.
Zeolites, not present in soil, 265.
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