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Edited by L. H. BAILEY

THE SOIL

'The

THE SOIL

ITS NATURE, RELATIONS, AND FUNDAMENTAL
PRINCIPLES OF MANAGEMENT

BY

F. H. KING

PROFESSOR OF AGRICULTURAL PHYSICS IN THE
UNIVERSITY OF WISCONSIN

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THE MACMILLAN COMPANY

LONDON: MACMILLAN & CO., Ltd.
1916

Copyright, 1896,
By F. H. king.

All rifjhtH reserved.

Set up, electrotyped, and published July, 1895. Reprinted. January,
1896; May, 1897; April, 1898; June. 1899; August, 1900; Februaiy,
December, 1902; February, 1904; January, November, 1905; October,
1906 ; October, 1907 ; June, December, 1908 ; July, 1909 ; July, 1910-
January, igii ; October, 1912; July, 1913 ; January, July, 1914;
February, 1916.

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EDITOR'S PREFACE TO THE RURAL
SCIENCE SERIES.

The rural industries have taken on a new and quick-
ened life in consequence of the recent teachings and
applications of science. Agriculture is no longer a mere
empiricism, not a congeries of detached experiences, but
it rests upon an irrevocable foundation of laws. These
fundamental laws or principles are numerous and often
abstruse, and they are interwoven into a most complex
fabric ; but we are now able to understand their general
purport, and we can often trace precisely the course of
certain minor principles in problems which, a few years
ago, seemed to be hopelessly obscure, and which, perhaps,
were considered to lie outside the sphere of investiga-
tion. Agriculture has developed into a system of clear
and correct thinking; and inasmuch as every man's
habit of thought is determined greatly by the accuracy
of his knowledge, it follows that the successful prosecu-
tion of rural pursuits is largely a subjective matter.
It is therefore fundamentally important that every rural
occupation should be contemplated from the point of view
of its underlying reasons. It should be approached in a
philosophic spirit. There was an attempt in the older

vi Editor s Preface.

agricultural literature to discuss rural matters fundamen-
tally; but the knowledge of the time was insufficient, and
such writings fell into disrepute as being unpractical and
theoretical. The revolt from this type of writing has
given us the present rural literature, which deals mostly
with the object, and which is too often Avooden in its
style. The time must certainly be at hand when the
new teaching of agriculture can be put into books.

For many years the writer has conceived of an author-
itative series of readable monographs, which shall treat
every rural problem in the light of the undying princi-
ples and concepts upon which it rests. It is fit that
such a series should be introduced by a discussion of
the soil, from which everything ultimately derives its
being. This initial volume is also an admirable illus-
tration of the method of science, for the soil is no longer
conceived to be an inert mixture, presenting only chemi-
cal and simple physical problems, but it is a scene of
life, and its physical attributes are so complex that no
amount of mere empirical or objective treatment can
ever elucidate them. If the venture should prove that
the opening century is ready for the unrestrained appli-
cation of science to rural life, then it is hoped that the
Rural Science Series, under the present direction or
another's, may ultimately cover the whole field of agri-
culture.

L. H. BAILEY.

Cornell University,

Ithaca, N.Y., June 1, 1895.

PREFACE.

In the preparation of the pages which follow, the
writer has endeavored to have them bear to the reader
a rational presentation of the fundamental principles of
the soil as they relate to the immediately practical
aspects of agriculture. The technicalities of the subject
matter, and the lines of experimentation which have
contributed the facts used, have been largely avoided,
not because they are deemed unimportant, but in the
hope that by so doing there might result a thirst for
wider reading which would lead to a search for these
matters in places where they are better presented than
they could be here.

No effort has been made to treat subjects in an
exhaustive manner, the aim being simply to use so
much of recorded facts as shall sufficiently enforce those
principles underlying the management of soils which
it is needful to understand in order that a rational
practice may follow. The soil has been considered as a
scene of life, where altered sunshine maintains an end-
less cycle of changes, rather than as a mere chemical and

vii

viii Preface.

mechanical mixture, and so far as possible the prob-
lems have been given definiteness by treating them
quantitively.

A free use has been made of all available literature,
and credit is usually given by author's name in the text
where the reference is made.

Special acknowledgment is due to the United States
Geological Survey for the use of cuts in Chapter I., and
also to the National Geographic Society for Fig. 11.

F. H. KING.

University of Wisconsin,
Madison, Wis., May, 1895.

CONTENTS.

INTRODUCTION.

PA.6B

Sunshine and its Work. Nature of sunshine — Absorption
and transformation of sunshine — Sunshine the motive
power in winds, in evaporation, and in plant growth —
The work of sunshine expressed in horse power — Move-
ment of water in the soil and the circulation of sap influ-
enced by sunshine — The complex character of sunshine . 3

The Atmosphere and its Work. The weight of the at-
mosphere — Part played in physiologic processes — Depth
and density of the atmosphere — Its composition — Influ-
ence of the atmosphere on the mean temperature of the
earth — Selective power of the constituents of the atmos-
phere — The distribution of water and plant food through
wind currents 9

Water and its Work. Part played in cooling the earth —
Influence of tides upon the rate of rotation of the earth

— Its work in corroding, dissolving, and transporting the
materials of land areas — The part of water in the physio-
logic processes of plant and animal life . . . . 15 -

Living Forms and their Work. The protective and de-
structive effects of life on land areas — Part life has
played in rock building and in producing mineral deposits

— The great number and variety of life forms immediately
important to agriculture 18

Over and Over again. Cycles in nature — Conservation of
energy — The circulation of the atmosphere — The mag-
nitude and extent of water movement — Rotation of the

materials of land areas 21

ix

X Contents,

CHAPTER I.

THE NATURE, FUNCTIONS, ORIGIN, AND WASTING OF SOILS.

PAGK

Nature and general composition of soil — Soil and subsoil —
Difference between subsoils of humid and arid regions —
Effect of lime on arid soils — The functions of soil —
Plants without true roots — Influence of soil in the
processes of evolution — The soil a water reservoir —
The soil a laboratory — Origin of soils — Agencies in
the formation of soil — Transition from rocks to soil —
Methods of rock disintegration — The action of streams
in soil growth — Sediments moved by streams — The
shifting of water courses — Mechanical action of rains —
Bad lands of Mississippi — Overplacement of soils — Gla-
cial action in soil production — Part played by animals in
soil formation — Formation of humus — Origin of swamp
soils — Wind-formed soils . . . . . . .27

CHAPTER II.

TEXTURE, COMPOSITION, AND KINDS OF SOIL.

Mechanical analyses of soils — Importance of the size of soil
grains in land values — Surface area of a cubic foot of
soil — Influence of size of soil grains on the rate of solu-
tion of plant food — Influence of texture on drainage and
aeration — Chemical elements in soils — The composition
of soils as shown by chemical analyses — Sandy soils
compared with clay soils — The interpretation of chemical
analyses of soils — Soils and subsoils contrasted — Soils
of humid and arid regions compared — Chemical compo-
sition and functions of humus — The nitrogen content of
humus in arid and humid soils — The functions of certain
chemical ingredients of soil — Kinds of soils — Relation of
plants to different types of soils — Relation between plant
food stored in the soil and that removed by crops — The
" running out " of soils .70

Contents. zi

CHAPTER III.

NITROGEN OF THE SOIL.

PAOF

Nitrogen content of soils of different regions — Nitrification in
humus — Great importance of nitrogen, sulfur, and phos-
phorus in plant life — The quantitive relation of the nitro-
gen in crops compared with their ash ingredients, and
these with the natural supplies in the soil — Forms in
which nitrogen occurs in the soil — Distribution of nitro-
gen in the soil — Distribution of nitrates in the soil —
Sources of soil nitrogen — Nitrogen compounds derived
from the air — Sulfuric acid derived from the air compared
with crop demands — Absorption of ammonia from the air
by soils — Free-nitrogen-fixing germs — Different varieties
or species of germs — Symbiosis — Observations of Frank,
Schlosing, Jr. , Laurent, and Kosswitsch on soil algae —
Processes of nitrification — Conditions which bring about
denitrification . 107

CHAPTER IV.

CAPILLARITY, SOLUTION, DIFFUSION, AND OSMOSIS.

Illustrations of capillarity — Nature of capillarity and relation
to surface tension — Strength of surface tension — Rise of
liquids in capillary tubes — Capillary movement of water
in soils — Measure of capillary work — Nature of solution

— Solution of plant food from soil grains — Source of
power in solution — Examples of osmosis — Measurement
of osmotic pressure — Method of osmotic movement —
Translocation of starch, etc., in plants — The so-called
selective power of plants 135

CHAPTER V.

SOIL WATER.

Functions of soil water — Amounts of water demanded by crops

— Rainfall in most countries insufficient for the- largest

xii Contents.

PAGE

yields — Capacity of the soil for water — Rate of percola-
tion from soils — Amount of soil water available to plants

— The water table — Relation of water table to the surface

— Wells — Contamination of well water by percolation —
Movements of soil water — Rate of percolation through dif-
ferent kinds of soil — Capillary movements of soil water in
field soils — Influence of fertilizers on the rate of capillary
movement — Barometric oscillations of the ground water

— Temperature oscillations of the ground water . . . 164

CHAPTER VI.

CONSERVATION OF SOIL MOISTURE.

Amount of water retained by field soils — Influence of plow-
ing land on the loss of soil water — Importance of early
tillage — Importance of early seeding — Use of catch crops
to diminish the loss of fertility — Danger in the use of
catch crops — Comparative losses of water on land culti-
vated and land not cultivated — Comparison between soil
mulches of different depths — Mulching effect of soils of
different kinds — Translocation of soil moisture caused by
rains — Effects of cultivation on translocation of soil moist-
ure — Translocation produced by firming the soil — Deep
tillage to conserve soil moisture — More water available on
drained lands — Flat and ridge culture — Influence of wind
breaks and grass lands on the rate of evaporation . .184

CHAPTER VII.

DISTRIBUTION OF ROOTS IN THE SOIL.

Distribution of corn roots under field conditions — Vertical
distribution of roots — Extent of root foraging in soils —
Influence of soil texture on symmetry of development . 207

Contents. liii

CHAPTER VIII.

SOIL TEMPERATURE.

PAGF,

Importance of right soil temperature — Temperature at which
vegetation becomes active — Observed soil temperatures at
different depths — Influence of temperature on solution and
diffusion in the soil — Influence of temperature on soil ven-
tilation and upon osmosis — Temperatures favorable to ger-
mination— Influence of soil temperature on nitrification —
Conditions which influence soil temperature — Specific heat
of water and of soils — Influence of evaporation on soil
temperature — Temperatures on drained and undrained
soils — Variation of temperature with kinds of soil — Vari-
ation of temperature with direction and amount of slope —
Influence of color on soil temperature — Influence of rolling
and smoothing on soil temperatures — Temperature modi-
fied by depth of cultivation — Percolation after rains modi-
fies soil temperature — Means of hastening the rise of soil
temperatures early in the season — Thorough tillage —
Rolling — Tillage to diminish the diurnal range of soil
temperature ..,,,,.... 218

CHAPTER IX.

RELATION or AIR TO SOIL.

Need of air in soil — Floating gardens and water culture —
Saltpetre farming — Aeration of soil to prevent denitrifica-
tion — Warington's experiments on water-logged soil —
Soil ventilation to admit free nitrogen — Natural processes
of soil ventilation — Blowing wells — Large ventilation of
certain types of soils — Means of controlling soil ventila-
tion — Flocculation increases soil ventilation — Influence of
underdraining on soil ventilation — Aerating power of
clover and other forms of vegetation — Soils may be too
thoroughly ventilated — Hygroscopic moisture of soils . 239

xiv Contents.

CHAPTER X.-

FARM DRAINAGE.

PAOE

Area of swamp lands in the United States — Reclamation of
swamp lands in Holland — Lands which may be improved
by draining — Drainage systems in Illinois — Necessity of
draining water-logged soils — Depth to which the water
table should be lowered — Provision to prevent too rapid
loss of water through tile drains — Distance between tile
drains — The gradient of the ground-water surface — Rate
of lowering the level of the water table — Natural sub-irri-
gation — Value of such lands for intensive farming — Needs
and methods of surface drainage — Celtic land beds —
Draining basins without outlets — Example of field under-
draining — Fall of drains — Cost of tile draining — Size of
tile — Outlet of drains — Joining laterals with mains —
Obstruction of tile drains by the roots of trees . . . 253

CHAPTER XL

IRRIGATION.

Encouragement for irrigating in humid climates — Results of
sewage irrigation — Effect of irrigation on yield of corn in
Wisconsin — Irrigation of grass lands in Europe — Devel-
opment of irrigation in early times — Extent of irrigation
at the present time — Amount of water used in irrigation —
Methods of obtaining water for irrigation — Cost of irriga-
tion — Irrigation of barren sands in Belgium . . . 268

CHAPTER XIL

PHYSICAL EFFECTS OF TILLAGE AND FERTILIZERS.

Importance of good tilth — Effect of cultivation on the texture
of the soil — Seeding to grass tends to restore texture sim-
ilar to that of virgin soil — Change of texture by puddling

Contents, xv

— The formation of clods — How plowiiit,^ affects tilth —
Early tillage after rains to preserve £;oo(l tilth — Subsoiling
in humid and semiarid regions — Winter weathering to
improve tilth — Huniing and paring — Influence of fertil-
izers of different kinds in altering the texture of soils —
Capillary power and rate of percolation affected by fertil-
izers — Physical action of soils in retaining certain salts —
Influence of farmyard manure on soil moisture — Influence
of summer fallowing on the relation of soil to water — The
Lois-Weedon system of tillage — Summer fallowing in
humid and semihumid climates 270

THE SOIL.

INTRODUCTION.

It was early one morning late in October after there
had been several very severe frosts that a fox squirrel,
either by chance or in deliberate search, passed under a
large tree and found the ground thickly strewn with
butternuts. All night these nuts had been falling by
ones and by twos until now the ground was nearly cov-
ered with them. As some other squirrel had done, one,
or maybe, two hundred years before, so did this one take
a nut, and hurrying off to a secluded spot, bury it in the
soil beneath the forest mold. Why this was done,
whether with the intention of recovering it for a future
meal, or whether, like a deliberate forester, he planted
it that another tree might grow, only that squirrel knew.
It lay there in the ground undisturbed the winter
through ; but in the spring, as with a thousand seeds of
other kinds, its obstinate shell opened without a jar or
sound. Water crept in, and the rich oil stored all winter
in the thick meat rapidly changed into sugar, so that out
of this and other materials borne along in streams of
water which now were setting in from the soil, the tini-
est cells began to form, some building a stem- upward

B 1

2 The Soil.

into the sunshine and air, and others building rootlets
downward and outward into the darkness and dampness
of the soil. As the building, or growth, went rapidly on,
it was not long before the materials stored in the nut and
which induced the squirrel to carry it away, had all
been used; but not, however, until, as a result of this
use, there stood in the rich, dark mold a perfect little
butternut tree with its roots brought into contact with
the water among the soil grains and its green leaves
spread where the throbbing pulses from the rising sun
shall be made to pump the water and do the work of
building a great forest tree.

The processes of sprouting, budding, growing, and
fruiting are marvelous ones, and the farmers, gardeners,
and florists whose lots are cast among them have the
grandest of opportunities for enjoyment and for intel-
lectual and moral uplifting, as well as for pecuniary
profit, if only they will train themselves to take advan-
tage of them and then allow themselves the opportunity
of doing so.

Believing fully in the soundness of these words, the
writer, in preparing this treatise, has aimed to present
the most practical and fundamental facts and principles
concerning the soil as largely as possible from the stand-
point of the How? and the Why? and at the same time
to pause now and then to view some of the wonderful
adaptations of structure to physical environment which
the long processes of evolution have finally produced.
We can well afford to do this because the future develop-
ment of agriculture can be made most rapid and most
sure, not more by giving to the farmer new facts than
by making him able to observe, interpret, and correlate
the facts which each and every year's planting, hoeing,

Suns/){ne and its Work, 3

and harvesting must inevitably bring under his own eyes.
The business of farming has now become so complex,
the sciences to which it must look for direction are so
numerous, and the needs of the world for great quantities
of materials for cheap, wholesome food and clothing are
growing so rapidly more urgent that the farmer of Nine-
teen Hundred must rise upon a plane of better directed
efforts and more economic methods. He can no longer
do as most of us say the squirrel did, — plant without
thought of adaptation or fitness, but simply as and
because his father, grandfather, and great-grandfather
did.

SUNSHINE AND ITS WORK.

Let US not drop at once into the soil and lose our-
selves in the darkness of its details, but first let us look
about and see how our field is related to the world at
large and to the powers that energize in it. Let us begin
with sunshine and the work it does.

While we are yet a long way from fully comprehend-
ing the nature of sunshine, we have learned enough to
know that it is a sort of motion which comes to us from
the sun, traveling through interplanetary space at the
rate of 186,000 miles in a second of time, and on reach-
ing us and being transformed into one or another form
of energy, it does almost the entire work of the world.
When the skillful man strikes a ball with a bat, he does
it in such a manner that almost the entire motion of the
bat passes into the ball, sending it far into the field,
while the bat is brought as completely to rest at his side
as if it had struck a bank of plastic clay. Now the sun-
shine, coming to us from the sun, is as definitely a source

4 The Soil.

of power and is as capable of doing work, of setting
something in motion, as is the bat when actuated by
the powerful arms of the man. When the solar energy,
or sunshine, falls upon the soil, the soil grains take up
or absorb a portion of it as definitely as does the ball
absorb the motion of the bat, the molecules making up
the grains of soil have their velocities increased just
as the ball had its motion as a whole augmented, and
this increase of molecular motion in the soil grains is
what raises its temperature.

When the motion in the surface grains becomes so
great that the soil is warm or hot, some of that motion
is transmitted to the molecules of air coming in contact
with the earth, and these, traveling faster than they did
before, push one another farther apart, thus causing the
air to expand and so become lighter, bulk for bulk, than
the air which has not been so heated. Once in this con-
dition, the lighter air is forced upward by that which is
heavier, and wind is the result. In this wind we unfurl
the sails of a vessel or set a windmill, when the motion of
the wind becomes transformed into a motion of the mill.
This mill attached to a pump drives the piston, and
water is raised from the well. Thus it is the sunshine
warms the soil, the soil expands the air, the air drives
the mill, and the mill lifts the water.

Take another case : When sunshine falls upon water,
its surface molecules are set into such violent motion
that the force of cohesion is overcome and the water
changes to a gas, or evaporates. These rapidly moving
molecules of water vapor rise quickly into the upper
regions of the air where, as their motion slows down,
the force of cohesion gains the ascendency again and
they coalesce, forming clouds and finally large drops of

Sunshine avl its Work. 5

rain, or flakes of snow, and fall back to the ocean again
or upon the land, giving rise to soil moisture, to springs,
rivulets, and rivers, or, where the temperature is perma-
nently low enough, to ice-fields and glaciers, all of which,
as we shall see, have had their part to play in the pro-
duction of soil.

But not all the sunshine goes directly back after
being transformed at the surface. Some of it, in its
altered guise, spreads downward in the soil, and after
the snow is gone and while spring is advancing into
summer and summer into autumn, a large amount of
sunshine is being stored. It is stored by increasing
the rate of motion in the soil, and in the lower atmos-
phere by increasing its temperature. Now, in the tem-
perate and polar zones, when the days become shorter
than the nights, the rate of molecular motion so much
slows down, because more altered sunshine is lost during
the night than is received during the day, from both the
surface air and surface soil in which plants live, tliat
finally the intensity of molecular swing becomes too
feeble to maintain longer the processes of growth, and
plants begin to ripen, to shed their leaves, and finally,
as the motion in the medium in which they live becomes
too feeble, they fall asleep and winter has come. Con-
versely, too, when the days become longer than the
nights, when more blows of sunshine reach the soil dur-
ing the light than can escape during the darkness, there
finally becomes an amount of molecular hustle and bustle
in which sleep is no longer possible, and spring, with all
its fresh verdure and joyous music, bursts upon us.

It is very essential that we fully grasp the important
part which both direct and altered sunshine play in
plant growth; for while we have no control over the

6 The Soil,

amount which may come to a given field, we can and do
control the amount stored in the soil, and we also deter-
mine the number of plants which shall stand upon the
tield to utilize the sunshine whicli does come to it.

In constructing a house, it is not sufficient to have upon
the ground stone, sand, lime, lumber, and nails, enough
and to spare, together with the master builder who
knows how these should be put together. In addition
there must be a moving power, a source of energy, which
is capable of raising these inert materials and bearing
them to their places. So in building the butternut tree,
it was not enough that the squirrel should plant the nut
in a fertile soil with abundant moisture; nor yet that
there lived in the midst of that oily meat a master but-
ternut builder capable of directing how the carbon, oxy-
gen, hydrogen, nitrogen, phosphorus, and other materials
should be compounded and brought together so that by
no possible slip an acorn could drop from the boughs of
the spreading tree; but, in addition, there must be a
moving power, a source of energy, and this is the ether
waves, born in the limitless ether ocean at the fiery sur-
face of the sun so rapidly that more than 400 million
millions of them arrive at each leaf every second, having
come across 93 millions of miles in about eight minutes
of time. It is under such hurried strokes as these that
starch and sugar are made in the cells of plants and that
cellulose is set in the framework of the tree.

So powerful is the work of the sun against the cold
ether of space that Lord Kelvin estimates it at 133 thou-
sand horse power for each square meter at the sun's
surface, and the working capacity of a cubic mile of sun-
shine near the surface of the earth he places at nearly
twenty-two horse power. Now, since the cubic miles of

Sunshine and its Work. 7

sunshine are arriving at the earth at the rate at* 186,680
per second, one section of land and the air resting upon
it must receive

186,680 X 12,050 = 2,249,494,000 ft. lbs.,

and this is equivalent to about one-seventh of a horse
power for each square foot of surface. Not all of this
power reaches the earth's surface, nor is all which strikes
the surface converted into work. It is not the chemical
work in the cells simply which is actuated by the sun-
shine, but, as we shall see in another place, both the cir-
culation of sap and the capillary flow of water in the soil
are dependent upon it, in part, at least.

There is another fact regarding sunshine which we
need to understand. It is this : The waves which come
to us from the sun are very complex in their character;
indeed, it appears as if there were a very large number
of them differing from one another chiefly in their length
or, what amounts to the same thing, in the number which
arrive in a given interval of time, much as we know to
be the fact with musical tones differing in pitch. In the
case of light there is a long series of wave lengths which
are characterized by being able, when they fall upon the
retina of the human eye, to produce the physiological
effect which we designate as color of one sort or another.
But associated with these color waves, there are many
others to which the human eye is not sensitive, and
these are designated as dark waves. Some of these are
much shorter than the color waves, and are specially
powerful in breaking down the molecular structure of
many substances; that is, in producing chemical changes.
Then again, on the other side of the light waves, there are
dark ones of much longer periods of vibration, and these

8 The Soil.

long waves, to which we are insensible through the sense
of sight, have a wonderful power of heating many sub-
stances when they fall upon them, and one of these sub-
stances in which we are specially interested in this study
of soils, is water. When you take a large lens and let
-the bright sunshine pass through it, the glass is very
little warmed by the passage, but if you hold paper at
the light focus, it is quickly set on fire by the strong
heating power of the dark or invisible rays. This has
been proved by allowing the light to pass first through
a solution of iodine in bisulphide of carbon, which is
very transparent to the dark waves, but opaque to the
light ones. When such waves are brought to a focus,
they produce intense heating effects, and water is made
to boil quickly under their influence. If, on the other
hand, the light from the sun is first passed through a
solution of alum in water, which is largely opaque to
the dark waves, these are sifted out, and when the light
waves by themselves are focused upon the water or
paper, very slight heating effects are observed.

The fact that water is opaque to the dark rays from
the sun, — that is, absorbs them instead of transmitting
or reflecting them unaltered, — lies at the foundation of
the evaporation of it from ocean, lakes, and streams, and
also from the soil and the leaves of vegetation in some
degree. When these waves fall upon the water, they set
its surface molecules in rapid vibration, that is, they
heat them, and this increased speed of to-and-fro move-
ment overcomes the force of cohesion and the molecules
fly off, or evaporate, as we say. Were the water not
opaque to these dark waves from the sun, neither snow
nor ice would be rapidly melted in the spring, nor would
there be as much evaporation from the ocean as we now

The AUnoHphere and its Work. 9

have, and hence rains would be less frequent and the
lands less productive.

THE ATMOSPHERE AND ITS WORK.

We have dwelt very briefly upon the nature of sun-
shine and the part it plays in the work of the world.
Let us next look at the atmosphere, for this, both in a
broad way and in many details, has to do with our sub-
ject, the soil.

In the first place let us note that, light and imponder-
able as the air seems to be, it nevertheless presses very
heavily upon all surfaces at or near sea level — so heavily,
indeed, that the pressure is nearly 15 pounds on each
square inch of surface and more than a ton to the square
foot. Each square rod of land lying near sea level sus-
tains a load amounting to 289 tons, and each acre 46,200
tons of air. Does it seem to you strange that, while the
extended palm of one hand is pressed downward by a load
of air equal in weight to that of the body, we are yet un-
conscious of it? If this puzzles you, place your hand
beneath the surface of a pail of water. The water does
not seem to bear it down. Carry your hand to the
bottom of the pail. Still you do not realize that it
presses any harder, and yet the bottom of the pail is
carrying a load of some 20 pounds, and this is evident
enough to you when you hold the pail upon the hand.
When the hand is immersed in the water, it is buoyed
up with a pressure equal to that which bears it down,
and the pressure which crowds it to the left equals that
which would move it to the right and, so long as the
pressures are equal in all directions, we are unconscious
of them. As tish move through the waters of the stream,

10 The Soil.

the lake, or the ocean, unconscious of and unimpeded by
the pressure of it, so do we travel along the bottom of
an ocean of air; for such in reality the atmosphere is.

In breathing, in drinking, and also in eating, we regu-
larly, but unconsciously, utilize atmospheric pressure.
Raising the ribs and lowering the diaphragm lifts off
the outside air-pressure in part, and at once the air
crowds in until the lungs are stretched and filled by it.
To drink, we project the lips under water, shut off com-
munication with the nostrils, using for this purpose the
curtain called the soft palate, and then draw down the
floor of the mouth, thus making the cavity larger; this
removes part of the pressure from the water inside the
lips, and at once the greater outside push upon the water
fills the mouth and we are ready to swallow. Then, too,
in eating, we place the morsel to be chewed between the
teeth with the tongue ; but how is it removed when the
work is finished? If you will watch yourself, you will
observe that with both the lips and the passage to the
nostrils closed, the lower jaw is dropped, which destroys
the balance of pressure on the flexible cheeks, when the
air on the outside immediately tucks them in between
the teeth, and this crowds the morsel out, all so easily,
so unconsciously, and in so brief a time that it is not
without difficulty that we can convince ourselves of the
real means used to do the work.

It is the unbalancing of this same atmospheric pres-
sure that produces the gentle breeze, and the terrible
tornado; that lifts the water in the pump and in the
siphon; that produces the draft in the chimney and the
in-going and out-going currents of air which constitute
soil-breathing or soil-ventilation, so essential to plant
life,

The Afmosjjhere and its Work. il

T have said that we are living at the bottom of an
aerial ocean, and this ocean has a depth of 200 or pos-
sibly of 500 miles, but, unlike the one of water, it grows
so rapidly less and less dense as its upper surface is
approached, that in rising upward from the ground
through it one would leave behind him in the first l/>
miles all but 4.8 per cent of the entire mass; and yet
this thin upper portion offers resistance enough to those
stone-like bodies called meteors, traversing space, so
that when they plunge beneath its surface, moving at
their fearful rate, they quickly become intensely hot or
are even converted entirely into gas by the great heat
produced during the fall, long before the lower depths
of the atmosphere are reached.

Were we to separate the molecules of different kinds
which together make up the atmosphere, we should find
a large variety of them, but if, after doing so, we were to
compare them, volume by volume, we should find, under
average conditions, in every 100 cubic feet of air not far
from 20.01 cubic feet of oxygen, 77.18 of. nitrogen, 1.4
of water vapor, .04 of carbon dioxide, and .78 cubic feet
of a recently discovered gas, named argon, reported at
the last meeting of the British Association by Lord
Rayleigh and Professor Ramsey, as composing about one
per cent of the nitrogen of the air. Professor Morley
found at Hudson, Ohio, in his very critical analyses,
made in duplicate daily and continued for six months,
that the oxygen composed 20.949 per cent of the oxygen
and nitrogen taken together, which would make the per
cent of nitrogen 79.051.

Besides the substances mentioned above as being found
in the air, there should also be named, on account of
their important relations to agriculture, ammonia and

12 The Soil

nitric acid, together with a modified and extremely active
form of oxygen, named ozone ; and when it is stated that
water, carbon dioxide, nitrogen, ammonia, and nitric
acid, taken directly or indirectly from the atmosphere,
contribute more than 97 p.er_jsgn.t_Qi' .alL the materials
which are built into the tissues of plants, we can begin
to understand how great a part is played by the aerial
ocean in the bottom of which we live.

There is another extremely important office which the
atmosphere performs, and that is to keep the earth
warm. When the sunshine reaches the upper limits of
our air, it enters it almost wholly unimpeded, and only
as the last few miles of the lower depths are reached is
there an appreciable number of its waves turned back
into space or absorbed by the air in their passage
through it. But when these ether waves break against
the land and water surface of our planet, their force is
very largely spent in setting the molecules of soil and of
water swinging to and fro more rapidly than before, and
this means to make them warmer. But to make it clear
just how the air is able to save this warmth for us,
another fact must be mentioned. It has been said that
the ether waves coming to us from the sun set the soil
and water molecules swinging when they strike against
them. Now the opposite of this is the case at the sur-
face of the sun. There the swinging molecules strike
the ether of space, and by that very act lose so much of
their power as speeds away to the earth in the waves
produced. The rate of vibration of the molecules at the
solar surface is, however, very rapid, so that the waves
which are sent down through our atmosphere to the
earth are very short, so short, indeed, that they seem to
make their way among the molecules of our air without

The Atmosphere and its Work. 13

disturbing them; but the to-and-fro motion which these
waves engender in the earth molecules is very much
slower, and hence when these in their turn start waves
back through the ether toward the sun, as they do, these
waves are much longer and are unable to make their way
past the air molecules without setting them swinging;
but this means to make the air warmer, it means to hold
the sunshine imprisoned for the time being, but in the
altered guise of terrestrial heat.

How great this accumulation of heat is will be appre-
ciated when it is stated that Professor Langley, after
making a long and very careful experimental study of
this property of our atmosphere, at the base and sum-
mit of Mt. Whitney, in California, reached the con-
clusion that, had our earth no atmosphere, its surface
temperature, even under the equator at noon, would be
200° C. below freezing, and this means a temperature
of -328° F.

With this fact before us, and remembering how slow-
ing down the molecular motion in the tissues of plants,
even to the rate of our winter temperatures, stops all
plant growth, there is no difficulty in realizing how
important this property of the atmosphere is to the life
of both plants and animals.

The transformed solar energy does not accumulate at
the earth's surface indefinitely, but only until a certain
degree of intensity is reached, and then the mean yearly
out-go exactly balances the mean yearly in-come. Just
how this balance is attained, one will readily understand
if we use an illustration from another field. Suppose we
have a tall vessel with a hole in one side near the
bottom, and that into this vessel a stream of water is
flowing over the top. Evidently the in-going stream

14 The Soil.

may be so large that, at first, more water enters over
the top than escapes through the opening at the bottom;
but there will come a time, if the vessel is deep enough,
Avhen the pressure forcing the water out becomes so
great as to cause the quantity of water escaping to exactly
equal that which enters, and under these conditions a
balance is established. So it is with the out-going heat
of our earth; its intensity increases under the resistance
to its escape by the atmosphere until the jostle of the
air molecules among themselves becomes so great that
enough waves of the long sort escape into empty space
to exactly compensate for those which are being trans-
formed at and near the surface of the earth.

Not all portions or constituents of our atmosphere
exert the same screening power over the long dark waves
radiated back into space by the earth. It is the lower
layers of the air, and especially those portions which
are heavily dust and moisture laden which exert this
power in a pre-eminent degree. And it is because of this
fact that soil temperatures decrease as the altitudes on
mountain sides increase until, even under the equator,
permanently frozen ground and eternal snow-fields and
glaciers may be met only four or five miles above sea
level. So, too, when the sky clears after a winter storm
and the air has been swept exceptionally clean of its
moisture and particles of dust by the forming crystals of
snow, each of which has its beginning about a particle
of dust, that the radiations escape rapidly through the
clear air, giving rise to the cold waves which traverse
the country in the rear of winter storms. This is also
the reason, in part, why killing frosts in fall and spring
usually occur only on clear nights; and why it is that
tlie temperature of arid regions falls so rapidly as soon
as the sun has set.

Wafer and itfi Work. 15

Looking at the atinospliere once more in its relation
to life, we find that it performs a very large and very
important work as a distributing agent or means of
transporting the food and waste of every living being.
Taking up the carbon dioxide as it is thrown off in the
soil by the germs which consume dead organic matter
there, from the lungs and tissues of animals living both
upon the land and in the water, from the craters of
active volcanoes, and from the fires kindled by man, it is
borne by the winds into contact with the green parts of
plants, where its carbon is appropriated in the processes
of growth. Taking up the oxygen, too, as it is set free
from the carbon dioxide in the tissues of plants, the
winds bear it back to the soil, to the tissues of animals,
and to the fires of the home and the workshop. Taking
up the water, too, of which the plant must use from 200
to 300 pounds for every pound of dry matter produced,
it is borne fresh and sweet from the salt sea and de-
posited upon the land, into which it sinks, to be drunk by
the roots of plants or brought back by gravity, in the
form of springs, to quench the thirst of animals.

WATER AND ITS WORK.

Water is another agent which plays an extremely im-
portant part in the processes going on in the soil, and it
will be helpful to us if, before entering upon details, we
can get a broad view of the work it has done and is now
doing.

Studies, both in astronomy and in geology, point to a
stage early in the history of the earth when the temper-
ature of the solid land was very far above even a red
heat. This being true, there must have been a time

16 The Soil

wlien the great ocean sheets Avhich now cover three*
fourths of our globe to a mean depth of 16,000 feet did
not exist as such, their waters then floating in the form of
vapor, shrouding the whole earth in an atmosphere of
great density. At this stage water began its great work
which to-day is still in progress. Let us see what it has
been.

If the small amount of water vapor and dust particles
existing to-day in our atmosphere play so important a
part in holding back the dark radiations from the earth's
surface and thus keeping it warm, as we have seen, how
extremely opaque in those early days the atmosphere
must have been to these long waves, and how slowly
must the surplus heat have passed away by this method !
And yet the first great work that water did was to greatly
hasten the cooling of the earth down to the temperature
at which it might become the abode of life. The man-
ner in which it did its work was this : The water in the
upper, clearer portions of the atmosphere lost its heat
by radiation and, condensing into drops, fell as rain to a
lower and much warmer level, where, at the expense of
the heat of the region into which it had fallen, it was
quickly evaporated, but only to rise once more into the
upper regions to send off into space the large amount of
heat which had been imparted to it. The vapor of water,
being much lighter than air, rose more quickly than
heated air currents could have done, and then, on being-
condensed into liquid drops, returned again far swifter
than it had risen, so that the number of journeys made
by these water molecules in their mission of cooling the
earth far outnumbered those made by the molecules of
oxj^gen, nitrogen, or carbon dioxide during equal intervals
of time. Nor is this all, for each pound of water carried

Water and ita Work. 1 7

with it on every jounioy many times the amount of heat
which an equivalent amount of air was able to bear.

The next great work that water did was to slow down
the rate of rotation of the earth upon its axis until,
according to the investigations of G. H. Darwin, our day
was changed from one perhaps not longer than three
hours to its present twenty-four. It is through the in-
strumentality of the tides, which, acting as a friction
brake upon the earth, have steadily slowed its motion
down, but much more rapidly in the early days than at
the present time ; for then, on account of the moon being
nearer to the earth, the tides had perhaps thirty-six
times their present magnitude.

As soon as large land areas emerged from the sea, then
the third great work of Avater began ; a work which,
through all this long time, has consisted in dissolving
out, in altering, in breaking into smaller fragments, in
grinding, and finally in transporting from higher to lower
levels the soil, the minerals, and the rocks of all lands.

This third work of water has been a vast one indeed,
but just how great our present knowledge does not make
it possible to form even an approximate estimate ; that
it has been very large, every considerable land area bears
ample and indisputable evidence. Take the state of
Wisconsin as an illustration : Leaving out of the count
the vast depth of deposits which together have been
grouped as Laurentian, in this state we have, lying above
them, a measured thickness of rock fragments exceeding
30,000 feet, built from materials taken from the soils, the
coast lines, the banks of streams, and the subterranean
waterways of earlier land areas by this never-ceasing
action of water. But great as has been the work of
water here in sweeping the dust and litter of land

18 The Soil.

sculpturing into the sea, the strata referred to are the
accumulations of less than half the years since the work
began.

Finally, with the advent of living forms upon our
planet, water took up still another very important work ;
for to both plants and animals it is indispensable. Mak-
ing up the larger part of their weight, it is the medium
in which the chemical transformations essential to the
processes of growth take place, if, indeed, it does not play
the part of an active and indispensable agent in bringing
these changes about. Then, too, water not only takes up
and holds in the liquid form those substances in the soil
which may become the food of plants, but it is the
medium of transportation by which all materials are
moved from root to leaf and from the leaf back to the
various places where the processes of growth are taking
place. In the physiological processes of the animal body,
it has a similar and equally important role to play ; for
here, too, it becomes first a solvent and then a medium
of transportation by which all food is taken to, and the
wastes removed from, the various organs of the body.
Finally, both in plants and animals, water acts as a tem-
perature regulator, tending, by its evaporation from the
surface, to prevent the tissues becoming too warm, and
among many animals this action is very marked ; for they
have the power, when the body is getting too warm, of
sweating or pouring water upon the surface;, where it may
evaporate quickly and thus cool the body.

LIVING FORMS AND THEIR WORK,

Not only are the various forms of terrestrial life greatly
dependent upon the soil for their well-being, but the soil

Living Forms and their Work. 10

itself throughout geologic time has been wrought upon in
many and very important ways, so that a general state-
ment of the work living forms have accomplished and
are now doing will be a helpful preliminary to our study
of the soil.

All are familiar with the very rapid washing away of
soil by the heavy rains which fall upon steep and naked
hillsides, and also with the equally marked protecting
influence exerted in the prevention of such washing by
the roots and close-lying herbage of plants of almost all
kinds. By this action land plants hold in check, in an
extremely important manner, the destructive power of
water and of wind, giving much deeper and far more
fertile soils than would otherwise be possible.

On the other hand, however, these same roots hasten
the destruction of rocks by growing into their fissures
and wedging them apart, and also by corroding and
dissolving away the surfaces both of rocks and of soil
grains wherever they may come in contact with them.
Nor is this all, for living in the soil, chiefly in the sur-
face 14 inches, are great numbers of microscopic forms,
which, feeding upon the dead tissues of plants and ani-
mals, evolve large quantities of carbon dioxide, nitric
and other acids, which in their turn become corrosive
agents, bearing off in the water which runs to the sea
vast quantities of soil in solution. Mr. T. M. Read has
estimated that the Mississippi alone carries annually to
the sea 150,000,000 tons of dissolved rock materials,
while other streams bear away proportionately large
amounts.

But in this world of never-ending change life has done
more than to protect the steep hillsides and to hasten the
solution of soil and the crumbling of rocks. In addition

20 The Soil.

it has been a great rock-builder and gatherer of mineral
wealth. Taking out of the sea-water the lime which the
carbonic acid has dissolved and floated to the ocean, the
great army of shell bearers and coral builders have, in
all the geologic ages, laid down their mantles and frame-
works to become the limestones of the world. In favored
situations, too, the decay of the organic tissues of plants
and of animals has resulted in the formation of gases,
which, rising through the water, have precipitated from
it iron and possibly lead, zinc, and copper as it was being
borne along in the slow coastal currents, thus bringing
into rich deposits in a few places these metals so indis-
pensable to the civilization of to-day. Then there are
our great beds of coal and peat, our deposits of asphalt
and bitumen, and our reservoirs of mineral oil and
natural gas, all of which are believed to have resulted
chiefly from the decomposition of the tissues of living
forms.

Truly, life, working in the laboratories of the lower-
most layers of the atmosphere, in the surface few
inches of the dark soil and more widely spread in the
transparent ocean waters, using direct and altered sun-
shine as its moving power, has done and is still doing a
very great work. And let the farmer never forget that
his life work is thrown among not a few cultivated plants
and domestic animals, but rather that every farm is in-
habited literally by thousands of kinds and millions of
individuals, most of them microscopic, it is true, but
powerful in their great numbers. Nor can we for a
moment think that only those forms which we con-
sciously aim to raise hold vital relations with us ; for
year by year, as the horizon of our knowledge of the life
histories of the living forms about us is made broader, it

Over and Over Again. 21

is only yet again and again that we learn of new and
important relations existing between them and us.

OVER AND OVER AGAIN.

The tide comes and goes and comes again. The morn-
ing dawns, the sun sets, the stars come out, and once
more the sun is in the east. The cold winds cease to
blow, the birds come and then are gone, the snows drift
high along the fences, but spring is sure to follow. This
method of cycles in the ongoings of nature is so general
and so fundamental to the constancy of results, especially
in agriculture, that we may well pause for a brief general
consideration of it.

The critical and quantitive methods of investigation
which so strongly characterize the nineteenth century
have led us to know that neither the material of things
nor the power which does work can be destroyed. No
discovery of modern science is more fundamental and
far-reaching than that of the indestructibility of both
matter and energy, and equally fundamental is the other
fact that, do what we will, we can create neither the one
nor the other.

We may, if we choose, conspire to have the energy of
burning straw, in the fire box of the engine, converted
into the energy of steam and transmit this through the
piston and driving belt to the thresher where the w^ork is
done ; but while this is going on, through the friction of
belts and bearings, and that of the agitation of the straw,
grain, and air, there reappears ultimately, in the form of
heat, an amount of energy equal to that given to the steam
which drove the piston while doing the work, and this
too is a measure of the direct and altered sunshine

22 The Soil

required to perform the labor of building the straw used
for fuel. Over and over again is energy used to do the
work of the world, but in altered form and in divers
places, nowhere destroyed and nowhere created.

The few bushels of ashes left after burning the win-
ter's supply of wood seem to point to a destruction of
matter, but their weight, added to that of the products
which escape through the chimney, is actually much
greater than the original weight of the fuel ; for much
oxygen from the air has united with it. So it is
with our domestic animals ; what we realize in their
increase of live weight, and in the weight of the dung
and urine, falls so far short of that of the food con-
sumed that here is a seeming destruction of matter, but
when the materials which are thrown oft' in the invisible
form from the lungs and from the skin are taken into
the count, the wastes exceed the food consumed by the
amount of oxygen which the animal has taken from the
air. Now, in both of these cases, the oxygen which
the sunshine released from the carbon in the tissues of
the growing plant finally returns to reclaim its carbon
again and bear it back as carbon dioxide to the atmos-
phere from which it was taken.

The water, too, falling as rain upon the soil, and rising
in the sap to contribute its constituents to the building
of the woody fibre of the fuel, or the starch and sugar
of the food, is again returned to the atmosphere to make
the rounds once more. It is the same way with the
nitrogen and with the ash ingredients, — each and all
are used over and over again, but nowhere in the round
is there any loss of matter or any gain.

Take our atmosphere as a whole : In the equatorial
zone of strongest heat the air is steadily rising to a con

Over and Over Arjain, 23

siderable height, where two rnrrents part and move
toward the poles, but only to return as under currents and
to make the trip over again. Then, besides this world-
wide circulation in the atmosphere, there is a tendency,
most of the time, for the air to travel from the land to
the sea and from the sea back to the land again, the
currents being along the land surface from the sea during
the warm portions of the year, but back again toward the
sea overhead ; then when the seasons are cold and the
sea is warmest, the air from the land areas slides along
their surfaces, out upon the sea, while, as an upper
current, it travels back again to return once more ; and
by these two great systems of winds the land is watered
by the moisture brought from the sea, and the general
composition of the whole atmosphere is maintained
remarkably constant.

In addition to these larger systems of circulation, the
greater absorption and transformation of sunshine at
the surface of the earth than takes place higher up in
the atmosphere, maintains everywhere and at all times
local ascending and descending currents, so that, no
matter how rapidly vegetation may consume the carbon
dioxide of the air, and put in its place free oxygen, or
how rapidly animal life in the air, or microbe life in the
soil, may use the free oxygen and put in its place carbon
dioxide, these local ascending and descending currents
keep the air so thoroughly stirred that the most care-
ful chemical analyses reveal only exceedingly small
variations in the relative proportions of the oxygen,
nitrogen, and carbon dioxide in the air ; and since both
plants and animals tend constantly to disturb this rela-
tive proportion of gases, it is plain that by this over
and over again process, a healthful atmosphere, so

24 The Soil.

essential to the well-being of both plants and animals,
is maintained.

Let us now try to gain an idea of the magnitude of the
movement in the endless round which water makes as it
journeys from the sea to the land, and back from the
land to the sea again. Observe the face of your watch
just one minute, and then reflect that, on the average,
during each such interval of time, the Mississippi River
empties into the Gulf of Mexico 40 acres of water
more than 21 feet deep; while in South America, its
great Amazon unloads a burden nearly live times as
large, or more than 103 40-acre-feet per minute. But
large as this work really is, it does not measure the
volume of water which, on the average, is steadily rising
from the earth's surface into the atmosphere under the
impulse of altered sunshine ; for a large part of the
water which falls upon the land is evaporated there, to
return as rain in another place instead of being carried
away by the rivers. On an area equal to the state of
Wisconsin, for example, where the mean annual precipi-
tation measures about 3 feet, the total fall must exceed an
average of 40 acres of water 5 feet deep, for each minute
of the year. But there are large areas of land where the
mean annual precipitation is 60 inches, and others still
where 8 feet of water fall : In these cases, for an area
equal to the state of Wisconsin, or 56,040 square miles,
the aggregate precipitation must exceed ^.^ 40-acre-feet
of water per minute in the first case, and 13.6 in the
second. Now, on only a moderately fertile soil, the
writer has grown maize, supplying it with water just as
rapidly as it could use it to the best advantage, and
found, as an average of two trials, that it did take,
during its growing season, or one-third of a year, the

Over and Over Ar/ain. 25

equivalent of a rainfall of 34.3 inches, and prodnced a
yield, when calrulated for an acre, of more than four
times a very lar^e held crop grown under the best natural
conditions of rainfall in Wisconsin ; so that to grow a
field of corn, of such quality, and the size of this state,
would require the delivery of water upon it at the rate of
40 acres more than 14 feet deep every minute during the
growing season, or a rainfall greater than the largest con-
sidered above. Large then as this movement of water is,
it is seldom great enough during the growing season to
enable a moderately fertile soil to produce its largest crops.

But it is neither to the gaseous nor to the liquid por-
tions of our earth that this process of over and over
again is limited ; for even the solid land is profoundly
involved in it. Careful measurement has shown that
there goes to the sea annually, dissolved in the waters
of the Mississippi River, 150 million tons of rock ; and
of these, 70 millions are the chief constituents of lime-
stone— carbonates of lime, and magnesia; so that the
selfsame materials which journeyed to the sea, dissolved
in the rivers of unnumbered centuries ago and laid down
there by the action of marine life, have since become a
part of the dry land, certainly once, if not many times,
and are now journeying back to be rebuilt into the coral
reef on the ocean's bottom yet once more.

Nor is it rock and soil held in solution simply which
water in its ceaseless rounds is bearing back to the sea ;
for with the dissolved materials there is borne along as
suspended sediment in the waters of the Mississippi
alone, in the space of a single year, 362 million tons,
making 513 million tons of rock and soil carried to the
sea by one river, besides 750 million cubic feet of matter
which are shoved along the bottom to form its delta.

26 The Soil.

The continual transfer of these large amounts of
material from the land to the margin of the sea bottom,
perpetually destroys the balance in the figure of the
earth, so that the land areas rise to compensate in large
measure for the materials borne away, while the marginal
sea bottom subsides in like proportion to readjust the
balance ; but as the sea sediments continue to subside,
they become plastic under the great pressure to which
they are subjected, and flow toward and under the rising
land areas where denudation has been going on, so that
in a very powerful but extremely slow manner there is
a real movement of the solid land toward the sea above
and from the sea back again to the land beneath. And
if such profound and long-enduring systems of rotation
as these are maintained as essential to the life of the
world as a whole, we may practice with great confidence
a rational rotation of crops in our systems of agricul-
ture.

" We cannot measure the need
Of even the tiniest flower,
Nor check the flow of the golden sands
That run through a single hour ;
But the morning dews must fall,
And the sun and the summer rain
Must do their part and perform it all
Over and over again.

"Over and over again
The brook through the meadow flows,
And over and over again
The ponderous mill-wheel goes.
Once doing will not suffice,
Though doing be not in vain."

CHAPTER I.

THE NATURE, FUNCTIONS, ORIGIN, AND WASTING OF

SOILS.

Of all commonplace things, it would be difficult to find
one more uninteresting to most people than soil. Walk-
ing over it all our lives, it has come to be, in our unre-
flective moods, simply dirt, something essentially unclean
and to be shunned. So deeply ingrained is this feeling
that it comes to many almost as an inheritance, and
people of culture, as well as the ignorant, find them-
selves stoutly inclined to shun everything and every-
body directly associated with it.

But the spirit and results of investigation, which have
grown so rapidly during our century, have already so
widened our horizon of knowledge, and so changed the
attitude of mind toward the phenomena of nature about
us, that we are coming to study, in the spirit of science,
many of those things which lie nearest to us, and with
great moral, intellectual, and pecuniary profit ; and since
soil, air, and water are indispensable to all forms of life,
we must know more and more of them as the demands
for food and homes increase.

Taking samples of soil from where we will, whether
from the fertile prairies of central North America, from
the tundras of Siberia, from the barren wastes of the
Sahara, or the rich river bottoms of the Amazon, every-
where we shall find them composed of mingled fragments

27

28 The Soil.

of materials of various kinds. Usually the soil is com-
posed chiefly of small fragments of rock of many
varieties, which may be regarded as the basis of them
all. Associated with these fine rock remnants there
is almost always a varying amount of organic matter
derived from the breaking-down of vegetable and ani-
mal remains. Then, too, adhering to the surface of
these fragments, or scattered among them in the
form of crystals, there are various substances which
have been deposited from over-saturated solutions of soil
moisture.

In clayey soil there is present among its fine silt-like
particles a small quantity of silicate of aluminum having
water combined with it, and which gives to it its sticky,
plastic, or putty-like quality. This adhesive clay, how-
ever, forms only a small part of the whole weight of
such soils, amounting to not more than 1.5 per cent,
according to Schlosing. Then, too, the soils in many
parts of the world have scattered through them larger or
smaller blocks of stone, varying in size from great masses
sometimes weighing tons, down through those Avhich a
man can barely move, to pebbles and coarse grains of
sand. These fragments form no part of the soil proper,
but instead are the materials out of which soils are
made. It is true that the roots of plants may place
themselves alongside of these coarse pieces of rock, and
by their action derive some nourishment from them, but
the amount thus obtained is insignificant when compared
with that which an equal volume of soil might contribute
if placed in their stead; so that such rock fragments,
while they will contribute their volume of soil to the
agriculture of the future, are a positive hindrance to that
of the present.

\1-

Surface Soil and Subsoil. 29

SURFACE SOIL AxNI) SUBSOIL.

In humid climates, where the rainfall is sufficient to
insure remunerative crops, it is common to speak of the
surface, 6 to 12 inches of the fine rock fragments, ^ oOy-^m? ' --^
as constituting the soil, while the deeper portions are
spoken of as the subsoil, and this distinction grows out
of the fact that oftentimes when the deeper soil is
brought to the surface, it is found to be unproductive for
a time, and, besides, there is generally a sharp line of
demarkation in the color of the two portions. In arid
regions, however, where crops can only be raised by irri-
gation, both of these distinctions largely or wholly dis-
appear ; so much so that, in leveling fields to fit them for
an easier distribution of water over the surface, little or
no care is taken to avoid exposing the subsoil or covering
even deeply the surface layer, experience having proved
that earth from the bottom of cellars, and even that from
depths of 30 feet, may be quite as productive, if not
more so, than that which has been long exposed to the
air.

This difference in the nature of the deep soils of arid
and humid regions appears to result from a variation
either in the abundance or arrangement of the finest of
the soil particles which exist in the deeper layers, the
deeper soils of humid regions being usually more close in
texture, and less easily penetrated by water.

This difference in the texture of the soils of humid
and arid regit)ns is not confined to the subsoil, but
involves the surface portions as well, so much so that
when most soils of humid climates become dry, the sur-
face is very hard and difficult to move, while those of
the arid regions of the world are so incoherent that the

30 The Soil.

slightest puff of wind is sufficient to raise a dust, and a
wind storm at any time is quite certain to raise great
clouds of sand so characteristic of desert regions.

Just why the soils of dry climates should lack in the
amount of adhesive materials is not readily explained by
unquestioned facts, but the condition appears to be in
some way related to the larger amount of lime which
Hilgard has shown these soils to contain. It has been
abundantly proved by different experimenters that when
the salts of lime are added to muddy water, it has the
effect of enabling the silt particles to be gathered to-
gether or to become flocculated, settling to the bottom
and leaving the water clear, while without the addition
of lime it would have remained turbid for an indefinite
period.

Hilgard has also shown by experiment that while any
clay or tough clay soil, after being worked into a plastic
mass and allowed to dry, acquires a texture of almost
stony hardness, if to another portion of the same mass
only half a per cent of caustic lime be added, a difference
in the degree of plasticity is at once observable, and on
drying the whole falls into a pile of crumbs at a mere
touch ; and this change is assumed to result from the
expulsion of the water of combination, from the grains
of colloid clay, and the gathering of them together into
compound particles of larger size, which then lose their
cementing power.

We do have, however, many clays very impervious to
water, becoming, when worked, quite plastic and adhesive,
but which cannot be used for brick or pottery on account
of the large amount of lime they contain, which slacks
after firing and by its expansion fractures the ware into
which it lias been shaped. Chemical analysis shows

Relation of the Soil to Organic Evolution. 31

such clays to contain in some cases as high as 5 per
cent of lime and yet for some reason the clay has not
lost its plastic character ; the lime has not produced the
flocculation it sometimes does.

Schlosing found, when he was trying to wash a soil
with which he was working, until water would pass away
from it clear, that, by passing a stream of carbon dioxide
through the soil, it had the desired effect, and he attrib-
uted the clearing of the filtered water to the formation
of more soluble lime carbonate, which, by coagulating the
fine clay passing the filter, causes it to be formed into
compound clusters too large to escape. In view of this
fact it may perhaps be urged that the lime once in the
impervious clay could not be acted upon by the carbonic
acid sufficiently to dissolve enough to do the work of
flocculation, and also that soils more open, as those of
arid regions must be when very dry, give easier and
more complete access to both the carbonic acid and to
what water does fall, so that with the usually relatively
larger amount of lime present, owing to the less leaching
in dry regions, enough would be dissolved to make a more
complete coagulation than generally takes place in the
soils of the more humid regions.

RELATION OF THE SOIL TO ORGANIC EVOLUTION.

But soil is very much more than a mass of broken and
weathered fragments of inert rock, among which are
strewn a small amount of the fast-decaying remnants of
plant and animal life. To appreciate the mechanism of
that great locomotive which in six days places the fruits
of California on the tables of Boston, one must look at it,
not cold and still, as so many nicely fitting pieces of

Fig. 1. — Showing surface denuded of its soil by glacial action and not

yet re-covered.

Relation of the Soil to Organic Evolution. 33

polished brass and steel, but alive, the great heart throb-
bing, the strong arms at the wheels, and the monster
starting, hurrying, halting, with its tons and tons of
burden, always responding with the utmost promptness
and the greatest exactitude to every beck and nod of the
intelligence at the throttle. He must realize how, in its
furnace open to the free air at both ends, the strength of
forty horses is brought out of lifeless coal and placed in a
chamber without an entrance doorway and only a chance
to escape by doing work against the great piston heads.
So if we will understand the soil, as farmers should,
we must see it in action, helping on the work of the
whole world as well as in producing the basket of apples,
the bushel of wheat, or the pound of pork.

How indispensable soil is to the life of both plants
and animals as they are now constituted, will be apparent
at a moment's reflection when we picture to ourselves the
conditions which would exist were all the soil of the
entire land area swept into the sea, leaving the surface
with the appearance shown in Fig. 1. Under these con-
ditions it is evident that all upright types of plants
would be without means for maintaining that position,
and there would be no provision, as these plants are now
constituted, whereby they could be supplied with water
except during times when the rains were actually falling ;
for the water would hurry swiftly from the surfaces of
the naked rock into the main waterways and oft* to the
sea.

Were the land without soil, the vegetation of these
areas could only consist of a meagre growth of such
forms, among living species, as now subsist upon the
naked rocks of mountain sides and similarly exposed
situations, where, for any reason, soil is not permitted tp

84 The Soil,

accumulate; forms which, like the lichens, algae and
fungi, are not provided with true roots, and which derive
almost their whole nourishment, including water, directly
from the air or from dead or living organic matter.

Under such conditions as these it is plain that, foi lack
of food, if for no other reason, there could be no such pro-
fusion of terrestrial animals as dwell in a land of plenty
among us to-day. It is true that the tundras of arctic
climates produce comparatively heavy crops of lichen
growths such as the " Iceland moss," which, it is said,
often forms the sole food of the poor inhabitants of that
lonely land, like the '' reindeer moss," which in northern
Europe and in Siberia is the chief food of the reindeer
and, in times of scarcity, ground and mixed with flour,
that of man as well, and like the "Tripe de Roche,"
eaten by Indians and Canadian hunters in arctic North
America. And then there is the " manna lichen " grow-
ing on the arid steppes of the countries between Algiers
and Tartary, which in times of drought and famine is used
as food for large numbers of men and their domestic
animals. But the luxuriance of growth in these cases,
although small when compared with that of other vege-
tation, is larger than it could be did it not grow lying
upon the soil which holds the water to be given to the air
about them by the more gradual process of evaporation as
they need it.

For not only does the soil make possible a very much
greater profusion of land life than could otherwise exist,
but it has also played an extremely important part in
that long-continued, never-ending, and sublime process of
evolution whereby, as lands have insensibly changed into
sea and seas into land, as mountains have risen so slowly
and silently out of level plains as to spring their broad

Relation of the Soil to Orffanic Evolution. 35

arches directly across wide rivers to the height of a mile
and yet leave their courses unaltered, as climates have
changed from cold to warm or from wet to dry, both
plants and animals in this great drama of world action
have been enabled to change, not simply their costumes,
but if the exigencies of the new scene demanded it, legs
for fins or even abandon them altogether and crawl upon
their bellies through the grass.

As the soil slowly became thicker and thicker, as its
water-holding power increased, as the soluble plant food
became more abundant, and as the winds and the rains
covered at times with soil portions of the purely super-
ficial and aerial early plants, the days of sunshine between
passing showers, and the weeks of drought intervening
between periods of rain, became the occasions for utiliz-
ing the moisture which the soil had held back from the
sea. These conditions, coupled with the universal ten-
dency of life to make the most of its surroundings, appear
to have induced the evolution of absorbing elongations,
which by slow degrees and centuries of repetition came
to be the true roots of plants as we now know them.

When plants came to have specially organized absorb-
ing surfaces placed in a supply of moisture which peri-
odic rains made practically permanent and bounteous and
which long contact with the finely divided soil grains
kept continuously supplied with plant food not obtainable
before, except in the most meagre quantities, the natural
consequence to follow was a much more vigorous and
larger growth, of the parts above ground.

But as bounteous feeding pushed the parts of plants
higher above the surface of the ground, they were brought
where they were obliged to withstand a much stronger
wind pressure than when a precarious supply of moisture

36 • The Soil.

kept, them close to the surface, and hence, in order to sur-
vive and utilize the new opportunities which a fertile soil
affords, it became necessary to develop a stronger and
more rigid tissue than the lower types of plants possess,
and woody fibre in its various forms was the result.

And then, with a deep, rich soil in regions of frequent
and bounteous rains, with roots spreading wide and deep
to gather and lift the percolating water, and with the
woody structure of stem fixed, there began that race for
sunshine which has led on and on from low to taller forms,
each contestant in the 'jattle striving always to lift and
unfold its leaves in the sunshine and free air above all
competitors, until there has resulted a vast array of for-
est trees culminating in the giant Sequoias of our Pacific
coast, some of which have attained a measured height
exceeding 20 rods or 352 feet.

The soil has made possible succulent, nutritious grass,
great forest trees and flowers with beautiful petals, fra-
grant odors and sweet nectars, while, with the slow evo-
lution of these forms, there has come into being, to use
them and to contribute to their welfare in return, the
cattle and horses of the plains, the birds and squirrels of
the forests, and the bees and butterflies which, guided by
the colors and the fragrance they have learned to know,
reach the nectar the flowers have provided for them that
they shall be sure to come and distribute the pollen and
secure to the plants, by cross-fertilization, that renewed
vigor so essential to them.

THE SOIL A SCENE OF LIFE AND ENERGY.

In the agricultural sense it should be observed that the
most important use of soil is to act as a storehouse of

TJie Soil a Scene of Life and Energy. 37

water for the use of plants, and tliat the productiveness
of any soil is determined in a very large degree by the
amount of water it can hold, by the manner in which that
water is held, and b}^ the facility and completeness with
which the plant growing in it is able to withdraw that
water for its use as it is needed. But while this state-
ment is true in the fullest sense, it must not for a moment
be thought that the composition of the soil is not an im-
portant factor in fixing land values for crop production.
The great importance of the water-holding power grows
out of the fact that without an adequate supply of water,
neither the other food constituents which the soil con-
tains, nor that larger part which is. derived from the air,
can be procured by the plant, nor transformed or assimi-
lated by it.

Then, again, the soil is a wonderful laboratory in which
a large variety of the Iqwer inicroscopic forms of life are
at work during those portions of the year when its
temperature is above freezing, breaking down dead or-
ganic matter and converting it into those forms in which
it again becomes available for plant food ; and the farmer
should never forget that the crop of these invisible organ-
isms which are produced each year in his soil, determines
in no small degree the magnitude of the harvest he re-
moves from the ground and the fitness of that ground for
a succeeding crop.

Finally, the soil is a means for transforming sunshine
and putting it into a form available for carrying on
the kinds of work which are there accomplished, and
the manner in which the soil is tilled and the way it is
fertilized have much to do with the quantity of altered
sunshine which becomes available in carrying on this
work. - — - • - .- • •

ss

The Soil.

INFLUENCE OF ROCK STRUCTURE IN SOIL
FORMATION.

There are many agencies at work in the production of
soil, and the process is one which is being carried forward
continuously night and day and almost incessantly the

Fig. 2. — A thin section of mica schist, showing the crystalline struc-
ture which lends itself to the conversion of rock into soil.

year through. It is taking place in the tilled field and
in the meadow ; in the depths of the forest and on the
prairie; in the driest desert regions of the world and
under the tropics where rains are of daily occurrence ; in
the polar regions and under the equator and on the top-

Influence of Rock Structure in Soil Formation. 39

most summits of mountain masses as well as along the
margins of the lake and the sea, or where streams at
times rise and overflow their banks.

Nearly all rocks are made up of fragments or crystals
of various sizes and kinds, and these are bound together
more or less firmly by some cementing material, but
usually there are places which have not been completely
filled with the cement, and these give to most rocks a
certain degree of permeability to water. Granite, for
example, has been found to absorb nearly .4 of a pound
of water to each 100 pounds of rock, and the fine-textured
agate is open enough to admit of coloring by capillary
absorption. Fig. 2 conveys a general idea of that struc-
ture of rocks here referred to, and which lends itself so
readily to their conversion into fine fragments and ulti-
mately into soil.

When such rocks are brought to the surface, where
they are exposed to wide ranges of temperature, the
different rates of expansion possessed by the different
minerals entering into their structure tend to loosen them
and open the natural cavities wider. Into these cavities
the rain water is drawn by capillarity, and on freezing
tends to open the cavities still more, and to flake off
from the surface minute fras^ments, adding so much to
the soil. Then as the rocks by this action become more
porous, the rain water, holding carbon dioxide in solution,
enters more freely and dissolves the more soluble min-
erals, and, as the surface dries, these dissolved materials
are brought out and washed away by the rain or blown
off by the winds, thus leaving the rock more and more
porous until finally it falls into fragments, illustrated so
well and so frequently by what are popularly called
" rotten stones. '^

40

The Soil.

In moist and warm climates the solvent power of water
here referred to, is exerted with the greatest vigor, but
in damp, cold countries the effects of freezing are most
apparent, while in desert regions neither the one nor the
other become soil-producing agents of any note.

Fig. 3. — Showing the conversion of rock into soil on a limestone hill.

Whoever will visit an abandoned stone quarry where
the rocks have lain undisturbed for ten or twenty years,
will readily observe in the stained and altered surfaces,
in the softer, more easily scratched outer layer, and in the
slight accumulations of soil, which the rains and the

Fig. 4. — Showing the transition from rock to soil on a limestone plane.

winds have swept into the small inequalities of the rock,
the initial process of soil formation as it is still taking
place and has been throughout geologic ages.

Passing from the abandoned quarry to some fresh cut
along the railway or roadside, where a hill has been

Influence of Rock Strvr.ture in Soil Formation. 41

graded down, there may be seen at the top the finished
soil, and between it and the unaltered placnal p^ravel or
orip^inal rock below, as the ease may be, every degree of
))rogress from the one into the other, re})resented in Figs.
3 and 4, where the first shows the stages of transition as

. ._ --^— ^-: ■ 'r^=^^-r,£^^^^-^^ __-_.^.^^^^::^^^^^ -^, =i^ -'- -,-^ - ^^ . - V.--

^W::y. ■ '^ - rft^^e^^v

Fig. 5. — Showing advanced state of erosion. Giant's Castle near
Camp Douglas, Wisconsin.

they have taken place over the summit of a limestone
hill, while the second shows the same facts for a more
level limestone surface.

Then, again, the rocks of almost any quarry, on exam-
ination, will be found to be divided into blocks of varying

42

The Soil.

size and form by fissures or breaks, which owe their
origin to a general shrinkage of the surface layers and to
small but ever-present bendings or wave-like motions of
the ground. These features are well brought out in
Figs. 5 and 6, and they introduce us to another process
in the formation of soil.

Fig. G. — Showing the last stage of the couversiou of cliffs into soil.

Such fissures as these, when not too deeply covered
with soil, are often penetrated by water and by the roots
of trees. Then as the water freezes and as the roots
grow, both expand with an a.lmost irresistible power and
open the old crevasses wider or make new breaks where

Munning Water as a Soil Builder. 43

none existed before, thus dividing the hirger blocks into
smaller ones, and often throwing the fragments to the
foot of the cliff, where they soon become overspread with
a mantle of vegetation under which they rapidly fall
into soil. This process as it is carried forward in nature
may be better appreciated by carefully studying Fig. 7.

Those who live near the foot of great rocky cliffs
which are subject to this sort of action of ice, like the
quartzite cliffs at Devil's Lake, Wisconsin, are frequently
startled during cold nights in winter by loud reports
followed by the sound of rolling stone as great blocks of
rock, sometimes many tons in weight, snap under this
action of frost and go bounding down the steep face of
the pile of angular fragments which have accumulated
at the foot under the same action many times repeated.
Then, again, where a great tree has grown up with its
roots reaching deep into some wide fissure filled with
soil, on the summit of an overhanging or vertical cliff,
it not unfrequently happens that a strong wind from
the right direction, pressing against the wide-spreading
boughs and using the tall trunk as a lever, pries off sec-
tions of the cliff, sometimes 20 feet long, as many deep,
and 6 to 10 feet thick. Such a block the writer has
known to fall during a wind storm.

RUNJ^ING WATER AS A SOIL BUILDER.

Kunning water is another agent which, by processes
peculiar to itself, has done very much in the production
of soil and in giving to it certain characteristics. Stand-
ing on the bank of any small stream and watching the
water as it slides over the bottom, it will be seen that
there are incessantly being moved along the bed, some-

Running Water as a Soil Builder. 45

times rolling, sometimes sliding, grains of sand of vary-
ing sizes. One set moves on for a short distance and
then stops, other grains follow after but halt at the same
place until a small but appreciable ridge is formed.
Similar tiny ridges are forming on its right and on its
left, some above it and others below. But these are only
brief resting places ; for a change in the velocity of the
current as the waters shift from side to side causes each
ridge to move another step farther down the stream.
But as the grains roll, tumble, and slide by turns in their
downward course, each has its corners worn away, each is
growing insensibly but surely smaller, and each is con-
tributing something to that impalpable powder, which,
rising into the body of the stream, remains suspended for
almost indefinite periods except in the stillest water,
where it is laid down in lakes or. carried to the sea to
slowly subside and become beds of clay, and when those
geographical changes come which drain a lake or elevate
the margin of the sea bottom into dry land, it then
becomes fields of clayey soil.

But what becomes of the grains of sand which are
only moving along step by step, and where was their
resting place before they joined this caravan traveling
toward the sea? A little observation will soon show
where their journey begins. Following along the bank
until a bend in the stream is reached, it will be at once
observed that the concave side of the channel is deep,
while the convex side is shallow. On the concave side
the current is swift and plainly cutting away the bank,
which now rises abruptly above the water, or perhaps
has come to be so far overhanging that a portion has
already broken loose and slid into the stream, where the
rapid current is sorting out the grains it is able to move

46 The Soil.

along and bearing them beyond the turn. But on the
convex side the ground slopes gently almost to the
water's edge ; the current is feeble, and hence the grains
of sand advancing from above are here being laid down
to fill the channel on this side as rapidly as the stream
cuts away the bank on the other. The bed of a stream,
then, is constantly shifting ; soil is being taken from one
side and borne along for a distance and then laid down
upon the other, where it constitutes a new soil, and will
remain as such until the stream sweeps back once more
across its valley. Looking at Fig. 8, which is a map of
a portion of the Mississippi below Vicksburg, it is
plainly shown how the action at the bends here referred
to is being carried on, the dotted areas in the channel
showing where the deposits are taking place, and the
clear portions where the banks are being crowded back.
There is one thing about this map, however, which it
is not so easy to comprehend, and that is the amazing
extent to which this great river is to-day sauntering
about upon its alluvial plain, some 40 miles in width,
as shown by Lakes Bruin, Palmyra, and St. Joseph,
which are only great ox-bow portions of its channel
which it has recently abandoned. Colonel Abbot says of
these shif tings of the river : " Chief among such changes
is the formation of cut-offs. Two eroding bends ap-
proach each other until the water forces a passage
across the narrow neck. As the channel distance
between these bends may be many miles, a cascade,
perhaps 5 or 6 feet in height, is formed, and the tor-
rent rushes through it with a roar audible for miles.
The banks dissolve like sugar. In a single day the
course of the river is changed, and steamboats pass where
a few hours before the plow had been at work." The

liuiinim/ Water an a Soil Builder. 47

Fig. 8. — Showiug the shit'tiugs of a river chauiiel ;',s it forms alluvial

soils.

work here is of course extraordinary, as it must be
when the run-off from more than 1,200,000. square miles

48 The Soil.

is brought together into one channel on a plain which
falls only one inch in 40 rods, and over which it winds
some 1100 miles in making a distance south of less than
half that number.

While such extreme windings as these are confined to
large rivers where they traverse very flat stretches of
country, this shifting of the streams, this picking up of
soil from one place and laying it down in another, is
nevertheless very general and very extensive ; and when
we speak of the Mississippi as carrying to the Gulf,
suspended in its waters or shoved along its bottom,
every year soil enough for 72 sections of land 4 feet
deep, this work is small when compared with that which
measures the shifting of sand from side to side by the
same stream even after it passes the city of Memphis ;
and vast as this work can but be, it must constitute a
standard all too small by which to measure that which
in the aggregate is done throughout the broad valley of
the Ohio, the Upper Mississippi, and the Missouri, with
their tributaries. Glance for a moment at Fig. 9 that
it may be realized, not only how many times the Madison
fork of the Missouri River must have crossed and re-
crossed its broad valley, but how many times over and
over again it must have handled that soil before it suc-
ceeded in carrying out of its field of labor the amount
which the unimpeachable testimony of those terraces
show it has transported to lower levels. Think also
how, again and again, a new vegetation must have
taken possession of the reworked land, as the soil was
being transferred now to the right bank and now to the
left. Years and years, and even centuries, must have
passed before a given field was entirely replowed,
resoiled, and reseeded; but everywhere in the past and

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50 The Soil

everywhere in the present this long-time rotation has
been and is now being carried on by the ceaseless action
of rivers.

WORK OF RAIN.

Besides the action upon the soil, of running water,
which we have considered, after it has reached the
perennial waterways, there is a large mechanical work
performed by the rain while on its way over the surface
toward the streams or before entering the ground to
emerge again in the form of springs. At the time of
heavy rains the surface of the ground, even on rather
steep slopes, becomes covered with a sheet of water, and
the raindrops, striking into this and upon the soil, work
up the looser grains so that, as the water moves down the
inclines, it bears along with it over shorter or longer dis-
tances a considerable body of soil. In cultivated fields,
especially where the soil has a fine texture and the prop-
erty of losing its coherence when flooded with water,
the amount of soil moved at such times on the more
rolling lands is very large indeed.

Whoever has the opportunity to traverse the uplands
in the state of Mississippi to-day will be confronted with
a gigantic but sorrowful example of what this action of
rain may accomplish in the brief period of thirty years
on such soils as are here referred to. I quote the lan-
guage of W. J. McGee, who has made a careful study of
this region : —

" With the moral revolution of the early sixties came
an industrial revolution ; the planter was impoverished,
his sons were slain, his slaves were liberated, and he
was fain either to va(;ate the plantation or greatly to

Wo)'k of Hal 71. 51

restrict his operations. So tlie cultivated acres were aban-
doned by thousands. Then tlie hills, no lon^^er pro-
tected by the forest foliage, no longer bound by the
forest roots, no longer guarded by the ])ark and brush
dam of the careful overseer, were attac^ked by raindrops
and rain-born rivulets and gullied and channeled in all
directions ; each streamlet reached a hundred arms into
the hills, each arm grasped with a hundred fingers a
hnndred shreds of soil, and as each shred was torn away,
the slope was steepened and the theft of the next storm
made easier.

" So, storm by storm and year by year, the old fields
were invaded by gullies, gorges, ravines, and gulches, ever
increasing in width and depth until whole hillsides were
carved away, until the soil of a thousand years' growth
melted into the streams, until the fair acres of ante-bellum
days were converted by hundreds into bad lands, desolate
and dreary, as those of the Dakotas. Over much of the
upland the traveler is never out of sight of glaring sand
wastes where once were fruitful fields ; his way lies some-
times in, sometimes between, gullies and gorges, the ' gulfs '
of the blacks whose superstitions they arouse, sometimes
shadowed by foliage, but oftener exposed to the glare of
the sun reflected from barren sands. Here the road
winds through a gorge so steep that the sunshine scarcely
enters ; there it traverses a narrow crest of earth between
the chasms, scores of feet deep, in which he might be
plunged by a single misstep. When the shower comes,
he may see the roadway rendered impassable, even oblit-
erated, within a few minutes ; always sees the falling
waters accumulate as viscid brown or red mud torrents,
while the myriad miniature pinnacles and deliles before
him are transformed by the beating raindrops and rushing

52 The Soil.

rills so completely, that when the sun shines again he
may not recognize the nearer landscape.

" This destruction is not confined to a single field or
a single region, but extends over much of the upland.
While the actual acreage of soil thus destroyed has not
been measured, the traveler through the region on horse-
back daily sees thousands or tens of thousands of for-
merly fertile acres now barren sands ; and it is probably
within the truth to estimate that 10 per cent of upland
Mississippi has been so far converted into bad lands as
to be practically ruined for agriculture under existing
commercial conditions, and that the annual loss in real
estate exceeds the revenues from all sources ; and all
this havoc has been wrought within a quarter century.
The processes, too, are cumulative ; each year's rate of
destruction is higher than the last.

" The transformation of the fertile hills into sand wastes
is not the sole injury. The sandy soil is carried into the
valleys to bury the fields, invade the roadways, and con-
vert the formerly rich bottom lands into treacherous
quicksands when wet, and blistering deserts when dry.
Hundreds of thousands of acres have thus been destroyed
since the gullying of hills began a quarter of a century
ago. Moreover, in much of the uplands the loss is not
alone that of the soil, i.e. the humus representing the
constructive product of water work and plant work for
thousands of years ; but the mantle of brown loam, most
excellent of soil stuffs, is cut through and carried away
by corrasion and sapping, leaving in its stead the in-
ferior soil stuff of the Lafayette formation. In such
cases the destruction is irremediable by human craft —
the fine loam, once removed, can never be restored.
The area from which this loam^ is already gone is ap-

Work of Hain. 58

palling, and the rate of loss is increasing in geometric
proportion."

It is not necessary, however, to go to the bad lands of
Mississippi or the Dakotas for examples of this work ; for
every careful farmer has witnessed it a hundred times on
every hillside of his farm, and has studiously tried to
prevent it. Hut this action of rain is much more general
and in the aggregate much greater than has yet been indi-
cated ; for it takes place, only in a less intense and less
obtrusive way, over the surface of all except swamp and
the most heavily wooded lands, always moving the sur-
face soil from the higher toward the lower grounds and
ultimately to within the reach of streams.

When the soils of hillsides expand witli increasing
moisture or with frost, there is a small but sure move-
ment downward, for while the push is equal in all
directions, the downward thrust has the force of gravity
on its side; and the same movement results when the
soil comes to shrink after drying, for it is easier to draw
the upper particles down than to pull the lower ones up.
Blocks of stone, too, lying upon the slope, expanding in
the hot sun and contracting during the night, tend to
creep insensibly into the valley. When the fox, and the
many burrowing animals of whatever sort, bring dirt to
the surface, or when great forest trees are uprooted by
the storm, the soil moved is without exception left one
step nearer to the sea. It is evident that by whatever
one of these methods of creeping the soil is moved, the
rate of travel will, other conditions being the same,
always be most rapid on tlie steepest slopes, so that
generally this action must result in the soils of the
summits or high lands crawling down and upon those
of the lowlands, producing an overplacement which gives

54 The Soil.

to the soils of the invaded areas characteristics derived
from the rocks Avhose destruction contributed the material
for the overplacing soil. For the same reason, too, the
resultant soils will usually be found more fertile and
more enduring, as every farmer knows, than that left
behind on the more sloping ground. The general facts
of soil creeping and of overplacement are indicated dia-
grammatically in Fig. 10.

Poor Soil

Rich Soil

Fig. 10. — Showing movement of soils from higher to lower levels.

GLACIAL SOILS.

In those portions of the world where the temperature
is so low that most of the moisture is frozen when it
falls and does not all melt during the summer, the snow
accumulates often to great depths and by its weight is
compressed into ice. When snow in this condition has
attained a considerable thickness, it begins to move along
sloping surfaces much as liquid water does, converging
into larger and larger streams, moving faster where the
slope steepens and slackening its speed again when the
descent becomes less. In Fig. 11 is shown one of these
ice streams descending from the Alaskan mountains
toward the Pacific Ocean, where it had its birth.

Glacial Soils.

66

"While the movements of glaciers are much less rapid
than those of rivers, their far greater depth and con-
sequent heavy pressure, together with the more ri^^irl
nature of the ice. give to these streams a grindincr.

Fig. 11. — Showing an Alaskan glacier.

scoring, and transporting power which is great almost
beyond measure ; and hence it is that in mountain dis-
tricts, which rise above the line of perpetual snow, and
in the frigid zone, glaciers become soil-producing agents
of great vigor.

56 The Soil.

In very recent geologic time, during the glacial epoch,
a vast ice sheet gathered in the higher latitudes and
spread from tlie direction of northern Labrador until
it overran two-thirds of the North American continent,
advancing so far southward as to place its front in the
shape of a rude crescent, stretching from Cape Cod and
Long Island through northern Pennsylvania into the
Ohio valley and from thence, following the course of this
stream and that of the Missouri River, to the Rocky
Mountains. At the same time there appears also to
have been on the Pacihc slope a lesser and apparently
more local sheet, which pushed itself southward through
the mountain valleys until it passed the foot of Puget
Sound.

What conditions conspired to induce this long geologic
winter has not yet been learned, but during its prevalence
the snows piled upon the land until a mantle hundreds
and perhaps thousands of feet in thickness overspread
the whole area outlined above, while the general level of
the ocean fell as its waters were drawn upon to feed the
ever-deepening snow fields as they spread over the north-
ern continents of the Eastern and Western Hemispheres
alike. As the specific gravity of ice varies between .917
and .922-, the mean weight of a cubic foot will exceed 57
pounds, and an ice sheet 10 feet in depth will press upon
its bed with a weight exceeding 570 pounds to the square
foot, while the burden imposed by 500 and 1000 feet of
ice must exceed 28 and 57 thousand pounds to the square
foot, or 198 and 396 pounds to the square inch respec-
tively. What a mill for grinding rock into soil we have
here ! For its nether stone one-half or two-thirds of the
North American continent, and for its upper one a block
of ice of corresponding size, five hundred to a thousand

^

w

o
a

O
CO

o

58 The Soil.

and more feet thick, having its grinding face thickly set
with sand and gravel, and those same hard bowlders,
large and small, which we now find strewn so thickly
over the surface and through the soil of this whole gla-
ciated area, while the two faces were set against each
other with a pressure exceeding 200 to 400 pounds to the
square inch and quite, probably double these amounts !
With such a mill as this, set up under no other roof
than the dome of a cold arctic sky, and run incessantly
day and night, year in and year out, for centuries,
numbered certainly by hundreds if not by thousands,
a great work must have been accomplished.

During all this time the great ice sheet was creeping
slowly toward the south and southwest, its whole front,
from the Atlantic to the Rocky Mountains, now advanc-
ing a little and now retreating as variations in the rate
of travel or the rate of melting occurred. Beneath the
bottom of this slowly moving sheet of pressure-plastic
ice, which, with more or less difficulty, kept itself com-
formable with the face of the land over which it was
riding, the sharper outstanding points were cut away
and the narrower and deeper river canons filled in.
Desolate and rugged rocky wastes were ground down and
overspread with rich soil, and regions with sandstone for
the surface rock, which by decay in place could give only
lands of the lighter type, became mantled with thick
layers of mixed gravel, sand, and clay, forming by slow
alteration rich and enduring soils.

Great streams of water emerging from the melting ice
sorted and resorted the glacial grist, leaving in some
places extensive beds of coarse, clean gravel with surfaces
sloping gently in the direction of discharge, over which
has since developed one type of extremely fertile prairie

n(!|t|'||:"iriir'i :;

II liiilliSiilili

a

o
7.

o

M

60

The Soil

soil; leaving in other places beds of sharp plastering
sand, often interstratified in the most curious and abrupt
manner with coarser or finer materials, while the finest
silt was farther removed to subside in innumerable lakes,
formed by glacial dams, or to be borne away to the sea to
contribute materials for the extensive deposits of our
coastal plains.

Wlien the ice front tarried long at a given place, the

Fig. 14. — Showing glacial scratches on north shore of Kelley's Island,

Lake Erie.

broken and worn fragments of rock continually brought
along by the ice were unloaded there, as it melted, until
great irregular ridges were formed, sometimes several
miles wide and from 20 to 400 feet in height, and these
have been named terminal moraines. Mingled with these
huge piles of rock, sand, and gravel there were left, at
the time of the final retreat, great blocks of ice, and when
these finally melted and the water drained away, they
left the surface of the moraine thickly set with deep and

Earthworms an Soil Workers. 61

abrupt hollows, to which the name of kettles came to be
applied; and Fig. 12 shows, as well as a picture can, a
surface thus formed, while Fig. 13 represents a section of
one of these morainic hills which was cut through in
grading for a railroad.

In very many parts of the country overrun at this
time, the harder and more enduring kinds of rock often
still show with remarkable distinctness the actual course
the ice stream took by the scratches, grooves, and furrows
which were left in the polished surface of the rock made
by stone, gravel, and grit imbedded in the bottom of the
glacier. An illustration of such a rock surface is repre-
sented in Fig. 14. And, since these rock surfaces have
sufficiently withstood all other methods of rock decay to
enable them to retain these records for so long a time as
has intervened between the close of the glacial period and
the present time, it is evident that glacial action must be
ranked as the greatest soil-producing agent of recent
geologic time.

EARTHWORMS AS SOIL WORKERS.

Then there are many animals which have contributed
largely to rock grinding and soil formation. INIany will
recall the great number of piles of earth which angle-
worms bring to the surface after heavy rains, and espe-
cially during the spring and early summer when the
ground is wet. Their method of action is this : in mov-
ing through the soil, they eat a narrow hole, swallowing
the earth, when the point of the head is held fast in this
excavation while an enlarged portion of the esophagus or
swallow is drawn forward forcing the cheeks outward in
all directions, thus crowding the soil aside and making

62

The Soil,

the opening wider, when more dirt is eaten and the proc-
ess repeated. After the swallowed earth has been worked
over in the muscular gizzard and the organic matter
associated with it digested, it is passed from the body,
but while in the stomach the grains of sand suffer a con-
siderable amount of
wear, much as is the
case with pebbles
and bits of glass
eaten by poultry and
all seed-eating birds
for the purpose of
grinding their food.
Charles Darwin,
who made a very
long and careful
study of this action
of earthworms, came
to the conclusion
that in many parts
of England these
animals pass more
than 10 tons of
dry earth per acre
through their bodies
annually, and that
the grains of sand
and bits of flint in
these earths are partially worn to fine silt by the action
of the gizzards of these animals; but this extensive
action is not peculiar to England, for the species of earth-
worms have a wide geographic distribution, and Fig. 15
represents a soil chimney made by a species in India,

Fig. 15. — Showing a tower-like casting
ejected by a species of earthworm
from the Botanic Garden, Calcutta.
Natural size. Engraved from a photo-
graph after Darwin.

Karthirorniif os Soil W(>rlccri<.

Fig. 16. —Showing the work of the common earthworm during a single
night after a heavy rain.

64 The Soil

while Fig. 16 shows the work of a single night on a Wis-
consin farm after a heavy rain.

HUMUS SOILS.

There is a class of soils in which humus is the dom-
inating characteristic, and these have their origin in
swamps of various types. In many parts of the world,
but especially in high latitudes or at considerable eleva-
tions, where the surface is too flat for rapid and com-
plete drainage and where the winter snows remain so long
that the duration of summer is insufficient to dry the soil
enough for it to become readily penetrated by the air,
there comes to be formed a deposit of humus or peat, min-
gled with varying proportions of mineral grains. When
soil is allowed to become dry and at the same time porous,
so that air has an unlimited access to it, all organic mat-
ter which it may contain is rapidly and completely re-
turned to the atmosphere, as is illustrated in an emphatic
manner in the use of the dry-earth closet; but when
organic matter falls upon an over-saturated soil, or be-
neath the surface of water, there is so slow an access of
oxygen to the decaying matter that only a partial decom-
position takes place, which results in the formation of
the black or broAvn humus so characteristic of swamp
soils. It frequently happens during the development of
soils of this type that heavy forest growths are slowly
droAvned out by it as it ac(;umulates in thickness and
more and more completely excludes the air from the
roots of the trees.

Under other conditions, where a great river like the
Mississippi, the Nile, or the Ganges approaches its outlet
or winds over a flat plain, it so builds up the bottom of

Humus Soils. 66

its channel, by laying down the sediments which it car-
ried with ease over the steeper portions of its course, as
to place it higher than the adjacent flats; and then, in
times of frequent overflow, the adjacent country is
periodically flooded, and the water, not finding ready
return to the river, furnishes the conditions for the
growth of aquatic plants and a swamp soil begins to
form. Then again when rivers change their course, as
in the case of the formation of ox-bows already referred
to, there result shallow lakes with muddy bottoms in
which aquatic plants are quick to spring up and begin
the formation of a rich humus which in later years may
lead to no little wonderment as to how such a soil in such
a shape could have had its origin. The swamp soils of
river origin, when they are drained and dry, on account
of the sand and silt mingh^d with the humus, fall among
the richest, most enduring, and quickest to respond to
agricultural treatment.

If one will study a detailed map of almost any portion
of North America lying north of the great glacial front,
to which we have referred, he will be surprised at the
very large number of small lakes there shown ; and then
if he could see a good soil map of the same section, he
would be still more surprised, not only at the even
greater number of small and large irregular isolated
areas of swamp soil, but also at the extent of the fringes
of these soils, which are shown bordering most of the
lakes. The isolated areas of swamp soil were once lakes
themselves, which, after partial drainage and the forma-
tion of marginal muddy flats by the wearing down of
their outlets, began the development of humus first over
the flats through the growth of aquatic plants rooted
on the bottom, and later, as the deeper water was

66 The Soil.

approached, by a rapid spread of these and the sphagnum
moss extending around the lake as a floating fringe.
As this sphagnum continues to grow above and die below,
with only partial decay, it settles deeper into the water
and finally rests upon the bottom. Or if the lake is
deep, the growth may advance steadily toward the centre
until finally the whole is overgrown. Upon this raft of
aquatic vegetation the sedges begin to grow, small wil-
low and heath-like plants follow, and finally, when a
sufficient thickness has been formed, the tamarack dis-
putes the ground and covers the whole with a forest of
straight green spires. As these trees grow to maturity

Fig. 17. — Showing the passage of a lake into a peat bed and swamp or

humus soil.

and the tall shafts fall to be buried in shrouds of anti-
septic sphagnum, the whole lake cover grows thicker,
heavier, and finally comes to rest upon the bottom.
Fig. 17 shows a section of a lake passing through the
stages here described.

It not infrequently happens in these lakes, during the
overgrowing period, that large areas of the floating peat
break away and drift from side to side, impelled by the
wind acting upon the vegetation as a sail. Such a de-
tachment, consisting of several acres, occurred in 1875
in Lake Butte des Morts, through which the Fox River
passes before entering Lake Winnebago in Wisconsin.
This field of swamp grass drifted against a long railroad

ffiimua So}l,9. 67

bridge, threatening its destruction, and had to be cut with
ice saws into blocks small enough to clear the water-
ways.

On the shores of the larger lakes and along the mar-
gins of the sea, the waves often throw up bars of sand,
cutting off lagoons whose waters, in the case of the sea,
by the shutting out of the tides, come to be converted
first into brackish and then fresh-water lakes and finally
into areas of swamp soil. And then when the sea has a
flat or gently sloping tidal plain over which the water
rises more than one or two feet, deposits of peat begin to
form in the sheltered bays through the growth of certain
grasses which have acquired the power of thriving in salt
water. Starting at the shore line, they advance by de-
grees toward the sea as the tidal sediments gather about
their feet, building the bed of peat up to near the level
of high tide, and in this way forming extensive deposits.
This work is very materially assisted, as Shaler has
shown, by the occasional breaking-up of these peat de-
posits through the action of waves and the redepositing
of them in deeper water, where they constitute a soil
upon which a peculiar flowering plant, the eel grass, has
acquired the habit of living entirely submerged beneath
the water. This plant, playing the same part in the deeper
water below low-tide mark which the grasses do above
it, gathers silt and builds up a platform upon which the
grasses may advance in their work of winning land from
the sea; and the amount done since the glacial period,
along the New England coast alone, is placed by Shaler
at more than 350,000 acres, while the total area of
marine marshes, which owe their formation to grass-
like plants, the same writer places at nearly 10,000
square miles in the United States. But the most inter-

68 The Soil.

esting and important fact about these lands is,' that, like
those of Holland, when won from the sea and made fit
for tillage, they become extremely rich and enduring
soils. And then to think that all this potential wealth
of food, happy, industrious homes, and moral lives should
lie unused in the very shadow of a great city where so
many thousands are worse than starving, where so much
wealth is seeking profitable investment, and where so
many charitable hearts are yearning to see some path-
way leading away from those dens of misery ! Why may
not intelligence, wealth seeking investment, charity and
poverty join hands in converting those great stretches
of waste land close by their doors into the richest acres,
where the poor who will may not only find employment,
but earn a garden and a home, with all these can mean ?

WIND-FORMED SOILS.

There is still another method and another agency by
which soil building and soil wasting are carried on. It
is probable that nowhere can soils be found which do not
contain larger or smaller amounts of wind-borne particles,
— particles which have traveled unknown distances, and
these often very great. There is never a raindrop falls,
never a hailstone reaches the ground, and never a snow-
flake, however white, but which brings to the soil it
moistens one or more particles of dust. The streaks of
dirt left upon the window pane with the melting of snow
which has drifted against the glass are a sufficient proof
to the housewife of the truth of the statement just made,
while the color of rain water and the sediment which
both it and the water of melted snow leave when evapo-
rated to dryness, bear witness to the same facts.

Wind-formed Soils. 69

But it is in arid regions more particularly and along
sandy coasts, that tliis action of the wind as a soil builder
and soil destroyer is most marked. On the leeward mar-
gins of arid regions sand-drowned forests, as well as cities
and ancient monuments, stand as silent witnesses of this
abraiding and transporting power of the wind. The
most extensive formations ascribed to the action of winds
are some types of a deposit which have been named loess.
Richthofen describes a formation of this character in
China as a Avholly unstratified calcareous clay of a very
line texture, which contains many land shells, bones of
land animals, and land vegetation. The formation as
described by him has a wide distribution, and attains
a thickness in places of 1500 and possibly 2000 feet.
It should be stated here, however, that formations very
similar to this have a much wider geographic distribu-
tion, being found extensively both in Europe and North
America, but these are so related to ancient glacial mar-
gins and channels of overflow as to suggest, for them at
least, an apparently different origin.

When we call to mind the experience we all have had
regarding the accumulations of wind-driven dust which
collect in abandoned houses and in rooms even when un-
occupied for only brief periods, when we recall the clouds
of dust raised from the road and from the surfaces of
light, dry soils, or watch the snow as it is driven from
field to field, we need not be surprised if the wind has
done a great work where it has had an unimpeded sweep
and the years of geologic time at its disposal.

CHAPTER II.

TEXTURE, COMPOSITION, AND KINDS OF SOILS.

We have seen that almost everywhere the land surface
is overspread with a mantle of rock fragments, sometimes
large but mostly very small, the upper portion of which
has been designated the soil. We have pointed out that
this soil is a water reservoir in which the rains are caught
and held, that it is a great laboratory in which certain
essential plant foods are being made, and that deeply into
it the roots of plants grow for support, moisture, and
nourishment.

SOIL TEXTURE AND ITS INFLUENCE.

In looking at the texture of the soil, so far as the size
of its grains is concerned, we may consider the valuable
results obtained by Hilgard in his mechanical analysis
of some Mississippi soils. By his method of treatment
he has so separated the grains of soil of different kinds
as to bring those having the same diameters together,
thus enabling him to determine the percentage amounts
of each size entering into the particular soil. The diam-
eters of the soil grains and the percentage amounts of
each size, as they occur in a sandy soil and subsoil from
the long-leaf pine plateau in Smith County, are given
below : —

70

Soil Texture and its Influence. 71

Soil.

Shbhoil.

Diameter.

Per Cent,

Per Cent

3937 to 4724 hundred thousandths of

an inch

.4

.4

2362 to 3937

u

3.0

.8

1575

"

6.9

6.3

1181

8.1

3.4

610

3.0

3.9

472

1.6

1.5

283

1.2

.6

185

3.6

2.6

142

6.8

5.4

98

14.6

7.9

59

14.8

17.0

31

30.7

38.3

4

4.6

10.9

In two other soils, one a " Hog-wallow " subsoil from
Jasper County, very clayey and difficult to work, and
another a loess soil from Claiborne County, we have
diameters and relative proportions as given below : —

Clay

Loess

Subsoil.

Soil.

Diameter.

Per Cent.

Per Cent

3937 to 4724 hundred thousandths of

an inch

.8

1-^

2362 to 3937

1.2

1575

2.0

.4

1181

1.6

.6

610

.9

.9

472

.3

1.7

283

.2

2.0

185

2.5

14.3

142

3.7

16.2'

98

5.6

20.1

59

10.6

5.6

31

24.7

33.6

4

48.0

2.5

The values given in these tables have great significance
in showing, first, how it is that soils can act as water

<:^

The Soil.

reservoirs of great capacity ; second, how even when they
are made up very largely of materials extremely difficult
of solution, they may, when kept supplied with an abun-
dance of water, dissolve in large quantities ; and third,
how it is that the roots of plants are brought into very
intimate contact with an immense surface of soil grains.

If you plunge a marble into water, and then withdraw
it, it comes forth surrounded by a film and the greater
the surface of the marble the larger will be the amount
of water which adheres to it. AVhen the rains saturate
any soil, the surface of each soil grain has its film of
water as in the case of the marble. It is not difficult to
see how reducing the diameters of soil grains, greatly
increases the number of them in a cubic inch, and at the
same time increases the total soil surface to which the
soil water may adhere. Suppose we take a marble exactly
one inch in diameter. It will just slip inside a cube one
inch on a side and will hold a lilm of water 3.1416 square
inches in area. But reduce the diameters of the marbles to
one-tenth of an inch and at least 1000 of them will be
required to fill the cubic inch, and their aggregate sur-
face area will be 31.416 square inches. If, however, the
diameters of these spheres be reduced to one-hundredth
of an inch, then 1,000,000 of them will be required to
make a cubic inch, and their total surface area will then
be 314.16 square inches. Suppose again the soil parti-
cles to have a diameter of one-thousandth of an inch. It
will then require 1,000,000,000 of them to completely
fill the cubic inch, while their aggregate surface area
must measure 3141.59 square inches.

Turning back to the tables which show the observed
sizes of grains obtained by the mechanical analyses,' it will
be noted that the smallest of them have diameters placed

Soil Texture and its Influence. 73

at .00004 of an inch, a size far below the last we have
considered, and yet a cnbic foot of soil grains having:? a
diameter of .001 of an inch will provide a surface for
holding water, as we have seen the marble do, equal to
.')7,700 square feet. Four feet in depth of such a soil, a
depth to which the roots of most farm plants penetrate,
would possess a water-holding surface not less than 3.4
acres for each column of soil one square foot in section.
An extremely thin film, therefore, on such a surface, must
aggregate a large amount of water, and we need not be
surprised to learn that only moderately fine-grained soils
have been observed to retain in the surface five feet,
under field conditions, no less than the equivalent of 12
to 20 inches of water on the level.

It should be observed here, regarding the very small
size of grains shown in the tables of mechanical analyses
given above, that it is extremely improbable that the
smallest of them are individually invested by films of
water as these occur undisturbed in the soil. On the
contrary, future study seems likely to demonstrate that
even the stiffest clay soils are made up of complex
grains, into which the capillary waters do not freely
pass, and that the extreme division shown by present
methods of mechanical analysis are in part the result of
a breaking down of compound grains which, under field
conditions, act largely as if they were solid particles of
greater size. These statements are made here to caution
the reader against carrying the computations made above
by the writer much farther than he has done.

Turning now to the influence of the texture of the
soil on its ability to supply the soluble ash ingredients
needed by the vegetation growing upon it, it will be at
once apparent that the broad surface which the soil

74 The Soil

water has been shown to cover must lead to a rapid
solution of soil material and a relatively rapid produc-
tion of plant foods, when they are present, even though
they may exist in the soil in forms soluble with extreme
difficulty.

An instructive experiment has been made by the
French chemist Pelouze, aiming to illustrate the influence
of a fine state of division, or of small particles, on the
rate of solution. In a flask holding a little more than
a pint, he kept water boiling constantly during five days,
and at the end of this time he emptied, dried, and weighed
the flask, finding it to have lost less than two grains in
weight. He next broke off the neck of the flask ; grind-
ing it to a fine powder and returning it to the body of
the flask, he repeated the boiling during five more days.
At the end of this time he found that fully one-third
of the total weight of his flask had been dissolved by the
water.

Storer states that the Messrs. Rogers found, by digest-
ing powdered feldspar, hornblende, and various other
minerals with water for a week, that from a third of
one per cent to one per cent of the mineral was dissolved
out by the water. Taking the lowest estimate, namely
one-third of a pound of mineral for each one hundred
pounds of the dry powdered rock, and multiplying the
result by the weight of soil in the surface foot of an acre
of land, we find that more than 10,000 pounds might be so
dissolved during one week. But Voelcker has shown
that 15 tons of good well-rotted manure to the acre will
supply no more than 150 pounds of potash and 140
pounds of phosphoric acid to the acre.

It is undoubtedly true that the rate of solution here
cited is much more rapid than ever occurs in natural

Soil Texture and its Influence, 75

soils, but the work may go forward more or less rapidly
during the whole year and throughout a depth of more
than five feet, and still be within the reach of root action ;
and more than this, it is probable that the state of divis-
ion in the soil much exceeds that which obtained in
the experiment of the Messrs. Rogers. It is not strange
therefore that, where due attention has been paid to
rotation of crops and where a fair amount of organic
matter in the form of stable manure has been supplied,
many soils have been found practically inexhaustible
even under centuries of cropping.

When we bear in mind that the roots of our cultivated
plants penetrate the soil to a depth of four or more feet,
that they extend horizontally away from the stems
through an equally great distance, and that throughout
all of this broad and deep mass of soil innumerable and
extremely minute root hairs thread their way among
the soil grains and come in touch with them throughout
their whole length and on all sides, we are confronted
with the great work which is conjointly done by the
sunshine, the plant, and the soil. Viewed in this light,
soil is not a grave where death and quiet reign, but
rather a birthplace where the cycles of life begin anew,
to run their courses over and over again.

There are some soils which, in their minuter structure,
are made up of extremely small particles, but which are
nevertheless so coarse-grained as to be more or less leachy
in character and to possess a quality of easy tillage
approaching that of sandy land. The loess soils are a
type of these, and they contain a large number of com-
pound grains in which the minute particles have been
cemented with carbonates of lime and magnesia into
small concretions which behave, so far as the texture of

76 The Soil

the soil is concerned, as though they were in reality
grains of sand. There must also be some of this sort of
structure in the more open types of clay soils, and it is
probable that the underdraining of such lands tends to
augment this tendency to granulation and thus improve
their quality. Stiff, clayey subsoils, too, have a tendency
to shrink and draw together into small cube-like blocks,
particularly during dry seasons and especially after
they have been underdrained, and this structure facili-
tates in a marked manner complete drainage, thorough
aeration and a deeper penetration of the roots of plants
into them. Such an opening up of a clay soil as this
makes it possible for the carbonic acid of soil water to
dissolve lime and bring it into contact with the deeper
and stiffer clays, and, by its flocculating or granulating
tendency, to so improve their texture, in the course of
years of proper tillage, as to render them more produc-
tive and more easily worked.

CHEMICAL CONSTITUENTS OF SOILS.

From what has been said regarding the origin of soils,
it will be evident, at once, that whether we look at them
from the standpoint of the chemical elements which
enter into their composition, whether we enumerate the
chemical compounds which a thorough analysis might
reveal, or whether we attempt to name the various min-
erals which time and the agents of geologic change have
brought together, we must expect to find almost any soil
a body of extreme complexity, so far as its composition
is concerned. The fact that few indeed, if any, of the
minerals entering into the rock structure of land masses
are wholly insoluble, even in pure water, the fact that

Chemical Constituents of SoiU.

77

this water carries its dissolved materials both through
and across the surface of the soil and over long distances,
and the fact that the movements of the surface waters,
winds, and burrowing animals of all kinds and even
plants work together in mixing and transporting soil
particles, must tend to give to all soils, wherever they
may be found, a general composition which is extremely
similar.

Of the many chemical elements occurring in the soil,
those which have the greatest abundance, or are of most
importance from the standpoint of agriculture, are named
below : —

Non-Metal8.

Metals.

Oxygen.

Chlorine.

Aluminum.

Sodium.

Silicon.

Phosphorus.'

-^Calcium.

Iron.

Carbon.

Nitrogen'T

Magnesium.

Manganese,

Sulfur.

Fluorine.

-Potassium.

Hydrogen.

Boron.

Oxygen occurs in the soil in the free state and in com-
bination with all of the elements named except fluorine.
Silicon, combined with oxygen, forms silica or quartz, so
familiar to us in the form of plastering sand, pebbles
of quartz, carnelian, and jasper. So abundant is silica
or quartz that it is estimated to compose more than one-
half of the known rocks of the earth. Because it is so
difficultly soluble and so hard, quartz, in larger or smaller
particles, is the chief ingredient by volume and by
weight of nearly all soils everywhere.

Carbon occurs in the soil as a part of the humus or
organic matter, united with calcium and with magnesium
in the form of cai'bonates, and also united with oxygen
in the form of carbon dioxide as one of the soil gases

78 The Soil

and which, dissolved in the soil water, plays so impor-
tant a part in the solution of plant food. But the plant
gets the carbon of its food from the free carbon dioxide
of the air.

Sulfur occurs in the soil in the form of sulfids united
with iron or as sulfates united with some metal, as
iron, lime, or magnesia. United with oxygen and calcium,
it forms land plaster or gypsum, an important fertilizer ;
it is also an essential part of many organic compounds
in the tissues of plants and animals.

Hydrogen plays its greatest part in agriculture, and in
the life of the world, while combined with oxygen in
the form of water, and it is in the form of water that
plants get most of the hydrogen and oxygen which go
to make up their tissues and the starches, sugars, and
other forms of stored food.

Chlorine is neither a large constituent of soil nor one
which plays a very important part in its work. It is
usually associated with sodium in the form of common
salt, which occurs in all soils, in all natural waters, and
even in rain. Chlorine is uniformly found in the com-
position of plants, and is regarded as in some way
essential.

Phosphorus, which in its uncombined state is used
in the manufacture of matches, because it so readily
ignites in the presence of oxygen, is never found in the
soil or in nature except combined with some other sub-
stance. It is very generally distributed in the soil,
though not in large quantities, but is a very essential
soil ingredient. It occurs as a constituent of the oldest
known rocks and from these, through the processes of
rock decay and rock building, it has been ever present
in the soils of all geologic ages. Through the action

Chemical OonMituentu of Soils, 79

of plants it is gathered up from the soil and concen-
trated in their tissues ; animals in their turn, feeding
upon the plants, or upon other animals, concentrate the
compounds of phosphorus still farther, so that now the
remains of animal life in rock deposits are valuable
sources of commercial fertilizers, and man, through his
intelligent effort, is taking advantage of these ancient
concentrations of plant food by bringing them forth and
redistributing them where they may be used over again
in carrying forward once more the life processes of the
present day.

Nitrogen, though the most abundant element in the
atmosphere, is one of the least abundant in the crust of
the earth as a rock ingredient. In the soil, in the com-
bined form, it occurs as a part of humus and the fragments
of the decaying tissues of plants and animals, from which,
through the instrumentality of microscopic life there, it is
converted ultimately into nitric acid, which, uniting with
potash, lime, or other soil ingredients, forms a soluble
salt taken up by the roots of plants and is then made to
yield up its nitrogen to build those nitrogenous compounds
so abundant in the tissues of animals.

Neither boron nor fluorine have any considerable abun-
dance in soils, and their percentage composition in the
ash of plants is small. Borax is the most familiar com-
pound in which boron occurs. Fluorine, united with
lime, occurs in Iceland spar, and it is a constituent of the
blood, milk, teeth, and bones of mammals.

Aluminum is placed third in abundance among the
elements of the surface ten miles of the solid land. It is
a beautiful white metal, remarkably light, and does not
readily tarnish. While it is not a plant food, it is a
fundamental constituent of true clay, which is derived

80 The Soil.

from the breaking-clown, by chemical action, of feldspar,
mica, and other constituents of granitic rock; and it is
important to keep in mind that the true clays, and the
fine clay-like particles play a very important part in de-
termining the texture and water-holding power of soils.

Calcium and magnesium are two metals very closely
associated, and, united with carbon dioxide, they consti-
tute the limestone beds of the world. Magnesium is an
indispensable plant food, as is also lime. Both collect
largely in the seeds of plants, the magnesia more abun-
dantly than the lime, wheat containing 12 per cent in its
ash of magnesia, as against 3 per cent of lime, while the
ashes of peas contain 8 per cent of the former to 4 per
cent of the latter. If phosphorus is counted a very im-
portant plant food because it occurs in the seeds of plants,
the same reasoning would be applicable to both lime and
magnesia, but both of these substances occur in most soils
in much larger quantities than does phosphorus, and be-
cause of this their need is not so often felt.

Potassium is one of the very essential elements of plant
food, and although it is almost universally distributed in
soils, the compounds which it forms are usually so sol-
uble that there is a strong tendency for them to leach
away and to be borne to the sea in the drainage waters.
On account of this characteristic of the potash salts, bad
management leads to a rapid depletion of the soil stores of
this element and a corresponding shortage in the yields of
crops. Potash occurs widely distributed in the earth's
crust, largely as a constituent of orthoclase feldspar^ and
. the biotite and muscovite micas. In certain places, too, it
occurs in the mineral glauconite of the greensands of Kew
Jersey and elsewhere, and also in certain layers of the
potsdam sandstone in various parts of the world. The

Chetniffd Oonstifuenfx o/ Soih. 81

Li^lauconite soinotimos composes as much as 90 per cent of
the greensands and is itself made up of 8 to 12 per cent
of potash. Potash, too, is also a notable constituent of
kaoline beds, those in Wisconsin showing an average
l)er cent of 1.975 for fifteen analyses.

Repeatedly, in geologic history, movements of the
earth's crust have shut off arms of the sea, whose waters
afterward evaporated, leaving very rich and extensive
deposits of those salts which were carried in solution by
the ocean waters ; and among these were laid down
vast beds of kajnite which are now being mined and
returned as fertilizers to the land, where the potash is
used over again. The ashes of land plants are rich in
potash as a carbonate, and, united with nitric acid, it is
produced in the soil in the form of nitre.

Sodium is the basis of common salt, and as such has a
world-wide distribution. It very much resembles potas-
sium as an element but can in no sense take its place in
the life of land plants. In the form of Chili saltpetre
sodium nitrate is largely used as a fertilizer, but for the
nitric acid it contains rather than for the sodium.

Iron and manganese are two of the most abundant of
the heavy metals and occur almost universally as constit-
uents of the soil, but the former in much larger quantities
than the latter. Iron, united with oxygen and with
water, constitutes the red and yellow ochres used so much
as pigments in painting, and which give to soils their red
and yellow colors. Iron, too, is an important plant food,
although it does not enter largely into the composition of
their tissues. It is so abundant, so universely present in
the soil, and so difficultly soluble that there is never a
deficiency of it so far as the purposes of the plant are
concerned.

82 The Soil.

If we look at the composition of soils as shown by chemi-
cal analysis, it will be observed that while there is a strong
likeness among them all, to which reference has been
made, there are nevertheless quite wide variations among
them, so far as the relative proportions of the constitu-
ents are concerned; and the truth of this statement will
be readily appreciated from the tables on pages 84-87,
which are taken from the papers of Hilgard in the tenth
census of the United States. Selecting for comparison
the most widely divergent types, so far as physical con-
ditions are concerned, we have set against the' sandy
soils the heavy clays.

That these analyses may have as great significance as
possible, brief descriptions of the soils are given in the
order in which they occur in the table, and the sandy soils
are first described under the numbers used by Hilgard.

No. 36. Little Mountain soil, Alabama. Native vege-
tation, chestnut, short-leaf pine, hickory, post oak, and
small sourwood. Depth 8 inches ; color, top soil, dark
brown 2 inches ; yellowish sand at 2 feet and at 5 feet
solid sandstone rock.

No. 11. Chunnenugga ridge soil, Alabama. Depth, 6
inches. Vegetation, chestnut, short-leaf pine, red oak,
and sour gum; color, dark gray, changing at G inches to
a lighter gray, and at 3 feet to a yellowish color.

No. 8. Pine upland soil, table-land, Florida. Vege-
tation, long-leaf pine, round and narrow leaf, black-jack,
red and post oaks, and hickory. Soil taken at a depth of

9 inches. Subsoil, a yellowish sand, with slight inter-
mixture of yellowish clay, becoming a hard yellow clay at
a depth of 2 to 6 feet.

No. 7. Gray, sandy pine woods soil, Florida. Depth,

10 inches. Vegetation, long-leaf pine and wire grass.

Chemical CoriMituents of Soils. 88

No. 142. Gray, sandy soil, Georgia. Taken 6 inches
deep. Vegetation, red and post oak, pine and hickory.

No. 322. Dark, sandy, upland soil, Georgia. Taken
6 inches deep. Timber growth, hickory, oak, and long-
leaf pine.

Ko. 359. Gray, sandy soil, Georgia. Deptli about 6
inches, with yellow sandy subsoil.

No. 252. Dark, sandy soil, Georgia. Depth, 6 inches,
underlaid at a depth of a few feet by white marl beds.
This and No. 359 are described as oak, hickory, and pine
uplands.

No. 307. Gray, sandy soil of oak and hickory lands,
Georgia. Sarsaparilla in abundance. Depth, 6 inches.

No. 165. Gray, sandy soil, Georgia. Depth, 6 inches.
Vegetation, long-leaf pine.

The clay soils are as follows : —

No. 98. Post-oak and flatwoods clay, Alabama.
Depth, 10 inches, reddish clay, spotted. Vegetation,
chiefly post oak.

No. 149. Red clay soil, Georgia. Vegetation, red,
white, and post oaks, dogwood, chestnut, hickory, and
pine. Depth, 5 inches.

No. 203. Deep red soil, Georgia. Growth, red and
post oak and hickory. Depth, 8 inches.

No. 166. Red hill lands, Georgia. Taken 6 inches
deep. Vegetation not given.

No. 513. Ash-colored clayey swamp land, Georgia.
Growth, cypress, water oak, gum, ash, maple, beech^
and saw palmetto. Blue clay stratum at 1 to 6 feet.

No. 10. Yellowish red clay. South Carolina. Timber,
post, white, and black oaks, short-leaf pine, and hickory.
Depth, 5 inches.

No. 141. Stiff red soil from the cretaceous prairie

84

The Soil.

CHEMICAL COMPOSITION OF SOILS.

Numbers.

Insoluble
Residue.

Soluble
Silica.

Total Insoluble

Residue and
Soluble Silica.

Sand.

Clay.

Sand.

C\w-

Sand.

Clay.

Sand.

Clay.

36

11

8

7

142

322

359

252

307

165

98

149

203

166

513

10

141

390

1

7

93.630
94.770
93.362
95.630
92.090
90.230
90.681
92.460
94.428
94.822

72.746
73.690
60.370
73.422
63.444
77.860
54.565
51.063
79.580
75.350

1.682

.486

1.721

.879

1.220

1.940

1.885

1.550

.529

1.037

8.926

3.370

2.000

2.709

11.325

1.790

13.219

20.704

3.628

7.310

95.312
95.256
95.083
9().509
93.310
92.170
92.566
94.010
94.957
95.859

81.672
77.060
62.370
76.131
74.769
79.650
67.784
71.767
83.208
82.660

Averages

93.210

68.209

1.293

7.498

94.503

75.707

374

91.498

1.722

93.220

SWAMP AND LOESS SOILS.

Iliimus.

Loess.

Humus.

Loess.

Humus.

Loess.

Averages ; 35.886

68.853

20.825

4.918

56.711

73.771

SOILS COMPARED WITH THEIR SUBSOILS.

SOILS.

Averages .

Sand.

Clay.

Sand.

Clay.

Sand.

93.222

73.978

1.019

5.034

94.241

Clay,

79.012

SUBSOILS.

Averages . . .,

90.714

66.290

2.212

7.446

92.926

73.736

Differences

+2.508

+7.688

-1.193

-2.412

+1.315

+5.276

ARID

AND HUMID

SOILS

COMPARED.

Humid.

Arid.

Humid.

Arid.

Humid.

Arid.

Avftrjisres

84.031

70.565

4.212

7.266

87.687

76.ia5

Chemical Compositioji of Soils. 86

CHEMICAL COMPOSiriON OF SOILS. — Continned.

Numbers.

Potash.

Soda.

Lime.

Maonehia.

Sand.

Clay.

Sand.

Clay.

Sand.

Clay.

Sand.

Clay.

Sand.

Clay.

36

98

.100

.416

.060

.112

.120

.080

.040

.691

11

149

.156

.176

.069

.004

.081

.090

.069

.112

8

203

.045

.186

.018

.119

.0()4

.071

.005

.065

7

166

.117

.134

.064

trace

.058

.219

.042

.289

142

513

.110

.242

.035

.079

.090

.387

.025

.508

322

10

.067

.092

.009

.041

.119

.036

.090

.070

359

141

.275

.431

.130

.277

.055

.540

.048

.83<)

252

390

.095

1.104

.036

.325

.076

1.349

.083

1.665

307

1

.209

.150

.069

.065

.141

3.054

.031

.029

165

7

.034

.255

.022

.258

.045

.340

.043

.290

Averages

.121

.319

.051

.128

.085

.617

.048

.456

374

.137

.054

.173

.203

SWAMP

AND

LOESS

SOILS

Humus.

Loess.

Humus.

Loess.

Humus.

Loess.

Humus.

Loess.

Averages

.639

.435

.109

.165

3.786

5.820

.886

3.692

SOILS COMPARED WITH THEIR SUBSOILS.

SOILS.

Sand.

Clay.

Sand.

Clay.

Sand.

Clay.

Sand.

Clay.

Averages

.157

.214

.072

.085

.115

1.761

.076

.182

SUBSOILS.

Averages

.143

.344

.064

.0&5 .096

1

1.481

.073

.240

Differences . . .

+.014

-.130

+ .008

.000

+.019

+.280

+.003

-.058

ARID

AND HUMID

SOILS

COMPARED.

Humid.

Arid.

Humid.

Arid.

Humid.

Arid.

Humid.

Arid.

Averages

.216

.729

.091

.264

.108

1.362

.225

1.411

86

The Soil.

CHEMICAL COMPOSITION OF SOILS. — Continued.

Numbers.

IJkown Oxide
OF Manganese.

Peroxide
OF Iron.

Alumina.

Sand.

Clay.

98

149

203

166

513

10

141

390

1

7

Sand.

Clay.

Sand.

(lay.

Sand.

Clay.

36

11

8

7

142

322

359

252

307

165

.102
.156
.220
.049
.126
.313
.172
.040
.101
.020

.106
.146
.196
.164
.052
.056
.079
.119
.195
.038

.761
.706
.941
.221
.96:5
1.927
1.8:57

.843
.6(51
.930

12.406
5.989
9.709
4.051
3.894
r).()46
7.089
5.818
3.420
5.784

1.532
.733
1.3:39
.473
1.959
2.141
1.4:5(5
2.649
1.195
1.576

2.473

7.305

18.066

10.598

13.454

7.538

16.071

10.539

4.988

5.567

Average

s

.130

.115

.979

6..381

1.503

9.660

374

.0(i6

1.372

1.522

SWAMP AND LOESS SOILS.

Averages.

Humus.

.098

Humus.

7.040

Loess.

3.569

Humus.

14.476

Averages.

Differences.

.080

.125

1.739

+.044

+.008

.577

6.947

-1.742

2.276

-1.131

Loess.

2.812

SOILS COMPARED WITH THEIR SUBSOILS.

SOILS.

Sand.

Clay.

Sand.

Clay.

Sand.

Clay.

Averages

.124

.133

1.162

5.205

1.145

6.998

SUBSOILS.

12.086

-5.088

ARID AND

HUMID

SOILS

COMPARED.

Humid.

Arid.

Humid.

Arid.

Humid.

Arid.

Averages

.133

.059

3.131

5.752

4.2%

7.888

Chemical Compoaition of Soils.

87

CHEMICAL COMPOSITION OF SOILS. — Concluded.

Numbers.

PhOSI'IIOKIC

Acid.

SUI-KUKIC

Arii».

Water and
Organic Matter.

Sand.

Clay.

Sand.

Clay.

Sand.

Clay.

Sand.

Clay.

m

98

.051

.103

.028

.061

2.055

1.906

11

149

.101

.071

.057

.055

2.642

8.891

8

203

.066

.204

.091

.285

2.422

8.953

7

IHC)

.092

.0()9

.058

.0.35

1.807

8.309

142

513

.191

.071

.105

.055

3.477

6.843

322

* 10

.111

.082

.054

.054

2.881

6.167

359

141

.105

.187

.034

.009

3.682

6.922

252

390

.039

.304

.045

.024

2.354

7.369

;i07

1

.103

.242

.046

.089

3.113

4.962

165

7

.014

.079

.035

.079

1.636

4.962

Averages

.087

.141

.055

.075

2.607

6.528

.374

.088

3.394

SWAMP AND LOESS SOILS.

Averages.

Humus.

Loess.

Humus.

Loess.

Humus.

.150

.200

.148

.090

13.943

SOILS COMPARED WITH THEIR SUBSOILS.

SOILS.

Averages.

Sand.
.128

Clay.

Sand.

Clay.
.090

Sand.

.207

.052

2.853

Loess.

1.205

Clay.

6.014

SUBSOILS.

Averages 124

.159

.060

.071

1.943

4.780

Differences

+ .004

+ .048

-.008 +.019

+ .910

+1.234

ARID AND HUMID SOILS COMPARED.

Averages .

Humid.

Arid.

Humid.

Arid.

Humid.

.113

.117

.052

.041

3.644

Arid.

4.945

88 The Soil.

region, Mississippi. Fairly productive in good seasons,
Vegetation, oak.

No. 390. Buckshot soil of Yazoo bottom, Louisiana.
Stiff dark-colored clay soil, mottled with spots of ferru-
ginous matter, traversed by numerous cracks. Very
fertile and no change in character to a depth of 10 feet.
Vegetation, sweet gum, pecan, water and willow oak,
hackberry, and honey locust.

No. 1. Red clay land from central basin, Tennessee.
Vegetation, hickory, red, white, and post oaks, elm, ash,
honey locust, black walnut, wild cherry, sugar trees,
poplar, hackberry, redbud, dogwood, and papaw. Depth,
7 inches, Avith heavy clay subsoil.

No. 7. Same region, depth, and vegetation as No. 1,
but subsoil not as heavy.

If reference is made to the table showing the chemical
composition of sandy soils as compared with that of clay
soils, it will be seen that during the process of analysis
31.791 per cent of the soil ingredients were dissolved
out of the clay, as shown by deducting the 68.209 per
cent of insoluble residue from 100, while only 6.790
per cent were dissolved from the sandy soils, making a
difference of 25.001 in favor of the clay soil. In the
average, too, of the ten different analyses, it will be
seen that the various soluble ingredients are shown to
be dissolved more abundantly from the clayey than from
the sandy soil.

How shall these results be understood? Do they mean
that in every 100 pounds of sandy soil, plants may find
nearly 7 pounds of soluble material, the larger part of
which is plant food, while in the clayey soil there are 31
pounds in each and every 100, or more than four times as
much? Do they mean that clay soils are capable of yield-

Chemical Composition of Soih. 89

mg the ash ingredients of plant food to growing crops
four times more rapidly than sandy soils can do? Or,
are we to understand that the ash ingredients of plant
food in clay soil are being carried away by the waters
which percolate through them four times more rapidly,
gallon for gallon of water, than they are from the sandy
soil?

If the results of the cliemical analyses of soil were to
be taken without qualification, one or the other of these
conclusions would seem to follow, but it is very unfor-
tunate for agriculture that it should seem necessary to
admit that the results of soil analyses, as they have
been made, can and do throw but a very dim and uncer-
tain light upon either the condition or the amount of
available plant food a soil may contain. The results of
chemical analyses do show, beyond question, that there
are marked differences between soils, but so far as the
data now at hand can be interpreted, these variations,
at least so far as the mere relative proportions of the
so-called soil ingredients are concerned, seem quite as
likely to be due to differences in the actual sizes of soil
grains, as to any real and marked difference in either the
chemical or mineralogical composition of them.

When given quantities of coarse and line grained soils,
having identical chemical composition, are subjected to
like quantities of dissolving acid, under like conditions,
it would appear to follow necessarily that, where all of
the materials are not dissolved, and wdiere a complete
saturation of the solvent has not resulted, more mate-
rials will enter into solution from the fine than from the
coarse grained sample; and simply because more points
of attack are presented by one than by the other. With
like quantities of soil and acid, the solution would not be

90 The Soil.

directly proportional to the total surface areas in the
two samples, because in the fine-grained sample, where
the solution is most rapid on account of the greater sur-
face, the strength of the acid would be most rapidly
reduced, thus tending to make the ratio between the
quantities dissolved somewhat less than the ratio between
the areas of the soil grains in the two samples.

If it should occur that certain kinds of soil grains in
both cases were more easily and completely dissolved
than the bulk of the soil materials, then the ratio, in
such cases, between the dissolved materials would be
less than between the surfaces of the original soil grains.
So, too, unless very vigorous stirring were constantly
maintained, the fine-grained soil would tend to dissolve
less rapidly in proportion to its surface than would the
coarse-grained soil, where diffusion would be relatively
more rapid.

But in spite of the condition just referred to, the much
larger surface area possessed by the two, three, or more
grams of clay soil taken for analysis appears to have
resulted in extracting a relatively larger amount of plant
food from this soil than was removed from the more
coarse-grained and relatively small-surfaced sandy soil.

If we compare the mechanical analyses of the two
Mississippi soils, jSTos. .390 and 377, as given by Wiley,
with their chemical analyses, as given by Hilgard, it will
he found that, while the surface area in one gram of the
fine soil is about seven times that of the one of coarser
grain, the soluble materials extracted were only about
four times as large, thus making the rate of solution,
when compared by equal surface areas, less for the clay
than for the sand. So, too, if we take the mean surface
area in one gram of twelve truck subsoils, of Maryland,

Chemical Oompositwn of Soih.

^1

as given by Whitney, and coinpar(^ this with the mean
area of one gram of six strong wheat subsoils, Ave shall
hnd their surface areas to be in the ratio of 934 to 3451,
while the ratio between the soluble ingredients of the
sandy and clayey subsoils, as given on pages 84-87,
is 9.286 to 33.71, or very nearly the same as that between
the surface areas of the soil grains in the similar cases
cited.

The reader should bear in mind that these remarks
are not intended to convey the idea that the chemical
composition of sandy and clayey soils are nearly iden-
tical, but rather that it seems more than probable that
the ratio between the more difficultly soluble and the
more readily soluble ingredients of plant food is not as
widely different in the coarse and fine grained types of
soil as the table of chemical analyses would appear at
first thought to indicate.

There has been placed in the table, just below the line
of averages for soils, the analysis of a clay soil, No. 374,
from Louisiana, which shows a relative proportion of
the more soluble ingredients bearing a striking resem-
blance to the more sandy types, the insoluble residue
being 91.498 per cent, while that of the sandy soil aver-
ages 93.210, there being two samples in the series of ten
having as low a per cent of "insoluble residue '^ as 90.6.
Hilgard describes this as a fair upland soil, yielding
700 to 800 pounds of seed cotton per acre, color gray,
depth 6 to 8 inches, not heavy, and underlaid by a subsoil
quite heavy in tillage and dark orange in color. The
case is cited to illustrate how a chemical analysis alone
does not always serve to distinguish between soils which
in their physical features may be strongly contrasted.

If we look at the differences between the indicated

92 The Soil

chemical composition of soils and their subsoils, as given
in the table, pages 84-87, it will be seen that the
insoluble residue, lime, phosphoric acid, and manganese
are more abundant in the surface soil, while in the sub-
soils the soluble silica, peroxide of iron, and alumina
appear in highest percentages, while the other ingredi-
ents are sometimes more abundant in one and sometimes
in the other.

If these soils were examined with reference to the sizes
of the grains composing them, it would be found that in
the subsoil the small particles, especially in humid
regions, are most abundant, and hence that the internal
surface area is much larger in the lower than in the
upper layers, which may in part explain the higher per-
centages of soluble ingredients shown by chemical
analysis.

Kef erring again to the table for a comparison of soils
of humid with those of arid regions, it will be observed
that these are in some respects quite strongly contrasted
as regards their chemical composition. The averages
there given are those of Hilgard, and for the humid
regions are made up of 466 analyses, while those for the
arid are a mean of 313 determinations.

It may be noted in the first place that, excepting the
insoluble residue, brown oxide of manganese and sulfuric
acid, all other ingredients are more abundant in the soils
of arid lands; and not only this, but these differences
are really large, the amounts being often more than
double, and in some cases much higher than this. It
should be said, however, regarding the analyses entering
into these averages, that all of them come from states
south of the Ohio E-iver or west of tlie Missouri, and for
this reason more fairly represent differences between

Chemical Composition of Soih. 93

soils of unglaciated areas in humid and arid regions
than of soils in general. It appears, too, that many
of the differences between the soils of the two regions
largely represented are made more striking than they
should be through the admission of a rehitively larger
proportion of sandy soils and light loams than of those
of heavier type, and this will be rendered apparent
on comparing the soils of the arid regions with the
ten heavy clay soils in the same table, and still more
so when the clay subsoils are compared with them.
The position would seem to be more fully justified,
too, when it is observed that the analyses of the ten
sandy soils given in the table approach more nearly
to the mean of the 466 for humid regions than do
those of the clay soils ; and also when it is observed that
the brown oxide of manganese, which is more abundant
in humid than in arid soils, appears also to be more
abundant in the sandy than in the clay soils.

But when all allowances have been made, there are
still outstanding differences between the soils, formed
under these widely contrasted climatic conditions, which
are sharply marked and beyond question.

In the first place, the insoluble residue is evidently
more abundant in humid than in arid soils, the ratios
being in round numbers, as 84 to 70, and this difference
is held to be due to the much greater amount of leach-
ing which necessarily takes place where rains fall fre-
quently and in large quantities.

The soluble silica, too, an ingredient characteristic of
the analyses of only heavy soils in humid regions, is
very abundant in those of arid regions, but the anoma-
lous feature regarding this is that in its combinations
in the soil it has not the power of imparting to these

94 The Soil.

soils the adhesive plastic quality so characteristic of
clay lands in humid regions. Whether the soluble
silica is, in the soil, united largely with alumina to form
kaolinite or true clay, or whether it is combined to form
varieties of zeolites, which may be lacking in power to
give adhesiveness to soil, is unknown.

Hilgard regards the large percentage of lime, with its
allied compound, magnesia, as one of the most distinc-
tive features of the soil of arid regions, and to this lime
he attributes a flocculation or granulation of the clay,
which destroys its adhesive quality. To the very gen-
eral abundance of lime, too, in these soils, alike on the
high lands and on the low, he attributes the high and
very uniform productiveness of all these soils whenever
an abundance of water is supplied to them.

It seems plain that the high percentages of soluble
ingredients in the soil of arid regions result from the
slow decomposition of soil grains brought about by the
conjoint action of the scanty water which does fall and
the carbonic acid of the air. Water enough falls for the
decomposition of rock and the formation of alkalies and
zeolitic minerals, but not enough to remove them when
formed, as is the case in humid regions.

The humus of soils, so far as its chemical composition
is concerned, is not well understood, neither have we
attained a satisfactory knowledge of its functions or
importance as a food for plants. It used to be held that
any soil deficient in humus was, because of this shortage,
necessarily poor or sterile, but it is now known that in
arid regions, where humus in the soil is very scanty or
even wanting, large crops are produced when only an
abundance of water is supplied. Experiments in water
culture, too, have proved that when nitrogen is supplied

Chemical Composition of Soils. 95

to plants in the form of purely inorganic or mineral
nitrates, plants will thrive in the complete absence of
humus.

Humus is derived from the partial decay in the soil of
organic matter, whether that be vegetable or animal, and
it imparts to the soil a black or brown color. From
what has been said regarding nature's method of running
in cycles, it will be readily understood that humus is
simply the abandoned tissues out of which life has
moved and which are falling back by degrees into the
carbonic acid, water, free nitrogen, and ashes out of which
life reared its marvelous structures. In tropical regions,
where the soil is warm the whole year through, and in
arid regions, where the soil is open and readily pene-
trated by the air, the rate of decay is so rapid that the
amount of humus found in any soil at any particular
time is relatively small; but in the temperate climates,
where the soil is damp and where the ground is too cold
to permit of decay during considerable portions of the
year, there the decaying organic matter accumulates in
considerable quantities and especially on wet soils and
in swampy places. Beds of peat and the black muck
soils are the best examples of what is meant by humus,
and it is excessively abundant in these places because
the soil is close in texture and so full of water that the
microscopic forms of life which feed upon this dead
matter are unable to get the necessary oxygen to thrive
in it. We should think of humus as the food of micro-
scopic life in the soil, and of the waste products of this
microscopic life as a very essential part of the food of
higher plants. Keeping. this in mind, we can better
appreciate the importance of farmyard manure, for
through its decay humus is formed. Both are organic

96 The Soil.

matter partially decayed and capable of contributing
food to plants.

But Hilgard and Jaffa have made the important
announcement that the humus of arid regions is much
richer in nitrogen than is that of humid regions, or of
the humid soils of arid regions. The results of their
observations, as reported in Agricultural Science for 1894,
are summarized below : —

No.
Samples.

HtJMus IN Soil.
Per Cent.

Nitrogen
IN Humus.
Per Cent.

HUMIO N1TRO6BN

IN Soil.
Per Cent.

Arid soils . .

18

.75

15.87

.101

Semi-arid soils .

8

.99

10.03

.102

Humid soils

8

3.04

5.24

.132

In speaking of these results, they say, "It thus
appears that, on the average, the humus of the arid soils
contains three times as much nitrogen as that of the
humid, that in the extreme cases the nitrogen percen-
tage in the arid humus actually exceeds that of the albu-
minoid group, the flesh-forming substances."

"It thus becomes intelligible that in the arid region a
humus percentage, which, under humid conditions, would
justly be considered entirely inadequate for the success
of normal crops, may, nevertheless, suffice even for the
more exacting crops. This is more closely seen on
inspection of the figures in the third column, which
represent the product resulting from the multiplication
of the humus percentage of the soil into the nitrogen of
the humus."

FUNCTIONS OF THE SOIL INGREDIENTS.

When we come to speak of the functions or impor.
tance of the different soil ingredients in vegetable life,

Functions of the Soil Ingredients. 97

it must be said that our knowledge is as yet very limited
and very indefinite. That plants cannot thrive in a soil
destitute of nitrogen, potash, lime, magnesia, and phos-
phoric acid has been proved in the most complete and
satisfactory manner. A soil entirely lacking in any one
of these is, for that reason, an infertile one.

Since sulfuric acid, in some of its combinations in the
soil, is the only known source of sulfur in plants, and
since sulfur is an essential element in the molecular con-
stitution of vegetable albumen and allied compounds, it
follows that fertile soils should always contain an ade-
quate percentage of sulfates in some form available to
plants. It will be seen, however, from the table of
chemical composition, that the amount present in any
soil, at any time, is usually relatively small.

Silica, although the most abundant of all the soil
ingredients, and although present in the tissues of nearly
all plants, in greater or less amounts, has not been
demonstrated to have any important part to play in
plant growth. Indeed, recorded observations go to shoAv
that plants get along perfectly well when grown in
media nearly or entirely devoid of this substance. It
has been supposed that it played an important part in
giving the necessary stiffness to the stems of cereals, but
Arendt has shown that the distribution of silica in dif-
ferent parts of the oat plant is as follows : —

Lower part of stem 1,7 parts in 1000 of dry substance.
Middle " " " 5.1 " " 1000 " " "

Upper " " " 13.3 " " 1000 " " "

Lower leaves 35.2 " " 1000 " " "

Upper leaves 43.8 " " 1000 " " "

Now if the silica were needed for stiffness, the largest
amounts should be found in the lower and middle per-

98 The Soil.

tions of the stem, and more in the stalk than in the
leaves, while the reverse distribution is observed.
Indeed, the distribution of silica in the oat makes it
appear that its presence there is due simply to the fact
that it was present in the water which passed through
the plant, and that it was left where the largest amounts
of evaporation had taken place ; that is, in the leaves and
in the higher portions of the stem where the wind cur-
rents are strongest.

A sufficient amount of an iron salt in the sap of a
plant appears to be essential to the development of the
green color of foliage, and without the green chlorophyll
carbon cannot be assimilated from the carbon dioxide of
the air. Sachs found, that while young plants of Indian
corn, when growing in solutions free from iron, had
their first three or four leaves green as usual, the next,
and those which followed, were first white at the base
and green at the tips and afterwards completely white;
but on adding a few drops of sulfate or chloride of iron
to the medium in which the plants were growing, the
green color began to be developed appreciably in twenty-
four hours, while the normal color was restored in three
or four days. It is plain, therefore, that iron is a very
important soil ingredient, although its universal presence
in the soil, and the small amount of it needed, makes it
unnecessary to pay any heed to it as a plant food which
should be supplied as a fertilizer under natural field
conditions.

In the movements which result in the transfer of the
starch-forming products from the green parts of plants
to their place in the seed, root, or tuber, potash, mag-
nesia, and lime appear to play an important part, but it
seems also that before the starch-forming products can

Ki)vh of Soils. 90

be moved a smiill luiiount of chlorine must also be pres-
ent. The amount of chlorine, however, may be very
small, and as it does not tend to accumulate in th<;
places where the starch is stored, it would appear that,
like the iron, it may be used over and over again.

KINDS OF SOILS.

In the language of practical men soils are variously
classified. They are sometimes spoken of as light or
heavy, but these terms do not refer to their weight in
pounds per cubic foot; for those which are called the
lightest are the heaviest soils we have. A heavy clay soil,
when dry, weighs only from 70 to 80 pounds per cubic
foot, while the lightest sandy soils have a weight of 105
to 110 pounds for the same volume. It is the ease or the
difficulty w4th which the soils are worked or tilled
which gives rise to the terms, light and heavy. In the
light soils the roots of plants have less difficulty in
threading their way than in those which are stiff and
not easily crowded to one side, and as a result of this
freedom to movement plants distribute their roots much
more symmetrically and occupy the whole soil more
completely in the lighter types than they are able to do
in the stiff and heavy ones. As a consequence of this
equitable distribution, no root trespasses upon the feed-
ing ground of another, and the whole soil is laid under
tribute with correspondingly better returns, when other
conditions are equally favorable.

Then, again, soils are spoken of as warm or cold, hav-
ing reference to their relative temperatures, especially
during the early part of the season. And here the
strongest factor in determining the temperature of a

100 The Soil.

soil is the amount of water it can hold and bring to the
surface for evaporation, those holding the most water
and delivering it most rapidly at the surface being usu-
ally the coldest, and why this is so will be explained in
another place.

Soils are sandy when not more than 40 to 65 per cent
of their weight is made up of particles so small that from
1000 to 400,000 of them must be placed in line to span a
linear inch, while the balance may be so large that only
20 to 100 of them are needed to stretch across the same
distance. The heaviest clay soils, on the other hand,
may have 80 to 95 per cent of their weights made up of
the smallest sizes of particles named above, while only
5 to 20 per cent of grains of the larger diameters are
found among them. Loamy soils are such as have their
grains intermediate between those of the sandy and heavy
clay types; while between this medium soil we have on
the coarser-grained side, sandy loams and loamy sands,
and on the finer-grained side, clayey loams and loamy
clays, there being, of course, an insensible shading of
one of these types of soil into another.

It has long been observed that these different types
of soils in all parts of the world are regularly inhabited
by kinds of plants peculiar to each, and by referring to
the descriptions of soils on pages 82 and 83, it will be
seen how sharply contrasted the types of vegetation are
in that particular region. In the battle of the forests,
in the race for sunshine and for moisture to meet the
needs of thirsty leaves, some plants have suited their
roots to the coarser and dryer soils, so that they feed
themselves here more economically than others can;
while other plants and other trees, in the long years of
fitting and refitting, have come to thrive better than

The Store of Plant Food.

101

their competitors on the heavy chiy soils. Nature, in
her system of evolution, has developed a division of
labor among plants just as she has among animals.
She saw, long ago, that in order that sunshine might
bring the largest returns out of soil, air, and water,
there must be special adaptations to a limited set of
conditions, and just as woodpeckers are a family of
birds peculiarly fitted to gleaning food from the trunks
of trees, so there are plants peculiarly adapted to the dif-
ferent types of soil.

Besides the soils just referred to there are the swamp,
muck, peat or humus soils, which contain a very high per
cent of decaying organic matter or humus, before referred
to but these only occur in wet, undrained localities.

THE STORE OF PLANT FOOD.

Let us look now to the relation between the amount
and kinds of mineral food materials stored in the soil
and that removed by crops. Professor Wolff gives the
composition of some fresh, or air-dry, agricultural prod-
ucts as follows : —

Maize.

Oats.

Winter
Wheat.

Winter
Eye.

Barley.

Red
Clover.

CO

1

M
c3

02

40.7

c
'3

Total ash . . .

47.2

12.3

44.0

26.4

42.6

17.7

17.3

48.9

21.8

56.5

36.9

Potash . . .

16.6

3.3

9.7

4.2

4.9

5.5

7.6

5.4

9.3

4.8

19.5

13.8

Soda ....

0.5

0.2

2.3

1.0

1.2

0.6

1.3

0.3

2.0

0.6

0.9

0.2

Magnesia . . .

2.6

1.8

1.8

1.8

1.1

2.2

1.3

1.9

1.1

1.8

6.9

4.5

Lime ....

5.0

0.3

3.6

1.0

2.6

0.6

3.1

0.5

3.3

0.5

19.2

2.3

Phosphoric acid

3.8

5.5

1.8

5.5

2.3

8.2

1.9

8.2

1.9

7.2

5.6

12.4

Sulfuric acid

2.5

0.1

1.5

0.4

1.2

0.4

0.8

0.4

1.6

0.5

1.7

1.7

Silica ....

17.9

0.3

21.2

12.3

28.2

0.3

23.7

0.3

23.6

5.9

1.5

0.9

Sulfur. . . .

3.9

1.2

1.7

1.7

1.6

1.5

0.9

1.7

1.3

1.4

2.1

102

The Soil

From this table it appears that each 1000 pounds of air-
dry product requires from the soil the lumiber of pounds
of each ingredient there indicated. Taking clover as an
illustration, each ton of clover hay demands for its pro-
duction 39 pounds of potash, 1.8 pounds of soda, 13.8
pounds of magnesia, 38.4 pounds of lime, 11.2 pounds of
phosphoric acid, and 3.4 pounds of sulfuric acid ; and two
tons of hay per acre makes the annual demand double
these amounts. What has the soil to offer ?

If we take the mean dry weight of a surface foot of
soil at 80 pounds and the mean soluble ingredients of soils
at the percentages given by Hilgard on pages 84-87,
regarding these as indicating the available plant food,
then the amounts in the surface foot of an acre of land
may be shown to be as follows : —

Potash
Soda
Magnesia
Lime

Phosphoric acid
Sulfuric acid
Soluble silica

in surface foot, per acre

3.76 tons.
1.58
3.92
1.88
1.97
.91
7:5. 40

It is not unfair to assume that every young man who
starts on a farm of his own may be interested in its main-
tenance for 50 years on his own account and for 50 more
years for the sake of his children. What then are the
demands on the soil for 100 years likely to be ? To
give definiteness and simplicity rather than exactness to
our problem, let us assume that a three-year rotation of
corn, clover, and oats shall be adhered to throughout;
that the clover shall all be cut as hay and w'lih. the straw
and corn stalks, or their equivalents, constitute a revolv-
ing fund, never to go permanently off the farm ; while

The Store of Phint Food.

108

the equivalent of the grain in somo form shall be sold
and no part returned to the land. Assume, further, that
each and every year the yields shall be exactly two tons
per acre of air-dry product, and that in the case of the
corn and oats one-half of the product shall be grain and
tlic other stalks or straw. Under these conditions how
long will the several credits — potash, soda, magnesia,
lijne, phosphoric acid, sulfuric acid, and silica — last?

On the basis of these assumptions the amounts of the
several ash ingredients required to be extracted from the
soil by each of the three crops during the 33 years out of
99 which it will have fed upon the ground would be, —

FOR THE REVOLVING FUND.

Pot-
ash.

Soda.

Mag-
nesia.

Lime.

Phos-
phoric
Acid.

Sulfur
AS Sul-
furic
Acid.

Silica.

lbs.

lbs.

lbs.

lbs.

lbs.

lbs.

lbs.

Clover ....
Oat straw . . .
Corn stalks . .

2574.0

640.0

1095.5

118.8

151.8

33.0

910.8
118.8
179.7

2534.0
237.6
330.0

739.2
118.8
250.8

536.5
442.6
953.0

198.0
1399.0
1181.5

Total in 100 yrs.

4309.5

303.6

] 209.3

3101.6

1108.8

1932.1

2778.5

FOR THE EQUIVALKXT

OF GRAIN i

SOLD.

Corn ....
Oats ....

217.8
277.2

13.2
66.0

118.8
118.8

19.8
66.0

363.0
363.1

249.2
370.0

19.8
812.0

Total

in 100 yrs.

495.0

79.2

237.6

85.8

726.1

619.2

831.8

If we now divide the amounts of the several ash
ingredients which chemical analysis points out as exist-
ing in the surface foot of the average soil of the humid
regions, included in Hilgard's studies, by the amounts of

104 The Soil

these ingredients supposed to be sold and hence removed
permanently from the land, the results will indicate the
number of years required for the removal of the amount
of the several ash ingredients standing to the credit of
the surface foot of soil at the beginning of the 100 years.
Making these divisions we get,

Potash enough to last 1521 years.

Soda

4050

Magnesia

3300

Lime

4387

Phosphoric acid

542

Sulfuric acid

292

Soluble silica

17650

When it is observed that cultivated plants send their
roots foraging through not less than the upper four feet
of soil, and that the amounts of ash ingredients which
have been considered are only those which chemical
analysis tells us are to be found in the surface foot, it
seems well-nigh impossible that there could ever be a
deficiency in any one of the ash ingredients which plants
find essential to their well-being.

Notwithstanding the apparently inexhaustible stores
of potash, magnesia, lime, phosphoric acid, etc., in the
soil, it must be remembered that we are nevertheless con-
fronted with the indisputable results of practical field
work which show, very often at least, that the addition
of purely mineral fertilizers have been associated with
larger yields per acre. We are confronted on every
hand, too, with the fact that lands do run out and
some varieties much more quickly than others ; so that,
when all has been said, the most important fact to
bear in mind is that here is a problem lying at the very

The Store of Plant Food. 105

foundations of agriculture upon which a vast work has
yet to be done.

In support of this view let me place in evidence some
of the results obtained by Sir J. B. Lawes and his associ-
ates during their classic experiments bearing upon the
conditions which determine the fertility of soils. By
growing various crops year after year on the same land,
to which no nitrogen-bearing manures were applied, they
found that when purely mineral fertilizers were added,
the crops were able to produce larger yields and to extract
more nitrogen from the soil than when these fertilizers
were omitted. Wheat, for example, grown continuously
on the same land for 32 years without manures of any
kind, was able to extract from the soil and build into its
product 20.7 pounds of nitrogen per acre, per annum, but
the same crop, on adjacent and similar lands, to which
mineral fertilizers without nitrogen were added, was able
to gather and store 22.1 pounds, an amount 6.76 per cent
larger. Barley, during 24 consecutive years, drew from
the soil 18.3 pounds of nitrogen per annum, where no
mineral fertilizers were added, but 22.4 pounds per acre
under the stimulus from them. Beans gathered from
their land 31.3 pounds of nitrogen per acre where no
fertilizer was added, as an average of 24 years, but 45.5
pounds where complex mineral food was given them.
Ground bearing 6 crops of clover in 22 years, with 1
of wheat, 3 of barley, and 12 years fallow ground, gave,
without fertilizers, 30.5 pounds of nitrogen per acre, but
with the mineral fertilizers, 39.8 pounds. So, too, in a
rotation of crops, 7 courses in 28 years, no fertilizers, gave
36.8 pounds, while with superphosphate of lime the
yield was 45.2 pounds per acre. Then, again, in the mixed
herbage of grass land, 20 years without fertilizers gave a

106 The Soil.

mean yield of 33 pounds, but with a mixed mineral fer-
tilizer, containing potash, the product of nitrogen was
55.6 pounds per acre, per annum.

Such results as these place beyond question the fact
that, in spite of the large stores in the soil of all the ash
ingredients used by plants, the addition of mineral salts
move or less closely allied to those found there do give to
the plant an added power over the natural resources of
the soil in which they may be growing ; and the marvel-
ous part of the whole problem is that so small an amount
of the fertilizer, when diluted by so much soil and water,
can exert the appreciable effects observed.

CHAPTER III.

NITROUKX OF THE SOIL.

In speaking of t\\f\ chemical composition of the soil,
very little has thus far been said regarding nitrogen, the
most important, perhaps, of all the ingredients ; and for
the reason that the loss of it from the soil is so rapid
under faulty management, and the demands for it so
urgent, as to claim for its consideration a separate
chapter.

THE STORE OF SOIL NITROGEN.

We have seen that the total amount of the ash ingredi-
ents of plant food stored in the surface four feet of soil
is very large, and so, too, is the total nitrogen, when con-
sidered in all its combinations. Storer, citing the obser-
vations of Krocker, to the effect that cultivated soils rarely
contain less than .1 per cent of nitrogen, calculates the
amount stored in the surface foot as seldom less than
3500 pounds per acre. This is an amount so large that i i'
we take Warington's estimate of the nitrogen removed
from the soil by wheat, when producing 30 bushel per
acre, there is enough for more than 70 such crops, count-
ing 33 pounds of nitrogen in the grain and 15 pounds in
the straw. The mean amount of nitrogen in eleven ara-
ble and grass soils at Rothamsted is j)laced by Lawes and
Gilbert at .149 per cent, and for eight other Great Britain

107

108

Tie Soil,

soils at .166 per cent. Four Illinois prairie soils were
shown by Voelcker to contain .308 per cent; while
seven rich Russian soils have been shown by C. Schmidt
to contain .341 per cent of nitrogen. If we bring all of
these thirty analyses together into one mean, we shall
have .219 per cent, an amount more than double that
used by Storer as stated above.

In studying the fertility of the rich prairie soils of
Manitoba, Lawes and Gilbert found that the surface foot,
from four different localities, contained an average of .373
per cent of nitrogen, or enough, could it all be utilized in
wheat production, for some 6500 bushels from each and
every acre of land.

But the nitrogen of these and other soils is not all con-
tained in the surface foot, and the distribution of it in the
surface four feet of the soils in question, as they learned
through chemical analysis, is given in the table below,
which shows that the total amount is more than as large
again as that given for the surface foot.

AMOUNT OF NITROGEN PER ACRE IN SURFACE FOUR FEET
OF FOUR MANITOBA SOILS.

Depth.

1st foot
2d foot
3d foot
4tli foot

Total

NlVERVILLE.

lbs.

Brandon.
lbs.

Selkirk.
lbs.

Winnipeg
lbs.

7308

5236

17304

11984

5408

3488

8448

10464

2484

2592

2736

5688

1520

870

1487

4045

16720

12186 29975

32181

Nor can it be urged with these soils that the nitrogen
is in a form which cannot, under favorable conditions
of tillage, be converted into nitric acid and nitrates, the
form in which nitrogen is largely used by cultivated

The Store of Soil Nitroi/en. 109

plants ; for Sir J. B. Lawes caused samples of these soils
to be placed under favorable conditions for nitrification,
where they were held, with some interruptions, during
something more than 300 days and during this time it is
estimated that not less than 799.8 pounds per acre, as an
average for the four soils, were converted into soluble
nitrates available for crop production, as shown in the
table which follows : —

AMOUNT OF NITROGEN PER ACRE CONVERTED INTO
SOLUBLE FORM.

Depth.

Mean Pkr Cent

OF Total
Nitrogen.

NiVERVILLE.

lbs.

Brandon.
lbs.

Selkirk.
lbs.

Winnipeg
lbs.

1st foot

4.295

234.1

250.4

655.1

650.0

2d foot

2.733

72.9

57.2

377.5

372.5

3d foot

2.108

12.6

53.7

27.2

276.0

4th foot

1.443

15.0

10.7

11.5

112.8

Total 334.6 372.0 1071.3 1411.3

While the conditions under which these samples were
placed for nitrification were much more favorable for the
rapid carrying forward of the process than could be pro-
duced in the natural soil, it should not be inferred that
the amount so changed represents the total available
nitrogen in these soils ; for there appears to be no reason
why time and favorable conditions may not transform
into soluble nitrates much the larger portion of that
which the analyses have shown them to contain.

The presence of these large amounts of nitrogen and
of ash ingredients which soils have been shown to pos-
sess are very fundamental facts, which must be kept ever
in mind in our efforts to restore the vigor of exhausted
soils and to maintain a high degree of productiveness in
them when so brought back.- They are important because

110 The Soil

they show very clearly that run-out lands, and lands tired
of this crop or of that, have been rendered so by some
change different from the consumption of the chemical
ingredients contained in soils out of which plant food is
elaborated. They are important because thej^ bring
clearly into view the fact that, as yet, our practices re-
garding the rotation of crops, regarding the fertilizers or
manures for this soil or that crop, and regarding many of
our efforts to improve our lands by this or that method
of tillage, are all of them far too much like those of a
man feeling his way in the dark. They are important
because they show that the agriculture which shall be
able to feed the crowded cities, so rapidly building, as
cheaply as they must be fed, must bring to its aid the
mightiest efforts of the strongest minds, and must place
the management of its lands under trained men whose
education is unexcelled in its kind by that of any other
trade or profession.

IMPORTANCE OF NITROGEN IN PLANT LIFE.

Nitrogen, sulfur, and phosphorus are the three elements,
'derived from the soil, which are largely peculiar to those
highly complex compounds so immediately associated
with the life processes of plants. It is true that oxygen,
carbon, and hydrogen, combined to form cellulose, out of
which the framework of vegetation is built, and to form
the starches, sugars, and gums, make up by far the larg-
est part of the dry weight of vegetable matter; but these
appear to be only products which have resulted from the
transformations which take place within the protoplas-
mic substance of which nitrogen, sulfur, and, at times,
phosphorus appear to be the controlling or life-leading

T'tnjK>rt(in<-p of Nitrogen in Pluut Life. Ill

elements. W'liilc carbon, oxygen, and liydrogen make
up the larger })art by weight of these responsive sul>
stances, yet by themselves they build into molecules too
strong and too stable to be again thrown down by sun
shine alone. Like the stick, which constitutes both the
bidk and the chief source of heat in the common match,
but a useless thing with which to kindle a fire unless
tipped with the easily upset molecules of phosphorus, sul
fur and nitre, which by their fall produce the necessary
heat to fire the bit of wood, so the starches, the gums,
and the fats stored in the seeds, in the fleshy roots and
thickened stems and leaves of plants, could not serve as
food and become sources of power, either in plants or in
animals, were there not associated with them enough of
those proteicl or albuminoid molecules containing nitro-
gen, sulfur, and perhaps also phosphorus which, after
absorbing a little too much water, are easily overturned
by the warmth of the soil, and thus in their fall set on
foot the train of changes it is their mission to start and
to maintain.

It is very suggestive and not a little strange, in this
connection, that one of the most powerful explosives we
have is now made by slipping out of cellulose three of
its hydrogen atoms and placing in their stead three
groups of three atoms taken from nitric acid, this result
being accomplished by simply steeping cotton wool in
strong nitric acid, made more active by mixing with it
twice its volume of concentrated sulfuric acid. When
this is done and the wool has been washed and dried, it
is found that, without having lost even its fibrous struc-
ture, the taking-out and slipping-in process has resulted
in so unsteady a structure that a trifling disturbance
tuwses! it to fall apart with explosive violencCo So,

112 The Soil.

too, when glycerine is treated in a similar manner, a
slipping-out and slipping-in change takes place ; three
bricks, so to speak, — three atoms of hydrogen, — are
replaced by three others derived from the nitric acid,
and instead of the oily, sweetish liquid, glycerine, we
have the fearful nitroglycerine which, when mixed with
earth, constitutes dynamite. Even in our old explosive,
gunpowder, we employ the same nitric acid in combina-
tion with potash as saltpetre, which, with the addition of
a trifling amount of heat, is made to give over its oxygen
to the carbon and sulfar with which it is mixed, and,
by uniting with them, almost instantaneously develops
the power sought.

Now we are not trying to point out here just how the
energy manifested in the tissues of plants and in the
bodies of animals is derived: we are rather trying to
point out how indispensable to the life of plants nitro-
gen is, that we may the more fully feel the urgency of
holding its amount and condition in the soils we till up
to the standard demanded by vigorous plant growth.
All are agreed that, varied as the constructive and de-
structive processes of plant life are, they take place
within or are directly or indirectly set up by, the molecu-
lar shif tings, adjustments, and readjustments within the
protoplasmic substance of cell life, of which nitrogen is
an indispensable ingredient.

RELATION OF SOIL NITROGEN TO CROP DEMANDS.

Just how is the amount of nitrogen removed by a
crop from the soil related quantitively to the ash ingre-
dients, and how are the amounts of these in the soil
related to the several amounts in the crop? The crop

Relation of Soil Nitrogen to Crop Demands. 118

of wheat which yiekls 30 bushels of grain per acre
demands, as indicated by chemical analysis, 48 pounds
of nitrogen, 21.1 pounds of phosphoric acid, 28.8 pounds
of potash, 9.2 pounds of lime, 7.1 of magnesia, 7.8 of
sulfur, and 96.9 pounds of silica. A crop of cats yield-
ing 60 bushels per acre would demand: of nitrogen, 73.3
pounds; phosphoric acid, 25.7 pounds; potash, 61.5
pounds ; lime, 15 pounds ; magnesia, 11.6 pounds ; sulfur,
10.7 pounds ; and of silica, 113.7 pounds. In the case of
red clover, yielding 2 tons of hay per acre, the demands
are: for nitrogen, 102 pounds; phosphoric acid, 24.9
pounds ; potash, 83.4 pounds ; lime, 90.1 pounds ; mag-
nesia, 28.2 pounds; sulfur, 9.4 pounds; and silica, 7
pounds. These are the amounts of plant food, of the
kinds named, demanded from each acre of ground in the
cases cited.

Taking the average per cent of nitrogen in the surface
foot of soil at .15 per cent, the weight of the soil at 80
pounds per cubic foot, and the ash ingredients as indi-
cated on page 101, it will be seen, after dividing the
amounts of the several ingredients in the soil by the
respective amounts demanded in the three cases, that,
could the materials be all used, there would be of

Wheat. Oats. Clover.

Crops. Crops. Crops.

Nitrogen,

enough

for 109

72

52

Phosphoric

acid.

" 187

153

158

Potash,

" 261

122

90

Lime,

" 409

251

42

Magnesia,

" 1104

676

278

Sulfur,

" 76

56

63

Soluble silica,

"

" 1516

1291

209V0

In these figures it is assumed that nothing is given

114 The Soil

back to the soil by tlie crops, wliich, however, is not
true regarding nitrogen, especially with the clover. It
will be seen from the figures that the supply of nitrogen
is relatively less than that of any other ingredient except
sulfur.

If it were true that all of these plant foods are both
equally available and necessary, and the possibilities of
loss the same, then the tendency would be for the nitro-
gen and sulfur to give out earliest. Now, in the case
of nitrogen, certainly no plant food from the soil is
more important and probably no one is subject to as
great loss under bad management as this ; and hence it
follows that much attention should be paid to this soil
ingredient.

FORMS OF NITROGEN IN THE SOIL.

Nitrogen occurs in the soil under several different con-
ditions, and is derived from several sources. As a part
of the soil air, it exists as free nitrogen where it is es-
sential to the life of certain microscopic forms which
seize upon it and render it available to higher plants.
Temporarily and in transition stages, nitrogen occurs in
the soil as ammonia and as nitrous acid, but these forms
pass rapidly, apparently, into nitric acid, from which
most of the higher plants derive their chief supply.
The amount, therefore, of ammonia or of nitrous acid
existing in a soil at any time is always small. In the
form of nitric acid, however, the soil contains con-
siderable amounts of nitrogen, as nitrates of lime or
other bases, but in this form Warington states that
the amount seldom reaches 5 T^er cent of the total nitro-
gen content.

Distribution of Nitrofjen in the Soil. 115

By far tko larger part of the iiitroj^aui (jI" soils is stored
in the form of liuinus, to wliicli reference has already
been made; and this, tlirou.ii^h the processes of fermen-
tation, is gradually made available to plants in the form
of nitric acid. The roots of held crox)s, too, contribute
no small amount of material to the store of organic mat-
ter in the soil, a part of which is converted into humus ;
but the plants whose roots leave in the soil the largest
amounts of nitrogen are the leguminous species, like the
clovers, beans, peas, and lupines.

DISTRIBUTION OF NITROGEN IN THE SOIL.

Kegarding the distribution of nitrogen in the soil, some
facts have already been given on page 10<S. Keferring to
the table, it will be seen that the amount decreases down-
ward until in the fourth foot the average is less than
one-fifth of that found in the first foot. This decrease
in the amount of nitrogen is evidently due in part to the
variation in the distribution of roots in the soil, and
perhaps largely to this cause; but there are other factors
which tend sometimes to cause a destruction of the nitric
acid, setting free the nitrogen in the gaseous form. Ob-
servation has shown that when a soil rich in nitrates is
saturated with water so as to exclude free oxygen, a
deoxidation may take place which sets free nitrogen gas ;
nor is this action limited to the nitrates, for organic mat-
ter is also broken down under these conditions, with a
setting free of both carbon dioxide and nitrogen gas.

The distribution of nitrogen in Rothamsted soils is
given by Waringtoii to a depth of 9 feet, and the results
are quoted as follows : —

116

The Soil

NITROGEN IN SOILS AT VARIOUS DEPTHS.

Arable Soils.

Old PA6TtTltB

Soils.

lbs. per acre.

lbs. per acre.

First 9 inches contained

3015

5351

Second 9 " " . ,

1629

2313

Third 9 "

1461

1580

Fourth 9 " "

1228

1412

Surface 3 feet contained .

7333

10656

Fifth 9 inches contained .

1090

1301

Sixth 9 " "

1131

1186

Seventh 9" "

1049

Eighth 9 " "

1096

Second 3 feet contained .

4365

Ninth 9 inches contained .

1173

Tenth 9 " "

1076

Eleventh 9 inches "

1112

Twelfth 9 " "

1198

Third 3 feet contained .

4559

Surface 9 feet contained

16257

It will be seen from this table that the amount of
nitrogen in an old arable soil may be really very large,
in this case enough, could it all be used, for 338 crops
of wheat of 30 bushels per acre, or more than 10,000
bushels. It will be seen also that, after the first three
feet are past, the total amount of nitrogen in the suc-
ceeding feet remains nearly constant, or that it tends
very slightly to increase. The figures suggest that at a
certain depth below the surface of arable fields, the
amount of nitrogen tends to remain approximately con-
stant from year to year, while the rise and fall of this
ingredient is a phenomenon largely peculiar to the surface
three or four feet.

Sources of Soil Nitrofjen. 117

Referring now to the distribution in the soil of the
nitrates simply, it must be said that the amounts of these
found at different depths varies with the season and to
some extent also with the crop. At the time crops are
growing, the roots remove the nitrates, where these roots
are found, so thoroughly that the measured amount at
any one place is small, the plants tending to pick it up
as rapidly as it may be formed. At the end of a season,
when percolation has been taking place for some time,
the nitrates are largely removed in the drainage waters,
or they are carried far below the surface. So too, if a
considerable quantity of nitrates have newly formed near
the surface and there comes a heavy rain which produces
percolation from the first foot into the second foot of
soil, the effect of this percolation is to shove along in its
front layer of moving water nearly all of the readily
soluble salts the soil may have contained, thus changing
their position from the first to the second foot in perhaps
one or two days. Such action as this tends to concen-
trate the nitrates in a thin zone and at times possibly
wholly below the territory occupied by the roots. Such
concentrations, however, cannot be permanent; for both
diffusion and capillarity tend to bring about a redistribu-
tion again.

SOURCES OF SOIL NITROGEN.

When we ask. From whence comes the nitrogen of the
soil ? we raise one of the most important questions of
practical agriculture, and one which is to-day taxing, to
the utmost, the skill of many very able investigators.
When the earlier investigators upon this subject found
their results, one after another and almost without

118 The Soil,

exception, pointing to one conclusion, namely, that the
plants upon which they experimented either did not in-
crease the total nitrogen given them or where an increase
appeared to be associated with their growth this was so
snuill, or of such a character, that it seemed more than
likely it might have been derived in some way outside of
the direct action of the plant under experiment, it came
to be almost accepted that the vegetable world depended
for its nitrogen upon the decay of organic substances sup-
plemented in small part by the nitric acid and ammonia
which are brought down by the rains and the snows or
condensed in the dews. It was indeed early observed
that clover could be grown upon land relatively poor in
nitrogen, and at the same time remove in the crop pro-
duced large amounts of that ingredient, while a crop of
wheat following the clover was able to procure more
nitrogen from the same field, following the clover, than
it was able to do before the clover had occupied the land
and taken from it its large amounts of nitrogen. We
now know that the growth of clover upon land may be
associated with the accession from the atmosphere of
large amounts of nitrogen, but the studies of the earlier
investigators prevented them from believing such an
explanation possible, and various hypotheses were ad-
vanced to explain the advantages derived from systems
of rotation in which clover was one of the series.

The fact that nitrates were early known to be drained
away from the land in large quantities and that nitrogen
gas is liberated during the processes of decay, when
coupled with the fact that life has existed upon the land
during untold geologic ages, should have made it appear
inevitable that there must be some way for drawing from
the free nitrogen of the air a supply sufficient to make

Sources^ of Soil Nitron en, 119

good the losses roferrod to, and esi)eoially when it was
known that tlie rocks thenis(dves, from whicli soil is de-
rived, do not contain the element in a})i)reciahle qnan
tities. And then whenever the question was asked,
From whence came the nitrogen which entered into the
very earliest forms of life and which made the very earliest
soils fertile ? it should have seemed almost axiomatic
that the nitrogen of the air must be used over and over
again, as we now know, but only through the studies of
the last decade, that it in reality is.

The amounts of nitrogen brought to the soil in the
form of nitric acid and ammonia, with the moisture precip-
itated as rain, snow, and dew, are known to be relatively
small, rarely more than the equivalent of 5 pounds per
acre per annum in the open country removed from the in-
fluence of the burning fuel and products of sewage decom-
position associated with the life of large cities. A
knowledge of the actual amounts of nitrogen so derived
has been gained by keeping records of the total precipita-
tion and by determining the amounts of nitrogen such
waters did actually contain. Some of the results which
were obtained through careful studies at Rothamsted are
given in the following table : —

NITROGEN AS AMMONIA AND NITRIC ACID, IN POUNDP
PER ACRE PER ANNUM, IN RAIN.

ROTIIAMSTED. LINCOLN, NeW ZEALAND. BaRBADOES

8 years. 3 years. 3 years

lbs. lbs. lbs.

Nitrogen as ammonia . 2.53 0.74 0.9^

Nitrogen as nitric acid . 0.84 1.00 2.84

3.37 1.74 3.77

These amounts, it will be seen, are only sufficient to
contribute the necessary nitrogen for about two bushels

120

The Soil

of wheat per acre where 48 pounds is counted sufficient
for 30 bushels of wheat.

Observations similar to the above have been made in
various parts of Europe, and the mean of 22 determina-
tions, each extending over a whole year, at nine different
stations, give results varying from 1.86 pounds of nitro-
gen per acre to 20.91 pounds, with a mean value of 10.23
pounds per acre where the average amount of rainfall was
27.03 inches. From these figures it will be readily seen
that even were any country to receive annually supplies
of nitrogen equal to the largest amount here stated, the
quantity would be insufficient for continuous large crops,
even could the whole of it be used for that purpose.

Before leaving this subject, — the contributions of rain
to the soil, — let us quote a table from Dr. Angus Smith
in " Air and RaiD," in which the average composition of
rain water from various parts of England and Scotland
are given.

AVERAGE COMPOSITION OF SAMPLES OF RAIN IN PARTS

PER MILLION.

England, conntry places, in-
land

Towns

Scotland, country places,

seacoast

Inland .

Towns o

Glasgow

Nitrogen as

Ammonia.

4.25

.61

.44

3.15

7.49

Nitric
Acid.

.19
.22

.11
.08
.30
.63

Chlorine.

3.88
8.46

12.24
3.28
5.70
8.72

Sulfuric
Acid.

6.52
34.27

6.64

2.06

16.50

70.19

Sources of Soil Nitrogen. 121

From this table it will be seen the rains bring down
larger amounts, both of chlorine and of sulfuric acid
than of nitrogen in both of its combinations. It will be
observed that in and about towns and cities all of the
ingredients are more abundant than they are in the open
country, and that the chlorine, which occurs in the air in
the form of common salt, is more abundant near the sea
than it is farther inland, as should be expected because
it is largely derived from sea-water. The salt does not
evaporate, but in times of high winds, when the water on
the crests of the waves and breakers is whipped into fine
spray, the water so taken into the air is evaporated, leav-
ing the salt floating in the air as fine particles of dust
about which the raindrops form and so bring them to
the ground. Since England a-nd Scotland together form
a relatively small body of land entirely surrounded by
salt water, it is probable that both the amounts of salt
and of sulfuric acid, even from the country places in-
land, are larger than are likely to be observed in the
interior of continental areas. The large differences be-
tween the cities and the country, shown in the table, are
due chiefly to products of combustion, issuing from the
many stoves, furnaces, and engines which are concen-
trated within their borders.

If we take the average uf the sulfuric acid from the
inland country places in England and Scotland and cal-
culate the amount of sulfur per acre with different depths
of rainfall, and then set these amounts alongside of the
amounts of sulfur which chemical analysis has shown to
occur in crops of wheat, oats, and clover, as given on page
101, we shall have the results which follow : —

With rain containing 3.79 parts of sulfuric acid per
million, —

122 The Soil.

• StT.LFUR/

12 inches of rain would yield ,89 pounds per acre.
24 " " " " " 1 78 "
36 " " '' " " 2.66 "
30 bushels of wheat demand 7.8 "
60 bushels of oats demand 10.7 "
2 tons of clover hay demand 9.4 "

It appears therefore, from these results, that even with
36 inches of rain per annum, less than one-third, of the
necessary amount of sulfur needed by large yields of
crops per acre can be supplied by the sulfuric acid of
rains.

It is held by some that gaseous ammonium carbonate
passing in the air over the foliage of vegetation may be
absorbed by the leaves, and thus contribute to the supply
of nitrogen for the purposes of plant growth ; but upon
this point the evidence appears to be insufficient even to
place beyond question the fact of such a source of nitro-
gen, much less to allow of a quantitative expression of
its amount.

Schlosing, however, in his experiments on moist soils
freely exposed to the air, believes he has shown that under
certain conditions soils may acquire nitrogen, through such
an exposure, at the rate of 38 pounds per acre per annum,
and the additions to his experimental soils appear to have
been largely in the form of ammonia. It will be readily
understood that if soils do have the power of removing
from the passing air the compounds of nitrogen it con-
tains, the amounts of nitrogen added to the soil in the
combined form might easily be more than that which is
brought down by the rains, because the steady ongoing of
the winds across the surface of the land must necessarily
bring a very large amount of air in contact with a given

Sources of Soil Nitrogen. VIZ

field of soil (liirin<^ the course of any season. Still, to
obtain 38 pounds of nitrogen from the air in the iorni of
ammonia, means the complete removal of this gas from
a very large volume of air.

The daily analysis of air on Montsouris from 187(> to
1881 gave the mean quantity of ammonia in the air at
2.2 milligrams for each 100 cubic metres, and for a soil to
acquire 38 pounds of nitrogen from the ammonia, it must
completely extract from the air that which is contained
in 951.4 millions of cubic metres. This means that if,
on an acre, the air one metre deep, which is a little more
than 3 feet, were to give up all of its ammonia to the
soil, that air would have to be changed more than 2.5
million times in order to bring the necessary amount
of ammonia to the acre to yield 38 pounds of nitrogen.
These and other considerations make it appear quite
certain that soils, under average field conditions, can-
not receive annually the above amount of nitrogen
in this form from the air, at least outside of tropical
regions.

It is well established that electrical discharges in the
atmosphere cause some of the oxygen of the air to unite
with nitrogen, giving rise to the nitrous and nitric acids
which the air is known to contain and which have been
referred to as being brought down by the rain. But it is
probable that a part of these combinations with oxygen
are derived from ammonia through the action of ozone, a
modified and highly active form of oxygen. This action
is believed by Warington to be supplemented by the per-
oxide of hydrogen, and hence that the nitrates brought
down in the rain do not represent so much nitrogen not
previously combined, but rather that a portion of these
may have resulted from the oxidation of ammonia.

124 , The Soil,

FREE-NITROGEN-FIXING GERMS.

We come now to consider one of the most important
discoveries of modern times ; a discovery which places
in the hands of every farmer a means, completely under
his control, whereby he can at any time cause to be drawn
directly from the atmosphere the free nitrogen of the air
and have it fixed in the soil of any field he may wish to
enrich.

The history of this important discovery cannot be given
here, but in 1888 Hellriegel published the results of his
experiments, which satisfactorily proved that we have in
nature great numbers of minute microscopic organisms
living in the soil, which have the habit of locating them-
selves upon the roots of certain kinds of plants and
especially upon the clovers, beans, peas, lupines, and other
leguminous species. These organisms, once seated upon
the roots of a plant congenial to them, cause the forma-
tion of little enlargements or tubercles, in which they
live, drawing nourishment from the plant upon which
they have established their home, but in return giving to
it compounds of nitrogen which these organisms are able
to produce from the free nitrogen of the soil air. Here
we have two neighbors changing work ; each performing
that sort of labor which, through long years of specializa-
tion, it has become best fitted to do, and then swapping
the products of their labor to the mutual advantage of
both. The clover, with its leaves outspread in the free
air and fitted to utilize the bright sunshine as a source of
power, breaks down the molecules of carbon dioxide,
forging them into such compounds as it needs ; but in its
efforts to utilize to the best advantage all of its surround-

Free-Nitrogen- Fixing Germs. 125

ings, it has given over the first rough forging of nitrogen
into food to the lowly organisms upon its roots, and now
sends down to them so much of such compounds best
brought together under the hammer of direct ether waves
as they need in doing their part of the work. Like the
coal brought up from the mine, like the fuel in the
engine, the products made in the green leaf and sent
down to the lightless cellars become the source of power
there used by the one-celled plants in bringing into com-
bination with oxygen the free nitrogen of the air, so
indispensable to the life of higher plants. What a com-
munity of life ! What a complete utilization of all forces
and all materials, both above and below ground, we have
here!

If the roots of clover plants are examined, there may
easily be seen upon their surfaces many little lumps,
knobs, or tubercles. Similar bodies may also be observed
upon the roots of peas, beans, lupines, and other legumi-
nous plants, and these are the places where colonies
of the bacteria here under consideration have located
themselves. These micro-organisms are found scattered
through the soil, and some believe that they have the
power, at least certain species, of withdrawing free nitro-
gen from the air without the aid of another plant on
which to live, but the matter still awaits positive demon-
stration.

Some of HellriegePs studies make it appear that differ-
ent species of leguminous plants are inhabited by varie-
ties of these minute organisms peculiar to themselves.
He found, for example, in preparing his sandy soils free
from nitrogen, in which he proposed to grow lupines,
that, in order to have these plants succeed, it was neces-
sary to wet the sands with water leached from lands

126

The Soil

where these plants had habitually grown. , The appUca-
tion of water from rich loams which had produced peas,
beans, and vetches appeared to do them no good ; the
inference being that these soils did not contain the
bacteria which live upon their roots, while the natural
lupine soils are rich in them. Experiments have been
made in introducing the bacteria from the tubercles from
})ea roots directly into the roots of lupines, but without

Fig. 18. — vShowing the influence of free-nitr()<;en-fixing germs on the
growth of peas. The large plants all grew in sand containing the
nitrogen-fixing bacteria, while the small plants grew in soils iden-
tically the same except that all bacteria were excluded from them.
After Hellriegel.

proving of any help to them. A full study of these
problems may lead to an explanation of why it is some-
times difficult at first to get clover to do Avell on certain
soils, and also what is the cause of " clover-sick " lands.

To show how great is the service of these f ree-nitrogen-
iixing germs, there is given below the results of eight
trials made by Hellriegel with lupines, in which all of
the plants were treated alike except that four of them

Free-Nltroyen-Fixiny Germs.

127

were, at the start, given loam water in order to add the
necessary bacteria, while the other four ])ots received
none. Taking the amount of nitrogen in the jjlants
forced to grow unaided by the nitrogen-fixing germs as
1, the amounts stand, —

Fig. 19. — Showing the growth of rye, oats, peas, wheat, tlax. and
buckwheat in soils fertile in all elements of plant food except nitro-
gen, and illustrating the power of the pea, through its root tuber-
cles, to procure nitrogen from the air. After P. Wagner.

Nitrogen.

No. 1, without germs 1

No. 3, '^ " 1

No. 5, " " 1

No. 7, " " 1

. If, "however, we. compare the weights of dry matter
.produced, ;these stand,- —

Nitrogen

No.

2,

with

germs

76.07

No.

4,

u

iL

82.36

No.

6,

u

U

91.15

No.

8,

i(

((

100.54

128 The Soil.

Dbt Mattke.

Drt Mattbr.

No.

1,

without germs

1

No. 2,

with germs

48.66

No.

3,

U ((

1

No. 4,

U ((

67.01

No.

5,

u u

1

No. 6,

u u

48.30

No.

7,

u u

1

No. 8,

(( ((

41.68

These two comparisons bring into strong relief the
great help the lupines received from the nitrogen-fixing
germs which grow upon their roots ; for they show that,
while there is a strong difference between the amounts
of dry matter produced under the two conditions, there
is a much larger difference between the amounts of nitro-
gen in the crops.

The same facts are rendered still more emphatic in
Fig. 18, which shows the results of growing peas in pots
of soil in which all germs had first been killed, and then
introducing them again in one set but not in the other .
In Fig. 19, too, will be seen how differently the plant
thrives which can get the nitrogen it needs from the air
through the aid of these germs than do those not able to
profit by their help, while Fig. 20 shows the importance
of nitric nitrogen to other plants.

SYMBIOSIS.

This living together of plants for their mutual benefit
or symbiosis, as it has been technically called, is not a
rare occurrence. Indeed the whole family of lichens,
already referred to, are now regarded as examples of
this phenomenon, the forms being in reality fungus, puff-
ball or toadstool-like plants densely inhabited by green
or chlorophyll-bearing algae. These two types of life
live together to the advantage of both. And what is
still more strange and interesting in this connection, is

Symbiosis,

129

the observation that members of the animai kingdom,
like the Radiolaria and Actiniae, owe their colors in part
to the many minute, one-celled algae living within their
bodies, and there consuming the carbon dioxide given off
by the animal and in their turn producing starch, under
the action of sunlight, which serves as food for their
host

Fig. 20. — Showing oats growing under conditions identical with those
of Fig. 19, except that the several pots received Chile saltpetre,
1, 2, and 3 grams respectively, thus enforcing the immense impor-
tance to such plants of nitric nitrogen. After P. Wagner.

Then, again, as a matter of immediate and practical
importance to agriculture, it appears from the studies of
Frank, and afterwards Schlosing, Jr., and Laurent in
1891, followed by Kosswitsch in 1894, that there are
in the soil certain nitrifying bacteria which, living in
symbiotic relation with soil algae, are able to and do,

130 The Soil,

under favorable conditions of light and moisture, fix
considerable amounts of free nitrogen. Further than
this, there is already at hand some evidence in favor of
the view that even upon the soilless rock, which has
become the abode of lichens, the process of fixing free
nitrogen is there carried forward, if not through the
double form of life which the lichen really is, then
through the aid of a process similar to the one just
mentioned.

After what has been said regarding these sources of
nitrogen in the soil, it may be asked. How then can there
ever occur a deficiency of it ? The answer of course is
that Nature, in her universal method of over and over
again, has her counter processes of denitrification, of
returning to the air from which it came the nitrogen,
just as is the case with carbon dioxide ; and man, when he
sets his will and his ignorance against natural methods,
has often given these latter agencies the ascendency.
This brings us to consider how the nitrogen, once fixed
in the soil, is used by plants, and how it may be lost.

NITRIFICATION AND DENITRIFICATION.

It has not yet been satisfactorily determined in what
form the nitrogen fixed by the bacteria living upon the
roots of plants, is used by those species, but the general
belief, regarding plants whose roots are not inhabited by
nitrogen-fixing germs, is that they are almost wholly, if
not entirely, dependent for their nitrogen supplies upon
the nitric acid, and possibly also to some extent upon
ammonia in the soil. We need, therefore, to learn how
these substances are brought to the soil, and how they
may be lost.

Nitrijir.ation and Drnifrijirafion-. 131

We have ulready Roeii tlwit, soiuc nitric Mcid and some
ammonia come to the soil from the atmosphere directly,
but in ([uantities too small to meet the demands for
them. By far the larger part of the nitric acid fonnrl in
soils is the final product of life processes there carried
on when conditions are favorable for tliem to go forward.

All are familiar with the odor of ammonia as it rises
from the heap of fermenting manure. This ammonia is
produced fi-om the compounds of nitrogen in plant
tissues and in the excretions of animals through the
action of certain kinds of bacteria. The same process,
too, takes place in the soil Avhere organic matter decays,
and through the same agencies ; but in the soil no sooner
is the ammonia produced than it is seized upon by an-
other organism, the nitrous ferment, and converted into
nitrous acid. But the process does not end here ; for no
sooner is the nitrous acid formed than it is seized upon
by still another distinct kind of micro-organism and con-
verted into nitric acid, when it becomes available to
higher plants.

It appears, therefore, from these facts, that we have in
nature, so far as the nitrogen is concerned, a short-cir-
cuit rotation, this element of plant food not starting from
its free, uncombined state in the air and passing through
the compounds of living tissues and then back to -gaseous
nitrogen again in each and every round. On the con-
trary, there is a very large amount of nitrogen, in the
form of nitric acid, being removed from the soil and
transformed into the higher compounds of plant life,
and then, after it has served its purposes in this form and
the plants which have used it die, it passes back through
ammonia and nitrous acid, reaching the nitric acid form
again without having become nitrogen gas. Then too,

132 The Soil.

when animals feed upon the higher plants, the circle in
which nitrogen makes its round is widened, and it is
rendered even still broader in those cases where flesh-
eating animals place themselves in the circuit.

There are, however, processes going on in nature
whereby the nitrates may be, for the time, entirely lost
to higher plants and animals, these compounds being
sometimes borne away in the drainage waters to the sea,
there to serve the purposes of marine life. Then, again,
there live within our soils microscopic forms of life
which, when a rich soil is kept over wet and not well
ventilated, are able to live, not only upon the nitrates,
converting them into free nitrogen gas, thus impoverish-
ing the soil, but also to feed upon the organic compounds
as well, here, too, restoring free nitrogen to the air.

Dr. Angus Smith showed in 1867 that nitrates in
sewage waters are decomposed with the liberation of free
atmospheric nitrogen. Schlosing has also shown that
a moist humic soil very quickly lost all traces of nitrates
after being kept in an atmosphere devoid of free oxygen.
Warington has shown that even sodium nitrate is de-
composed in a water-logged soil, and a large part of the
nitrogen set free as nitrogen gas. So great does the
demand for oxygen appear to be in these water-soaked
soils, that certain micro-organisms are even able, accord-
ing to the observations of Muntz, to withdraw it from
chlorates, bromates, and iodates, leaving in their stead
chlorides, bromides, and iodides. So too it has been
shown that when suitable forms of organic matter are
brought into the presence of nitrates, even though some
oxygen be there, the life demands for it may be so urgent
that the nitrates may be broken down and nitrogen gas
set free.

Nitrification and Denitrification. 133

There is still another condition under which the proc-
esses of denitrification take place. It is the rapid, large,
and almost complete loss of nitrogen from human excre-
ment, where dry earth is used in the dry-earth closets.
Storer quotes from various authorities a considerable
amount of evidence relating to this phase of the subject.
One of the most striking cases cited, is that where Colonel
Waring kept two tons of dry earth for a number of years,
having it used over and over again in order to see how
long it might be employed without losing its efficiency.
It is stated that the closets were filled with this dry earth
about six times each year, and that when the vaults were
emptied the earth was thrown into a heap in a well-venti-
lated cellar to dry. After this material had been used
over not less than ten times, samples were sent to Pro-
fessor Atwater for analysis. His examination showed
that these ten-times-used soils contained no more than 11
pounds of nitrogen in the 4000 pounds of soil, and yet it is
estimated that not less than 280 pounds of nitrogen had
been added and that not less than 3 pounds existed in the
soil when it was taken for use. It thus appears that all
but 8 pounds of the 230 pounds of nitrogen added to this
d-ry soil had been, during the interval, converted into gas.
Nor was this all. So complete had been the destructive
processes that nearly all the carbonaceous materials,
including the paper used, had entirely disappeared.

Nature, then, so far as nitrogen compounds are con-
cerned, just as with other matters, has her constructive
and destructive processes pitted one against the other in
such a manner that they tend all the while to balance.
Go where you will, in almost any natural meadow or
natural wood, and you will find growing there some plant
of the leguminous species upon whose roots the free-

134 The Soil.

nitrogen-fixing bacteria have their home, and where they
are performing tliat service so indispensable to the higher
types of life. Living with these nitrogen gatherers, there
are, of course, other species which feed upon the nitrogen
compounds produced by the plants referred to, while still
other forms return to the atmosphere the nitrogen in its
free and uncombined form. But man, not understanding
how the nitrogen supply of the soil must be maintained,
has shut out completely for many years in succession the
symbiotic life referred to, and has attempted to grow crop
after crop of wheat and other plants able only to con-
sume the nitrogen of the soil without adding appreciable
amounts to it, and with the inevitable result that the
available nitrogen supply has fallen below the level need=
ful to large yields.

CHAPTER IV.

CAPILLARITY, SOLUTION, DIFFUSION, AND OSMOSIS.

Before taking up the pliysical problems of the soil, it
will be very helpful if we can first get a clear conception
of the processes of capillarity, solution, diffusion, and
osmosis.

This is important, because they are the modes by which
all the food of plants is conveyed to them, whether this
food comes from the air or from the soil.

Whenever a lamp is lighted, there is at once started
a current of oil, rising from the bowl through the many
interspaces between the threads of the loosely woven
wick, and this flow continues so long as the oil is removed
from the upper end by burning. So, too, when a wet soil
is exposed to a drying wind, the removal of water from
its surface results in setting up a flow from deep in the
ground, upward toward and to the drying surface, to make
good these losses. Then, again, when the root of a plant
threads its way among the soil grains and withdraws from
their surfaces a portion of the water with which they
are charged, there is at once set up, to make good this
loss, currents of water traveling from various directions
in the soil toward the absorbing root. By what mechan-
ism are these movements maintained, and what is the
source of energy by which the work is performed ?

When the water rises from a well through the action
of the pump, we know that the energy generated in the
muscles of some man's arm has been transferred, through

135

136 The Soil

the pump handle and the piston, to the rising column of
water ; or i f not the energy of human muscles, then that
from the moving wind, acting through the windmill, or
some other equally evident source of power. Matter is
never moved, work is never performed except at the
expense of energy in one form or another; so in the
capillary movements of water through the soil, and in
the rise of oil through the wick of a lamp, work is being
done, and energy from some source must be expended.

SUBFACE TENSION AND CAPILLARITY.

The first careful study of the rise of water in capillary
tubes was made by Hauksbee nearly 200 years ago, but
history shows that the phenomena were known to Leo-
nardo da Vinci, the famous artist, who lived between 1452
and 1519. But notwithstanding the large amount of very
careful study which these phenomena have received even
during recent years, we are yet in the dark as to just how
the energy which forces the capillary fluids to move is
transformed into current motion ; but all are agreed that
it is in some way brought about through the surface ten-
sion of liquids.

During the blowing of soap bubbles, every one has
observed that the bubble left hanging from the bowl of
the pipe contracts, grows rapidly smaller, and forces a
strong current of air out through the stem, showing that
the thin film of water is acting like a stretched rubber
ball. Now, if a large drop of water or a marble could be
placed in the centre of the bubble, it is evident that the
thin film would close down upon it, compressing it with
so much force as it is able to exert, and in the case of the
drop of water, the film would tend to keep it spherical in

Surface Tension and Capillarity. 137

form. Many different phenomena show that the free
surfaces of all liquids act upon the mass within or
beneath them very much as if they were elastic and
contracting membranes, and the spherical form of the
raindrop, of the melted lead as it falls from the shot
tower, of the dewdrop on the ('abl)age leaf, and the
spherule of water as it rolls along the dusty floor, or
glides from side to side on the surface of a hot stove,
each and all owe their shape to this surface tension.
It is this surface tension which allows a polished needle,
although seven times heavier than water, to float easily
upon its surface, and it is advantage of this, too, which
the water spider takes as it glides easily along the water
surface of ponds and slow streams.

This surface tension is a condition which results from
the fact that all molecules in the surface of a liquid are
being pulled more strongly into the liquid, by the mole-
cules in the deeper portions of the liquid itself, than
they are being drawn outward by the gaseous molecules
of the air or vapor outside. In the interior of any liquid,
after a very short distance below the surface is reached,
each and every molecule is pulled on every side equally,
so that a perfect balance of pulls exists. This makes it
possible for the slightest disturbance to make these mole-
cules move from place to place. But on the surface the
molecules all behave as if they were being drawn into
the liquid by a stretched rubber band or spring, and the
strength of this pull is really something very great. It is
because the pull toward the interior of a liquid is so strong
that such large amounts of work are required to be done
to convert a liquid into a gas, as in the case of changing
water into steam. You set a basin of water on the stove,
and work is being done through its bottom, which tends

138 The Soil.

to drive, and does drive, the water molecules out through
the surface film, but against a pressure which is enor-
mous. Ostwald states that this pressure, for the liquid
ether, amounts to something like 1284 atmospheres. Or
more than 9 tons to the square inch ; and yet the latent
heat of water is nearly six times as great as that of
ether. It is not strange, therefore, that to change a
pound of water at 212"^ F. into steam at the same
temperature, and under the pressure of 1 atmosphere,
requires an amount of work which, when expressed in
the terms of tons lifted against the force of gravity, finds
its equivalent in no less than 37 tons lifted 10 feet high.

These enormous pressures are not felt by bodies
placed in the interior of water, because they are sur-
rounded by a water surface which pushes away from the
body with equal force.

Now in the phenomena of capillarity a small part of
these pressures are brought into play, giving rise to the
movements of water in the soil, to the ascent of oil in
the wick of a lamp, and to other similar phenomena.

If a clean glass tube .055 inches in diameter is placed
upright in pure water at a temperature near freezing,
the water will be seen to rise on the inside to the height
of 1 inch above the surface of the liquid in the vessel,
and the smaller the diameter of the tube is the greater
will be the height to which the water will rise in it,
the height being inversely proportional to the size of the
tube at the surface of the water within, as shown in the
table below : —

In a tube 1 inch in diameter the water rises .054 inches.

U U \ (.(. U U tt U tt .545 "

" " .01 " " " " " " 5.456 "

" " .001 " " " " " " 54.56 "

Surface Tension and Capillar it ij. 139

To understand tliorouj^dily just vvliy water rises to a
jjjreater lioiij^lit in tlu^ narrow tidx's tlian it does in tlic
wider ones, will \\v,\[) us the more elc^arly to understand
the capillary niovenients of water in the soil, and as the
manner of action of the forces which produce the rise
can be more simply stated for the tubes than for the
soil itself, it will be best to explain the action as it takes
place in the tubes first.

Thrusting a clean glass tube beneath the surface of
water and then withdrawing it, it comes forth wet, that
is, with a layer of water adhering to it. This proves
that the force acting between the molecules of water
and those of the glass is stronger than the force acting
between the molecules of the water ; for, were this not so,
the glass must necessarily come from the water dry, just
as it does when withdrawn from a dish of mercury.

Not only is the attracting force of the glass molecules
stronger than is that of the water molecules, but this
force reaches out and is felt over some distance beyond
the surface, a distance which Quincke estimates at not
far from one five-hundred-thousandth of an inch. Now
when the glass tube is thrust into the water, the row
of glass molecules just above the water draw up toward
them all around a row of water molecules ; but as these
move up, other water molecules are made to follow,
and the whole surface film is somewhat raised. When
this lifting process is once started, it goes on until so
much water has been lifted above the level of the water
in the vessel as will balance, by its weight, the total pull
of the molecules in the wall of the glass tube at the
margin of the surface film.

Now, as the circumferences of cylindrical tubes in-
crease in length in the same ratio, as ; their diameters do,

140 The Soil

it is plain that if we take the distance around a tube
whose diameter is .001 of an inch as 1, then in the case of
tubes whose diameters are .01, .1, and 1 inch respectively,
their circumferences will be 10, 100, and 1000 times as long.
Their walls will also contain 10, 100, and 1000 times as
many molecules, and as each and every molecule is able
to do a like amount of work, it follows that the total work
done by the walls of these several tubes in lifting water
will stand in the relation of 1 to 10, to 100, to 1000.

But the areas of the cross-sections of these tubes, and
their volumes also, grow larger in the ratio of the
squares of their diameters, so that the surfaces of the
columns of water in the several tubes will be in the ratio
of 1, 100, 10,000, and 1,000,000, where their diameters
are 1, 10, 100, and 1000 respectively.

We have seen before that the height to which the
surface of the water is raised is the greater the smaller
the diameter of the tube, so that if we call the height
to which the largest tube raises its water 1, then the
heights in the other cases will be 10, 100, and 1000.
But only the very surface layer of water is raised
through these heights, while the bottom layer has not
been lifted, and, this being true, the average height
through which the water has been raised in each case
will be .5, 5, 50, and 500.

Now to get a relative measure of the amount of work
done in each case, we must multiply the mean height of
the respective columns by their areas, and, doing so, we

have, —

Kklative
Mean Height.

Area.

Total
Work Doxb.

Eelative
Work Done.

For the 1

inch tube .5

1000000

500000

1000

" " .1

" " 5.0

10000

50000

100

" " .01

" " 50.0

100

5000

10

" ** .001

*' " 600.0

1

600

1

r

Surface Tension and Capillarity. 141

It is here seen that while the amount of water lifted,
or the work done, by the walls of the largest tube is
much more than that done by the smallest tube, it is
only so much more as the number of molecules constitut-
ing its circumference is greater. It is also seen that
before the molecules in the walls of the smaller tubes
have accomplished relatively the same amount of work
as those in the walls of the larger tubes, they must
necessarily have lifted their columns of water higher,
and because the weight of the water in the column
increases as the square of the diameters of the tubes,
but only directly as the heights.

In order to apply these principles to the capillary
movement of water in the soil, we need to call to mind
the cavities or openings which are left between the soil
grains, which are similar to, but much more irregular,
than those left between shot when they are filled into a
dish. While these cavities do not form straight capil-
lary tubes leading from deep in the ground to the sur-
face, they do in fact form broken or zigzag passageways
which in effect act in the manner of the capillary tubes,
but with greater resistance to flow, on account of the
water being forced, during the course of its rise, to
change its direction so many times before reaching the
surface of the ground or the root of a plant.

If we ask ourselves how much work this surface
tension, or capillary power, is able to do, the answer
must be sought in the amount of water which can be
raised by it through a known height in a given time.
The writer has found that a very fine sand did lift water
through four feet at the rate of .91 pounds per square
foot in twenty-four hours, while a clay loam lifted it at
the rate of .9 pounds per square foot through the same

u

142 The Soil

distance in the same time. Now, this amount of work,
when measured in horse power of 550 pounds lifted one
foot high per second, is very small ; so small indeed is
it, that one horse power may do the effective work of
the surface tension for 302 acres when moving water at
the observed rate mentioned above.

It would be a very grave mistake, however, to conclude
that because this form of energy is so small in amount, we
may pay no heed to it. On the contrary, it is because
the amount of work it can do is so small that it becomes
of the utmost importance to so manage the soil as to
enable it to act imder the most favorable conditions.
And when it is stated that this surface tension is the
only available power for moving the water of the soil to
the roots of plants, then there can be no question regard-
ing the importance of all those processes which tend to
favor capillary movement and the conservation of soil
moisture.

THE NATURE OF SOLUTION.

Let us now consider the process of solution, the means
by which the soil gives to the capillary water the ash
in-Tjredients and the nitrogen compounds of plant food.
The real na,ture of this process will be most easily under-
stood if we first consider what takes place when we
detect the odor of some fragrant flower or the perfume
from some unstoppled bottle placed at a distance from us.
In these cases there are traveling away from the blossom,
or from the open bottle, molecules of that substance
whose odor we detect; these perfumes are going into
solution in the air, and we detect them as they are
brought into contact with the organs of smell. We

The Nuture of Solution, 143

know there is :i movement of the perfume in these cases,
because they reach us at a distan(;e ; we know, too, tliat
this movement is taking i)lace in all directions, and at the
same time, because, on whatever side we stand, the odor
comes to us. We know, too, that these molecules tend to
spread wider and wider, until the whole air has been
permeated with them. The evaporation of water is
simply another case of solution in the air, where the
water molecules, through the absorption of heat, have
been so violently disturbed as to be thrown beyond the
sphere of molecular attraction in the liquid, when they
become a gas and travel indiscriminately in all directions
through the air.

When a lump of salt or of sugar is dropped to the
bottom of a vessel of water, our experience has demon-
strated time and again that, after a longer or a shorter
interval, and in spite of the fact that these substances
are heavier than water, they will be found uniformly
distributed throughout the whole. Here, too, the mole-
cules of sugar or of salt wander about from place to
place in the water, until there is no portion of it they
have not reached. At the outset, the action of surface
tension results in overcoming the cohesive or binding
power which makes the sugar a solid. Its molecules are
being dislodged, and, once free to move, they are never
again relatively at rest until some cause is brought into
operation to convert them once more into a solid.

So, too, when water is brought into contact with the sur-
face of soil grains, or particles of various kinds of fertili-
zers which may chance to be present among them, there
is here set up a disengagement of the surface molecules,
and these, hnding themselves free in. the capillary water,
travel from place to place in it, or they are borne along

144 The Soil.

with the current movements as they rise to meet the
losses due to evaporation, and pass laterally to make good
the amounts withdrawn by the roots of plants.

Nearly all substances dissolve more rapidly at high tem-
peratures than at low, so that a warm soil prepares food
faster than a cold one can, and this brings us to consider
the work which altered sunshine does in the prepara-
tion and movement of plant food in the soil. In speak-
ing of the surface tension of liquids, we have referred to
the strong power which is exerted among the molecules,
tending to draw them together, and which is only over-
come through the expenditure of an enormous amount of
heat energy when evaporation takes place. Now, as a
basis for understanding the solution of plant food in soil
water, let us get clearly in mind that, fundamentally, the
solution of a solid in water is not very different from the
evaporation of water in air, and let us keep in mind, too,
that, strong as the attractive force is between molecule
and molecule of water, the dynamic effects of heat are
great enough, even when water is frozen into solid ice, to
throw its molecules entirely beyond the bounds of cohe-
sive attraction, thus causing frozen garments to dry
rapidly even when hung in an atmosphere far below freez-
ing. Solid camphor evaporates, too, as we know from its
odor, under the dynamic action of heat.

We have seen that it is only the surface molecules
of water which find great difficulty in moving from
place to place. Within the liquid mass the forces are
very great, but so nearly balanced on all sides that only
a little heat energy is required to cause a movement.
So, too, in the case of the soil grains, the surface mole-
cules are under a strong tension, which makes it ex-
tremely difficult for altered sunshine to throw any

The Nature of Solution, 145

of them out, or, in other words, to cause them to
evaporate.

But when a soil grain becomes invested by a film of
water, this water, through its strong outward action, so
much weakens the surface tension of the soil grain that
the absorbed heat, the altered sunshine, is now able
to throw some of its molecules through the surface film
and into the water outside, thus dissolving it, and
this process of solution will go on until the water which
surrounds the soil grain has become saturated with the
dissolved substance.

Through the studies of van't Hoff, W. Nernst and
others, it appears that water saturated with a dissolved
solid is not widely different from air saturated with
water; and it is now generally agreed that a saturated
air is simply one so full of flying molecules of water
that just as many of them fall back again into the w^ater
each second of time as are driven out of it through the
action of heat. In this view evaporation has not stopped,
but rather the rate of condensation has come to equal
the rate of evaporation. If, however, the temperature
shoidd fall, then the stream of outflowing molecules
would become smaller, because the engine is slowing
down, while the incoming molecules, reaching the water,
remain there, thus rendering the air drier. On the
other hand if, when the air has become saturated, the
temperature of both air and water should rise, — that is,
if altered sunshine should enter the water at a more
rapid rate, — then more water molecules would be forced
out each second than, for the time being, are returned
to it, and hence evaporation would commence again and
the air would come to contain a higher per cent of
moisture. It would be a stronger solution.

L

146 The Soil.

If we carry this method of work to the solution of
plant food in the soil, we shall understand that, as the
ground warms up in the spring, as the altered sunshine
becomes more concentrated in the soil grains, as the
molecular swing becomes stronger and stronger, the rate
at which the molecules of plant food are driven out into
the film of water mounts higher and higher until finally
the soil water, like the atmosphere, has become saturated.
In this condition the play back upon the soil grains is
equaled by the outward discharge, and a balance is
reached, but not a condition of rest; for solution and
precipitation are going on even-handed. If the tem-
perature of the soil should go up, then the amount of
plant food in solution would increase ; while if it should
fall, then some of the dissolved materials would again
take on the solid form.

On the other hand, if the root hairs of plants, or the
cell walls of the microscopic life of the soil, come in
contact with the water in which this process of solution
is being carried on, and they utilize a portion of these
dissolved materials, then they Avill cause the solution
to go forward at a more rapid rate. The solution will
be more rapid because every outgoing molecule which is
captured and prevented from returning, with its heavy
blow, by so much reduces the resistance which the
outflowing molecules are obliged to overcome.

We must not lose sight of the fact, in this connection,
that the capillary movement which bears the dissolved
food materials toward the surface of the ground and to
the roots of plants must in some way represent altered
sunshine. Somehow the molecular swing of the soil
grains is transformed into current flow; for a stream
of watet (cannot rise continuously through the sail, the

Os))ioi<is and Diffusion in l*lant Feedinrj. 1 IT

whole suiniiKM- tliioiigh, agcainst gravity, against Mm frirv
tion of the very great soil surface, and against the resist-
ance necessitated by the many turns the currents are
forced to take, without the expenditure of much more
energy than is represented by the amount of water lifted.

OSMOSIS AND DIFFUSION IN PLANT FEEDING.

We have seen how altered sunshine, working through
the soil moisture, brings into liquid form the food of
plants ; we have seen, too, how this prepared food is borne
along in the capillary currents to the places where it is to
be used. Let us next consider how the food-laden water,
after reaching the root hairs, is made to enter them and
rise through the stems into the leaves and sunshine above.

The process by which this work has been accomplished
has been technically named osmosis, and we have })een
made perfectly familiar with some of its results in many
ways. When dry beans, prunes, or raisins are put in
water to soak, it is not long before they have increased
in size through the absorption of water. Osmosis has
taken place in each of these cases, and they illustrate,
so far as the real mode of action is concerned, the flow
of sap in plants. When juicy fruits are covered with
sugar or are placed in a strong syrup, they shrivel and
become much smaller ; here, too, osmosis has occurred,
but the strongest movements have taken place in the
opposite direction. In both of these classes of cases
movements have taken place, very similar to evaporation
and to solution, and the dynamic power of heat or the en-
ergy of molecular motion has been the actuating energy.

In trying to understand this process as it comes into
play in the feeding of plants, we need first to consider

148 The Soil.

some physical experiments which have served to demon-
strate the intensity of pressures which, under favorable
conditions, are developed during the action of osmosis.
The swelling of the dry bean to two or three times its
original volume certainly represents no small amount
of pressure ; for it is evident enough that, could we con-
nect a column of water with the bean and undertake
to distend it by direct hydrostatic pressure, a very high
column of water would be required to do the work.

Abbe Nollet, who lived between 1700 and 1770, appears
to have been the first to record that, if a glass vessel
be filled with wine and covered with a bladder and
then immersed in water, the contents of the vessel
would increase and sometimes to such an extent as to
burst the membrane. The same fact was rediscovered
a second, third, and even a fourth time before it came
to be the common property of science and was thor-
oughly investigated.

It was reserved, however, for W. Pfeffer, in 1877, to
conduct experiments in osmosis under such conditions
that a full measure of its power could be obtained. He
used a porous clay cell, lined with a membrane, produced
by precipitating on its inner wall a coating of copper fer-
rocyanide. Attaching a pressure gauge to this, he found
that when this cell was filled with a solution containing
1.5 per cent of potassium nitrate and then set in a vessel
of pure water, the water continued to flow into it until a
pressure of 3 atmospheres had been reached, and this is
equivalent to a column of water at sea level, more than
100 feet high ; while de Yries showed that a solution of
potassium citrate developed a pressure of more than 5
atmospheres, equal to a column of water rising to a height
of 170 feet, or a pressure exceeding 70 pounds to the

Oitmosis a7id Uiffuaion in Plant Feeding. 149

square inch. It is not strange, therefore, that dry beans
swell when placed in water, nor that dry wood, when lie-
coming wet, exerts such high pressure.

When two dissolved or liquid substances are separated
by a membrane through which one of these liquids can
pass more readily than the other, then that liquid whose
molecules are small enough to enable them to make their
way through the separating membrane most rapidly, does
so. This causes an accumulation, within the bean, for
example, thus increasing its volume and at the same
time the pressure. Under these conditions the mole-
cules of water wandering about or diffusing, impelled
by their heat energy, continue to pass through the por-
ous membrane, continue to pass into the bean, until the
same number, in their vagrant wandering, tend to emerge
from the porous membrane, from the bean, each second
of time, as tend to enter it. When this state has been
reached, the in-and-out play goes on even-handed, a bal-
ance has been reached, and apparent change has stopped ;
a condition similar to air saturated with water has been
attained.

We may consider first the movement of water in and
through the plant. If in any plant cell water is being
consumed as food, if it is being changed into some other
substance, or if it is evaporating and leaving the cell in
this way, the removal of these molecules from the solu-
tion leaves space unoccupied, diminishes the osmotic
pressure at that place, and this diminution of pressure
causes a flow of molecules from contiguous cells to
make good this loss. Suppose that in a certain portion
of a plant water is being used in the manufacture of sugar
or starch. Then so long as this demand continues, there
will be a lowering of the osmotic water pressure, and so

150 The Son.

long will water move toward that place. It is as if there
were a long line of vessels full of water, all of tliem con-
nected by means of pipes, and at one end of tlie line
water is being dipped out, so that the water level or pres-
sure in that is being lowered. When this is done, water
will flow from the nearest vessel to take the place of
that which has been removed, but no sooner is the water
pressure or level in the second vessel lowered than a
flow sets in from the third, and this to be followed by
water from the fourth, flfth, and so on to the end of the
line. Then, if water is added to the far end of the line
as rapidly as it is being removed at the other, a continu-
ous flow will be maintained. On the other hand, if the
dipping ceases, then the water surface becomes level
throughout the whole system, the water pressure be-
comes uniform, and flow ceases.

Now in the case of the plant supposed, tlie diminution
of the osmotic water pressure at the place of growth is
propagated backward toward the end root hairs in the
ground, and so soon as some of the root cells which are
in contact with the soil water have their pressure re-
duced by the flow toward the place where the water
is being used, then the balance of pressure between
the water in the root hairs and that which is in contact
outside is destroyed, and more molecules enter than escape,
impelled by the dynamic energy of molecular swing. So,
too, if the reduction of osmotic pressure in the leaves is
due to evaporation rather than the fixation of water,
the same result follows.

Then regarding the movement of nitrates from the
soil into and through the plant; so long as there is
no consumption of this substance in the tissues, just so
many molecules of the nitrate, impelled by altered sun-

Osmosis and [diffusion In Plant Fee<Hn(j. 151

shine, leavo the soil water and wander ilirou^di the fluids of
the plant as are required to produce a halancc^ of osmotic
pressure throughout it, or, what is tlie same thing, an even
distribution of nitrnte in the sap. Under these condi-
tions accumulation ceases. If, however, growth is going
on which results in the removal and fixation of the nitrate,
then, where this is taking place, the back play of the
molecules is reduced, the balance is destroyed, and more
nitrate advances to make good the loss ; a flow sets in
from the soil toward the place of consumption."

It follows from wdiat has been said regarding osmotic
pressure and its action, that there is a tendency for each
ingredient of ])lant food to travel in a large measure in-
dependently of every other material, the movements not
being in the nature of currents. So that if the escape
of water from the plant were to be stopped altogether,
the osmotic pressure might be fully able to convey
nitrogen and the ash ingredients to the plant dissolved
in the water which, under these conditions, would act
simply as a medium through which the diffusion is
carried on.

It will also be understood from these statements that
the transfer of the assimilated products to the places
where they are stored, whether in the seeds, thickened
leaves, or fleshy roots and tubers, must also be effected
by this process of diffusion through osmotic pressure.
As the soluble forms, out of which the insoluble
starches, gums, and fats are constructed, are withdrawn
from solution, at their respective places, there must
necessarily result a diminished pressure in the ear of
corn, in the head of wheat, in the expanding apple
and in the tubers of the potato, the bulb of the onion or
the root of the carrot, tow^ard which the products com-

152 The Soil

pounded in the green parts of the plants must be im-
pelled by the energy of altered sunshine.

In justice to the reader and to the truth, it should be
said in closing this subject that not all physiologists are
fully agreed that osmotic pressure is the only power
which actuates the movement of sap in plants, but the
most reliable data we now have go to show that it is the
prime, if not the sole, mover, and to this physiologists
are agreed.

The so-called selective power of plants, whereby they
obtain those substances dissolved in the soil water which
contribute to growth, and those substances which are
brought into solution by the corroding power of juices
exuded from their roots, finds its explanation in osmotic
pressure. Eegarding this point, it should be understood
that any substance held in solution in the soil water may
make its way through the tissues of plants, and usually
does so until the sap contains the same number of mole-
cules per unit volume as the soil water contains. Under
these conditions, if that substance is not being used by
the plant, no further accumulation of it 'can take place ;
for the outflow from the root into the soil keeps exact
pace with the inflow from the soil toward the tissues.
The loss of water by evaporation through the surface of
the plant or the consumption of it as food, which tends
to make the strength of the solution of those substances
not used as food stronger, cannot result in a permanent
increase of them in the plant, because, unless these sub-
stances are actually taken out of solution, they travel
back toward the root again and escape into the soil water
so long as the solution inside is stronger than is that out-
side.

If the molecules of any substance in solution are too

Osmosis and Diffusion in Plant Feedinr/. 1 53

large to easily make their way through the walls of root
hairs, as seems to be the case with some of the colloidal
salts, then there is a positive exclusion of these sub-
stances from the plant, or they only enter in diminished
quantities, just as the colloidal substances in the plant
cells do not readily escape into the soil water under the
impulse of this osmotic pressure.

So, too, when a soil coni,ains any substance which is
poisonous to the plant or which by its presence in the
sap would be harmful, the roots have no power to exclude
it. The process of osmosis tends to carry it to all parts
of the plant, just as when a soluble poison is taken into
the stomach of an animal it is absorbed and goes quickly
through the system.

The plant then simply takes out of the solution brought
to it those substances which it needs. It is not overloaded
with other substances, because it leaves those in solution,
and this is a sufficient check to a further accumulation of
fchem.

CHAPTER V.

SOIL WATER.

From what has been said in the preceding chapter, it
is evident that water plays an extremely important part
in the fertility of soils and in the feeding and life of the
plant. Surronnding the soil grains as a surface film, it
acts directly upon even the most difficultly soluble of the
soil ingredients, taking them into solution in larger or
smaller quantities. Holding carbonic, hnmic, and other
acids in solution and bringing them into close contact with
the surfaces of the soil grains under a diminished surface
tension, these substances are enabled to bring into soluble
form the ash ingredients of plant food as they could not
without the aid of water. Wood kept permanently so dry
that it contains only a small amount of hygroscopic mois-
ture never decays, and such perishable articles as fruits
and even flesh may be preserved for indefinite periods of
time if only they are kept permanently dry ; and so in the
return of dead organic matter in the soil to the ash in-
gredients, nitrates and carbon dioxide, the forms in which
they can be used over again by higher plants, the pres-
ence of a certain amount of soil moisture is indispensable.

After the plant food has been prepared in the soil or
in the air, it is useless until endowed with the possibilities
of movement toward and through the living tissues. But
water, through the action of capillarity and osmotic pres-
sure, is the medium of transport by which the ash ingredi-
ents and the nitrogen of the soil are moved to the roots

154

Amount of Wafer Used hy Crops. 155

of plants, by wliicli they arc; drii'tcMl into Uk; sunsliinc, of
the laboratories in the green leavers and l)ark, and from
which they are again taken to their final ])laces in the
strncture of the i)lant. Nor is this all, for watf^r is itself
a food snbstance used in large quantities by all plants of
whatever sort. By its eva})oration from the foliage ol'
plants, it not only holds the temperature down within the
normal range of the vital processes there going on, but,
because of this lowering of the temperature, it also hastens
the osmotic flow of sap toward the leaves.

AMOUNT OF WATER USED BY CROPS.

T'he amount of water demanded by (;rops under our
methods of culture is very large. So large, indeed, that
in Wisconsin the following amounts in tons of water per
ton of dry matter and in inches of water per ton have
been lost by transpiration through the plant and evapora-
tion from the soil : —

Dent corn used 309.8 T. equal to 2.64 in. of water per 1 T. of dry matter.

Flint " "

233.9 "

li

2.14 "

Red clover "

452.8 "

n

4.03 "

Barley used

392.9 "

ii

3.43 "

Oats

522.4 "

ii

4.76 "

Field peas used 477.4 "

4.21 "

Potatoes used

422.7 "

((

3.73 "

Hellriegel found, through experiments conducted in
Prussia, that the amounts of water withdrawn from the
soil and given to the air, almost wholly through the
plant, were as follows : —

Barley used 310 pounds of water for each pound of
dry matter produced, summer rye 353 pounds, oats 376
pounds, summer wheat 338 pounds, horse beans 282
pounds, peas '273 pounds, red clover 310 pounds, and

156 The Soil.

buckwheat 363 pounds of water for one pound of dry
matter. This is at the mean rate of 325 tons of water
for each ton of dry matter produced.

These large amounts of water used by vegetation in
the maintenance of its functions are necessitated partly
by the rapid evaporation which results from the extreme
exposure of the foliage under conditions best suited to
facilitate a rapid loss of water in this way ; but evidently
also, in no small degree, by the physiological processes
of the plant itself, which demand a large movement of
water through the growing tissues.

The fact, however, that the growth of vegetation is
often extremely rapid during the times when the rate of
evaporation must be relatively slow, makes it appear more
than probable that the large losses of water by evapora-
tion from cultivated fields, through the transpiration of
growing crops, is not really demanded, so far as the needs
of growth are concerned ; and if this is true, it follows
that wherever we can adopt means which tend to avoid
needless loss of water through the foliage of plants, we
are practicing economy regarding soil moisture just as
we are in our methods of mulching, by cultivation or
otherwise, which aim to reduce the evaporation from the
surface of the soil.

There are very few countries, indeed, where the distri-
bution of rainfall in time and amount is such as to permit
fertile soils to produce the largest crops they are able to
bear ; and this being true, those soils which are able to
store the largest quantities of rain in a condition which
shall permit vegetation to use it to the best advantage
are likely to be the most productive. On this account
the water capacity of soils is an important factor in the
determination of land values.

Capacity of Soils to Hold Water. 167

CAPACITY OF SOILS TO HOLD WATER.

Since each independent soil grain of a moist soil is
more or less completely s\irrounded by a film of water, it
is evident that, other conditions being the same, that soil
whose grains present the largest aggregate surface area
may retain the most water per cubic foot. Now a cubic
foot of marbles one inch in diameter possesses an aggre-
gate surface of 37.7 square feet, while if the marbles
were reduced in diameter to one one-thousandth of an
inch, then the total area per cubic foot is increased to
37,700 square feet. From these differences it is evident
that the amounts of water coarse and fine grained soils
retain will be very different.

Under field conditions the amount of water a soil can
hold varies, not simply with the size of the soil grains,
but also with the distance of standing water in the
ground below the surface and the length of time which
has elapsed since it has rained.

To illustrate the influence of the size of the soil grains
on the amount of water a soil may retain, let me cite
some observations upon columns of sand 10 feet long,
from which water had been allowed to percolate during
111 days under conditions where no evaporation could
take place from their surfaces. The column whose mean
grains had diameters of y^f|^ of an inch contained, in
the upper 30 inches, 2.16 per cent, in the second 30
inches, 2.41 per cent, in the third 30 inches, 2.73 per
cent, and in the fourth, 7.77 per cent ; but a sand whose
average grains were y-g^^o^-o of an inch in diameter retained
3.06 per cent for the upper, 3.71 per cent for the second,
5.46 per cent for the third, and 18.05 per cent for the
lower 30 inches. The first column had retained only

158 The Soil.

3.77 per cent of its dry weight of water, while the second,
or finer, one had retained 7.57 per cent of its dry weight,
or about twice the amount. Two other sands, with grains
about -Y-^-^-^Q and yoVor ^^ ^^ inoh. in diameter, placed
under the same conditions, had retained 4.92 and 5.76
per cent respectively ; that is to say, columns of sand 10
feet long composed of grains

T^fff 0 ^^ ^^'^ moh in diameter retained 3.77 per cent of water,

TOOOO ^'^^

6 1 U 44 (4 44 !\ na 44 (;

To 070 '^^ ' "

45__ " " " " 7 .^7 " '<

TOGOO '•"* ,

after a period of percolation of 111 days.

It will be understood that the smaller the size ot the
soil grains, the smaller will be the size of the pores
through which the water is obliged to flow in percolating
downward under the influence of gravity, and hence the
slower will be the rate at which it will move.

The table given below will show the influence of the
size of the soil grains on the rate at which the water
may be lost by percolation downward. The results here
given were obtained from columns of sand 8 feet long,
and composed of grains having the same diameters as
those just referred to.

At the end of 9 days these several soils had lost
water, in the order from the coarsest to the finest, 15.29,
14.35, 12.86, 10.02, and 8.42 per cent respectively of
the dry weight of the sand.

A strange thing about these soils is that they con-
tinued percolating slowly for more than 259 days, and dur-
ing the last 250 days they lost respectively, beginning
with the coarsest, at the rate of 9.15, 7.77, 6.56, 7.69,
and 7. 56 pounds of water for each square foot of surface,

Capacitij of Sollif to Hold Water.

159

RATE OF PERCOLATION FROM VMWVV FKI-:T OF SAND OF
DIFFERENT DEGREIJS OF FINENESS.

Size of Gkain8.

Time of Percolation.

1 Hour.

2 Hours.

'24 Hours.

4f5 Hours.

tJUo ol an inch . . .
ruVou of an inch . . .
Tu'oVo of an incii . . .
T#(Jo of an inch . . .
T^¥oo- of an inch . . .

Per cent.

9.10

7.95
0.22
1.70
1.28

Per cent.

10.45
9.47
9.21

2.83
1.91

Per cent.

i;5.05

12.31

11.71

7.04

5.83

Per cent.

13.52

12.72

11.53

8.44

0.79

amounts ranging from 1.2 to 1.8 inches of rain ; nor had
percolation at this time ceased.

It must be understood that with true soils of much
finer texture, the rate of percolation from them would in
all probability be much slower and the water-holding
power much larger, but no measurements have been made
for any of these under the conditions stated above.

To show what actual field soils may hold when their
surfaces are only 11 inches above standing water, this
water having been lifted into them by capillarity, the fol-
lowing results may be cited : —

Per cent of
Water.

Lbs. of
Water.

Liches of
Water.

Surface foot of clay loam contained
Second " reddish clay "
Third " " " "
Fourth " clay and sand "
Fifth " line sand "

32.2
23.8
24.5
22.0
17.5

23.9
22.2
22.7
22.1
19.0

4.59
4.20
4.37
4.25
3.77

Total . . . . .

. -. .

110.5

21.24

160 The Soil.

Then, again, to show the water-holding power of natural
soils under field conditions, the table below gives the
water content of a piece of fallow ground at three differ-
ent times during the season, the soil being a medium clay-
loam with clay subsoil in the second and third feet and
followed with sand in the fourth foot. The field was tile
drained, the drains being 4 feet below the surface of
the ground.

Depth. May 16. July 18. Aug. 30.

per cent. per cent. per cent.

Firstfoot I _ _ 25.77

Second foot
Third foot
Fourth foot

Average 24.32 23.68 23.83

22.87

24.27

24.71

23.62

24.30

23.52

24.03

23.32

22.29

It is evident from the cases cited that the water-hold-
ing power of soils under field conditions is really large,
and that, where there is no crop upon the ground to con-
sume the water, and the water table is not more than
5 feet below the surface, the ordinary summer rainfall,
assisted by capillarity, may nearly conpensate for the
loss of water by percolation and by surface evaporation ;
but this is far from being true when a crop is occupying
the land, unless the rainfall is more than usually heavy
and frequent.

It may be said in general, regarding the capacity of
soils to hold water, that the finer the soil grains the more
the soil will hold, and the greater the number of spaces
which are larger than caj)illary size the less it will hold.
The capacity of a soil for water decreases to some extent
also as its temperature rises, but under field conditions
the effects of temperature are not large. It is certainly
true for sandy soils that their capacity for water de-

Capacity of Soila to Hold Water. 161

creases in a marked manner tlie higher their surfaces
are above standing water, and it is probably true that all
soils, unless we must except the finest clays, fall under
the same law.

If it were true that all of the water which a soil may
retain were available to crops, and it were not neces-
sary to allow some of the water of completely saturated
soils to percolate away before agricultural plants will
thrive in them, then in most humid regions it would be
possible to obtain much larger crops than can now be
raised without irrigation. The facts are that not only
must a considerable amount of the soil moisture be left
unused by the crop, if large yields are expected, but from
30 to 40 per cent of their saturation amounts must have
drained away before the soil can contain air enough to
maintain the breathing of ordinary roots and germinat-
ing seeds. Hellriegel places the amount of water which
should drain away from the soil before it becomes habi-
table by cultivated plants as high as 40 to 50 per cent of
their full capacity, and in order that maximum results
may be reached, the water content should not fall very
far below these amounts.

The soils having a small water capacity will yield their
water to plants more readily and completely than the
heavier types. The writer has observed that, in a sandy
soil whose maximum water capacity was about 18 per
cent, corn was able to draw the water in it down to 4.17
per cent, while in a clay soil, having a water capacity of
about 26 per cent and lying nearer the surface and far-
ther from standing water in the ground, the same plant
had only succeeded in using the water down to 11.79
per cent.

Now if we compare the absolute amounts of water

162 The Soil.

given over to the corn by these soils, we shall find that
the sandy soil contributed 13.83 pounds of its amount
per cubic foot, while the clay had only yielded 12.5
pounds. It thus becomes evident that while the percen-
tage capacity of the sandy soil is much below that of the
clay, its greater weight per cubic foot and the greater
freedom with which it yields water to plants makes its
storage capacity of available water more nearly equal to
that of the loamy clay than would at first be supposed.
It is on this account, in part, that a sandy soil, kept well
fertilized, has many advantages over the colder, less per-
fectly aerated, and more obstinate clayey ones, which
crack badly in excessively dry weather and become over-
saturated in wet seasons.

It follows from what has been said regarding the
capacity of long columns of soil for water, that the dis-
tance of standing water below the surface, or below the
level to which the roots of cultivated crops may reach,
must materially influence their agricultural value. In
general the nearer the surface of the ground water or
water table is maintained to the lower surface of the
root zone, the more productive the lands will be ; for then
capillarity is able to hold the water content of the soil
more nearly up to the standard required for maximum
yields. This is the chief reason why lands which
require underdraining are so valuable when they have
been thus improved.

THE GROUND WATER AND WELLS.

In all humid climates where the soil, or unsoliaified
sand and gravel, has a depth of 50 to 200 feet, there is
a certain distance below the surface at which all of the

The Ground Water and IVellft. ]f)3

interspacps between the incoliereiit grains are completely
filled with water, and the upper surface of this water-
filled soil is called the water table. Above this water
table the soil contains only capillary water. When
wells are sunk into the water-filled soil, the surface of
the water in these wells represents the level of the
water table, at that i)lace. We should think of all j)er-
manent lakes and ponds, too, as extensions of the water
table, where the surfaces of low lands are beneath it.
It must not be understood, however, that the height
of the water table under the land is at the level of the
water in the lakes. On the contrary, the water table
Jilmost invariably rises as the distance from the mar-
gins of lakes and other permanent bodies of water
increases. Indeed, the surface of the water table fol-
lows in a rough way the general contour of the land, the
water-filled soil beneath the surface standing highest
where the ground is highest, and lowest where the land
is low. The water tabic has its hills and valleys, which
coincide with those of the country it underlies, only they
are not as steep, the water being nearer the surface
under the low ground than it is under the high. An
inspection of Figs. 21 and 22 will show how the ground
water is related to the surface in one locality. In one
of these figures the contour lines show the surface of the
land, y/hile in the other they show the surface of the
water-filled soil beneath, on the date there specified, as
determined by measurements taken at the wells indicated
by the numbers in the figure.

There is one marked difference between the hills and
valleys of the water-filled soil .,nd those of the surface
of the ground which overlie them, and that is that the
height of the water table is not constant. This surface

^KE ^$^

Fig. 21. — Showing the contour of the surface of the ground. Figures
in the liiTes show height of contours above lake level ; other figures
indicate wells where the height of the water table was measured.

Fig. 22. — Showing the contour ol the water table beneath the stirlace
of the area represented by Fig. 21.

166 The Soil,

rises and falls with the season, being higher usually
in the early summer and lowest late in the winter. Its
surface, too, in many places, tends to rise higher and
higher when several wet seasons succeed one another,
and then to fall with the recurrence of dry years.

The reason why the surface of the water-filled soil is
not level is because the soil grains offer so much resist-
ance to tlie lateral flow of the water toward lakes and
streams, that the rains which percolate beneath the sur-
face do not have time to drain away before another rain
comes to add its water to the soil. But if there should
be a long term of years with little rainfall, the water
table would sink lower and lower, and fastest where
it is highest, until it became nearly or quite horizontal.

When wells are sunk into the water-hlled soil, it is
evident that water may be reached at very different
levels in different localities, and that it will not be neces-
sary to dig to tlie level of some lake or stream before
water is reached, as is commonly believed. To illus-
trate how far this idea is from being true, it may be cited
that a well on the campus of the University of Wiscon-
sin has its water surface 52 feet above the level of Lake
Mendota, only 1250 feet distant, and yet this well is dug
all the way in a coarse sand and gravel which makes up
the axis of an isolated glacial drumlin from 88 to 109
feet above the surface of the lake. Now the water of
this well owes its origin wholly to the rain which falls
upon the hill and percolates slowly into it; and how
slowly this may be can be understood from what has
been cited regarding the percolation from the columns of
sand only 8 to 10 feet long.

In digging wells into the water-filled soil, it is evident
that those sunk in the valleys will be less affected by

The Ground Water and Wells. HIT

s<'aKonal cliaiip^os aiul will usiuilly ^ivo a larj^jor water
supply, for tlu^ I'casuu that the water under tlu^ higher
lands tends to How toward the valleys below ground
just as it does above ground. 'I'hen, too, in digging
wells, can) should l)e taken to sink the bottom of the
well so far below the level of the water table, that sea-
sonal changes will not cause it to go dry. More than
this, the larger the su})ply of water which must V^e
drawn from the well, the deeper it should be sunk belo.sy
the level of the water table, and if the well is being dug
during the season when its natural level is highest, and
particularly if a series of wet years have preceded the
digging, then a special effort should be made to carry
the bottom a considerable distance below the level at
which water will stand in it at the time. The deeper
the well is below the water-filled soil, the farther the
water surface may be lowered below the level of
the water table, and the farther the pumping carries the
water level in the well below that of the water-filled soil,
the faster will the water flow into the well, and the
larger will be the amount of water it can deliver in a
given time.

There is another matter regarding such wells which
should be emphasized hero, and that is the danger of
surface waters percolating into them and rendering them
unfit for use. The soil containing only capillary water
above the water-filled zone has in its interspaces larger
or smaller quantities of air, so much so that all space not
occupied with water is taken possession of by it. Now
when heavy rains come, the surface soil is first com-
pletely filled Avith water, and under these conditions it
is at first difficult for the water to enter the soil deeply
and also for the now confined soil air to escape. Then

168

The Soil

the air, borne down by the pressure of the water above,
has a tendency to move away in any direction where it can

• •••••• !••• • •• . '• ••■ ^spr^

r.v:V;:-:r:;.vvV;.-v--::

-• ''/Zo'rie'.'Jof.\soil- ':

/v.V.-.-V.;%;..|*T.
I V :'ciir ' ' wnicA, '.

I .V* ••..••? ■,•.•. • »•

*.♦.•*• . 1 • • .■ •.»,*♦ vr„
• ....;•.;.;.•.;• . * -. -K

'.. 'Air esca/finQ' v ..

)J3"^J£!'JS/«*

* ."•»'•

• - •

f^^i&tJ^-'.-^

m

Fig. 23. — Showing the method of percolation of water into and out

of wells.

find the easiest escape, and whenever the well is not pro-
vided with a water-tight curbing, the air tends to escape
into the well, and then the percolating waters follow it

The Ground Water and WelU. 169

under the conditions represented in Fig. 23. In conse-
quence of this tendency of both the air and the water to
flow toward and into the well, the confined soil air forms
a sort of broad, sloping funnel, down the sides of which
large quantities of water from close to the surface of the
ground are drained into the well, carrying many of the
impurities they may have dissolved in the neigliborhood.
The sanitary aspect of tins question should not be lost
sight of; for the sudden large rise and fall of tlie water
in a well associated with heavy rains is a pretty sure
indication that that well has received surface waters,
which, if the surroundings are bad, is liable to render
the water unsafe to use. And observations show that
wells in close, impervious soils are much more liable to
surface contamination in this manner than are those in
the more open soils, where the interspaces near the sur-
face do not readily become closed with the fine sedi-
ment moved by the water, as is the case with the clayey
types.

Just how far it is practicable to protect wells which
are subject to contamination in this manner by using
iron tubing or other similar impervious curbing, is a
matter which merits careful investigation; for it is a
vital question in the building of country homes. It is
generally taken for granted that wells thus constructed
are safe against the infiltration of surface water, and it
may be true to a large extent ; but it does not appear
improbable, in pumping water from a well tubed up with
iron, that the rapid withdrawal of water from about the
immediate terminus of the tubing would tend quite as
strongly to bring down a new supply from the super-
saturated soil above, as to induce it to come from below
or from lateral directions, and, if this is true, it is evi-

170 The Soil.

dent that the surface surroundings of a well used for
domestic purposes should be scrupulously cared for, even
when provided with impervious curbing.

When we consider the movements to which the soil
water is subject, it must be said that these belong to not
less than three classes, — those due to the action of
gravity upon the soil water direct, those due to capil-
larity or surface tension, and again those which result
from changes in the tension or pressure of the soil air.

PERCOLATION MOVEMENTS OF SOIL WATER.

The movements of the gravitational class are the most
extensive, the most rapid, and find an expression of their
aggregate magnitude in the vast volumes of water which
the great rivers of the world pour into the sea. To
appreciate the full significance of these movements of
the ground water, we need to think of the water-satu-
rated soil as being almost as extended and as continuous
as the land areas of the world ; for, beneath almost every
square foot of soil-covered surface, unless the frozen
zones and desert regions must be excepted, there is a
perennial percolation of water, at first downward in the
slow fashion already referred to as taking place in the
sand, but as the deeper, and often more porous, layers
are reached, the movements become stronger, and finally
tlie waters emerge as springs, at the foot of hillsides or
in the bottom of lakes.

The direction of percolation is by no means always
downward nor even lateral. In many places it comes to
be vertically upward, toward the surface, giving rise to
larger or smaller areas, which require underdraining
before they are fit for agricultural purposes. In very

Percolation Movements of Soil Water, 171

many localities, wliere a sandy or otherwise porous stra-
tum underlies botli th(i fiat, inarsliy areas and the sur-
rounding higlier ground, the much greater elevation of
the water table under the high ground causes it to act by
direct hydrostatic pressure, to force the water to the sur-
face on the low ground, not in tlie form of springs, ])ut
in a broad sheet which tends to keep a wide area more or
less uniformly wet. !Su(di areas, when they are under-
drained, come to be the most productive lands we have,
and largely because of the natural sub-irrigation which
is, in such cases, taking place; and it must be remem-
bered that lands so situated are receiving, with the
-underflow of water, not simply the lime, in the form of
carbonates, which may have been dissolved, but also some
of the nitrates and other soluble forms of plant food,
which may have percolated beyond the reach of root
action on the higher ground.

The rate at which water percolates through soils
varies between wide limits. In a coarse, sandy soil,
whose grains pass a screen of 40 meshes to the inch, but
are retained by one of 60, the writer found that water
would percolate through a column 14 inches in length.
and .1 of a square foot in section, at the rate of 301
inches in depth in 24 hours ; where the grains passed a
screen of 60 meshes, but were retained by one of 80, the
percolation was 160 inches in the same time. Reducing
the size of the grains still further, so as to pass a screen
of 80 meshes, but not one of 100, then the percolation
falls to 73.2 inches in 24 hours. While sand, which
passed a screen of 100 meshes to the inch, allowed 39.7
inches to pass. A clay loam, on the other hand, was so
much more impervious that only 1.6 inches passed a
column of the same length in 24 hours, while a line-

172 The Soil.

textured black marsh soil passed only .7 inches in the
same interval.

Adding 20 per cent of blue clay to the sand which
percolated 73.2 inches during 24 hours reduced the
amount passed through it to only 10.5 inches, while 50
per cent of clay caused a decrease to 2.7 inches during
the same time. In all of these cases, while percolation
was going on, the several soils were kept covered with
water to a depth of 2 inches.

Wollny showed, from experimental studies, that, under
like conditions of pressure, soils having different sizes
of grains allowed water to pass through columns 11.81
inches deep and 1.97 inches in diameter, at the rates
indicated below : —

Depth in

Inches.

Quartz sand .0004 to .0028 in. in diam. percolated 7.27 in 24 hours.

" .0028 to .0045 "

" .0045 to .0067 "

Calcareous " .0004 to .0028 "

*' .0028 to .0045 "

•* " .0045 to .0067 "

68.59 " "

669.7 ♦' "

6.64 •' "

63.74 •' ♦•
304.3 " "

In these experiments of Wollny's, as in those of the
writer, the sizes were obtained by sorting the grains
with sieves ; but it should be observed that this method
of separation is not very exact, as it permits varying
amounts of grains of smaller sizes to remain among
those having the dimensions sought, and it may be this
fact which causes the observed differences between the
quartz and calcareous sands.

It must be evident therefore, from the facts here given,
that soils differ very widely in their tendency to retain
the rains which fall upon them, and also in their tendency
to lose their soluble plant foods during wet periods. It

Capillary Movements of Soil Water. 173

is evident, also that, while a small per cent of clay added
to a sand will greatly increase its power to retain water,
relatively large amounts of sand would have to be added
to the stiff clays to render them very open.

A very wrong impression would be left if it were not
stated here that the amounts of percolation recorded
above for the several cases are at maximum rates, and
that such rates of percolation seldom occur in the field
anywhere in nature. Indeed, such rates can only take
place after all air has been expelled from the soil and the
spaces between the grains have been completely filled
with water. This condition rarely occurs except in the
spring and after protracted and very heavy rains. After
vegetation is once well under way, the surface two and
three feet of soil are so rapidly dried that ordinary rains
can only partially maintain such slow percolation as has
been shown to take place from the long columns of sand
cited above. Indeed, it more frequently happens in our
climate, during the middle and later part of the growing
season, that the rains we do have tend rather to strengthen
the upward flow of water toward the surface by capillarity
than to result in gravitational losses downward by perco-
lation. Much the larger part of the water which goes to
feed perennial springs is that which finds its way into
the soil when vegetation is dormant or only feebly active.

CAPILLARY MOVEMENTS OF SOIL WATER.

The capillary movement of water in field soils is the
slow creeping over the soil grains due to the action of
surface tension, as already described. It takes place in
any and all directions, but usually from below toward the
surface of the ground where evaporation is taking place,

174 The Soil.

and toward absorbing root hairs where the surfaces of
soil grains are being depleted of their capillary water. •

The rate at which water can be moved through soils
by capillary action is never very rapid when compared
with the gravitational movements we have just considered.
It is, however, sufficiently great and extensive to be of
the highest agricultural importance.

When a cylinder of very fine sand, 12 inches in diame-
ter and 4 feet high, was saturated with water and ar-
ranged so that water could be automatically admitted to
it from below as rapidly as it could be removed by evapo-
ration from the surface, it was found, on placing this cyl-
inder in a strong current of dry air, and under conditions
where the water must be lifted 12 inches by capillarity,
that the work of lifting was done at the mean rate of 2.37
pounds per square foot daily during 10 days. On chang-
ing the level of standing water in the cylinder to 2 feet
below the surface, the mean daily capillary rise came to
be 2.07 pounds. When the capillary lifting went on
through 3 feet, the work done daily was at the rate of
1.23 pounds per each square foot of surface ; while at 4
feet it became .91 pounds.

A similar trial with a medium clay loam gave mean
rates of lifting water amounting to 2.05 pounds, where
the lifting was through 1 foot, 1.62. pounds where it was
through 2 feet, 1 pound where it was through 3 feet, and
.9 pound where the rise was through 4 feet of this soil.
It is very certain that the rate of capillary rise of water
in each of these cases might have been larger had the
evaporation from the surface been greater ; for the sur-
face of the soil remained wet throughout all of the
experiments. It is also certain that the decrease with the
depth is larger than it would have been had not the de-

Cap'dlnrij Movementa of Soil Water. 175

posit of salts oil the; surraco, teii(lin<^ to form a crust,
(liniinislied the (ivaporatiou. This fact was proven con-
chisivcly in both cases by reniovin<^ the crust formed on
the surface at tli(^ (;h)S(^ of th(i trials, wh(;n tlui mean rate
of evaporation, and hence also of capillary rise of water
throu«>h these soils, became 1.38 pounds for the line sand
and 1.27 pounds for the clay loam per square foot and
per day.

Ill another experiment, under perfectly natural field
conditions, it was found that the surface four feet of soil
lost, during 7 days, 9.13 pounds of water from each square
foot of surface, and this, too, under conditions which make
it certain that this loss was wholly due to a capillary rise
and to evaporation from the si^'face. This loss gives a
mean capillary movement amounting to 1.3 pounds daily.
In this Held case the water table was 4.5 to 5 feet below
the surface, or rather more than in the laboratory trials
referred to above.

The writer has also made other field determinations of
the capillary rise of water in field soils under field con-
ditions, and has found, as the mean of 10 determinations
in as many different places, a measured loss of water
amounting to 1.65 pounds per square foot per day. In
these trials it is quite possible that a portion of the ob-
served loss may have been due to percolation downward.
But, on the other hand, it should be added that it is more
than probable that the real losses from the ground up-
ward, and hence also the total capillary work done, were
larger than the measured losses, because it is only fair to
assume that capillary action was bringing water from
below. into the layers of soil, where the losses were meas-
ured,, an^, if this was true, such action could only tend to
make the observed changes less than they in reality were.

176 The Soil,

It must not be inferred that the capillary action is uni-
formly as rapid as the cases just cited. These should be
looked upon, not as extremes, but as representing rates
of movement of the soil moisture toward the surface
which are above the average.

When the soil, for any reason, has become very dry,
and also when it has been rendered loose and open so
that it contains numerous large spaces which are many
times the diameters of the soil grains, the rate of capil-
lary rise of water then becomes much slower. In illus-
tration of the slower rise of capillary water in a dry soil
may be cited the case where cylinders of dry soil 6 inches
in diameter and 12 inches long were placed with their
feet standing one inch in water, under conditions where
no evaporation could take place from their surfaces.
Thus situated, no one of five samples was completely
saturated at the end of 34 days. Before these soils
appeared damp at the surface, the times given below were
required : —

In clay loam, time required to travel 11 inches, 6 days.
" reddish clay " " " " 11 " 22 "

U U 4( (( i( U (( YY ^^ 18 '^

" clay with sand " " ♦' " 11 " 6 '*
" fine sand " " " *' 11 " 2 "

During the first 24 days of this trial, the mean rate of
capillary rise was .79 pounds per square foot daily, but
when fully saturated, these soils were shown to lift the
water at a rate exceeding 2.05 pounds per square foot
and per day. In the case of the line sand, the mean
daily movement during the first 24 days was .69 pounds
per square foot, but when fully saturated, it exceeded 2.37
pounds, a rate more than three times as fast.

Capillary Movements of Soil Water. 177

When the soil grains are separated from one another,
so as to develop an open, crumbly condition, then the
rate of capillary rise of water through it is greatly re-
duced. Thus, plowing so thoroughly checks the loss of
water from the soil beneath the stirred portion, that in
one case seven very drying days failed to appreciably
decrease the mean amount of water in the upper four
feet of a field soil, while an immediately adjacent and
entirely similar land, not plowed, lost, during the same
time, the full equivalent of 1.75 inches of rain, or more
than 9.13 pounds per square foot. So, too, in the case of
the fine sand referred to above, while it was losing water
at the surface at the rate of 1.38 pounds per day as a
mean of ten days' trial, when two inches of the surface
was removed and then laid directly back again, but in
the loose, unfirmed condition, this treatment had the
effect of reducing the loss of water at the surface, during
the ten days immediately following, to a little less than
.5 pounds per square foot daily, an amount, it will be
seen, so small that the other rate exceeded it by more
than 2.7 times.

The rate, too, at which surface tension or capillarity is
able to move water through the soil is materially influ-
enced by the presence of various substances dissolved in
the soil water. The writer has found that when .08 per
cent of potassium nitrate was added to distilled water,
which was being lifted by capillarity through columns of
rather coarse sand 18 inches long, the rate at which the
water passed up and away by evaporation exceeded that
with the pure distilled water by 22.84 per cent. The
presence of lime water, of common salt, and of sulphate
of lime or land plaster decreased the rate at which the
water was lifted and evaporated from the surface, whUe

178

The Soil

potassium carbonate did not appreciably affect the rate
of movement. A saturated solution of land plaster de-
creased the rise 27.36 per cent, while solutions of .08 per
cent of common salt and potassium carbonate decreased
the flow by 12.82 per cent and .Q^ per cent respectively.

Fig. 24. — Showing self-recording apparatus for registering fluctua-
tions of water in wells.

MOVEMENTS DUE TO SOIL AIR.

We have now to consider the movements of soil water
due to expansions and contractions of the soil air. When
a self-recording instrument similar to the one represented
in Pig. J24 is placed so that. its float is resting iii the

Movements Due to Soil Air.

179

water of a Well' or spring, or, if it is properly placed,, in
the water discharging from a system of tile drains, it
will be found that the water levels in all of these cases
are subject to numerous and sometimes very complex
movements. So, too, this instrument, suitably placed
upon small lakes, and even rivers, shows their surfaces
subject to oscillations of longer and shorter periods, many
of which are associated with changes in air pressure.
When the barometer falls, the water in wells rises, springs
and tile drains flow more rapidly ; but when the barom-
eter rises again, the level of the water in wells falls, and

Fig. 25. — Showing changes in the rate of discharge of water from a
tile drain coincident with those of barometric pressure. The
upper line represents the tile drain.

springs and tile drains flow less rapidly. In Fig. 25
will be seen the synchronous changes of the barometer
and of the flow of water from a tile drain as they oc-
curred during one week.

To understand how changes in the barometer can
affect the percolation of water into tile drains and into
the natural waterways, it must be observed that there
is always more or less air in the soil above the ground
water, and that this air cannot easily and quickly
escape, the soil offering resistance to its flow. Then,

180 The Soil,

when the air pressure outside becomes less, this
change is felt soonest at all natural openings to the
ground water, such as wells, springs, and tile drains, and
this lessening of the pressure at the outlets allows the
water to escape more easily, and at the same time the air
confined within the soil above the water table tends to
expand and thus exert a downward pressure upon the
water, tending to cause it to flow more rapidly and to
percolate into tile drains and the natural outlets which
lead to springs. But when the barometer rises again,
when the air pressure becomes higher, then, as before,
this pressure is felt first and strongest at places where
the ground water is most exposed, and as a consequence
some water is forced from wells back again into the soil
which surrounds it, and the rate at which the water can
emerge into tile drains and from the ground into springs
is diminished for the time. These barometric changes
have been observed to produce a change in the rate of
flow of water from a tile drain amounting to 15 per cent,
and in the case of a spring to 8 per cent.

Beginning in July and extending on through Septem-
ber, in Wisconsin, the surface of the ground water and
the rate of percolation into tile drains are subject to
diurnal oscillations in level and changes in the rate of
flow which owe their origin to the daily expansion and
contraction of air retained among the upper two to three
feet of soil grains. The changes of pressure thus de-
veloped react upon the capillary water of the soil in the
zone where the cavities are nearly or quite filled, forcing
the water down and out into drainage channels when the
air is expanding, but allowing such as has not been
permanently lost to return again to its normal level when
the pressure becomes less with the cooling and contraction

Fig. 26. — Showing diurnal changes of the ground water under condi-
tions represented in Fig. 27. The lower curve represents changes
in the inner well, and the upper one in the outer well.

182

The Soil.

of the soil air. In Fig. 26 are shown the diurnal changes
here referred to as they occurred under the conditions
represented in Fig. 27. It will be seen that the water

Fig. 27. — Showing the soil structure giving rise to the oscillations of
ground water represented in Fig. 26.

in the well rose and fell with great regularity each day,
and also with the slower changes of the barometer. The
-lowei- curve in this figure represents the changes in level

Movements Due to Soil Air. 183

as they occurred inside the H-incli tile curbing in the
centre of the main silt well, while the uy)per curve, where
the diurnal changes are so pronounced, represents the
changes in level as they occurred in the main well out-
side of the 5-inch tile curbing. The facts are, strange
as they may seem, that the water in the outer well os-
cillated during the period of 20 days covered by the chart
so as to stand, in the morning, from .1 to ..3 inch above
the level of the water in the inner one, and at night from
.5 to 1.5 inches below that surface. To understand these
movements, it must be observed that the well sunk in the
centre of the larger one furnished the easiest escape for
the water which was being lifted by the pressure of the
surrounding higher water table under the adjacent hills,
while vegetation in the vicinity of the well was using
the water faster than it could percolate through the walls
of the tile into the soil outside. On this account, and
on account of the contraction of the air due to cooling of
the soil, the water in the outer well fell each day, so as
to stand below the level of the water in the inner one.
But during the night, as the heat of the day was being
slowly conducted downward, its expansion of the soil
air forced out part of the water standing in the filled
capillary spaces, until the water in the outer well rose
from .1 to .3 inch above the water in the inner well.
So far as the writer has observed, these diurnal changes
due to temperature are not appreciable where the water
table is more than 10 feet below the surface of the
ground.

CHAPTER VI.

THE CONSERVATION OF SOIL MOISTURE.

To appreciate the need of conserving the soil moisture,
it is important to know the relation which exists between
the amount of rain received, and the possible loss of this
rain in ways which do not contribute to crop production.
Now, the waters which fall as rain upon a field may be
lost to it by running off its surface, as is too often the
case on hilly farms ; it may be lost by percolating down-
ward beyond the reach of root action ; or it may be lost
by surface evaporation from the ground itself. As a
rule, it is only that water which passes through the
plant which materially contributes to its growth. That
which evaporates from the surface of the soil does indi-
rectly help the plant by leaving the food it may have
held in solution nearer the surface of the ground, where
it is more likely to be taken up by the roots, and in
assisting that soil life which develops fertility.

NEED OF CONSERVING SOIL MtilSTURE,

We have no productive lands which, under field con-
ditions, can retain as much as 30 pounds of water to the
100 pounds of soil, unless they lie close to or below the
water table. In proof of this statement may be cited
the water content oi several field soils 32 hours after
a rain of 3.19 inches which fell during 4 days.

184

First Foot.

Pounds.

Second Foot,

Per cent.

Percu. ft.

Per cent.

38.91

26.79

26.60

28.88

26.67

26.45

28.75

26.45

27.06

ed 26.48

26.95

25.46

24.69

24.76

22.81

24.61

24.12*

21.44

17.65

18.00

15.81

17.66

18.00

14.59

Need of Conserving Soil Moisture. 185

These same fields had received 3.41 inches 20 days
earlier, and during ihe intervening 20 days there had
been a rainfall of 1.3 inches.

No. 1, Clay soil contained

No. 2, Clay loam "

No. 3, Clay loam "

No. 4, Sandy clay loam contained 26.48

No. 6, " " "

No. 6, " " • "

No. 7, Sandy loam

No. 8, " "

In these cases the clay soil will weigh about 79 pounds
per cubic foot, the clay loams 92 pounds, the sandy clay
loams not more than 98 pounds, and the sandy loams
about 102 pounds per cubic foot, so that the amounts of
water retained in the surface foot in the several cases
were as given in the table above.

It will be safe to say that those lands which can
retain, in the upper five feet of soil, as much as 20 inches
of water are very rare indeed. Then, were there no loss
by surface evaporation nor by percolation downward, not
more than 10 inches out of the supposed 20 inches of the
stored water could be counted as available to a crop
growing on the ground where large yields are expected;
and it has been said that for lands to do their best, their
water content should be steadily held up to from 40 to
50 per cent of saturation, and Hellriegel says 50 to 60
per cent.

In stating the rate of capillary movement of water in
field soils, as measured by surface evaporation, we have
seen that the daily losses may be as high as 1.3 to 1.6

186 . The Soil

pounds per square foot. On well-tilled, fallow ground,
too, we have observed a mean loss of water amounting to
.67 pounds per square foot, during a period of 64 sum-
mer days, which is equivalent to 8.24 inches. If we
take the average daily loss from the soil at only .25
pounds per square foot, from May 1 to Sept. 1, this
would be equivalent to 5.77 inches of rain, and deduct-
ing this from a mean rainfall of 12 inches for the same
period, we should have left 6.23 inches for the use of a
field crop, which, added to the 10 inches we have sup-
posed might be withdrawn from that stored in the upper
five feet of soil, gives a total for crop production of 16.23
inches.

Were it possible to have 16 inches of water to the acre
for crop production, over and above losses by percolation
and evaporation from the soil surface, large yields, so
far as water contributes to them, would be certain, —
yields amounting to from 3.5 to 7 tons of dry matter to
the acre. In our experiments, where we have attempted
to measure the water used in the production of a ton of
dry matter, our smallest yield has been at the rate of 4
tons, and our largest at the rate of 17 tons, with an
average for 22 cases of over 7 tons of dry matter per
acre. In all of these trials, however, whether with
oats, barley, corn, peas, clover, or potatoes, water was
so added to the soil, from time to time, as to maintain
for it a constant saturation of 40 to 50 per cent. Now,
since ordinarily fertile lands, when well watered, will
yield such large returns, and since it is seldom true that
16 inches of water are available for the use of crops
under natural conditions, it follows that by whatever
means we can diminish the loss of water from the soil,
or render a larger per cent of it available to the c^-ops

Saving Soil Moisture hy Plowing. 187

growing upon it, their adoption may reasonably be
expected to give larger yields. Wliat, then, may be done
to conserve soil moisture?

SAVING SOIL MOISTURE BY PLOWING.

Plowing land in the fall has a very appreciable influ-
ence on the per cent of water the surface three or four
feet of such soil may contain tlie following spring, and
the writer has observed a mean difference of 2.31 per
cent more water in the upper three feet of immediately
adjacent lands plowed late in the fall, as compared
with that not plowed, the surface of neither having been
disturbed until May 14. The larger quantity of water in
the fall-plowed ground, in this case amounting to not
less than 6 pounds to the square foot, was due partly to
two causes; namely, the loose, open character of the
overturned soil, causing it to act as a mulch during the
fall, and again in the spring, after the snows had disap-
peared; and the more uneven surface, which tended to
permit more of the melting snow and early spring rains
to percolate into the soil.

Late fall plowing, leaving the surface uneven and
the furrows in such a direction as to diminish washing,
works in a decided manner, on rolling land, to hold the
winter snows and rains where they fall, giving to such
fields a more even distribution of soil water in the spring.
And when it is observed that heavy lands, after a dry
season, seldom become fully saturated with water during
the winter and spring, the importance of fall plowing
in such cases can be appreciated.

From the standpoint of large crops, which result from
the best use of the soil moisture, there is no one thing

188 The Soil.

more important for a farmer to strive for than the earli-
est possible stirring of the soil in the spring, after it
has sufficiently dried so as not to suffer in texture from
puddling. When the soil is wet, when its texture is
close from the packing which has resulted from the
winter snows and early spring rains, the loss of water is
very rapid, as has been pointed out ; it may be more than
20 tons daily per acre, and this loss may extend to depths
exceeding four feet.

We must give here the details of an experiment aim-
ing to measure the influence of early spring plowing
on the loss of water from the soil, some of the results
of which have already been referred to.

On April 28, a piece of corn ground was plowed and
sowed to oats, and on the next day samples of soil were
taken, in one-foot sections, down to a depth of four feet.
Seven days later samples of soil were again taken, and
below are given the percentages of water as they were
found on the two dates.

1st Foot. 2d Foot. 3d Foot. 4th Foot.
Per cent. Per cent. Per cent. Per cent.

Water in soil April 29 20.13 22.61 20.51 17.72
Water in soil May 6 19.86 23.24 20.86 17.17

Difference, -.27 +.63 +.35 -.55

It is thus seen that there had been little change in
the water content of the soil during the week, the
capillary movement upward nearly keeping pace with
the loss by surface evaporation. Adjoining this piece
and separated from it by a strip of grass only 10 feet
wide, lay another piece of ground which was not plowed
until May 6, and on this date, before plowing, samples
of soil were taken from it in the manner already de-

Saving Soil Moisture by Plowing. 180

scribed, and below are given the amount of water which
this unplowed land contained, and with these, for com-
parison, the amounts which were found in the piece
which had been plowed seven days earlier.

1st Foot.

2d Foot.

3d Foot.

4Tn Foot.

Lbs. Water.

Lbs. Water.

Lbs. Water.

Lbs. Wator.

Land plowed

13.87

20.66

18.32

16.05

Land not plowed

10.58
3.29

17.98

17.28

13.94

Loss

2.68

1.05

2.11

It is thus seen that the unplowed ground had lost,
during the seven days, in consequence of not having been
plowed, not less than 9.13 pounds of water per square
foot more than the plowed ground had, an amount
equivalent to 1.75 inches of rain, and more than 198 tons
of water per acre ; and it should be said in this connection
that there can be no reasonable doubt but that the actual
loss was greater than this, because there must have been,
during all this time, a movement of water upward from
below the level at which the samples were taken into
the four feet above, and whatever this movement may
have been, it by so much diminished the observed losses.

There was another very serious result which followed
this delay in plowing, for there were developed in the
unplowed ground, as a consequence of the rapid loss of
water from the soil, great numbers of very large and
hard clods. So that, instead of having this piece of land
in excellent tilth with plowing and once harrowing, it
became necessary to go over the ground twice with a
loaded harrow, twice with a disk harrow, and twice with
a heavy roller, before it was brought into a condition of
tilth even approximating what it might have had had it
been plowed seven days earlier.

190 The Soil.

It follows from, these observations that all lands, with,
but few exceptions, should he tilled at as early a date
in the spring as their condition of moisture will permit,
and not simply to save the all-important soil moisture
and the formation of clods, but for other and very weighty
reasons which will be stated in another place.

EARLY SEEDING AND CATCH CROPS.

The farmer who gets his crop to growing upon the
ground at as early a date as the temperature of the air
and of the soil will permit, is conserving soil moisture
in still another way ; for so soon as a crop gets possession
of the land, so soon does it begin to use the water which
is certainly running to waste upward, and possibly also
downward; and more than this, the farmer who fails to
give his crop possession of the land as soon as the
season will permit, fails to get full advantage from the
sheltering of the ground by the plants, and the dimin-
ished surface evaporation which results from the drying
action of the crop. On all soils which do not have a
strong tendency to run together after heavy rains, as a
consequence of working, early surface tillage may often
be adopted with great advantage even when the crops,
like corn and potatoes, are not to be put in until late;
a richer seed bed in better tilth, with more moisture and
fewer weeds, being among the gains.

Where fields are naked through the winter, there is
necessarily a large waste of moisture from the melt-
ing snows and earliest spring rains, which is often
worse than a dead loss, because, so far as these waters
drain away downward, they carry, with them, and often
beyond recovery, considerable amounts of nitrates and

Early Seeding and Catch Crops. 191

other valuable soluble and immediately available forms
of plant food. Now, it is a matter worthy of serious
consideration in studying this problem of conservation
of soil moisture, whether it is not best in most cases of
fall plowing to have some catch crop on the ground for
the express purpose of utilizing the excess of moisture in
the spring, which must be allowed to drain away or to
evaporate before the ground is in condition to work.
With the catch crop, the ground is dried earlier, and
the moisture turned to account in preventing loss of fer-
tility by drainage.

In the use of catch crops for this purpose, as in all
cases of green-manuring, great judgment must always be
exercised in order not to allow them to remain so long
upon the ground as to so thoroughly exhaust the stock
of soil moisture that the main crop is placed at a disad-
vantage on this account. In illustration of this danger,
and as serving to enforce the great importance of keep-
ing all fields free from weeds, an observation on the dry-
ing effect of clover will be instructive.

On May 13, the water content of soil m a field just
planted to corn, and in a field of clover adjacent to it,
was determined, the two sets of samples being taken
within less than two rods of each other. The differ-
ences in the amount of water in the two cases were as
given below.

1 TO 6 Inches. 12 to 18 Inches. 18 to 24 iNcusa.
Per cent. Per cent. Per cent.

Corn ground 23.33 19.13 16.85

Clover ground 9.59 14.75 13.75

Difference 13.74 4.38 3.10

We have here a very forcible illustration of the danger
of using catch crops, and of the evil consequences of

192 The Soil

allowing a field, when occupied with another crop, to
become encumbered with weeds. In the case of the
weeds, the soil is not only robbed of its moisture, but
soluble plant food is also locked up in the tissues of the
weed, in a form in which it is not immediately available.
Had the clover field been plowed a week earlier than
the samples were taken, it is quite likely that even then
so much moisture had already been used that not enough
remained to quickly decompose the material turned
under, and at the same time meet the needs of the crop
put upon the ground.

In plowing under coarse herbage, too, when the soil
has a scanty supply of moisture, it is very difficult to
establish such a capillary connection with the soil
below as will allow a sufficient amount of water to rise
into the overturned portion to start and properly feed a
crop.

CULTIVATING AKD HARROWING.

In the conservation of soil moisture by tillage, there
is no way of developing a mulch more effective than that
which is produced by a tool working in the manner of
the plow, to completely remove a layer of soil and lay
it down again, bottom up, in a loose, open condition.
The harrow, when it scratches or cuts the surface of a
field, without completely covering it with a layer of
loose crumbs, hastens rather than retards the loss of
moisture from the soil. So, too, when a tool is used
which plows deep and wide grooves, leaving untouched
and only partly covered ridges between them, it increases
instead of lessening the rate of evaporation. That most

Cultivating and Harrowing. 193

excellent tool, the disk harrow, may be used so as either
to hasten or check the loss of moisture from the soil,
according as its disks are set at a very small or a large
angle. In one trial, the writer increased the rate of
evaporation from the surface of a 12-inch cylinder of
soil from .75 pounds per square foot in 24 liours to 1.38
pounds in the same time by simply making vertical cross-
cuts in the surface with a sharp knife; but when a whole
layer was removed in the fashion of the plow, and
replaced in the loose condition, the rate of loss was then
reduced to .5 pounds. When a strip of land is culti-
vated to a depth of 3 inches frequently during a whole
season, while an adjacent strip is left smooth and
unstirred, both pieces being fallow and kept free from
weeds, the difference in the amount of moisture in the
soil becomes very appreciable. In a test of this sort,
where the amount of water in the soil was determined
in one-foot sections to a depth of 6 feet, the mean daily
loss per acre was at the rate of 14.48 tons on the culti-
vated ground, and 17.6 tons on the ground not cultivated,
and these amounts are over and above what may have
been brought up into the 6 feet by capillary action from
below, and are the averages for 49 days. This repre-
sents a saving of water in that time equivalent to 1.7
inches of rainfall.

When stirring the soil to a depth of 3 inches is com-
pared with that of 1 to 1.5 inches, the 3-inch mulch is
decidedly more effective, so far as its conserving soil
moisture is concerned. Through extended and repeated
field trials, on different soils and in different seasons,
the writer has found that invariably there is left at the
end of the season a larger amount of water in the soil
where it is stirred to a depth of 3 inches than when

194

The Soil

stirred to a depth less than this amount- The observed
differences in a field of corn for one season are given
below.

1st Foot.
Per cent.

2d Foot.
Per cent.

3d Foot.
Per cent.

4th Foot.
Per cent.

Cultivated 3 inches deep
Cultivated 1 inch deep .

23.14

22.70

23.30
21.08

21.94
19.65

22.46
19.58

Difference . . .

.44

2.22

2.29

2.88

These differences at the end of the growing season,
represent 167.4 tons more water per acre in favor of the
deeper mulch.

SOIL MULCHES.

When the effectiveness of very thin soil mulches is
measvired, it is found that here, too, the lessening of the
rate of evaporation may be very considerable. Thus
it was found, by laboratory methods, that when the
evaporation from an unstirred surface was at the rate of
6.24 tons per acre daily, from the same surface, when
stirred to a depth of .5 inch and .75 inch, the loss
was only 5.73 tons and 4.52 tons respectively. Again,
when the surfaces were covered with a fine, dry clay
loam to a depth of .5 inch and .75 inch, the daily loss
was then at the rate of 6.33 tons per acre per day for
the naked surface, but only 4.54 tons and 2.4 tons for the
mulches, respectively. ■ '

There is thus left no room to doubt the efficacy of dry
earth mulches as conservators of soil moisture, but it

Translocation of Soil Moisture. 195

should be said that not all soils are equally effective in
their power. to diminish evaporation.

The writer has found that, taking the evaporation
throupfh a mulch of 2 inches of dry quartz sand, which
passes a screen of 20 meshes, but is retained by one of
40 meshes to the inch, as 1, the rate of evaporation
through the same depth of finely pulverized, air-dry clay
loam was 3.5 times more rapid ; the latter giving, in the
still air of the laboratory, a loss of 3.474 inches in depth
per 100 days, while the loss through the sand was .995
inch in the same time. This difference in the effective-
ness of the two soils to act as mulches depends appar-
ently upon the difference in their capillary power, the
fine soil with its small pores, even when air-dry, lifting
the water faster than the sand.

It is to be observed, further, that the mulching effect
of a soil decreases with time, the capillary power becom-
ing stronger as the per cent of water in the mulch
increases. Experiments showed that the coarse sand
referred to above, which had been allowing water to pass
through it during 30 days at the mean rate of .027 inch,
decreased the rate to .0099 inch when a fresh mulch
was substituted. So, too, in the case of the fine clay the
rate of evaporation decreased from a mean daily loss of
.071 inch to .034 inch when the old mulch was re-
placed by the fresh. It follows, therefore, that to main-
tain the most effective mulches in the field requires
frequent stirring, even though a rain may not have
occurred to pack the soil.

TRANSLOCATION OF SOIL MOISTURE.

When a surface soil has its water content reduced, so
that the upper 6 to 12 inches is beginning to be dry, the

196 The Soil.

rate of capillary rise of water through it is decreased and
it begins to assume the properties of a mulch. But
when this condition has been reached, if a rain increases
the thickness of the water film on the soil grains with-
out causing percolation, the capillary flow may be so
strengthened that the surface foot draws upon the deeper
soil moisture at a more rapid rate than before, causing a
translocation of the lower soil moisture, the deeper soil
becoming measurably drier soon after such a rain than it
was before it, while the surface foot is found to contain
more water than has fallen upon it.

The following experiment may be cited in proof of
this important principle. At 5.30 p.m. samples of soil
were taken on a piece of fallow ground in one-foot sec-
tions to a depth of four feet. Water was then applied
to this surface at the rate of 1.33 pounds per square foot.
Samples of soil were also taken adjacent to this wetted
area to serve as a control experiment, and 19 hours later
corresponding sets of samples were again taken with the
results stated below.

POUNDS OF WATER PER CUBIC FEET OF WET AREA.

IsT Foot. 2d Foot. 3d Foot. 4th Foot.
Before wetting 11.78 15.79 14.73 14.03

After wetting 14.06 17.52 15.58 15.40

Gain 2.28 1.73 .85 1.43

POUNDS OF WATER PER CUBIC FOOT OF AREA NOT WET

1st Foot. 2d Foot. 3d Foot. 4th Foot.
First samples 12.38 17.05 14.92 14.48
Second samples 12.75 17.72 15.40 14.17
Gain .37 .67 .48 -.31

Now, it will be seen from these results that the water
content of the soil increased on both areas, but at the

Translocation of Soil Moisture. 197

rate of 6.23 pounds per square foot on the wet area,
and 1.21 pounds on the area not wet. The 19 liours
which intervened between the taking of the two sets of
samples was a period of very little evaporation, most of
it being in the night, and the following morning was
cloudy and very damp, and the result was that capil-
larity gave to the area not wet 1.21 pounds more water
per square foot than it lost by evaporation. But the wet
area had gained 6.23 pounds, and yet only 1.33 pounds
had been added to the surface, making the increase by
capillarity

6.23 - 1.33 = 4.90 lbs.

and if we subtract from this the amount which the con-
trol area gained, we shall have 3.69 pounds as the water
of translocation due to the wetting of the surface.

This is not an isolated observation ; for the experiment
was twice repeated, and the fact had been several time£
observed in the field when taking samples of soil just
before and again immediately after rains, these observa-
tions leading to making the experiments.

Now, when it is recognized that rains which do not
cause percolation tend to strengthen the flow of the
deeper soil water toward the surface, while they have at
the same time greatly diminished the power of this soil
to act as a mulch, it should be very evident that, at criti-
cal times like these, no time should be lost in developing
a new mulch which shall retain in the upper soil, not
simply the rain which has fallen, but the moisture it has
caused to be brought up from below; for if this is not
done, the ground as a whole will have become drier in a
few days than it would have been had no rain fallen.

198 The Soil

It will often happen in farm practice, after a field of
corn or of potatoes has been laid by in perfect condition,
so far as being free from weeds and in possessing a good
mulch are concerned, that a rain may come, making it
advisable to cultivate the field once more in order to
restore the mulch, and to retain the water which trans-
location has brought up within the reach of root action.

It will be evident also that when watering transplanted
trees or other plants, during a dry time,_care should be
taken to add water enough to produce percolation, and
then to protect the wet surface with some sort of mulch ;
for unless this is done, the chances are that more harm
than good will result. It is evident, too, from what has
been said regarding mulches, that transplanted trees
should be early protected by an ample mulch and by
keeping the ground above and near the roots entirely free
from grass and weeds, whose power to withdraw water
from a dry soil far exceeds that of the pruned and muti-
lated roots of transplanted trees.

There is another effect resulting from the transloca-
tion of soil moisture, as influenced by cultivation and
the use of mulches in other ways, which is very impor-
tant in the saving and utilization of the water deep in
the ground. It is in the upper 18 inches of soil that
the nitrates are developed through the processes of
nitrification, and it is from here, too, that plants must
obtain them. To the upper soil also other fertilizers are
applied, and from it these must be removed, and it can
only be done when water enough is present to allow the
processes of diffusion to be carried forward.

Now, keeping the upper 18 inches of soil sufficiently
moist enables the process of translocation to bring into
use a larger amount of the water deep in the ground;

Translocation of Soil Moisture^

199

that is, to lift it into the zone of soil near the surface,
where, through a more plentiful supply of air, carbon
dioxide and the presence of micro-organisms, it is far
more serviceable in preparing and giving to the plant
the food it needs than it could be if absorbed by the
roots at a lower level in the ground.

That a sufficiently deep mulch, prepared by cultivation,
does act in this manner is proved by the observed dis-
tribution of water in the soil when cultivated deep and
shallow and when cultivated and left unstirred. In
both of these classes of cases the writer has repeatedly
observed at a certain stage in the drying of field soils
that, while the surface two or three feet of the better
mulched soil will contain more water than the corre-
sponding layer of the unmulched or poorly mulched soil,
the third and fourth or the fifth and sixth feet may be
wetter beneath, where the surface has been least protected.

On three different fields of corn, with as many different
kinds of soil, where the ground was cultivated 3 inches
and 1.5 inches deep respectively, the writer found on
July 16, 1894, the following distribution of soil moisture.

1st Foot.
Per cent.

2d Foot.
Per cent.

3d Foot.
Per cent.

4th Foot.
Per cent.

No. 1, cultivated 3 in
No. 1, " 1.5

ches

u

ii

li

u

11.30
9.92

15.57
15.43

10.54
11.56

11.37
13.99

Difference,

No. 2, cultivated 3
No. 2, " 1.5

-1-1.38
13.96
12.98

+ .14

22.74
20.44

-1.02

23.39
24.02

-1.62

19.47
21.34

Difference,

No. 3, cultivated 3
No. 3, " 1.5

+ .98

11.65
10.65

+2.30

17.47
16.85

-.63

■ 16.44
17.81

-1.87
13.03
13.32

Difference,

+ 1.00

+ .62

-1.37

-.29

200 The Soil.

Differences similar to these were obtained in cornfields
in 1893 and also on fallow ground, where the rates of
evaporation on cultivated and uncultivated soil were
compared, and that these differences are effective in crop
production is borne out by the fact that in fifteen trials
out of twenty the yield of corn was larger on land culti-
vated 3 inches deep than it was on land cultivated only
1.5 inches deep. The facts appear to be that wherever
we can succeed in holding the per cent of water relatively
high in the surface two feet, a larger per cent of the
water in the next four feet at least becomes available
and is actually brought nearer the surface, where it has
the highest value in crop production ; and then, if what
has been said is true, it follows that less water and less
fertility are lost by percolation.

EFFECT OF ROLLING ON SOIL MOISTURE.

It used to be generally believed by farmers, and per.
haps the majority of them still have the impression,
that firming the surface of the ground, as with the roller
or with the wheels of the press drill, increases the water
content of the soil ; and that this belief should have
been so generally entertained is what would be expected
from the very evident fact that firming the surface of
the ground does, for the time, increase the amount of
water in the compacted portion.

When, however, the changes in the water content of
the surface four feet of soil which follow the use of a
heavy roller are studied, it is found that we have here
another case of the translocation of soil moisture ; a
case where, by destroying the many large non-capillary
pores in the soil and bringing its grains more closely

Effect of Rolling on Soil Moisture, 201

togetlier, its water-lifting power is increased and to such
an extent that often within 24 hours after rolling, the
upper one or two feet of the firmed ground have come to
contain more moisture than similar and immediately
adjacent land does at the same level, while the lower
two feet have become drier. Water has been lifted from
the lower into the upper soil.

In the table below will be seen the difference in the
water content of the soils which have been rolled, and
immediately adjacent ones not so treated. These results
are averages derived from 147 pairs of samples.

Surface 36 to 54 inches, unrolled 19.43 per cent."
" 36 to 54 " rolled 18.72 '' "

difference

-.71

((

24

((

unrolled

19.85

((

24

u

rolled
difference

19.49
-.36

((

2 to 18

((

unrolled

15.64

((

2 to 18

u

rolled

15.85

difference + .21 " "

It is here seen that when samples are taken to a depth
exceeding two feet, the rolled ground as a whole is drier
than that not rolled, and that this difference is greater
when the samples are taken to depths of from three to
four or more feet. The data presented also show that
the surface 2 to 18 inches of loose ground recently firmed
contains more water than that which has not been so
treated.

While firming loose soil tends, therefore, at first, to
increase the moisture in the surface soil at the expense of
the deeper layers, the whole ground soon comes to con-
tain less, on account of an increased rate of evaporation.

202 The Soil,

. It. is not simply because the water is brought to the
surface by firming that a more rapid loss of water takes
place after rolling, but making the ground very smooth
increases the wind velocity close to the surface, and to
such an extent that it may exceed that on the unrolled
ground by more than 70 per cent. It is plain, therefore,
that whenever it becomes desirable to firm the surface
for the purpose of increasing the amount of water in it,
a light harrow should follow the roller in order to restore
a thin mulch which shall retain the water brought up
by the firming ; for unless it is done, only a temporary
advantage is derived from it.

It sometimes occurs, after sowing spring grain, that
heavy rains develop a crust, which diminishes the poros-
ity of the soil beyond what is most desirable. When
this has taken place, and if the surface is uneven, owing
to harrow ridges and numerous lumps, then, by using the
roller when the ground is dry, the crust and the lumps
may be crushed and a partial mulch formed, while at
the same time the porosity of the surface will be to
some extent restored.

DEEP TILLAGE AND LEVEL CULTURE.

In the conservation of rains in regions where they are
scanty and where surface evaporation is very rapid, it
may sometimes be desirable to work the soil unusually
deep in order to insure a deeper percolation of water
into the ground and a slower return of it to the surface.
Deep working, through the formation of numerous non-
capillary spaces, increases the rate of percolation and at
the same time decreases the capillary return to the sur-
face J so that in climates where so little water falls that

Deep Tilla(/e and Level Culture, 203

only a small amount ever drains away, methods of tillage
may be desirable which in humid regions would not be
prudent. In regions of large rainfall, at times when
fields are not bearing crops, the great danger lies in the
loss of fertility through excessive percolation ; so that in
such countries and at such times a rapid evaporation of
soil moisture is to be encouraged.

Ample root room is a very necessary condition for the
largest utilization of soil moisture. When, for any rea-
son, the roots of plants are forced to develop close to or
near the surface of the ground, as is the case when a
tield is insufficiently underdrained, then, as the plants
approach the fruiting stage and begin to use water very
rapidly, the zone of soil in which the roots lie is so
rapidly depleted of its moisture that capillarity is unable
to prevent it from becoming dry, and the result is that
a large amount of moisture near at hand becomes unavail-
able, when, if the water table in the early part of the
season had occupied a lower level, the roots would have
developed more deeply, and they could have come into near
contact with a larger volume of soil and of water. Then
by taking water at a relatively slower rate and from a
greater depth, a strong capillary flow upward is longer
maintained and from lower levels in the ground, so that a
much larger amount of the soil moisture becomes available.

Then, too, those methods of tillage which leave the
surface of the field nearly flat rather than thrown up
into ridges and hills are less wasteful of soil moisture.
To hill potatoes or corn to a height of 6 inches when the
rows are 3 feet apart may increase the surface ex-
posed to the sun and evaporation more than 5 per cent,
and if ridged to a height of 9 inches more than 9 per
cent. Under these conditions the water must rise to a

204 The Soil

greater height under the rows before reaching the sur-
face roots, while midway between them and where the
ground is least shaded, the unmulched surface lies near-
est the water supply. These being the conditions, ridge
culture must be more wasteful of soil water than level
tillage, whence it becomes evident that naturally dry
soils everywhere, and most soils in dry climates, should,
wherever practicable, be given flat cultivation.

On stiff, heavy soils in wet climates and during wet
seasons it may become desirable to practice ridge culture
with potatoes and some of the root crops, but not so
much to increase the rate of evaporation from the soil
as to provide a soil bed in which it will be less difiicult
for fleshy tubers and roots which form beneath the sur-
face to expand. A clay soil, after having been thor-
oughly wet and then allowed to dry, shrinks into so
firm a mass that it is very difficult for potatoes to ex-
pand in it; and under these conditions they tend to
form at or above the surface. Hilling in such cases is
very beneficial, although more wasteful of soil moisture.

DESTRUCTIVE EFFECT OF WINDS.

In arid or semiarid countries and in districts where
the soil is light and leachy, but especially where there
are large tracts of land whose incoherent soils suffer
from the drifting action of winds, it is important that
the velocity of the winds near the ground should be
reduced to the minimum. We have in Wisconsin exten-
sive areas of light lands which are now being developed
for purposes of potato culture ; but while these lands are
^ving fair yields of potatoes of good quality, they are
in many places suffering great injury from the destructive

•A

Destructive Effect of Winds. 205

effects of winds. On these lands, wherever broad, open
fields lie unprotected by windbreaks of any sort, the
clearing west and northwest winds after storms often
sweep entirely away crops of grain after they are 4
inches high, uncovering the roots by the removal of
from 1 to o inches of the surface soil. It has been
observed, however, that such slight barriers as fences
and even fields of grass afford a marked protection
against drifting for several hundred feet to the leeward
of them.

In the case of groves, hedgerows, and fields of grass,
their protection results partly through their tendency
to render the air which passes across them cooler and
more moist, and partly by diminishing the surface veloc-
ity of the wind. The writer has observed that when the
rate of evaporation at 20, 40, and 60 feet to the leeward
of a grove of black oak 15 to 20 feet high was 11.5 cc,
11.6 cc, and 11.9 cc, respectively, from a wet surface of
27 square inches, it was 14.5, 14.2, and 14.7 at 280, 300,
and 320 feet distance, or 24 per cent greater at the three
outer stations than at the nearer ones. So, too, a scanty
hedgerow produced observed differences in the rate of
evaporation, as follows, during an interval of one hour : —

At 20 feet from the hedgerow the evaporation was 10.3 cc.
At 150 " " " " " " " 12.5 cc.

At 300 " " " " " " " 13.4 cc.

Here the drying effect of the wind at 300 feet was 30
per cent greater than at 20 feet, and 7 per cent greater
than at 150 feet from the hedge.

When the air came across a clover field 780 feet wide,
the observed rates of evaporation were, —

206 The Soil

• : • \- '• .• At 20 feet from clover, 9.3 cc. . ...

'At 150 " " " 12.1 cc.

At 300 " " " 13.0 cc.

or 40 per cent greater at 300 feet away than at 20 feet,
and 7.4 per cent greater than at 150 feet.

The protective influence of grass lands and the dis-
advantage of very broad fields of these light soils was
further shown by the increasingly poorer stand of young
clover as the eastern margin of these fields was ap-
proached, even on fields where the drifting had been
inappreciable. Below are given the number of clover
plants per equal areas on three different farms, as the dis-
tance to the eastward of grass fields increased : —

No. 1, at 50 feet, 574 plants ; at 200 feet, 390 plants ; at 400 feet,
231 plants.

No. 2, at 100 feet, 249 plants ; at 200 feet, 277 plants ; at 400
feet, 193 plants ; at 600 feet, 189 plants ; at 800 feet, 138 plants ;
at 1000 feet, 48 plants.

No. 3, at 50 feet, 1130 plants ; at 400 feet, 600 plants ; at 700
feet, 543 plants.

In these cases the difference in stand appears to have
resulted from an increasing drying action of the wind.
On the majority of fields the destructive effects of the
winds were very evident to the eye, and augmented as
the distance from the windbreaks increased.

It appears from these observations, and from the pro-
tection against drifting which is afforded by grass fields,
hedgerows, and groves, that a system of rotation should
be followed on such lands, which avoids broad, continuous
fields. The fields should be laid out in narrow lands and
alternate ones kept in clover and grass. Windbreaks of
suitable trees must also have a beneficial effect when
maintained in narrow belts along line fences and rail-
roads and perhaps wagon roads, in places.

CHAPTER VTT.

THE DISTRIBUTION OF ROOTS IN THE SOIL.

When we look at the liabit of growth among higher
plants, it is to be noted that, excepting a few very consoli-
dated forms of vegetation like the cacti, whose natural
habitat is in arid or semiarid regions, plants spread out in
the air and in the soil two very broad surfaces joined by
a relatively narrow and rigid stem. The roots, branching
in the ground, dividing and subdividing until numberless
root hairs have threaded themselves through the capil-
lary spaces among the soil grains, are there to gather
water, nitrogen, and ash ingredients for growth. So large
is the quantity of water demanded by plants, so small is
the amount of water within a small area of soil, and so
slow is the method by which the roots obtain it, that
nothing short of an enormous root surface could do the
work, and how great this surface really is may be par-
tially appreciated from the photo-engraving of the roots
of corn, clover, oats, and barley shown in Fig. 2S. These
roots were obtained by growing the plants in a deep cylin-
der holding between '500 and 600 pounds of earth and
then, at maturity, carefully washing the soil away with
a fine stream of water.

THE NEED AND GREAT EXTENT OF ROOT SURFACE.

That we may the more clearly appreciate the great
need there is for the vast extent of root surface spread

207

208

The Soil,

out by agricultural crops, and how important it is that
there shall be a deep, well-drained, and well-tilled soil
in which they may expand, let me give the measured
amounts of water used by four stalks of corn and with-
drawn by their roots from the soil between July 29 and
August 11. Two stalks of maize were growing in each of

Fig. 28. — Showing the total root of four stalks of maize, and of oats,

clover, and barley.

two cylinders filled with soil, having a depth of 42 and a
diameter of 18 inches. These four stalks of corn, as they
were coming into tassel and their ears were forming, used
during 13 days 150.6 pounds of water, or at the mean
daily rate of 2.896 pounds for each stalk. Had an acre
of ground been planted to corn in rows 3 feet 8 inches
each way and four stalks in a hill, then, with an average

Need and Great Extent of Root Surface. 209

consumption of water at the observed rate given above,
there would have been withdrawn from that acre an
amount of water during those 13 days equal to 244 tons
or 2.42 acre-inches ; and when it is observed that this
must be withdrawn from a soil so dry that no amount of
pressure could express from it a drop of water, it is not

Fig. 29. — Showing the natural distribution of coru roots in a tield soil
under natural conditions.

strange that a mass of roots like those shown in Fig. 28
should be required to do the work with sufficient rapidity.
Referring now to Fig. 29, it will be seen how completely
the whole soil of the field is threaded with roots ; for in
both cases two hills of corn, standing opposite each other
in adjacent rows, are shown and the roots meet and pass
one another between the hills, and in the younger stage

210 The Soil

these had already exceeded a depth of two feet, while in
the second case, taken just as the corn was coming into
tassel, the roots had descended until at this time the
whole upper three feet of the field soil appeared to
be so fully occupied with corn roots that not a cube of
earth one inch on a side existed in the three feet of depth
which was not penetrated b}'' more than one fibre of
thread-like size. In many portions of the soil the roots
were mucli closer than this, and the minute root hairs
which branch out from the thread-like fibres referred to,
and which constitute the chief absorbing surfaces of the
roots, are not included in making this statement of root
occupancy.

At the distance apart of planting in the field from
which these roots were taken, there were in the surface
three feet 401 cubic feet of soil available for each four
stalks, so by multiplying the 1728 cubic inches in one
cubic foot by 40i-, the number of cubic feet of soil occu-
pied, we get a total of 69,696 cubic inches. If, then, each
cubic inch of this soil contains not less than one linear
inch of thread-like root, their aggregate length could not
be less than one-twelfth of 69,696, or 5808 feet, which is
just 1.1 miles.

Let the reader keep in mind that the corn roots here
under consideration grew in the field under perfectly
natural conditions, and that the cage of wire shown in
the engraving was simply slipped over the block of soil
which contained the roots there shown, after the corn had
reached the stage of maturity represented in the figure.
It should also be understood that the four stalks of corn
which drank the 150.6 pounds of water in 13 days,
did it at the stage of growth represented by the oldest
plants in T'ig. 29 ; and, further, that these stalks were

NeeAl and Great Krterit of Ilool Surf (ire. 211

only good average i)lants, such .'is would make a yield of
4.5 tons of dry matter per acre.

Is this not a sublime expression of one of nature's
nu^thods of utilizing all her oi)portunities and making
the most out of whatever is at hand ? The rocks liad
fallen into decay, the sun warmed the bed of incoherent
fragments, the winds liad brought the rains, ca])illarity
had retained a portion of them on the surfaces of the
soil grains, tlie forces of solution had charged these
waters with plant food, but roots w^ere needed by whicli
plants could utilize these resources. As man, standing
on the bank of the stream and looking for means to
better his condition, was led to jmt his wheel into the
water and withdraw some of the energy running by un-
used, so have plants, during the long ages of fitting and
refitting, learned to build into the capillary and percola-
tion streams which flow past the grains of soil such
wonderful systems of absorbing surfaces as we have
seen that greatest of American food plants, tlie maize,
to possess, and of which America's most revered poet
wrote, in 1855 : —

Day by day did Hiawatha
Go to wait and watch beside it ;
Kept the dark mold soft above it,
Kept it clean from weeds and insects,

Till at length a small green feather
From the earth shot slowly upward,
Then another and another,
And before the summer ended
Stood the maize in all its beauty,
With its sliining robes above it,
And its long soft yellow tresses ;

212 The Soil,

And in rapture Hiawatha
Cried aloud, " It is Mondamin !
Yes, the friend of man, Mondamin ! "
Then he called to old Nokomis
And lagoo, the great boaster,
. Showed them where the maize was growing,
Told them of his wondrous vision,
Of his wrestling and his triumph,
Of this new gift to the nations,
Which should be their food forever.
And still later, when the Autumn
Changed the long green leaves to yellow,
And the soft and juicy kernels
Grew like wampum hard and yellow,
Then the ripened ears he gathered,
Stripped the withered husks from off them,
As he once had stripped the wrestler,
Gave the first feast of Mondamin,
And made known unto the people
This new gift of the Great Spirit.

Looking at Fig. 30, which shows the roots of winter
wheat, barley, oats, blue grass, timothy, clover, and
another leguminous plant, Lathyrus sylvestris, it will
be observed that with these plants, all except the blue
grass send their roots into the fourth foot of soil, and
in these cases, as with the corn, there is no portion of
soil in the upper three or four feet which a root can
penetrate that is not threaded by roots much closer to-
gether than one in every cubic inch. Not all of the roots
belonging to the tops shown in the figure just referred
to were retained, but simply those which grew vertically-
downward within the area of a circle 12 inches in
diameter.

How great may be the mass of roots associated with
the tops of clover, oats, and barley, is clearly shown in

Need and Grreal Extent of Root Surface. 21 o

Fig. 28, where the total root system of these plants was
recovered from the soil in which they grew. It is very
probable that, had the cylinders been deeper in which
these plants were grown, their roots would have attained
a greater length, and this would certainly have been the

Fig. 30, — Showing the vertical distribution, under field conditions, of
the roots of blue grass, timothy, Lathyrus sylvestris, clover, winter
wheat, barley, and oats.

case with the clover, whose roots matted thickly at the
bottom of the barrel in which they grew.

Looking at the roots of winter wheat in Fig. 30, it will
be seen that a mass of other roots have been entangled
with them at a depth of 2 to 3 feet below the surface.
These are from a second-growth black oak standing in a
pasture 33 feet distant from the place where the sample of

214

Th

le Soil.

wheat roots were taken. In Fig. 31 may be seen the roots
from a smaller tree of the same species as they were
drawn from a sandy soil with the aid of a stump puller.
In digging in a field adjacent to an apple orchard, the
writer has found roots of the apple as large in diameter
as a slender lead pencil at a distance of 45 feet from tbe
trunk of the tree to which it was attached.

Fig. ."ll. — Showing the roots of second-growth Wack oak as drawn

from a sandy soil.

Such facts as these illustrate in a forcible manner how
deeply and broadly the roots of plants are sent foraging
through the soil, and how much soil it is needful for
them to come in contact with in order to procure the
food and water they need.

Schubart, a German farmer, Storer tells us, made
measurements of various roots which he washed out

Need and Great. Extent of Ro\t Surface. 215

from the soil of fields whero the orops were growinp^.
He found the roots of wheat, sowed in September, ex-
tending to a depth of 7 Rhenish feet in a subsoil eoni-
posed of sandy loam ; and Lawes ()l)served tlie roots
of lucern penetrating to a depth of 9 feet below the
surface.

Referring again to the roots of maize which we re-
covered from the field at different stages of maturity, it
may be stated here, as having an important bearing on
the depth of cultivation of this crop, that as the corn
advances towards maturity a jiortion of the roots whicli
are thrown off at higher levels on the stem develop more
nearly horizontally and come closer and closer to the
surface, making it more difficult to cultivate deep late in
the season than when the corn is small.

At the time when the corn had a height of about IS
inches, July 9, the roots in the centre between the rows
3.5 feet apart were nearly 8 inches below the surface,
rising in a festoon to near the surface of the ground at
the hill on either side. At this time, too, most of the
roots were confined to the upper 18 inches of soil.
When the corn had attained a height of 2.5 to 3 feet,
the surface leaders, midway between the rows, had risen
to within 6 inches of the top of the ground and now
occupied the upper 2 feet of soil. Just as the corn
was coming into tassel, the upper leaders were then
scarcely 5 inches below, while at maturity they were
less than 4 inches from the surface.

It is evident from these facts that corn may safely be
cultivated more deeply early in the season than when it
is more mature.

Each of the trunk roots or leaders of the Q,ctY\\ plant
sends out on opposite sides, much as the stalk does its

216 The Soil.

leaves, slender rootlets from 2 to 6 inches long, and
those on the surface leaders rise directly upward and
nearly reach the top of the ground in the latter part of
the season.

Those soils which are sandy and loamy in character
rather than clayey, and whose grains have little tendency
to draw together into block-like masses of varying sizes,
as do the stiff clays, allow a much more symmetrical de-
velopment of the roots in them, and as a consequence of
this there is less trespassing of one root upon another ;
there is not so much soil far removed from the root hairs,
and hence the soil water is more easily, rapidly, and
completely removed for the purposes of the plant, and
finally in these soils the roots find less difficulty in wedg-
ing the soil grains apart as they need more room in their
growth.

In the clayey soils, too, as they shrink and crack, draw-
ing themselves together in small cube-like blocks, there
is a tendency, during dry seasons, to tear or break off
many of the smaller rootlets, and thus deprive the plant
of its means of water supply when water is most needed,
and when, if the roots were left intact, it might be had.

There seems to be operative in the plant a power or
directive influence, which leads to the most rapid growth
of roots in those directions in the soil where the most
bountiful supplies of food and the best conditions for
growth exist.

AVhen cultivated fields lie along one side of a grove or
row of trees, these trees develop the strongest roots
beneath the tilled fields, in just the same manner as the
branches grow most rapidly in the direction of the most
sunshine and the largest amount of room. Whether the
lines of most rapid growth are determined solely by, and

Need and Great Extent of Root Surface. 217

are the result of the most complete feeding, — that is,
whether those roots which lie where the most food mate-
rials in the form of water and ash ingredients can diffuse
into them, are in precisely the condition which causes the
assimilated material from the stem to be brought to the
roots to make a more rapid growth possible, — need not be
discussed here. It is true, however, that a plant does
not usually waste its energies in developing roots in a
direction where no benefit could be derived from it.

CHAPTER VIII,

SOIL TEMPERATURE.

There is no pliysiological fact more evident tnan tlie
extreme importance of maintaining the right temperature
surroundings for living forms of all kinds, ^n our own
case a deviation of the mean temperature of the body
a few degrees either above or below 98° F. results in
very serious consequences, if long continued. So impera-
tive is the right bodily temperature in many animals,
and so narrow is the admissible limit of variation, that
it is necessary to have in the body compensating devices
which are automatically under the control of the nervous
system. When we are in health if, for any reason, the
mean temperature of the body is becoming too high, the
sweat glands are set at work and the surface of the body
covered with perspiration, the evaporation of which with-
draws so much heat from the body that the temperature
is brought down to the normal point. Then, should the
temperature tend to fall too low, the activity of the skin
is diminished, and at the same time a larger amount of
oxygen is taken into the body to unite with the food eaten,
for the definite object of producing heat more rapidly.

In the vegetable world the extremes of temperature
which are destructive to life are usually much farther
apart than they are among animals ; that is, the tempera-
ture may be allowed to fall much loAver and to rise much
higher with no other serious consequences than the

21 H

Soil Temj>erature. 219

partial or complete cessiition of pliysiolo^^ncal processes,
but usually here tli('r(^ is botli an up[)eran(l a lowei- liniitj
beyond wliieh life is destroyed.

It is not difficult to understand why these temperature
relations should be so essentia ^^ and from the practi(;al
point of view it is very important that they should be.
Many of the essential changes which take place in the
bod}' of a plant or of an animal, and which constitute the
life processes, are chemical in their character, as is that
of the burning of wood. But when we desire wood to
burn, in ordinary air, when we wish oxygen to unite with
it chemically, we have first to apply heat to it and raise
its temperature up to a certain ])oint before burning will
begin. When the chemical action has been once started,
then there is usually heat enough produced to maintain
the action so long as there is a plentiful supply of oxygen
and of wood. Then, Avhen water is thrown upon a fire to
extinguish it, it does so chiefly by withdrawing heat from
the flames so rapidly in the evaporation of the water that
the temperature is lowered to such an extent as to stop
the chemical action. The steam formed by the evapora-
tion also occupies so much space as to greatly dilute the
oxygen, and in this way tends to make the burning slower
or to stop it altogether.

To light the match, we rub it vigorously upon some
rough surface, but this is only to raise its temperature
up to the point at which oxygen will begin to unite with
it; to warm the prepared end in any other way would
produce the same result, and the sole reason for using the
preparation at the end of the match is because chemical
action can be started in it at a temperature so low that
it can easily be produced by friction.

Now the chemical changes in the animal body and Id

220 The Soil

the tissues of plants, which result in the various phe-
nomena of growth and manifestations of power, require
that the materials which react one upon another should
first be raised to a certain temperature, should have a
certain rate of molecular swing, before it is possible for
the changes to take place. Just as water evaporates the
faster the more heat is communicated to it whereby its
molecules, by absorbing that heat, are thrown outside of
the liquid mass and become a gas ; and just as the fuel
in the stove must be warmed up to a certain temperature
before the force of cohesion is enough weakened to allow
the oxygen of the air to unite with it; so must the
materials within the seed, in the roots, stems, and leaves
of plants have their temperature raised to a certain point
before those chemical and physical changes which con-
stitute the phenomena of growth can take place.

IMPORTANCE OF SOIL WARMTH.

Now the lowest soil temperature, according to Eber-
mayer, at which the processes of growth are started in
most cultivated crops is from 45° to 48° F., but the maxi-
mum results are attained only after the soil has reached
a temperature of 68° to 70°. Let us compare these tem-
peratures with those observed in the soil at different
depths, for the six months, April to September inclusive.
Dr. Frear reports the soil temperatures at State College.
Pennsylvania, from which we derive the mean of five
years, as given in the table below : — -

Depth. April. May. June.

3 inches 43.74 55.13 67.29

6 " 43.08 54.72 66.34

12 " 42.69 53.83 65.03

24 '' 41.43 51.45 61.90

July.

Aug.

Sept.

70.16

68.70

61.32

69.75

68.49

61.70

68.89

68.66

62.73

66.42

67.41

63.50

Importance of Soil Warmth. 221

These temperatures, it will be observed, for the month
of April, are below the minimum for growth given above,
while the August temperatures only barely reach 68° F.

Ebermayer, at Munich, found the temperatures in a
loess-like loam as follows, for a mean of four years : —

Dbpth. April. Mat. Jttvr. Jitlt. Kvc. 8p;pt.

6.9 inches

44.65

66.79

61.11

67.26

64.09

58.21

11.8 "

44.31

57.51

60.06

66.16

63.61

57.88

23.7 "

44.40

53.58

59.11

63.12

63.55

58.82

85.4 "

43.66

51.24

57.33

62.92

62.26

68.51

These temperatures, it will be observed, are higher in
April and May, but lower the balance of the season, than
they are in Pennsylvania.

Now if it is true that the vital processes of plant life
can only go forward rapidly and normally when the
surrounding temperatures are right, it is evident that
this factor in the culture of plants must be of even
greater importance than it is in the successful manage-
ment of animals; for the latter have it within their
power to raise or lower their own bodily temperature
as the surrounding conditions may demand, while this
power is not to any notable degree possessed by plants.

Let us then consider some of the ways in which too
low or too high soil temperatures may work to the dis-
advantage of a crop growing upon it. It may be stated
at the outset that in temperate climates, where the soils
are supplied with the needed amount of moisture, there is
little likelihood that the temperature will become too
high for the majority of our cultivated crops. The dan-
ger lies in the direction that the soil will be too cold.

If we desire to dissolve almost any substance quickly
in water, or indeed in almost any acid, we can greatly

222 The Soil.

Hasten the solution by using heat; and froni what has
been said regarding the method' of solution, this should
be expected. But one of the chief functions of soil
water is to take into solution, from the soil constituents,
substances which, for the most part, dissolve, under the
most favorable conditions, very slowly. Now, raising
the temperature of the soil grains, weakens the attractive
force which holds the plant food locked in the solid
state, while at the same time it makes the diffusion of
the dissolved materials, away from the seat of action,
more rapid; and unless the dissolved materials are
removed as soon as formed, they, by their reaction
against the face of the soil grains, tend to prevent any
further action from taking place.

It is not only important that there should be a rapid
diffusion of the dissolved food away from the places
where it is being formed, through the action of soil
water, but it is even more important that this process
should be carried forward in the soil air, in order that
a sufficient amount of fresh oxygen and nitrogen should
enter the soil to replace that which is being used by
roots, seeds, micro-organisms, and chemical processes
needful to a fertile soil ; and the higher the soil tem-
perature is, the greater are the absolute velocities of
the molecules of air, and the faster will they reach the
place in the soil where they are needed, and the sooner
will the rapidly forming carbon dioxide escape into the
air, leaving room for more to form. A high soil temper-
ature, then, is conducive to a more rapid and thorough
soil aeration or ventilation, a process of extreme impor-
tance, as we shall see in another place.

It is not enough that a rapid solution of plant food
shall take place in the soil, but in order that growth

Importayice of Soil Warmth. 223

may be vigorous, it is iicocssary that the dissolved food
riliouhl be transported quickly to tlu^ ])huM's in the plant
Avhere it is to be used. Now the strength of osmotic
pressure, and the rate of its action, increases as the tem-
perature of the medium in which it is taking place is
higher. We must keep in mind that in the process of
osmosis, as in the diffusion of gases or in the evaporation
of water, the molecules go from ])lace to place by virtue
of the rate at which they are thrown by the heat imparted
to them, and hence, if the soil temperature is held high,
the molecules of water are hurled into the root hairs and
on into the other tissues faster than they can be if the
surrounding temperature, the supply of power, is low ;
but when the molecules are once within the plant cells,
then the higher speed they possess in virtue of their
higher temperature is just the condition which develops
the strong osmotic pressure required to force the sap
onward toward and into the leaves, no matter how high
the stem which bears them may be.

Sachs has shown, for example, in the case of both the
tobacco plant and the pumpkin, that they wilted, even
at night and with an abundance of moisture in the soil,
so soon as the soil temperature fell much below 55° F.
Under this temperature the power which moved the
water from the roots to the leaves was too feeble to
compensate for the slow evaporation which takes place
at night.

Then, again, when seeds germinate in the soil, work
'nust be done, and in no small degree, at the expense of
the heat absorbed by the soil. Haberlandt found, for
example, that the germination of wheat, rye, oats, and
flax goes forward most rapidly at 77"^ to 87.8'' ¥., and that
corn and pumpkins germinate best at 92° to 101° F. He

224 The Soil.

found that when corn would germinate in three days at
a temperature of 65.3° F., it required eleven days when
the temperature of the soil was as low as 51° F. He
found, further, that when oats would germinate in two
days impelled by a temperature of 65.3° F., it required
seven days to do the same work when the temperature
was as low as 41° F.

These are forcible illustrations of the need of a warm
soil, and should be a sufficient spur to every thoughtful
farmer to do whatever he can to meet the conditions
here made evident. That certain seeds require a higher
soil temperature for their germination than others do,
must be understood as meaning that the necessary trans-
formations do not take place so easily. It must not be
understood, however, that when a seed is placed in a
cold soil, the food stored in it for the development of the
young plant cannot undergo a change. Quite the con-
trary ; there are organisms in the soil which are able to
do their work at low temperatures, and if a seed, under
these conditions, comes into their presence, it absorbs
moisture and, being unable to grow, becomes a prey to
these lower forms and decays.

In speaking of the sources of nitrogen for higher
plants, it was stated that the nitrates formed their chief
supply. But in studying the conditions under which the
nitric ferment works most vigorously, it has been learned
that the germs cease to develop nitric acid from humus
when the temperature falls below 41° F. ; that its action
is only appreciable at 54° F., while it becomes most vigor-
ous at 98° F., but that at 113° F. its activity drops back
again to what it was at 59° F. Here, again, is another
and very urgent need for the right soil temperature.

What, then, are the conditions which influence soil

Conditions Influencing Soil Warmth. 226

temperatures ? And, since a soil is more often too cold
than too warm, what can be done to raise its tem-
perature ?

CONDITIONS INFLUENCING SOIL WARMTH.

There is no one cause so effective in holding the
temperature of a soil down as the water which it contains,
and which may be evaporating from its surface. This is
because jnore work must be done to raise the temperature
of one pound of water through one degree than of almost
any other substance. Thus, while 100 units of heat must
be used to raise 100 pounds of water from 32° to 33° F.,
only 19.09 units, according to R. Ulrich, are required to
warm the same weight of dry sand, and 22.43 units an
equal weight of pure clay, through the same range of
temperature. To raise the temperature of 100 pounds
of dry humus through 1° F., it is necessary to give to it
44.31 heat units, while 100 pounds of carbonate of lime
require 20.82 units.

From these figures it is evident that when the sun
imparts equivalent amounts of heat to equal weights of
sand, clay, humus, and water, the sand will be the warm-
est, while the water will be the coldest. To make the
differences definite, suppose the water has its tempera-
ture raised 10° F., then the same amount of heat enter-
ing an equal weight of humus w411 make it 22.6° warmer,
clay 44.58° and sand 52.38° warmer. But while the tem-
peratures of these soils Vv^ould stand in the relation of the
figures here given when they are dry, it is not true that
under field conditions such large differences of tempera-
ture would be observed, because there are other factors

Q

226 The Soil

which modify the effect of differences of specific heat,
whose influence alone we have thus far considered.

Since the weights of dry soils per cubic foot are not
the same, it is evident that the heaviest soil, were other
conditions alike, would be the coolest, because while the
same amount of sunshine can fall upon a square foot of
sandy soil as falls upon an equal area of clay soil, the
cubic foot of sand weighs 110 pounds, while that of
clay may only weigh 75 pounds ; hence, a surface foot of
sandy soil, instead of being 7.8° warmer, would be 8.6°
colder than the clay soil. But the fact that the water-
holding power of the clay soil is greater than that of the
sandy soil, works again in the opposite direction, on ac-
count of the large amount of heat needed to warm the
water, to make the clay colder than the sand ; so that, if
we assume the clay and sand saturated, the same number
of heat units per surface foot of each soil would give the
sand a temperature 3° F. warmer than the clay.

The chief cause, however, which makes a wet or un-
drained clay soil colder than a well-drained or sandy soil is
the large amount of heat which is used up in evapora-
ting the excess of water from the surface. While 100
heat units will raise the temperature of one pound of
water through 100° F., it is necessary to use 966.6 heat
units to evaporate one pound of water from the soil ;
but this, if withdrawn directly from the cubic foot of
saturated clay, would lower its temperature about 10.3° F.
It must be evident therefore, that to allow the surplus
water to drain away from a field rapidly, rather than to
hold it there until it has time to evaporate, must greatly
favor the warming of the soil.

The writer has observed the following differences of
temperature in the surface inch of a well-drained sandy

Conditions Influencing Soil Warmth. 227

/oam and an iindrained black marsh soil, both of them
naked and level.

Date.

Time.

Condition of
Weather.

o

H

H
•<

« .

^- 1

o

H O

Li
H Q

w -

6- <

? a;

H

H

Q

Apr. 24

3.30 to
4.00 P.M.

Cloudy, with
brisk east
wind.

60.5° F.

66.5°

54.00°

12.50°

Apr. 25

3.00 to
3.30 p.m.

Cloudy, with
brisk east
wind.

64.0^ F.

70.0°

58.00°

12.00°

Apr. 26

1.30 to
2.00 P.M.

Cloudy, rain
all the fore-
noon.

45.0° F.

50.0°

44.00°

6.00°

Apr. 27

1.30 to
2.00 P.M.

Cloudy and
sunshine,
wind S.W.
brisk.

53.0° F.

55.0°

50.75°

4.25°

Apr. 28

7.00 to
8.30 A.M.

Cloudy and
sunshine,
wind N.W.
brisk.

45.0° F.

47.0°

44.50°

2.50°

It should be noted in connection with this table that
the differences in temperature in favor of the drier soil
have occurred when the amounts of evaporation would be
relatively small, and hence when the differences would be
below rather than above the average.

Comparing the temperatures of a well-drained clay soil
with that of a sandy loam, also well drained, when each

IsT Foot.

2d Foot.

a© Foot.

76.5° F.

74.70 F.

72.1° F.

69.5^

69. 30

67. 0^

228 The Soil

was less than half saturated, the following differences
were observed on August 6 : —

Sandy loam . . .
Clay loam . . .

Difference, 7.0° 5.4^ 6.1°

Now, from what has been said in regard to the advan-
tages of a vvrarm soil, it is plain why a sandy loam, when
well fertilized, is for so many purposes superior to the
heavy clay soils.

The slope of the land surface, and the direction of this
slope with reference to the points of the compass, often
have a marked effect upon the temperature even when
the soils are identical. Thus, on the south shore of Lake
Superior the writer found the temperature of a stiff red
clay on a level table and on a south exposure sloping
about 18° to have the following values on July 31 : —

1st Foot. 2d Foot. 3d Foot.

Red clay, south slope 70.3° F. 68.1° F. 66.4° F.

" " level 67.2Q 65.4° 63.6°

Difference, 3.1° 2.7° 2.8°

In a level, sandy, alluvial soil close by the above and at
the same time, the temperatures were 71.2° F. 70.1°, and
67.6° for the first, second, and third feet respectively.
Here, again, the influence of the character of the soil on
its temperature is well marked, but the differences are
smaller than in the former case, as the tabulation shows.
In these two cases both soils were more than half saturated
with water : —

1st Foot. 2d Foot. 3d Foot.

Alluvial sand, level 71.2° F. 70.1° F. 67.6° F.

Red clay, level 67.2° j. 65.4° 63.6°

4,0° - 4.7° 4.0°

Coiiditions Influencing Soil Warmth. 229

Wollny, in his study of soil temperatures as affected
by slope and direction of exposure to the sky, found,
through observations on small artificial hills with incli-
nations of 15° and 30° to the horizon, that the south side
has an average temperature of 1.5° F. when the slope
was 15°, and 3.1° F. with a slope of 30°, warmer than the
north side; but, comparing the east with the west slope,
he found less than .2° F. difference. Comparing the east
and west slopes with the south, he found, for 15° inclina-

FiG. 32. — Showing how the slope of the surface influences the amount
of heat received per unit area.

tion, the east .71° F. and the west .5&^ F. colder than the
south side; but when the 30° slopes were compared,
the differences were 1.31° F. for the east and 1.44° F. for
the west colder than the south slope.

Just why a south slope should be warmer than a north
slope will be readily seen from an inspection of Fig. 32.
Suppose A65B represents a prism of sunshine falling
upon the hill AEB, where AE is the south slope and EB
the north. Here it will be seen that, on account of the

280 The Soil

sun not being directly above the hill, the south slope gets
as much more sunshine than the north slope does as the
line 46 is longer than the line 45 Avhich, for the angle of
20°, is about one-third more per each square foot of sur-
face.

The color of a soil, too, has not a little influence in de.
termining its temperature, the darker soils, if other condi-
tions are the same, being the warmer. All are familiar
with the fact that a black garment is much warmer in
bright sunshine than a white one. This is because the
black surface absorbs the ether waves as they come from
the sun in much larger proportions than the white gar-
ments do. The leaves which drift upon the white snow,
and the dirt also, as all have observed, cause the snow to
melt much more rapidly than where the snow is clean
and white. So the sandy soils which are light in color
do not become as warm as they might if their light
color and glistening surface did not cause much of the
sunlight to be turned directly back without doing any
work upon them.

A rough, uneven, lumpy, or ridged surface has a ten-
dency to make the soil colder than the smoother, more
nearly level surfaces do, and there are several causes
which co-operate to produce these results. If the surface
is ridged east and west, or if it is covered with lumps, the
south sides of these inequalities receive more heat than
the north sides do, causing them to become relatively
very warm, and in this condition they lose much more
heat by radiating it away and by the air coming in
contact with and being warmed by them.

The effect of rolling the land on the temperature of the
soil is often very marked, its general tendency being to make
it warmer during bright clear weather, but in cloudy and

Conditions Influencimj Soil Warmth. 231

cold weather it has the opposite effect, rolled land tend-
ing to cool more rapidly. The wi-iter has found through
extended studies, under li(dd conditions on soils of vari-
ous kinds, that a rolled field may have a temperature, at
1.5 inches below the surface, as much as 10° F. above en-
tirely similar soil not so treated, and at a depth of 3
inches, a difference of 6.5° has been observed. The dif-
ferences in temperature observed on one date are shown
in Fig. 38. Here, it will be seen, the air temperature

Fig. 33. — Showing observed differences of temperature on rolled and

on unrolled ground.

over the unrolled ground is warmer, except early in the
morning, than it is over the rolled surface, showing that
the dry lumps and uneven surface are imparting their
heat to the air more rapidly, and, since both surfaces are
receiving the same amounts of heat from the sun, it is
plain that if the air is warmed more over the unrolled
ground the soil must be warmed less. The fact that the
surface soil is less firmly packed on the unrolled ground
also causes the heat to be conducted downward less rap-
idly, and thus tends to make the deeper soil cooler. Dur-

232

The Soil.

ing the night and cold, cloudy weather, when little heat is
being received from the sun, the loose soil on the unrolled
land acts as a blanket and tends at such times to make
the rolled land the coolest at the surface, as shown in the
figure.

The observed temperatures between 1 p.m. and 4 p.m.,
on eight Wisconsin farms, are given below : —

H

-91

Soil Temperatures.

Soil.

At 1.5 Inches.

At 3 Inches.

Rolled.

Unrolled.

Rolled.

Unrolled.

F.

F.

F.

F.

F.

Sandy

56.75°

65.55°

63.50°

61.92°

59.45°

Clay loam

61.17°

56.55°

53.60°

56.48°

53.55°

(( u

59.00°

70.21°

64.40°

64.85°

59.90°

Sandy . .

69.62°

73.40°

72.05°

70.79°

69.26°

Clay . .

72.64°

79.77°

78.20°

73.02°

71.82°

Sandy clay

73.30°

76.83°

71.90°

72.58°

69.09°

Yellow clay

60.80°

61.34°

58.82°

57.38°

65.58°

Clay loam

79.70°

89.89°

86.12°

81.49°

76.47°

Mean .

65.37

71.69

68.57

67.31

64.39

Difference

3.12

2.92

. . .

I

These results were all obtained in the spring, on land
sowed to grain, and show an average difference of 3.1° F.
and 2.9° F. higher temperature on the rolled ground.

The character and depth of cultivation also has an
appreciable effect upon the soil temperature, stirring it
deeply, tending to make the deeper soil cooler than where
the depth of cultivation is less. This tendency is due to
the fact that the loose soil of greater depth is a poorer

Conditions Influencing Soil Warmth. 233

conductor of heat, and tends to shut out the heat from the
sun. The temperatures where corn ground was cultivated
3 inches deep and 1.5 inches deep were found by the
writer to be .82° F. warmer in the surface foot, .59° F. in
the second foot and .36° warmer in the third foot on land
cultivated 1.5 inches deep than they were on adjacent and
similar soils cultivated to a depth of 3 inches. These
differences were determined by a self-recording maxi-
mum and minimum thermometer, which had a bulb one
foot long, enabling it to record the mean temperature of
the foot of soil in which it was placed, and the differ-
ences given above are the means of measurements in
eleven fields in different parts of Wisconsin.

It is also true that the fermentations of organic matter
which go on in the soil under the influence of various
microscopic organisms, produce no inconsiderable amount
of heat, and for this reason, among others, a field heavily
fertilized with farmyard or green manures enjoys a higher
soil temperature because of the treatment.

There is perhaps no method of soil w^arming at consid-
erable depths in the ground so effective as that of warm,
percolating rains. In the spring of the year the soil is
usually thoroughly saturated with the water from the
winter rains and melting snows, and under these condi-
tions, when the warm spring rains come they usually
percolate deeply into the ground, shoving the colder soil
water in front of them beyond the depth of the root zone.
When we recall that each pound of rain at 60° F. carries
10 heat units into the ground, which can be applied to
raising the temperature of soil colder than 50° F. up to
that point, and that each such heat unit can raise
the temperature of a pound of sand 5.24°, the great
advantage of warm April showers in bringing an early

234 The Soil

spring can be appreciated. But of course, when cold
rains come to the fields, the opposite effect must result.

It is evident therefore, from what has been said regard-
ing the temperature of soils, that not only is the right
degree of warmth very important, but the farmer has it
within his power at times to make the soil warmer or
colder. It will be remembered that the vital processes
of plant life only begin after the temperature has risen
above 45° to 48° F., while the mean April temperatures of
soils cited on a preceding page fall below these figures,
and since the earlier we can bring the soil up to the
growing temperature the larger will be the conservation
of both soil moisture and other plant food, it is evident
that if we can, without undue expense, hasten the warm-
ing of the soil to a practical extent, it is important that it
should be done.

MEANS OF CONTROLLING SOIL WARMTH.

Now the thorough preparation of the seed bed which
good farmers so much insist upon is justified in a large
measure by the warming effect which judicious, thorough
tillage has. In the first place, the development of a mulch
over the ground lessens the loss of water from the surface
by evaporation, and if by this means we have saved from
loss into the air 10 pounds of water per square foot, we
have avoided by this saving the withdrawal of 10 times
966.6 heat units from the same area; so that early thor-
ough tillage not only saves moisture, but it at the same
time permits the seed bed to become quickly both dry
and warm enough to allow nitrification to begin and to
hurry forward. It is very important, too, that this should

MeauH of ControUlnii Soil Warmth. 235

be (lone ; for the melting snows and spring rains have car-
ried down beyond the reach of yonng plants most of the
soluble nitrates tlie soil mjiy have possessed the fall be-
fore. Early thorough tillage, then, develops to an im])or-
tant extent needed plant food by warming and aerating
the soil, while at the same time it hastens the germina-
tion and gets the plant into condition to take advantage
of the food being prepared.

It is not so important early in the spring that the ground
should be warmed deeply, but better only so far as to
provide ample available plant food for the start, and
room enough for the first roots, and this is what early
tillage does; the loose, open soil conducts neither the
cold ground water up to become still colder by evapora-
tion, nor the absorbed sunshine down where it is not yet
needed. In effect this method converts the whole field
into a hotbed or cold frame, and commences irrigation
by saving water at the start. It does even more ; for
while it develops early a little soluble plant food, it
holds in abeyance these processes in the deeper soil,
which, by starting too early, would cause a needless loss
by developing nitrates which may be leached away
before the crop has its roots ready to use them.

We have pointed out how and to what extent rolling
warms the soil. Should the farmer use his roller to
warm his soil? Yes, at times; but he must do so with
good judgment. From what has been said, it follows
that rolling may warm the ground too deeply, and at the
same time waste soil moisture. Evidently the practice
to follow, so far as the problem here under consideration
is concerned, is to wait after using the tool only so long
as to permit enough moisture to reach the surface, and
enough warmth to pass downward to meet the imme-

236 The Soil.

diate needs, and then the harrow should follow without
a moment's delay.

A roller, to do its work properly, must have a con-
siderable weight, and the larger the diameter of the
roller, the heavier it should be. The plank can seldom
be used as a substitute for the roller, when firming the
ground is what is demanded. This will be readily
understood, when it is recalled that the much lighter
weight the plank must have is spread out over many
times the extent of surface covered by the roller, and
hence its pressure, per square foot, must be proportion-
ately less. The roller presses, with its whole weight
concentrated, along a narrow line, and the narrower the
smaller the diameter of the roller. But the smaller the
diameter of the roller, the harder it must draw in pro*
portion to its weight.

When a mellow, open seed bed has been prepared, and
its temperatiire has been raised to the proper point,
should a rain fall upon it, that water will tend to pass
through its wide pores quickly to the deeper soil, and
without leaching it as badly as would be the case were
the soil more compact; so that in the early season when
there is an over-abundance of moisture, it is best, for
warmth, for aeration, and to lessen loss of fertility by
percolation, to have a mellow seed bed.

It seems to the writer probable that there may be
times when we should till the surface for the express
purpose of keeping the deeper soil cool even late in the
season, when it has become desirable that it should have
a good degree of warmth. Eeference has already been
made to the diurnal changes in the ground water, due to
diurnal oscillations of soil temperature. But under cer-
tain conditions these oscillations result in a loss of

Means of Controlling Soil Warmth.

23?

soil moisture through increased drainage, and with this
an increased loss of plant food.

In Fig. 34 are shown automatic records of the diurnal
changes in the level of the ground water in a tile-drained
field, and of the rate of flow of water from the system
of tiles which was carrying the percolating waters
away. The highest portions of these curves mark the

7ukmj,his

Tuli, 27 \Jui,2i

iti •■Jf* ,'if' ,r

}r4( <'M" i'jt.'' J

4-^2

4 \ t

-^ t-.-^^

JtM ^'.

i" ^Z3

_,<^-'

^ -V ^ J

% -

.- ^4 "

4 \ -J -

^^ I-

4 \l -i"-

t c^Xt-t-

\ iV^^^^t

^4 ^^Uj -

V

-^ t % t -

2^ ^^ -

it

£t

h^~i~S"-l

4 -r-. -^^-

/wJ ^^-9r

c i.T

t--/\T -^

1 :

^

Pig. 34. — Showing the diurnal oscillations of the water table and of
the rate of flow of water from a tile drain due to diurnal tempera-
ture changes.

time when the water was flowing slowest, and when
the water in the wells stood at the lowest level, while
the lower parts of the curves mark the time when the
water was flowing fastest from the tile drains, when
percolation was most rapid. Referring now to Fig. 35,
which shows the changes in soil temperature 18 inches
below the surface, and of the air temperature above, it
will be seen that the warmest time in the soil is a little

238

The Soil

after midnight, while it is coldest a little after noon;
The most rapid flow of water from the drain, and the
highest level of the water in the wells, occur about 7
o'clock in the morning, hence some hours later than the
highest soil temperature; and since it is the expansion
of the soil air, due to the rising temperature, which pro-
duces this effect, a certain amount of lagging should be
expected.

Fig. 35. — Showing diurnal changes in the soil temperature at 18 inches
below the surface and of air temperatures one foot above the sur-
face, as given by thermograph.

Now in such localities as tliese, and possibly also
where the ground water is not as near the surface,
the developing over the field of a loose, non-conducting
mulch of soil, produced by cultivation, must make the
diurnal changes of temperature less, and hence the per-
colation of the soil water also, saving the water for the
crop.

CHAPTER IX.

THE RELATION OF AIR TO SOIL.

The presence of an ample amount of air in the soil is
as indispensable to the life of upland plants as is that
of water, and whatever method of tillage is adopted, it
should not hinder soil breathing to an injurious extent.

It has been abundantly demonstrated that when free
oxygen is completely excluded from seeds placed under
otherwise good conditions for germination, growth will
not take place; if after seeds have commenced to sprout
the oxygen supply is cut off, they cease to develop. It
is true that the germination of seeds will take place in
an atmosphere very poor in oxygen, but after the percen-
tage amount has been reduced below -^ of the normal
quantity, growth is much retarded and sickly plants
usually are the result.

NEEDS OF SOIL VENTILATION.

Practical experience teaches that when a soil bearing
other than swamp vegetation is flooded, or even if it is
kept long with its pores filled with water, the plants
soon sicken and die, and this, too, when they are in full
leaf and abundantly supplied with food and warmth.
The difficulty is the lack of root breathing; the plants
are drowned, and as effectually as an animal would be

239

240 The Soil.

under water, because enough free oxygen cannot reach
them.

It is true, to be sure, that on the floating gardens of
the Chinese and the Mexicans, crops are matured under
conditions where the roots of the plants must be im-
mersed in water during their whole period of growth,
and this fact appears to be a contradiction of the state-
ments just made. In these cases, great rafts of basket-
work are covered with soil, and floated upon a lake or
stream, so that here the roots of whatever crop the
floating islands may have produced must have occupied
saturated soil or the water itself below the raft. So, too,
in the cases of water culture, where plants have been
grown without soil, in water holding in solution the
needed nitrogen and ash ingredients, there is an appar-
ent contradiction. In these cases, however, the water
is free from the soil, where, by absorption and diffusion,
oxygen from the air can enter it even more readily
than it is able to do in a good soil, for there a
large part of the space is occupied by impenetrable soil
grains; and more than this, wind and convection cur-
rents are powerful adjuncts in bringing fresh oxygen
to the submerged roots of the plants just as they are
in bringing to the fish and other animals the oxygen
they need.

In the compact, water-filled soil, however, all current
motion is prohibited, and the roots of plants can only
secure the free oxygen which the water may have brought
with it when it fell as rain, but as this amount is small,
it soon becomes exhausted. On the other hand, if the
field is underlaid by a deep, porous subsoil, into which
the rains may quickly penetrate, or if the field is under-
drained, then, as the water runs away, leaving empty

Needs of Soil Ventilation. 241

spaces behind, air must be drawn in to take the place,
and needed oxygen is thus supplied.

We have seen in another place, that the germs which
develop nitric acid in the soil find oxygen indispensable
to their life, and so important is a large supply of it in
the soil that in olden times, when saltpetre farming
was practiced to procure potassium nitrate for use in the
manufacture of gunpowder, great pains were taken to
thoroughly aerate the soil in which the nitrate was being
developed, and as one of the chief objects of tillage is
the production of nitrates in the soil, we may profitably
recall the old method of raising saltpetre.

In the growing of nitrate of potash in Europe, a mix-
ture of soil, manure, and leached ashes or marl was
formed into beds, sometimes made more open and porous
by the use of gratings or racks. Great care was taken
to keep the beds warm and of the proper degree of moist-
ure, while from time to time they were shoveled over or
otherwise stirred for the purpose of introducing air and
warmth. Then when a new field or bed was to be
started, care was taken to bring to it soil from an old nitre
bed, or, in the language of that time, adding " mother of
petre,'' a term so appropriate in the light of our knowl-
edge of to-day that nothing more significant could have
been used. It is thus seen that the old nitre farming
found its best results, its largest yields of saltpetre, in a
rich soil kept well moistened, well stirred, and thoroughly
warmed, all of them conditions which we now recognize
as very important for any crop, and we cannot doubt that
they are so because they favor the rapid development of
that important plant food, nitric acid.

We have just been speaking of the need of oxygen in
the soil to carry forward the process of nitrification.

242 The Soil.

It must now be said thafe oxygen is also needed to pre-
vent the destruction of thre nitrates after they have once
been formed. From Warington's review of our acquain-
tance with the phenomena of denitrification, we learn
that the destruction of nitrates with the setting free of
nitrogen in waters containing sewage was observed by
Dr. Angus Smith in 1867, and in 1868 Schlosing showed
that nitrogen gas, or some of its lower oxides, are set
free in several putrefactive and ferment ive processes.
He also found that when a moist soil, rich in humus,
was kept in an atmosphere of free nitrogen, from which
all oxygen had been excluded, all nitrates which they
may have contained quickly disappeared. He found,
further, that the same denitrifying process took place
when a limited quantity of ordinary air was present.
It was even true with the soils rich in organic matter
that they often gave off more free nitrogen than was
represented by the nitrates present in them; that is,
other organic nitrogen was broken down and set free,
this process consuming the oxygen derived from the
decomposed nitric acid.

With these facts before us, it is plain that we are in
danger of having the soil depleted of its needful nitrates,
not only by excessive leaching, l3ut also through the
destruction of the organic matter from which these are
evolved, if the land is allowed to remain too long with
insufficient ventilation, as the result of poor drainage.

Warington conducted experiments in the Eothamsted
laboratory on an artificially water-logged soil to which
he had applied sodium nitrate at the rate of 519 pounds
per acre, and found that, in less than three weeks, all
but 21 per cent of the nitrate had disappeared, its oxy-
gen having been used in the carrying on of life proc-

Needs of Soil Ventilation. 243

esses for which free oxygen would have been used had
it been present in tl»o soil in sufhcicuit quantity. We
must see to it, then, that our soils are sufti{;icntly venti-
lated to insure the production of nitrates on the one
hand, and to prevent their destruction on the other.

Now that we know how free nitrogen from the air is
fixed in the tubercles on the roots of leguminous plants,
it is evident that here is another reason why air must be
admitted to the soil, and not simply to the surface layers
which are tilled, but deeply into the root zone two and
three or more feet. It will be seen that oxygen must be
admitted to the soil in order tliat the nitrogen of decay-
ing organic matter may be converted into forms available
to higher plants, while free atmospheric nitrogen is
demanded to hold up the stock of organic nitrogen by
making good the losses in the drainage waters and by
the processes of denitrification.

Those fermenting processes which result in the return
of carbon as carbon dioxide to the air after it has
answered the purposes of living tissues, require, many of
them, oxygen from the air; hence, in order that the vast
root systems which grow and die in the soil may not
accumulate unduly, air in sufficient quantity must pene-
trate deeply. We have sufficient evidence of the advan-
tage of good ventilation in the strong heating of the
well-aerated heaps of horse manure, when contrasted
with the much slower fermentation which takes place in
close cow dung, free from litter.

There are many purely chemical reactions essential to
soil production and soil fertility which demand a cer-
tain measure of oxygen and carbon dioxide for their con-
tinuance, so that here is another need for a fair measure
of openness in the soil. And then if oxygen must be

244 The Soil

admitted to the soil for the setting free of nitrogen and
carbon dioxide, it is equally necessary that these gases
shall be allowed to escape with sufficient freedom, so
that they shall not exclude the atmospheric air, or so
dilute it as to render it ineffective.

We have now in mind the chief needs for a sufficiently
free passage of atmospheric air in and out of the soil.
How, then, is soil ventilation accomplished? How is it
hindered, and what may we do to control it?

NATURAL PROCESSES OF SOIL VENTILATION.

The most general and constant mode of interchange of
gases in the soil, and in the air above, is that of diffu-
sion, whose motive power is the sunshine absorbed by
the surface layers. As the molecular motion of the soil
grains increases during the day, as the temperature rises,
a part is transmitted to the gases contained in its pores,
and more of these molecules are driven out than enter it;
but when the soil temperature falls, then the reverse
condition takes place, so that we have in the upper layers
of the soil an incessant temperature breathing. But if
the surface of the soil did not warm and cool by turns,
there would still be an interchange of soil and atmos-
pheric gases so long as their compositions were not iden-
tical; for, owing to the never-ending to-and-fro motion of
the air molecules, wherever the oxygen is being con-
sumed in the soil, there is produced at that place an
oxygen vacuum into which other molecules are sure to
find their way, unless the soil pores are in some way
blocked to them. On the other hand, if carbon dioxide
is being produced in the soil at any place, then an excess

Natural ProcesffeH of Soil Ventilation. 245

of pressure of this gas results, which pushes some of the
molecules out into the open air.

We have already seen how the temperature effect in the
soil is felt even in the deeper ground water and to such
an extent as to force it out into drainage channels. So,
too, if for any reason carbon dioxide is more rapidly
set free than it can escape, the increased pressure which
results will affect the ground water in the same manner
as the temperature changes do. In like manner a more
rapid consumption of oxygen or nitrogen in the soil than
is compensated for by inflow from above tends to develop
a negative pressure on the soil water, which would per-
mit capillarity to return to the soil spaces water which
had been forced into the beginnings of drainage channels
or passages.

The aeration of the deeper soil is favored by the fact
that, owing to the lagging of the diurnal changes of
temperature to which reference has been made, the
second foot may be growing warmer at the same time
the surface foot is becoming colder, and vice versa. The
second foot, for example, being warmest at the same time
the surface foot is approaching its lowest temperature,
more air from the second foot is forced into the surface
foot by diffusion than would occur were there no tempera-
ture lagging. Then in the daytime, when the surface
foot is becoming warmest, while at the same time the
second foot is growing colder, the air then diffuses more
rapidly downward into the deeper soil.

Every change which takes place in the barometer or in
the atmospheric pressure above a field has a tendency to
cause some air to pass either into or out from the soil.
These alterations of pressure in the soil air are so marked
that the movement of the ground water is very sensibly

246

The Soil.

affected by them, as will be seen by referring to Fig. 36,
which shows the changes in the rate of flow of water
from a spring as they were modified by variations in the
atmospheric pressure. In Fig. 37, too, may be seen the
changes of level of water in a well during 24 hours, most
of which were coincident with fluctuations in atmospheric

i

M

u

/.„

AJLL

s

-J

6 126

h

10

6126

612 6

12

m

fiOJi

£j2i.

14

iJ2i

Fig. 36. — Showing fluctuations in the rate of flow of water from a
spring at Whitewater, Wisconsin, May 4 to May 16, and the baro-
graph record at Madison, Wisconsin, for the same period. Both
reduced to natural scale. Heavy curve represents the spring.

pressure. But every change in atmospheric pressure
which is large enough to affect the level of water in
wells must also be large enough to cause some air to
enter or leave the surface layers of soil.

When the wind is blowing strongly across the surface
of the ground, but with greatly varying velocities, as is
usually the case, there is a tendency to alternately suck

Natural Procesnes of Soil Ventilation.

247

air out from the soil pores, and again to allow it to
return, thus ])ro(luf'ing an irrof^^ular but sometimes very
strong soil breathing. Tliis aetion of the wind is made very
evident, too, oftentimes by the rise and fall of a carpet on
the floor, and by the buckling of a tin roof as stronger
and feebler gusts of wind pass in turn over the house.

In certain sections of the country which are underlaid
by extensive beds of coarse gravel, the wells sunk into
these beds are often subject to strong draughts, which
alternately pass into and out of them. In Sauk County,
Wisconsin, there is a district of this sort where the air

Fig. 37. — Showing the oscillations of water in a well during 24 hours,
most of which were coincident with corresponding changes in the
barometer.

passes into the wells at times of high barometric pressure
and in such large volumes in cold winter weather as to
freeze and burst the suction and discharge pipes of pumps
at depths greater than 70 feet ; then when a low pressure
passes over the well, the outgoing current is so strong
that even a hat may be lifted by it, and in winter the
snow about the well is melted away.

There are many prairies in various parts of the world
which are underlaid with layers of coarse gravel, be-
ginning at three to ten feet below the surface and often
extending to depths of many feet. The soils of such

248 The Soil,

districts must be subject to a peculiarly strong venti
lation or breathing, which may have not a little to do
with the wonderful productiveness usually characteristic
of such lands. It will be evident, too, from what has
been said, that sandy and otherwise light and open soils,
especially when they are deep and the distance to the
water table is large, will be subject to peculiarly thorough
ventilation or breathing, while all close-textured soils,
like the heavy and stiff: clays, will naturally be aerated
less perfectly.

WAYS OF INFLUENCING SOIL VENTILATION.

This leads us to consider some of the means which are
available to control soil breathing. It may be said at
first that all methods of tillage which tend to develop
large, open, non-capillary spaces in the soil must greatly
facilitate the change of air, not only in that layer
of soil so loosened, but at the same time in that which
comes in contact with it below ; and in the more thor-
ough soil breathing which deep tillage and the plow-
ing in of coarse manure insures to the stiff clay soils, we
find a large part of the good results which follow these
treatments.

Then when heavy lands are underdrained, these soils
are so much better and more deeply aerated that we must
look to this more complete ventilation for the chief ad-
vantage which this type of land improvement assures.
The aeration of the soil which is rendered possible by
thorough underdraining has rarely been sufficiently em-
phasized, neither has the method by which it is brought
about been fully stated.

Ways of Influencing Soil Ventilation, 249

When the level of the ground water is permanently
lowered 2 or 3 feet, as is done in underdraining, the
roots of plants penetrate more deeply into the field, and,
as they die and decay, leave a system of passage-ways
leading toward the surface, into and out of which the
soil air finds a more ready ingress and egress. Earth-
worms, ants, and other burrowing animals also penetrate
the ground more deeply, and thus form open ventilating
flues of much larger magnitude than those left by the
roots of plants.

Then, again, as the under clays dry out, they shrink
upon themselves and develop unnumbered fissures, through
which the air more freely moves with every change of
pressure and temperature, and in which the roots of
plants place themselves, the better to profit by renovated
air. With the deeper and more thorough penetration of
the soil air, carrying with it the carbonic acid developed
near the surface, it acts through the soil water upon the
lime, producing the bicarbonate, which in its turn tends
to flocculate the finer silt particles of the clay, causing
them to congregate into larger compound grains and thus
render the soil more open in its texture and hence better
drained and better aerated, as well as more easily and
thoroughly occupied by the roots of plants.

But all of these changes wliich have been referred to
as resulting from thorough drainage are only means for
widening and rendering the direct effect of underdrains
more prompt in their influence and far-reaching in the
renewal of soil air which they secure. In an underdrained
field where lines of tile are laid 3 to 4 feet deep and 50 to
100 feet apart, there is provided a ventilation system
which operates in an effective manner to hasten the
change of the soil air. It must be evident that when

250 The Soil.

the diurnal changes in the temperature of the confined
soil air and the changes due to alterations of barometric
pressure are sufficiently pronounced to affect the rate of
flow of water from tile drains, as has been demonstrated
in another place, there must also be draining out of a tile
system, at times of rising soil temperature and of falling
barometer, considerable quantities of soil air. This must
be so because, as the soil air expands and pushes upon
the soil water, forcing it out, some portion of the air
itself must escape into the drains through their upper
sides. Then when the temperature falls and the barome-
ter rises, air will be forced into the soil to take the place of
that which had been lost, not simply from the surface
of the ground, but simultaneously along the whole extent
of the system of underdrains. It is important to recog-
nize in this connection, that the air which underdrains
admit to the soil from beneath is in a large measure
atmospheric air, containing the normal amount of oxygen,
and since under these conditions the soil can breathe free
air both from above and below the zone occupied by the
roots of plants, it is plain that the soil of a tile-drained
field must be much more thoroughly ventilated than that
of another entirely similar field having its water table at
the same distance below the surface and equally open in
texture, but without tile drains.

A word should be said regarding the aerating power of
clover as compared with the similar action of other plants.
The roots of the red clover being larger than those of
cereals, and in part fleshy, tend to separate the soil parti-
cles farther, leaving more effective air passages and drain-
age channels when they decay than do the roots of wheat,
oats, barley, or rye. But there is another way in which
all free-nitrogen-fixing plants help to aerate the soil dur-

W<iyif of Tufltiencinjf Soil Ventilation. 2ol

ing their periods of growth. As these withdraw from tlie
soil air the free nitrogen it contains and fix it in the solid or
li(|nid form, a redu(;tion of air i)r('ssure is produced and a
fresh supply of air must be crowded in to supply this
deficiency. In so far as other plants work in a similar
manner to withdraw oxygen and fix it in solid or liquid
form, without putting in its place an equal volume of
some other gas, a similar tendency must result, but in a
less pronounced degree than in the leguminous plants
which remove both oxygen and free nitrogen.

Just as the withdrawal of water through underdrains
forces air to follow it more deeply into the vacated spaces,
so must the osmotic pressure of all roots, by forcing water
out of the soil to be evaporated from the leaves, tend also
''jo bring fresh supplies of atmospheric air into the soil,
equal in volume to the water withdrawn.

It may well be that some soils are so open that they
are too thoroughly ventilated, just as they are too thor-
oughly drained. In such cases the decaying organic
matter is converted into nitrates more rapidly than they
can be used by the crop, which results in impoverishing
the soil of its nitrogen store.

Soils of this type are helped by shallow tillage and a
thorough firming of all soil except so much as shall be
needful for a mulch. Keeping such soils thoroughly moist
diminishes their porosity, as does farmyard manure, which
tends to clog the pores.

The loss of the fine dust particles from light soils so
liable to occur in the spring when the winds are strong is
a great injury to such lands, both on account of the point
here under consideration and because the water-holding
power is greatly decreased thereby, as has been pointed
out.

252 The Soil

HYGROSCOPIC MOISTURE.

The moisture which exists in the air in the form of
vapor is to a greater or less extent absorbed by soils as
air enters or comes in contact with the ground during the
process of soil breathing. The water so taken up by soils
or other objects is spoken of as hygroscopic moisture.
Usually the finest grained soils, in the air-dry condition,
contain more moisture than the coarser grained samples
do, but the amounts so retained do not appear to hold any
discovered numerical relation to the amount of such sur-
face. It is usually more the lower the soil temperature,
and decreases in quantity as the temperature rises during
the day. Our knowledge of the laws governing the
hygroscopic moisture of soils, and of the importance of
this moisture to plant life, is as yet too indefinite to per-
mit any very trustworthy statements regarding it to be
made. There are eminent writers who hold that its im-
portance, especially in dry climates, is very great, while
others feel that vegetation can derive but little profit
from it.

CHAPTER X.

FARM DRAINAGE.

Enough has been said regarding the influence of under-
drainage on the important matters of soil temperature,
soil ventilation, and the conservation of soil moisture, to
show how important this method of improvement may
be on certain lands. But as land drainage is certain to
play a much larger part in the future of agriculture than
it has in the past, it is important that something more
should be said regarding it.

We have in the United States, according to Professor
Shaler's estimate, more than 100,000 square miles of
swamp lands lying east of the 100th meridian; and these,
when reclaimed by drainage, are destined to become the
most productive lands we have. They will be so, not
Only because of the large stores of humic nitrogen which,
under proper methods of tillage, may be turned into
forms available to higher plants, but also because they
lie in huinid climates, and are so related to the water table
that only surplus rains need be lost. Indeed, not only
can there be no percolation of soil water from these lands
below the reach of root action; but in very many, if
not in the majority of instances, they are perennially
supplied with water through the underfloAv from the
surrounding higher land, and are thus naturally sub-
irrigated.

That our swamp lands are destined to become rich

253

254 The Soil,

agricultural fields must be evident when we consider
that during the 44 years following 1833 the country of
Holland added to itself lands exceeding in square miles
the combined area of Rhode Island and Delaware, by
systems of dikes and methods of drainage so difficult as
removing the surplus water over the sea barriers with
pumps. And so fertile are these reclaimed swamp lands
that nearly 20 years ago there lived on the 12,731 square
miles, a population averaging, for each square mile, 302
people, 20 horses, 118 cows, 70 sheep, 12 goats, and 27
hogs ; and, side by side with this population, there were
raised 2907 square miles of field crops, exclusive of
pastures and hay, and the average yearly product of
these fields between 1871 and 1875 is placed at $45.36
per acre.

There are lands other than the swamp areas referred
to above which may be much improved by draining;
and it may be said, in general, regarding these that all
lands will be made more productive by draining where
standing water in the ground may be found at seeding
time not more than 4 feet below the surface. All
very flat areas of fine-textured soil underlaid at four to
six feet or less with a stratum of highly impervious clay
or rock, and ponds and slews, as well as springy hill-
sides, are likely to profit much from a thorough system
of drainage.

SOME LARGE DRAINAGE SYSTEMS.

As an instance of the pains which in some parts of
this country are now being taken to improve lands by
underdraining, reference may be made to work which
is being done in the state of Illinois, where, in many

Some Large Drainat/e Syatemn.

256

parts, the fields for long distances are so flat that it is
difficult to obtain adec^uate fall or to provide suitable out-
lets for the drains when laid. Here, in many instances,
the citizens combine their energies and resources and
dig broad, open ditches, sometimes many miles in length
and deep enough to provide suitable outlets for under-

FiG. 38. — Showing plan of the drainage of lands of the Illinois Agri-
cultural Company, Rontoul, Illinois. After Professor J. O. Baker.
The smallest squares represent 40 acres ; double lines show open
ditches ; single lines are tile drains.

drains. One such drainage system is found in Mason
and Tazewell counties. It was begun in 1883 and com-
pleted in 1886, and has a main ditch 17.5 miles long with
a width of 30 to 60 feet at the top and a depth of 8 to
11 feet ; while, leading into this main channel, there are
five laterals averaging 30 feet wide at the top, and from

256

The Soil

7 to 9 feet deep, the whole system embracing 70 miles of
open ditch.

A clearer idea of the character and magnitude of some
of these drainage systems may be gained from Fig. 38,
where the double lines indicate open ditches, and the
single ones tile drains, many of which it was found
necessary to lay very nearly level. This system was
begun in 1881 and completed in 1884, and its effect upon
the total yield of grains of all kinds is stated by Pro-
fessor Baker as follows : —

Total yield of grain in 1881, 26,057 bushels.

" 1882, 58,647

" 1883, 92,360 "

" 1884, 113,660 ''

" 1885, 122,160* "

" 1886, 202,000 "

It is plain from these figures that there has been a
marked influence following the underdraining in this
case ; but it should not be understood that the yields per
acre increased to the extent indicated by the figures, for,
before the land was drained, there was much of the area
too wet to be cropped at all, and hence the larger totals
with successive years are due in part to an increase in
the acreage.

It has been pointed out that no lands will produce
other than swamp vegetation, unless they have first been
more or less perfectly drained, because, until this is
done, those biologic processes in the soil necessary to
cultivated crops cannot be carried forward. They can-
not for several reasons : the temperature is too low ;
there is inadequate soil ventilation ; and there is an

* 400 acres of maize destroyed by a water spout.

Depth of Under draina. 267

insufficient amount of room in which the roots can
develop and perform their functions.

There are two other ways in which imperfect drainage
works disadvantageously ; first, by preventing early seed-
ing and thus shortening the growing season and the
amount of available water and other forms of plant food
derived from the soil ; and second, besides increasing the
labor of tillage, it shortens the time in which the work
can be performed.

DEPTH OF UNDERDRAINS AND DISTANCE BETWEEN

THEM.

The depth to which the water should be lowered by
drainage, below the surface of the ground, need seldom
exceed 4 feet for ordinary farm crops, while under
some conditions the lowering of the water table may be
less. We have many cases on springy hillsides and on
flat areas between rises of ground, where the w^ater is main-
tained within 4 feet of the surface for only a short
period in the spring. In instances like these, w^here the
water table falls normally 5 to 7 feet below the surface
as the season advances, it is only necessary to insure a
sufficient drying of the surface 18 inches in which the
plants may begin their growth. When this is done,
the gradual fall of the water table as the crop grow.,
allows the subsoil to become sufficiently dry and open
through the natural process of drainage and evaporation
from the surface. Where such lands are deeply tile
drained, there is liable to be a needless waste of much
water.

In sandy soils, too, and others which are naturally
leachy and open, it is not as important to draw the ground

258

The Soil.

water down as low as when the soil is more close and
impervious in texture. But in all cases where the water
table usually remains as near the surface as 4 feet during
the whole summer, the drainage system should be planned
to draw the water down at once to from 3.5 to 4 feet below
the surface, and hold it there.

There are times when the ground has become very
dry, and especially when the soil is a stiff clay and has
checked to a large extent as the result of drying, when
heavy rains come they percolate so rapidly into the sys-
tem of tiles that a large share of the water is lost before

Fig. 39. — Showing how the distance between drains affects the depth
of drainage. With drains at A and C the water will be highest
at B; but with drains at A, D, and C the surface of the ground
water will be more nearly the line AEDFC.

it has time to be absorbed by the soil. In such cases,
although no provision is usually made for it, the writer
feels that, were tile drains provided with a few valves at
different places in the system, which might be closed at
such times and thus retain the bulk of the water for
a day or more, until sufficient time has elapsed for the
water to be taken up by the capillary pores of the soil,
no inconsiderable advantage would be derived from it.
The writer has seen, on three different occasions when
a heavy rain has followed a dry period, tha>t on tile-
drained ground . a. very large part of the water was lost

Depth of Under drains.

250

through the drains when the soil was much in need of
more than had fallen.

The distance between underdrains will vary with the
closeness of the soil texture and the depth at which they
are laid. Since the water table rises as the distance
from the outlet increases, it is plain that midway be-
tween lines of tile the surface of the ground water must
approach nearer to the top of the ground, and the nearer,
the farther the lines of tile are apart, as illustrated in
Fig. 39.

The actual contour of the water table in an under-

FiG. 40. — Showing the observed surface of the ground water in a tile-
drained field 48 hours after a rainfall of .87 inches.

drained field, where the lines of tile are placed at dis-
tances of 33 feet and 4 feet below the surface of the
ground, is shown in Fig. 40, which gives the contours
as they existed 48 hours after a rainfall of .87 inches.
In this case the height of the water midway between the
lines of tile varied from 4 inches to 12 inches above the
tops of the tile, and the mean rate of rise was 1 foot in
every 25 feet ; that is to say, in soils of this character,
when the drains are bid 50 feet apart, the water may
stand in the ground midway between, the lines 1 foot
nearer the surface than the tiles themselves 48 hours
after such a rain ; and if 100 feet apart, then 2 feet nearer

260 The Soil

the surface of the ground. In well 29, Fig. 21, situated
150 feet from the lake, and hence from the drainage out-
let, the water stood on June 27, 1892, 7.214 feet above
the lake level, thus showing a rise of 1 foot in every
24.4 feet ; but later in the season, when the ground had
become drier, the level had fallen until the rise was 1
foot in 35.86. As this slope occurred in September, when
percolation from the surface had long since ceased, it
may be regarded for such soil as a minimum gradient.
Taking the rise as 1 foot in 36 feet, lines of tile 72 feet
apart and 3 feet deep would allow the water table to rise
to within 2 feet of the surface along a line midway
between the drains.

SUB-IRRIGATED LANDS.

Just how quickly the water table may be drawn down
after a rain by a system of tile drains is shown in Fig.
41, where the broken lines represent the surface of the
ground water on May 12, 13, and 16, the latter date
being 5 days after a rainfall of .87 inches. It will
be seen that the changes in level of the water table were
very far from being uniform in different parts of the
field, the fall being fastest under the highest ground,
where it passed entirely below the upper three lines of
tile. In this case, as indicated by the arrows, the lower
portion of the field is subject to sub-irrigation, the water
under the higher ground tending, through its greater
hydrostatic pressure, to move toward and up into the
soil of the lower field.

Sub-irrigated lands of this character occur in many
places and under conditions where the geological struc-
ture is much as represented in Fig. 42. In these cases

Sub- Irrigate J Lands.

26a

the surrounding high lands are more or less open in
texture, so that the rains percolate into them readily,
but drain away slowly, making the adjacent flat lands
more or less springy or marshy, and only fit for tillage
after they have been underdrained. Such lands, however,
once they are underdrained, become very valuable on ac-
jount of their abundant water supply. Nor is this type of
land at all uncommon in the northern part of the United
States. Indeed, the glacial hills referred to in an earlier
chapter are impounding reservoirs of great extent and
capacity, into which the rains sink immediately, and are

Fig. 41. — Showing the rate of change in the level of the ground water
after a rainfall of .87 inches.

there stored, under conditions of least possible loss by
evaporation, to be given out gradually in restricted but
innumerable areas. Heavy rains which in countries of
different structure are lost to agriculture in disastrous
floods are here safely and economically stored ; and it is
to this stored water escaping slowly again from the
ground, more than to direct rainfall and flat topography,
that we owe the existence of our innumerable small
lakes, and the many areas of swamp and lowland pas-
tures so characteristic of glaciated regions. These many
naturally sub-irrigated tracts are especially promising for
market gardening and other forms of intensive farming.

262

The Soil.

There is another phase of this question to which atten-
tion should be called. There are many and extended
tracts of country underlaid by artesian waters, where
water can be had at the surface whenever the overlying
impervious strata are penetrated. Now, in view of the
fact that the best of Portland cements are not wholly
impervious to water, even under moderate pressures, it
may also be true that in many parts of artesian districts
there is a slow, upward penetration of the deeper waters
into the field soils, which possibly contributes not a little
to the natural productiveness of such lands.

Fig. 42. — Sbovviug the geologic structure favorable to natural sub-
irrigation.

SURFACE DRAINAGE.

Where extensive flat fields of very fine-textured, im-
pervious soils occur, it is often desirable, and even neces-
sary, to adopt some form of surface drainage. There
are some clayey soils in their virgin state which are so
impervious to water that it would be useless to lay
drains deeply in them, even were the lines near to-
gether, because the water would percolate into them too
slowly to render them efficient. In such cases surface
drainage must be resorted to. This is done by plow-
ing the fields in narrow lands, leaving dead furrows

Surface, Drainafie. 263

extending in the direction of tlio natural slope, and from
20 to 60 feet apart. Where the lay of the land makes it
necessary to do so, the dead furrows may be connected
by cross furrows, in order to load the water away
through some low place.

It is often desirable, even where underdrains are used,
to have some surface drains to carry away surplus water
in times of freshets. Such ditches are V)est made wide
with very sloping sides, so as to be grassed over and to
permit a team and wagon to be driven across them at
any place.

The Celtic land beds of olden times represented an
effort to secure deep drainage Avith surface or open
ditches. Marshall, writing of this method of land im-
provement in 1796, says that the ridges of that time were
8 yards wide and from 2 to 2.5 feet high, but he meas-
ured some which were 15 yards w^ide and 4 feet high,
while others were 20 to 25 yards wide, and so high that
a horseman riding in one ditch could hardly see his com-
panion riding in the other. This method of drainage
must be very wasteful of land, and is only to be resorted
to when, for any reason, covered drains cannot be made.

There are many depressions or low places which, on
account of being surrounded on all sides by higher land,
cannot be made dry either by surface or underdraining.
It is frequently true of such cases that the water is held
by a pan of clay which has been formed from washings
from the higher ground, while under this pan the soil
is open and capable of readily carrying the water away.
When this is true, and the area which drains into the
basin is not too large, it may be drained by boring or
digging through the clay in one or more places, making
exits for the water to escape by percolation downward.

264

The Soil.

These drainage ways may be kept open, or they may be
filled in with coarse stone, sand, and gravel.

When the clay is too deep to permit of draining in
this way, the result may be accomplished, if the amount
of water to be removed is not too large, by sinking a
well or reservoir of considerable size at the lowest place,
into which the drains lead from various directions. This
water may then be lifted by wind or other power, and
used to irrigate grass or other fields bordering the wet

Fig. 43. — Showing the drainage system of 80 acres in northern Illinois.
After Q>. G. Elliott, C.E. Double lines represent mains ; single
lines are laterals. Numbers give length of drains and size of tile.

area, thus getting rid of the water by evaporation and
making it do service at the same time.

COST AND ARRANGEMENT OF UNDERDRAINS.

We cannot in this place discuss the practical details of
underdraining, but as an illustration of the method of
distributing and joining main drains with laterals, we
have selected an actual piece of work done where a
farm of 80 acres in northern Illinois has been drained

Cost and Arranr/emenf of Underdrainn. 265

under the supervision of Mr. C. Ct. Elliott, C.E. The
land he describes as a rich black loam, approaching muck
in the ponds and flats, underlaid with a yellow clay sub-
soil at a depth of 2.5 feet from the surface. In draining
this piece the object has been to fit it for growing corn,
grass, and grain in all seasons, and it will be seen (Fig.
43) that the laterals are, where nearest, about 150 feet
apart ; but it should be understood that the aim has not
been to provide perfect drainage, but rather as good as
would pay a fair interest on the money invested where
general farming is practiced.

The fall of drains should not be less than 2 inches
per each 100 feet when it is practicable to secure this
amount. A smaller fall may, if necessary, be used, but
more is better. In the field represented by the figure
the main drains have a fall of 2 inches per 100 feet, and
the laterals more rather than less.

I give below the cost of doing this piece of work with
the items as stated by Mr. Elliott.

COST OF MAIN DRAINS PER 1000 FEET.

No. OF
Feet.

Size.

Depth.

Tile.

Digging,
Laying,

AND

Filling.

Total.

Cost pbk

KOD.

1000

7 in.

5 ft.

$60.00

137.20

$97.20

$1.60

2700

6 in.

5 ft.

40.00

36.60

206.82

1.26

850

5 in.

4 ft.

30.00

24.20

46.07

.89

COST OF LATERAL DRA

.INS.

8280

4 in.

3.5 ft.

20.00

20.00

331.20

.66

7030

3 in.

3 ft.

13.20

20.00

233.40

.56

Total .

. . .

$914.69

The total cost of $914.69 makes an average per acre of
$11.43.

266

The Soil

- "It will seldom be best to use.-, tile smaller- thari -3
inches,; and- in laying them great care shoiild be exercised
to place them on a true grade, because if the lines of tile
have high and low places in them, whose differences
exceed the diameter of the tile, silt will tend to collect
in the low places and sooner or later close them up.

The outlet of a drain should be carefully made and
end above water as represented in Fig. 44. If the out-
let is below standing water, the silt which is brought
down tends to close up the main, and thus render the
whole system useless. So, too, when a lateral is led into

Fig. 44. — Showing proper and improper outlets of drains. ^, proper
outlet; ^, improper outlet ; C, proper junction of lateral with
main; D, improper junction.

a main the union should be made at an angle as at C
rather than as at D.

Care must always be exercised to remove water-loving
trees from near lines of underdrains, lest their roots
penetrate the joints and there branch into a vast network,
entirely filling the tile, when, by retaining the silt brought
by the water, they will sooner or later completely close
up the tile. Fig. 45 represents a mass of roots thus
formed in a tile drain. These roots are those of the
European larch, and they penetrated a main drain at a
depth of 5 feet below the surface, the trees standing at

Cost and Arramjeinent of Underdrains. 267

a distance of 15 feet from the line. As will be seen, the
roots, after entering the main, branched into a great
system of fibres, which effe(;tually closed a 6-inch drain,
making it necessary to take up the line of tile in that
vicinity.

Fig. 45. — Showing the roots of European larch removed from a 6-inch
tile drain, which they had ei^ctually clogged.

CHAPTER XI.

IRRIGATION.

Eeference was made in the last chapter to the large
acreage of lands now lying idle and practically worth-
less, so far as the needs of civilization are concerned,
which have yet to be won to remunerative agriculture
through a judicious application of methods of drainage ;
and to still other lands which may be made more produc-
tive than they now are through the same means.

It is not the purpose here to speak of methods of irri-
gation in detail, nor of irrigation as applied to arid and
semiarid regions, because there its value is appreciated
and needs no enforcement ; but rather to consider in
a general way the great promise it has for lands receiv-
ing moderate amounts of rain during the growing season.
This is done because we are fully persuaded that the
maximum limit of productiveness of lands in humid
regions can only be attained through a suitable combina-
tion of both drainage and irrigation. Further than this,
there are many hundred square miles of light lands lying
east of the Mississippi, which are now almost as unproduc-
tive as the undrained swamps are, but which irrigation,
properly handled, would cause to bloom into the richest of
gardens. The rainfall of the eastern and central United
States is so capricious, the amount of water needed for
large yields so great, and the difficulties in the way of
making our soils retain enough of the water which falls

268

Irrigation in Humid Climaten. 269

to meet the demands are so many, that it must be plain
to every practical man and student of agriculture, who
has devoted much thought to the subject, that the time
must come when the waters now running to the sea,
with their tons of unused fertility, will be turned to
use in irrigating many of the fields through which
they flow.

IRRIGATION IN HUMID CLIMATES.

The advantage of irrigating lands in humid climates
has been abundantly proved by long trial in many
parts of the world, and it is the object here to call
attention to the facts and to point out a very important
and remunerative channel in which American capital
should seek investment. If it will pay to irrigate in
arid climates, where all the needed water must be sup-
plied under conditions of cost far exceeding what will
be needed in humid districts, there must certainly be
many lands near large markets and close to water which
can be irrigated with great profit.

In illustration of what sewage irrigation is doing in
Scotland, the statements of Storer, made after visiting
the irrigated meadows near Edinburgh, may be cited.
He says : —

" In 1877 there were 400 acres of these ^ forced mead-
ows ' near Edinburgh, and they are said to increase
gradually. The Craigentinny meadows, just now men-
tioned, were about 200 acres in extent, and they had been
irrigated for thirty years and more. They were laid down
at first to Italian ray grass and a mixture of other
grass seeds, but the artificial grasses disappeared long
ago, couch grass and various natural grasses having

270 The Soil.

taken -their place.. The grass is sold green to. -cow
keepers, and yields from ^80. to $150 per acre. One
year the price reached $220 per acre. They get five cuts
between the 1st of April and the end of October. This
farm of 200 acres turns in to its owner every year from
$15,000 to $20,000 at the least calculation, and his run-
ning expenses consist in the wages of two men, who
keep the ditches in order. The sewage he gets free.
The jdeld of grass is estimated at from 50 to 70 tons
per acre. The total produce of the sewage irrigation
at Edinburgh amounts to at least $30,000 per annum,
taking one year with another. The grass goes to some
2000 cows, and the milkmen all acknowledge that they
cannot get any milk-producing food to compare with
it for the same amount of money, notwithstanding the
seemingly high price that is paid for the grass per
acre. Of course the dung from these cows goes to
fertilize other farm land."

The lands from which these large returns are being
realized are described as having been a worthless, sandy
waste previous to their improvement by sewage irrigation.

Referring to results obtained on the Myremill farm
of 508 acres near May bole, in Ayrshire, Scotland, John
Wilson quotes at length from the " Minutes of Informa-
tion " issued by the General Board of Health, to the
effect that some 400 imperial acres were laid down to
iron pipes placed from 1.5 feet to 2 feet below the surface,
and provided with hydrants at intervals, to which hose
are attached for the distribution of the water contain-
ing the fertilizers. In this case the water used in irri-
gating the farm was lifted 70 feet with pumps driven by
a 12-horse-power engine and stored in large reservoirs,
the- cost of which, including pipes and hose, is placed

Irriyation in Humid Climates. 271

at $7676. Counting 7.5 jjer cent on this sum, for interest
and wear and tear, and a working expense in distribu-
ting the water of ^15786.50 per annum, the total annual
cost of irrigation equals $1862, or $2.68 per acre. The
land laid down to grass is said to have produced 70
tons of green weight per acre, so that at this rate the
70 acres in Italian ray grass gave a gross crop of 4900
tons, and the market value of this one crop of meadow
grass exceeded, by a large sum, the first cost of the
irrigating plant. It is said that this same land before
being treated in the manner described would barely
pasture 5 sheep or 1 bullock to the acre, but under
the irrigation system it was easy to keep 20 sheep or
5 bullocks to the acre by hurdling and moving from
place to place.

Fabulous as these results appear, fourteen other cases
are cited by the same author, and they all have the
same import. To illustrate: In one case a weighed
crop of 10 tons per acre of ray grass was taken, and
this is said to be the lightest of four cuttings in one
season. In another, where 12 stacks per annum were
formerly taken, now 80 are obtained. And again where
the yield was worth $1 per acre, it is now ^5^.

It should be understood that all of the cases here
referred to are looked upon as methods of manuring
the land, that is, fertilizers are added to the water and
with it distributed over the fields ; but there can be no
question but that the larger yields secured are due
much more to the water than to the fertilizers added
to it,. or more exactly to a proper combination of both
rather than to either one of them alone. . . •:::.: .: ..

In -proof of the possibilities of. obtaining very'hreavy
yields of dry matter per acre, it may be stated that the

272 The Soil,

writer grew, under field conditions in 1894, by irrigating,
14.5 tons of dry matter to the acre on J^ of an
acre of ground, when the crop was a variety of flint corn.
The ground upon which this maize was grown was a
clover sod, well fertilized with a dressing of farmyard
manure, and the same ground with the same variety of
maize gave less than 4 tons to the acre where only the
natural rainfall was available.

The irrigation of grass lands has been widely practiced
in Europe and for a long time. For pasture land and
meadows the system is in use in Germany, Switzerland,
France, Spain, and in many provinces of Italy. We are
told that in 1856 the old kingdom of Sardinia had
600,000 acres of land under irrigation; in Lombardy
there were 1,100,000 acres and 300,000 in France. Marsh
states that two canals in Lombardy, which now irrigate
some 250,000 acres, were dug in the twelfth century.
Palestine and Persia are noted for the extensive and
highly perfected systems of irrigation which brought
wealth to those countries in the days of Babylonian
greatness, but which are now in utter ruin. So, too, in
Ceylon the native rulers in ancient times covered the
whole face of their island with a network of irrigation
reservoirs, through which Ceylon became the great gran-
ary for southern Asia, but through the devastation of
wars they have long since passed into ruins, and it is said
that what were once highly productive irrigated fields
are now swampy wastes or dense forests.

Even in Mexico and Peru, the Spaniards brought
destruction to elaborate systems of irrigation, as they
had done before to those in their native land which had
been built in the sixth century by the hands of the
thrifty Moors.

Coat of Irrigating. 278

H. M. Wilson, in speaking of the extent of irriga-
tion, places the acreage in various countries as follows :
Total area irrigated in India, 25,000,000 acres ; in Egypt,
6,000,000 acres ; and in Italy, 3,700,000 acres. In Spain
there are 500,000 acres, in France 400,000, and in the
United States 4,000,000, acres of irrigated land. In
addition to this, he states that there are some millions
more of acres cultivated by the aid of irrigation in
China, Japan, Australia, Algeria, and South America.

COST OF IRRIGATING AND AMOUNT OF WATER USED.

The amount of water used in irrigating is very large,
as indeed it must be when large fields are to be dealt
with. In Italy often as much as 4 inches of water on
the level are applied to the meadows at a single wetting,
and amounts equivalent are applied at intervals of ten
days or two weeks, varying of course with the weather ;
but it usually happens, in these cases, that a considerable
portion of the water passes beyond the field to which it
is directly applied and is utilized on lower lying areas.
Smith concludes from statistics in India that there
1 cubic foot of water per second is sufficient for 180 acres
of land where the water is used the whole year through,
and this is equal to 48 inches on the level. Five esti-
mates of the amounts of water required in French and
Italian experience for water meadows, where the period
of consumption is about half the year, gives an average
of 86 acres of land watered by a continuous flow of 1
cubic foot per second, and this amounts to covering the
ground with a depth of water equal to about 50 inches,
the water being used from the middle of March to the
middle of September. This is a very large amount of

274 The Soil

water when considered in connection with the natural
rainfall, amounting to from 20 to 40 inches, but it must
be observed that three and sometimes four crops of
grass are cut from the land each season, besides using it
for pasture in the fall.

In obtaining water for irrigation purposes, there are
many methods which may be used and are to-day in use
in various parts of the world. The most natural method,
where the topography of the country will permit of it,
is to lead the water out from some point up stream into
irrigating canals, which convey the water to flat lands
farther down. Or various forms of lifting wheels are
placed in the stream, and considerable quantities of water
are raised by them and discharged into side channels.
Hydraulic rams are used and a great variety of pumps
driven by steam or other power. Using a No. 4 rotary
pump driven by an 8-horse portable farm engine, the
writer has drawn water through 110 feet of 6-inch suc-
tion pipe, raising the water to a height of 26 feet, at the
rate of 80,320 cubic feet per ton of soft coal, which is
equivalent to 22^ inches of water per acre, or over 7
acres covered to a depth of 3 inches. But this amount
is much less than could have been moved with the
same fuel had the pump been provided with a larger
discharge, and could the water have been used as rapidly
as pumped, so as to have made frequent stops unneces-
sary. Windmills may be used to advantage in many
cases where the lift is small, where the area to be
watered is not large, and particularly where reservoirs of
considerable capacity may be used for storage.

While it is true that much profit may be realized
through irrigation in humid climates on a small scale,
yet the largest returns can be secured only when a con-

Cost of IrrigafAng. 27 h

siderable capital is involved, but this is no argument
against the development of the system, provided the
income is sufficient to keep the cajiital profitably era-
ployed.

The cost of irrigation west of the 100th meridian in
the United States, as given in the United States census
for 1890, averages ^8.15 per acre for the construction
of canals to bring water to the land, while the average
value of the water per acre, when once there, is placed
as high as $26, but the average annual cost of water
per acre is $.99. The value of the lands before irriga-
tion improvements were added is placed at from $2.50
to $5.00 per acre, but after the water was added to it
the same lands are valued at $83.28 per acre.

To show what has been done on barren sands in
Belgium, it may be stated that 5636 acres of sand dunes
have been reclaimed by irrigation, under government
control, and that these lands yield 6615 pounds of hay
per acre, with an aftermath valued at $2.00 per acre,
which, with the hay, gives an income placed at $29.93
per acre.

CHAPTER XII.

THE PHYSICAL EFFECTS OF TILLAGE AND FER-
TILIZERS.

The great importance of good tilth has always been
appreciated by thoroughgoing practical men, and ex-
perience has abundantly taught that the stiffer and
more resistant the soil, the greater should be the care
and attention given to the field to bring it into perfect
tilth before receiving the seeds or plants which it is
expected to bring to maturity.

But Nature neither plows, harrows, nor hoes her fields,
and yet where water is abundant and the temperature
right, the grasses thrive, the flowers bloom and fruit, and
tree and shrub vie with one another for the occupancy
of the whole surface of the earth even to vertical, rocky
cliffs and steep mountain sides. Why, then, should tilth
be so important a matter in successful farming ?

"When we reflect upon Nature's methods, we see plainly
that they are quite different from those adopted by thrifty
husbandry. In the first place, by Nature's method's, not
one seed in many hundreds ever germinates and comes to
maturity, but in farming no such chances can be taken.
Conditions must be favorable not only for every seed to
germinate, but also for each plant to come to full matur-
rity and bear fruit. In the second place, by Nature's
methods, almost all fields bear a mixed vegetation, and
her rotations are maintained by slipping in a different

276

The Importance of Good Tilth. 277

plant where the accidents of life, or death from age, have
left vacant places ; but in agriculture certain crops must
occupy the field for the season to the exclusion of all
others, and in these differences in aims and methods we
find the chief needs for, and the great importance of,
good tilth and thorough tillage.

THE IMPORTANCE OF GOOD TILTH.

From what has been said regarding the thorough oc-
cupancy of the soil by the roots of our cultivated crops,
penetrating as they do three and four feet into the stiff'
clay subsoils, which have never been stirred, it may
seem tTiat a mellow seed bed should have no significance
so far as the growth and spread of roots are concerned.
Practical experience, however, proves beyond question
that a mellow seed bed is important, and a little reflec-
tion will make it clear why it must be so.

In the first place, when seeds are beginning to grow,
or when sets are transplanted into a new soil, there is
yet no organic connection between the plant and the soil
upon which it must depend for the supply of indispen-
sable moisture ; both the plant in the seed, and the set,
have limited stores of nourishment which can be devoted
to the development of a root system, placing that in vital
connection with the soil grains, and these stores must
be used up quickly, once the draft upon them has been
begun ; for, if they are not, pathogenic changes set in,
which result in their destruction and the death of the
seed or the set. Now, if the seed is placed under con-
ditions where it finds many obstacles in the way of a
free and symmetrical development of the first roots, it
loses time and food is wasted in getting so connected

278 The Soil.

with the soil as to be able to feed itself. A mellow seed
bed, with its many well-aerated pores, allows the roots
to grow unhindered in any and every direction, and to
place their absorbing surfaces in vital touch with the soil
grains and soil moisture. In this way the nourishment
in the seed produces the maximum root surface in the
shortest time, which is an evident and great advantage.

In the second place, our methods of tillage tend inevit-
ably to so alter the texture of the surface soils, especially'
if they are heavy, as to make the spread of young roots
through them more difficult, and hence thorough stirring
for tilth becomes more important than it was in the vir-
gin state. The frequent stirring tends to break down
the compound grain structure, so that the action of rains,
and of stirring when too wet, causes the soil grains to
run together into masses of so close a texture that the
young roots find difficulty in making their way among
them, and are insufficiently supplied with air even if they
succeed in doing so. It is this physical change forced upon
heavy clay soils which makes it so essential that they be
laid down frequently to grass and given time for bring-
ing together again into compound grains the minute
particles which frequent tillage tends to separate, and
which the rains cause to run together into masses of
close texture.

The perfect tilth and freedom from clods so character-
istic of virgin soils, is always more or less completely re-
stored whenever soils have been laid down to grass for a
sufficient length of time. After they are covered with
sod, the puddling action of rains is prevented, and, as the
roots grow and decay, the soil particles are wedged apart
in some places and crowded together in others. Then
the solvent action of carbon dioxide in the soil water re-

Management of Soil to Secure Good Tilth. 279

isults, through the deposit of the dissolved lime or other
materials, in cementing together the grains and in restor-
ing the more open and mellow texture characteristic of
virgin soils. It is plain from these facts that the laying
down of land to grass at frequent intervals is beneficial
in other ways than that of increasing the stores of cer-
tain kinds of plant food, and rotation of crops is seen to
have a significance in the good influence it has upon soil
texture.

MANAGEMENT OF SOIL TO SECURE GOOD TILTH.

When stirring soil to improve its texture, the amount
of moisture present at the time plays a very important
part in the final result. If water enough is present to
nearly or quite fill all the capillary spaces, leaving no
free water surface upon which surface tension can come
into play, then the individual soil particles move over
one another with the least resistance, and a little pres-
sure or stirring at such a time causes them to slip into
all large empty spaces and to assume the most compact
arrangement possible, but one very unfriendly to the
normal life processes going on in the soil. When the
amount of water becomes less, however, so that free
water surfaces are formed in all the larger non-capillary
pores, then surface tension comes into action, tending to
bind the particles of the compound soil grains and smaller
shrinkage lumps together, and plowing or otherwise stir-
ring the soil in this stage causes it to crumble and assume
that open texture so much sought for by those who ap-
preciate the importance of good tilth.

It sometimes happens, however, to clayey soils, which
are naked, that they become excessively wet through

280 The Soil

drenching rains, and if, under these conditions, not, drying
winds follow, so that water is evaporated from the sur-
face rapidly, an internal stress or strain is set up, which
tends to force the soil grains into the places vacated by
the water. Now if the drying is very rapid at the time
when the soil grains float together most easily, that is,
when the 5 or 6 inches below the surface the soil is nearly
full of water, then certain spots which, for any reason,
chance to be more resistant than others, come to be
centres toward which the surrounding soil grains begin
to move under the pull of surface tension, like the walls
of a soap bubble, and cracks are formed bounding large
blocks of soil, which are forming into clods. The width
of the cracks shows how much the internal pore space of
the blocks has been reduced, and how much the texture
of the soil is being injured by the destruction of needed
passage ways.

But if the drying after such wet times is slow, giving
time for the water to drain away as well as to evaporate,
then the soil moves upon itself with more difficulty, and
the effect of surface tension is to cause shrinkage about
very many rather than a few centres, and the formation
of large clods is averted. This being true, it is plain
that the formation of large clods under the former con-
ditions may be prevented by stirring the surface just as
soon as the ground is dry enough to permit this to be
done. Stirring the surface, as with a harrow or culti-
vator, at such times operates in two ways to prevent
the shrinkage into large blocks. It lessens the loss of
water at the surface, and thus gives more time for drain-
age before much drawing together has taken place, and
also by cutting or scratching the surfaces of large blocks
which have begun to form, they tend to divide it into

Management of Soil to Secure Good Tilth. 281

smaller sections on account of weakening due to the sur-
face cutting.

So, too, if the ground is plowed at such times, as soon
as the soil is dry enough not to puddle, then, as the
furrow slice is bent and doubled upon itself, it tends to
divide into innumerable layers, which, in shearing over
one another, break and pulverize any clods which have
commenced to form. This shearing or pulverizing action
of tlie plow will be seen at once, if the reader will close
this book and bend its leaves abruptly upon themselves.
As this is done, it will be observed that each leaf slips
past or upon the other. Just so it is with the plow,
and the steeper the mold board, that is, the more
abruptly the furrow slice is bent, the greater is the pul-
verizing effect; and it follows from this, that soils natu-
rally hard should, as a rule, be plowed with a steeper
plow than is necessary or desirable for the lighter and
naturally mellow lands.

If the leaves of this book were all glued rigidly
together, so that one could not slip upon the other when
bent, then no shearing would take place; but under
sufficient force, the leaves would break. So, too, with
the furrow slice; if the soil has become too dry before
plowing, the shearing or pulverizing effect of the mold
board is prevented, and the furrow simply breaks into
larger or smaller lumps, instead of small crumbs; and
not only is a poorer quality of work done, but more
energy must be expended to do it. It is evident, there-
fore, that those who have stiff clay soils to work need
to exercise great judgment regarding the condition the
soil is in when it is stirred, and these remarks apply to
harrowing and cultivation as well as to plowing.

In the case of corn ground, if a heavy rain has fallen

282 The Soil.

upon clay land after the crop is planted, great effort
should be made to stir the surface of that soil just as
soon as the team can walk upon it without sinking into
it more than 1 to 1.5 inches, and the heavier the soil,
the more important it is that just the right moment be
seized upon. If a light harrow is used in such cases, so
that a very shallow surface layer is moved, it is surpris-
ing to see how soon after a rain such land may be stirred,
and how helpful this slight stirring is in preserving the
open, mellow texture as well as needed moisture. It is
at such times as these that very shallow cultivation for
heavy soils is specially to be recommended, but to be fol-
lowed by deeper stirring as soon as the ground is drier.

We have already pointed out how important good
tilth is in securing the right temperature, adequate soil
ventilation, and less loss of water by evaporation.

From what has been said here, and in other places, it
follows that subsoiling for the sake of improving texture
will be desirable only in special cases. Well-drained
subsoils, which have been long under the influence of
vegetation and the action of burrowing animals, like the
earthworms and ants, appear to have become sufficiently
porous to meet the demands of most crops in humid
regions, so that deeper tillage than that needful to set
a crop fairly upon its feet is unnecessary. The depth
of surface tillage, for the sake of texture, should vary
somewhat with the crop, soil, and season. Where crops
with fleshy roots are to be grown in heavy soils, it
becomes specially important to secure an open texture
in order that the rapidly expanding tubers may find it
not too difficult to crowd the soil aside and make room
for themselves, and it is the difficulty in maintaining a
sufficiently yielding soil on the heavy clay, which makes

Burning and Paring. 283

hill qr ridge culture preferable many times to tlie level
tillage more generally used on the loose, friable lands.

In the semiarid regions, where irrigation is not ])rac-
ticed, and where the soil is fertile to considerable de})ths,
deep tillage, preparatory to seeding, and deep planting
are sometimes desirable to produce a texture so open
tliat the scanty rains may enter the soil deejjly and at
once, in order that it sliall not be lost by surface evapo-
ration, and that capillarity shall not return too mucli
water to the surface, as has been referred to. In such
cases the deep, open texture and methods of listing
allow seeds and roots adequate ventilation with a likeli-
hood of more water.

The texture of clayey soils, when fall plowed and
exposed to winter freezing, becomes sensibly altered and
usually for the better, a more crumbly and friable char-
acter being the result. As the soil water in wet clays
freezes, it is withdrawn from tlie interspaces to a con-
siderable extent, and built into crystals of varying sizes,
among the soil grains, in such a manner as to fissure and
crumble the clay, and if in the spring drenching rains
do not undo, by puddling, the action of the ice crystals,
the soil is left more open.

It is not improbable, however, that the action of
carbonic acid, in its tendency to flocculate the colloidal
clay, may play a very important, if not the chief, part
in transforming the cold, obstinate disposition of these
soils into a more friendly nature during the winter
weathering.

BURNING AND PARING.

It has been a common practice in some countries to
improve the texture of heavy clay soils by burning, and

284 The Soil,

the allied operation of paring and burning had, at one
time, an even more extended use.

Properly burnt clay loses its plastic quality and falls
easily into a light, friable powder, and those clays which
contain silicate of potash, with some carbonate of lime,
are most improved by the process.

It is essential in the burning of clay that it be not
allowed to pass much above a dull red heat; for other-
wise it becomes hard and brick-like and loses its chemi-
cal vigor to a large extent. When so treated, clay loses
its power of again becoming adhesive when wet, while it
apparently imparts the same quality to a considerable vol-
ume of that which has not been burned, thus giving to the
whole a much more open texture and less adhesive quality.

It has long been known to the arts that raw clay is
not easily acted upon, even by strong acids, and so in the
manufacture of chemicals the inert clay is exposed for
some time to a dull red heat, and in this process it
comes to be readily acted upon by sulfuric acid in the
operation of alum making. Whether the burning has
any other effect than to destroy the colloidal clay, and
thus render the mass easily penetrated by the acids, and
hence more readily acted upon, does not appear to be
well understood. But it is true that the clay becomes
much more porous, more easily worked and attacked by
chemical agents; and these are valuable qualities in any
agricultural soil. In burning clay, it is usually mixed
with brushwood or peat or sometimes with soft coal.
To better control the operation and hold the fire in check,
long, narrow trenches are sometimes dug and then filled
in with alternate layers of brushwood and clay and,
after being fired, more clay and fuel added as the burn-
ing proceeds.

Texture of Soils Influenced hy Fertilizer?^. 285

The allied process of paring and burning seems now
to have largely gone out of use, though in parts of Europe
it was quite general on certain lands. It consisted in
shaving off 1 to 3 inches of the surface soil with its
sod or stubble and gathering it together into heaps to be
burned, when dry enough, with the aid of the roots,
stubble, and other organic matter it may have contained.
The process was, of course, attended with considerable
losses of nitrogen, and hence was wasteful besides being
laborious and costly, but it did produce marked beneficial
effects on many soils.

It seems that liming, and the thorough underdraining
of such lands, which have come into vogue, have now
rendered these methods of tillage nearly or quite obsolete.

TEXTURE OF SOILS INFLUENCED BY FERTILIZERS.

There appears to be a large number of substances, and
among them many of the chemical fertilizers, which have
an appreciable influence in altering the texture of the
soil, making it more or less open and friable. Among
those which have the power of flocculating colloidal clay,
lime has been most generally recognized, and it appears
that this may be applied to the soil either as the oxide,
hydrate, or carbonate, with the same ultimate effect,
though perhaps with varying rates of action. We
have already referred to Hilgard's and Schlosing's
observations regarding this action of lime.

More recently R. Sachsse and A. Becker have experi-
mented with lime-water, gypsum, sulfate of magnesia,
sulfate of ammonia, chlorides of potassium, sodium,
and ammonium, and carbonic, hydrochloric, nitric, sul-
furic, and silicic acids^ as regards their power to bring

286 The Soil.

about a compounding of minute silt particles into clus-
ters constituting grains of larger size. Working with a
nearly pure kaolin, consisting of particles so small that
only .5 per cent of them were as coarse as .0004 of an
inch, they found one part of lime would flocculate 20.7
parts of kaolin which had remained suspended in 27.777
parts of water. A similar effect was observed upon a
heavy clay loam, but not upon a humus alluvial loam.
On examining the sizes of the particles, after flocculation
had taken place, it was found that in the case of the
kaolin and clay loam, the diameters of very many of
them had materially increased, but that in the case of
the alluvial soil no appreciable change had occurred.

Studying the effects of lime on the percolation of
water through kaolin and the clay loam, the persons
referred to above found that while no water would pass
through the untreated clay loam, yet when 61.2 cc. of
water were poured over the tube treated with lime, it
reached the bottom of the column in 1 hour and 10 min-
utes, and 22.5 cc. drained through. In the case of the
kaolin, of the 40 cc. added, 19 drained from the limed
tube, while only a few drops percolated from the one
untreated, and in that the kaolin swelled so much as to
finally burst the tube.

Carbonic acid flocculated the kaolin readily, and so did
the hydrochloric, nitric, and sulfuric acids. While land
plaster and the sulfates of magnesia and of ammonia
were found to have the same power to some extent, their
influence was not marked. Common salt and the chlo-
rides of potash and ammonia also flocculated the clay
and the kaolin, but the nitrate of soda had the opposite
effect.

If it is true that nitrate of soda has a tendency to

Texture of Soils Influenced by Fertilizers. 287

destroy the flocculatiou of clay soils and render them
closer in texture, it would follow that, when supplies of
nitrogen need to be added to these soils, they should be
given in some other form than the Chile saltpetre.

Either directly or indirectly, fertilizers exert an influ-
ence upon the relation of water to the soil, as, indeed,
has been implied in what has been said regarding their
power to make the texture of the soil finer or coarser.
If, by making the soil coarser grained, water percolates
through it more readily, and its water-holding power is
decreased, it should be expected that the capillary power
will also be influenced; and observations have already
been cited, showing that potassium nitrate increases the
amount of water lifted by capillarity through a column
of sand, while solutions of lime, land plaster, and salt
decrease the amount, when compared with distilled
water. Now, these effects may be brought about through
changes in the texture of the soil or through a strength-
ening or weakening of the surface tension. In the cases
we have cited, on a former page, however, only the effect
of the potassium nitrate is readily explained by either of
these modes of action, taking Whitney's measurements of
surface tension as a basis, because all of these salts are
given as increasing it, while only one of them increased
the rate of capillary rise through the sand ; which cannot
be assumed to have been materially altered by floccu-
latiou.

When fertilizers are applied, the soil may react upon
them either chemically or physically, and in such, a
manner as often to wholly prevent or greatly diminish
their loss in drainage waters at times when percolation
is taking place. Many observers have noted that, on
filtering salt water through sand, the first which comes

288 The Soil.

through is nearly free from salt, but when any soil
becomes saturated, so to speak, with any particular
fertilizer, then all excess may be leached away, and this
fact has an important bearing on the application of ferti-
lizers to lands, and shows that lighter dressings, often
repeated, are likely to be less wasteful than heavier ones
applied at longer intervals. This statement has even
greater importance when applied to the organic ferti-
lizers, like farmyard manure ; for the richer a soil is in
organic matter, the more rapidly will fermentation be set
up in it under good tillage, and under these conditions
nitrification is liable to be more rapid than is required
to meet the demands of the crop on the ground. But if
this is true, the soil becomes charged so that when per-
colation takes place a large loss of nitrogen may occur.
It is plain, therefore, that it is better to spread the
manure over a larger area in the right amount than to
concentrate it in heavy dressings on small areas.

INFLUENCE OF FARMYARD MANURE ON SOIL
MOISTURE.

Farmyard manure has a marked effect upon the amount
and distribution of soil moisture in cultivated fields.
When coarse manure is plowed under, its first effect is
to act as a mulch to the unstirred soil, by breaking the
capillary connection between it and the surface layer.
The tendency, therefore, is to cause the surface soil to
become drier than it would otherwise have become in
the same time, and frequently to an injurious extent,
especially in times of spring droughts, before seeds have
germinated or young plants have developed a root system
reaching into the deeper soil. On such occasions as

Farmyard Manure on Soil Moisture. 289

these, the heavy roller is of service in making a better/
capillary connection with the unstirred subsoil.

Farmyard manure has a general tendency to leave the
upper three feet of soil more moist than it would be with-
out it, and the drier the season and the more thorough
the manuring, the more marked is its influence. In ex-
periments to measure this influence under field conditions,
the writer has found, as a mean of 3 years' work, that for
manured fallow ground the surface foot contained 18.75
tons more water per acre than adjacent and similar but
unmanured land did, while the second foot contained
9.28 tons and the third 6.38 tons more water, making a
total difference in favor of the manured ground amount-
ing to 34.41 tons per acre. The largest observed differ-
ence was 72.04 tons in the dry season of 1891. Early in
the spring, on ground manured the year before and
fallow, there was an observed difference amounting to
31.58 tons per acre.

It is a fact long ago observed that increasing the
organic matter in the soil increases its water-holding
power, and this being true, it was to be expected that
the surface foot would be more moist as a consequence
of manuring, but by referring to the table on the next
page, it will be seen that the influence of the manure is
felt below the level to which it is applied.

A part of the observed difference in the water content
of manured and unmanured soils is to be explained by
the fact that the rate of surface evaporation is dimin-
ished by the dressing of dung. In the case of two
cylinders 42 inches deep and holding nearly 600 pounds
of soil, one manured and the other not, the writer found
that the unmanured cylinder lost, in 105 days, at the rate
of 108.5 tons more water per acre, a difference. of about

290

The Soil.

TABLE SHOWING EFFECT OF FARMYARD MANURE ON THE
WATER CONTENT OF THE SOIL AT DIFFERENT DEPTHS
BELOW THE SURFACE.

Surface
Foot.

2d Foot.

3d Foot.

4th Foot.

5tii Foot.

6th Foot.

Date.

<

12;
<

o

<

»
r,

o

<

- w

t>
I?
<

o

M
U
Iz;
<

■A
O

<

<
o

w ■

'A

o
12;

Per cent.

Per cent.

Per cent.

Per cent.

Per cent.

Per cent.

July 22,1891

17.37

16.41

19.87

17.63

17.03

16.36

12.00

12.78

14.69

15.40

18.01

20.06

Sept. 12, 1891

13.75

12.76

16 41

14.89

15.67

14.49

12.96

11.59

11.49

10.96

15.61

15.99

Apr. 11, 1892

23.56

22.86

20.66

20.55

18.26

17.50

16.50

16.53

16.88

17.53

19.72

19.41

July 13, 1892

25.89

24.36

24.01

23.87

23.72

23.29

23.74

23.32

Aug. 80, 1892

25.64

24.76

24.42

24.34

24.21

23.74

21.69

21.72

Aug. 12, 1893

19.07

17.91

17.35

17,7S

16.37

17.88

17.45

17 99

Sept, 9, 1893

13.55

12.50

16.13

1G.22

16.90

16.94

16 71

17.30

Mean . . .

19.88

18.79

19.79

19.33

18.88

18.60

17.29

17.32

14.35

14.63

16.98

17.13

Difference ,

1.09

.46

.28

.03

.28

.15

Tons per acre

18.75

9.28

6.38

.69

6.75

3.63

1 ton per day. In another case wetting tlie surface of
sand with water leached from manure reduced the rate
of evaporation from the surface from 64.98 pounds per
unit area to 32.72 pounds in the same time, under othei-
wise identical conditions.

But the table shows that farmyard manure exerts an
influence different from simply decreasing the surface
evaporation ; for, while the upper three feet of the dunged
land is more moist than that not so treated, the reverse
is -true when the next three feet are compared. Indeed,
results analogous to wetting the surface soil and to
firming it are observed. It appears as though the deeper
soil water had been brought nearer to the surface, .where

Physical and Chemical Effects of Fallowinrf. 291

it may become available for crop production, and in the
writer's opinion this really does take place.

On manured ground which is producing a crop,, while
a much larger yield of dry matter is produced per acre,
the soil at the end of the growing season is found only
a little drier, from which it follows, either that less
water is required to produce a pound of dry matter in
the rich soil, or else that the manure in some way makes
more Avater available, and when the matter comes to be
thoroughly understood, it is not improbable that both
propositions will be found true.

PHYSICAL AND CHEMICAL EFFECTS OF FALLOWING.

That form of tillage known as fallowing exerts
marked physical and chemical effects upon a soil, not
felt, at least with like intensity, on lands heavily
cropped. One of the most marked effects produced by
fallowing is that exerted upon the water content of the
soil. Not only is the fallow ground more moist during
the fallowing period, as indeed should be expected, but
the influence is felt the following spring, and even at the
end of the harvest after the crop has been removed
from the ground.

The writer found, for example, in the spring succeed-
ing a summer fallow, after all of the fall, winter, and
spring rains, that the land which had been fallowed con-
tained, in its upper four feet, 9.35 pounds to the square
foot, or 203 tons per acre, more water than did that which
had been cropped the season before. Nor was this all ;
for at the end of the growing season and after large
crops of oats and barley had been harvested from the
land, there WAS still a difference in the water content of

292 The Soil

the upper four feet amounting to 8.21 pounds on both the
oat and barley ground, or 179 tons per acre. That the
.differences here recorded were not due to inherent dif-
ferences in the soil, is proved by the water content of
the same lands taken at three different times before the
fallowing experiments began. The mean of these three
determinations showed a difference of only .7 pounds in
favor of the piece which was subsequently fallowed, as
against 9.35 pounds in the spring and 8.21 pounds after
the harvest succeeding the fallowing. It is plain, there-
fore, that summer fallowing a piece of land exerts a
strong influence over its relation to soil moisture, and
one which is not outgrown for more than a year.

Common experience, too, shows that the productiveness
of the same lands is much increased, nor is it strange
that this should be so. For when we call to mind the
large stores of comparatively inert nitrogen which all
good soils have been shown to possess, and then reflect
upon the conditions which are most favorable to the
nitrification of this humus, it must be very evident that
in the warmer, more moist, and frequently stirred and
aerated fallow field there must be a much larger conver-
sion of inert nitrogen into active forms than could pos-
sibly take place in the soil so thoroughly occupied by
the roots of a crop ; that neither sufficient moisture nor
other forms of food are available for the full and vigor-
ous development of the microscopic soil life so indispen-
sable to the processes here in question. When a soil is
sapped to dryness and depleted of its soluble phosphates,
lime and potash, the action of microscopic life in it
must come nearly to a standstill and the development of
fertility nearly cease.

The Lois-Weedon system of tillage, which the Rev.

Physical and Chemical Effects of Fallowing. 293

Mr. Smith practiced in Northamptonshire for many
years, was simply a judicious application of summer
fallowing and a revival, in modern form, of the doctrine
taught by Jethro Tull, between 1G80 and 1740, that thor-
ough and proper tillage might take the place of manure.

Mr. Smith laid off his fields in lands 5 feet wide,
and on these in successive years, by alternation, he grew
wheat continuously, raising the yield per acre from 10
bushels to 34, as an average of many years. In this
rotation the fallow strips were frequently and deeply
stirred, which favored the complete utilization of the
native fertility of his soil and that left in the ground
by the roots and stubble of the crop harvested.

In adopting this system, Mr. Smith left a considerable
portion of his land where nitrates could be developed
in it under the best of conditions, and at the same time
where the plants along the margins of the tilled lands
could reach their roots out into the enriched soil and
avail themselves of both its native moisture and its
nitrates as they formed.

The practice now in vogue in parts of Europe of grow-
ing grain in drills far enough apart to permit of cultivat-
ing the soil between the drills with horse cultivators, is
carrying the idea of Tull and of Smith to the extreme
limit, and is, of course, placing the growing of these
crops on the same basis as that which we follow with so
much success with corn, potatoes, and the like.

The special advantage which these methods of summer
fallowing, for such they in reality are, have over the old
method of broad fields, is that the fertility developed
may be utilized by the crop the same season, and thus the
risk of losing a part of it through leaching by the winter
and spring rains may be largely reduced.

294 The Soil,

In very wet climates or more especially in those whicli
have heavy rainfall outside the growing season, so that
excessive percolation and loss of plant food through
drainage is large, summer fallowing in broad fields can-
not be recommended. But in dry countries, Avhere the
loss of plant food through drainage channels is small,
broad-field summer fallowing may in some cases prove
decidedly advantageous, because, with the deficient rain-
fall, there may not be moisture enough to mature a
paying crop and at the same time to develop a suffi-
cient store of plant food from the native fertility of
the soil to meet the demands of the next season. At
all events, the arguments urged against fallowing in
countries like England do not apply to the semiarid
districts of the world with equal force.

INDEX.

A.

Abbot, Col., cut-offs in Mississippi
River, 46.

Actiniae, symbiotic life of, 129.

Aeration of soil, influenced by
drainage, 76.

Aeration of soils, 230.

Air and soil, 239.

Air in soil retards percolation,
173.

Algae, symbiotic life of, 129.

Aluminum, 79.

Amazon, volume of discharge, 24.

Ammonia, in air, 12 ; brought down
by rain and snow, 119; absorbed

- by soil, 122; in air on Mont-
souris, 123; decomposed by mi-
cro-organisms. 131.

Ammonium carbonate, absorbed
by plants from the air, 122.

Arendt, distribution of silica in
plants, 97.

Argon, amount of, in the atmos-
phere, 11.

Arid soils, texture, 29, 31 ; effect
of lime in, .30, 94 ; amount of lime
in, 30, 94; chemical composition
of, 84, 85, 8(), 87 ; compared with
humid soils, 92.

Ash ingredients, of plants, 101 ;
relation between demand and
supply, 113.

Asphalt, origin of, 20.

Atmosphere, its work, 9; pressure
of, 9', relation of, to eating.

drinking, and breathing, 10;
depth of, 11 ; composition of, 11,
23, 123; retains solar heat, 12;
selective power of different con-
stituents, 14; a distributing
agent, 15; currents in, 23.
Atwater, Prof., analysis of night-
soil, 133.

B.

Bacteria, nitrifying, 125; observa-
tions of Frank, Schlosing, Jr.,
Laurent, 129; producing ammo-
nia, 131.

Baker, J. O., quoted, 255.

Barley, roots of, 208, 212.

Barley, water used by, 155.

Barometric pressure, oscillation
due to changes in, 179.

Beans, fixation of free nitrogen
by, 124 ; water used by, 155.

Becker, A., quoted, 285.

Hisulfid of carbon, absorption of
solar energy by, 8.

Bitumen, origin of, 20.

Blue grass, roots of, 212.

Borax, 79.

Boron, 79.

Buckwheat, water used by, 156.

Burning land, 283.

C.

Calcium, 80.

Capillarity, 135, 138 ; measured in

296

296

Index.

horse power, 142; the work of
sunshine in, 146.

Capillary movement, 142; of soil
water, 173; rate of, 174; in dry
soil, 176 ; decreased by plowing,
177 ; influenced by dissolved
salts, 177.

Capillary tubes, height of water
in, 140.

Carbon, in soil, 77.

Carbon dioxide, in air, 11 ; corrosive
power of, 19; liocculation by,
31, 76, 78.

Catch crops, in relation to mois-
ture, 190.

Celtic land beds, 263.

Chemical analyses of soils, 84, 85,
86, 87 ; interpretation of, 89.

Chile saltpetre, 81.

Chlorine, 78, functions, 99; in
rain water, 121.

Chlorophyll, importance of iron, 98.

Clay, in soil, 28; flocculated by
lime, 30; colloid, 30; flocculated
by carbon dioxide, 31 ; influence
of drainage on texture of, 76;
alumina in, 79 ; influence on per-
colation, 172.

Clayey soil, compared with sandy
soil, 90 ; yields water to plants
with diflSculty, 161 ; contamina-
tion of well water in, 169.

Clover, ash ingredients, 102; in-
creases soil nitrogen, 118, 124;
water used by, 155.

Clover, roots of, 208, 212.

Coal, formed by life, 20.

Cold waves, relation to storms, 14.

Colloids, movements of, 153.

Color of soil, and warmth, 230.

Color waves, 7.

Conservation of energy, 21.

Conservation of moisture, 184.

Corn, amount of water used by,
155.

Corn, roots of, 208, 209.

Craigentiany meadows, 269.

Crocker, amount of nitrogen in

cultivated soil, 107.
Cultivating to conserve moisture,

192.

D.

Darwin, G. H., tidal friction, 17.

Darwin, Charles, action of earth-
worms, 62.

Denitrification, 130, 132, 133.

De Vries, observations on osmotic
pressure, 148.

Diffusion, 147.

Drainage, 253.

Drainage, influence of, on soil tex-
ture, 76.

Drains, movements of water in,
due to soil air, 179.

Dry-earth closets, 133.

Dust, retards radiation, 14.

E.

Early seeding, 190.

Earth, cooled by water, 16.

Earthworms, 61.

Eel grass, 67.

Electricity, production of nitrous
and nitric acids by, 123.

Elliott, C. G., quoted, 264,265.

Erosion, by rains, 50 ; by glaciers,
55, 58.

Ether waves, velocity of, 6 ; complex
character of, 7 ; absorbed by bi-
sulfid of carbon and alum water,
8 ; absorbed by water, 8.

Evaporation and soil temperature,
225.

Evaporation, caused by sunshine,
4, 145; nature of, 143; unneces-
sary amount from plants, 156;
retarded by deposit of salts on
soil, 175.

Evolution, organic, 31 ; relation of
soil to, 31; of true roots, 35; of
woody fibre, 36; of forest trees,
36.

Index.

297

Fallowing, effects of, 291.

Fall plowing, 187.

Farm drainage, 253.

Farming, need for improved meth-
ods, 3.

Farmyard manure and soil mois-
ture, 288.

Fertilizers and soil texture, 285.

Fertilizers, effects of, 27(5.

Fertilizers, experiments of Sir J.
B. Lawes, 105.

Flocculation, by lime, 30; by car-
bon dioxide, 76.

Fluorine, 79.

Forced meadows, 269.

Frank, nitrifying bacteria, 129.

Free nitrogen-fixing germs, 124.

G.

Gases, precipitation of minerals
by, 20; origin of natural, 20.

Glaciers, origin of, 54 ; in soil for-
mation, 55 ; extent of action, 56 ;
mode of action, 58; moraines of,
60; magnitude of work, 61.

Glauconite, 80.

Granite, water absorbed by, 39.

Greensand, 80.

Gypsum, 78.

H.

Hauksbee, early studies of capil-
larity, 136.

Harrowing, to conserve moisture,
192.

Heat, absorption and radiation of,
3 ; causing air currents, 4 ; part
played in solution, 144.

Hellriegel, fixation of free nitro-
gen, 124; fixation of nitrogen by
lupines, 126 ; water used by
plants, 135 ; best amount of soil
moisture, 161.

Hiawatha, quoted, 211.

Hilgard, E. W., effect of lime on
clay, .30; lime in arid soils, 30,
M ; mechanical analyses of soils
by, 70 ; composition of humus, 96.

Hilgard, quoted, 285.

Horse power, measure of solar
energy expressed in, 6.

Humid soils, 64; texture of, 29, 31 ;
formation of, 64 ; in lakes, 6() ; by
rivers, 65; chemical composition
of, 84, 85, 86, 87 ; compared with
arid soil, 92.

Humus, 94 ; relation to fertility, 94 ;
origin, 95 ; richer in nitrogen in
arid regions, 96 ; Hilgard and
Jaffa on composition, i)6.

Hydrogen, 78.

Hygroscopic moisture, 252.

Iceland moss, 34.

Illinois, drainage in, 254.

Iron, 81 ; importance in plant life,

98.
Irrigation, 268.

J.

Jaffa, composition of humus, 96.

K.

Kainite, 81.
Kaolin, potash in, 81.
Kelvin, Lord, 6.

Kosswitsch, nitrifying bacteria,
129.

L.

Lakes, overgrowing, 66 ; formation
of swamp soils in, GQ ; oscillations
of, 179.

Land plaster, 78 ; decreases capil-
lary movement, 177.

298

Index.

Langley, Professor, observations
on atmospheric absorption, 13.

Lathyrus sylvestris, roots of, 212.

Laurent, nitrifying bacteria, 129.

Lawes, Sir J. B., experiments on
the influence of fertilizers, 105;
nitrification of soils, 109.

Leguminous plants, fixation of
free nitrogen by, 124.

Leonardo da Vinci, phenomena of
capillarity, 136.

Level culture and moisture, 202.

Lichens, 34; examples of symbiosis,
128, 130.

Life, relation of water to, 18; its
work in rock and soil building,
18, 20; microscopic forms in soil,
19; formation of coal, peat, etc.,
20 ; accumulation of phosphorus
by, 79 ; symbiotic, 128 ; processes
producing nitric acid, 131.

Lime, effect on soil texture, 30;
flocculation by, 30 ; in arid soils,
94 ; amount in soil, 102; decreases
capillary movement, 177.

Limestones, formed by life, 20;
composition, 80.

Loess, 69 ; texture of, 75 ; chemical
composition, 84, 85, 86, 87.

Lois-Weedon system, 292.

Lupines, fixation of free nitrogen
by, 124 ; experiments by Hellrie-
gel, 126.

M.

Madison River, shiftings of its

course, 48.
Magnesia, amount in soil, 102.
Magnesium, 80.
Maize, roots of, 208, 209.
Maize, water used by, 24, 155.
Manganese, 81 ; brown oxide of,

93.
Manitoba, amount of nitrogen in

soils, 108.
Manna, 34.

Manure and moisture, 288.

Marshall, quoted, 263.

McGee, W. J., Mississippi bad
lands, 50.

Mechanical analj'sis of soil, 71, 90.

Microscopic life in soil, 19, 20, 37 ;
in fixation of nitrogen, 124; in
the production of nitrous and
nitric acids, 131; in denitrifica-
tion, 1.32 ; deoxidation by, 132.

Mississippi, bad lands, 50 ; soils, 70.

Mississippi River, materials borne
in solution, 17, 25 ; volume of dis-
charge, 24; solids moved by, 25,
48 ; bends in, 46 ; ox-bones, 46.

Moisture and manure, 288.

Moisture, conservation of, 184.

Moisture, in air retards radiation,
14.

Montsouris, analysis of air on, 123

Moraines, 60.

Moss, Iceland, 34; Reindeer, 34;
Tripe de Roche, 34; sphagnum;
66.

Mother of petre, 241.

Mulches, to conserve moisturcj 19<L.

Miintz, deoxidation in water-
logged soils, 132.

Myremill farm, 270.

N.

Nerust, W., nature of solution,
145.

Night soils, denitrification of, 133.

Nitrates, deoxidation of, in soils,
115 ; effects of percolation on
distribution, 117 ; destruction of,
131, 132; movement of, in plants,
150.

Nitre farming, 241.

Nitric acid, 79; constituent of the
atmosphere, 12; corrosive power
of, 19; amount in soil, 114; in
rain and snow, 119 ; produced by
electricity, 123; life processes
producing, 131.

Index.

299

Nitrification, 130,

Nitrogen, 11, 7i>; .imoniit in tlu;
soil, 107; in soils of Manitoba,
108; importance of, in plant
growth. 111 ; relation between
demand and supply, 113; forms
of, in the soil, 114; stored as liu-
mus, 115 ; distribution in the soil,
115; sources of, in soil, 117; in
soil increased by clover, 118;
brought down by rain and snow,
119; fixed by microscopic life,
124; fixation by lupines, 127;
Wagner's experiments, 127, 129;
loss of, in night soils, 133.

Nitrous acid, produced by elec-
tricity, 123 ; produced by nitrous
ferment, 131.

Nitrous ferment, 131.

Nollet, Abbe, early observation on
osmosis, 148.

O.

Oak, roots of, 214.

Oats, amount of water used by,
155.

Oats, roots of, 208, 212.

Ocean, mean depth of, 16.

OchrOj red and yellow, 81.

Oil, origin of mineral, 20.

Organic laatter, deoxidation of, in
soil, 115.

Osmosis, 147; experiments i:i, 148.

Ostwald, magnitude of surface ten-
sion, 138,

Outlets of drains, 266.

Oxygen, 11 ; in soil, 77.

Ozone, 1-j ; action in producing ni-
trous and nitric acids, 123.

Paring land, 283,

Peas, fixation of free nitrogen by,

124, 126, 128; amount of water

used by, 155.
Pelouze, influence of size of grains

on rate of solution, 74.

Percolation, effect on distribution
of nitrates, 117; rate of, from
sand, 158. 171 ; of water into
wells, 167; direction of, 170;
rate of, through different soils,
171 ; observations by Wollny,
172; retarded by air in soil, 173;
effected by barometric changes,
179.

Peroxide of hydrogen, action in the
production of nitrous and nitric
acids, 123.

Pfeffer, W., observations on osmo-
tic pressure, 148.

Phosphoric acid, amount of, in
manure, 74; amount in soil, 102.

Phosphorus, 78 ; importance in
plant life, 110.

Physical effects of tillage, 276.

Plants, relation to soil formation
and soil destruction, 19; rela-
tion to types of soil, 100; ash
ingredients, 101 ; circulation in,
149; movement of nitrates in,
150; movements of starch, gum,
and fats, 151; selective power
in, 152; amount of water used
by, 155 ; unnecessary evapora-
tion from, 156.

Plant feeding, process of, 149.

Plant grow^th, part played by sun-
shine in, 5 ; importance of nitro-
gen, 110; amount of nitrogen
demanded, 113.

Plowing decreases the rate of
capillary movement, 177.

Plowing to save moisture, 187.

Potash, amount of, in manure, 74 ;
distribution, 80; amount in soil,
102.

Potassium, 80.

Potassium carbonate, effect on
capillary movement, 178.

Potassium nitrate increases cap-
illary movement, 177.

Potatoes, amount of water used by,
155.

800

Index.

Precipitation, nature of, 4.

Pressure of atmosphere, 9; meas-
ure of, 9 ; relation of, to breath-
ing, eating, and drinking, 10;
variations of, the cause of winds,
10; variations with light, 11.

Q.

Quartz, abundance of, in soil, 77.
Quincke, surface tension, 139.

R.

Radiolaria, symbiotic life of, 129.

Rainfall, insufficiency of, 25, 156.

Rains, action in soil formation, 50;
erosion by, in Mississippi, 50;
ammonia and nitric acid brought
down by, 119; composition of,
120.

Rains and soil warmth, 233.

Rains for irrigating, 274.

Ramsey, Prof., 11.

Read, T. M., rock dissolved by
water, 19.

Reighley, Lord, 11.

Richthofen, formation of loess,
69.

Rivers, action in soil formation,
46, 48; in formation of swamp
soils, 65 ; oscillations in, 179.

Rock, thickness formed by water,
17; structure of, in soil forma-
tion, 38 ; fissures in soil forma-
tion, 42; fractured by roots, 42.

Rogers, the Messrs., experiments
on the rate of solution, 74.

Rolling, and soil temperature, 235.

Rolling, effect on moisture, 200.

Root hairs, part played in solution,
146; osmotic movement in, 150.

Roots, distribution of, 207.

Roots, evolution of, 35 ; rocks frac-
tured by, 42, 43; extent of con-
tact with soil, 75; development
in light soil, 99.

Roots in drains, 266.

Root surface, 207.

Rotation of solid land, 26; of allu-
vial soils, 48.

Rothamsted, distribution of nitro-
gen in soils, 115.

Rye, amount of water used by
155. *

S.

Sachs, observations on function of
iron, 98.

Sachsse, quoted, 285.

Salt, in rain water, 121; decreases
capillary movement, 177.

Sand, water retained by, 157.

Sandy soil, compared with clay
soil, 90 ; size of grains, 100 ; water
capacity influenced by distance
to water table, 160; yields water
to plants readily, 161.

Schlosing, per cent of clay in soil,
28; flocculation by carbon di-
oxide, 31 ; absorption of ammo-
nia by soil, 122; denitrification,
132.

Schlosing, quoted, 285.

Seeding, early, 190.

Seeds, ash ingredients of, 80.

Shaler, formation of salt marshes,
67.

Shaler, quoted, 253.

Shrinking of soils, 249.

Silica, abundance of, in soils, 77;
soluble, 84, 93, 102 ; functions, 97;
distribution in oat plant, 97.

Slope of land, and warmth, 228.

Smith, Dr. Angus, composition of
rain water, 120 ; denitrification in
sewerage, 132.

Smith, Rev., quoted, 292.

Snow, ammonia and nitric acid
brought down by, 119.

Soap bubbles, illustrating surface
tension, 136.

Soda, amount in soil, 102.

Index.

801

Sodium, 78, 81 ; chloride decreases
capillary movement, 177.

Soil, nature of, 27; clay in, 28;
comparison of subsoil with, 29;.
texture of arid and humid, 29;
a storehouse of water, 37 ; micro-
scopic life in, 19, .'57; formation
by running water, 45, 4G; over-
placement of, 53 ; of glacial ori-
gin, 55, 56; prairie, relation to
glacial action, 60; swamp or
humus, 64; formation by winds,
68; loess, 69; texture of, 70;
mechanical analyses of, 71 ; ex-
tent of contact of roots with, 75 ;
chemical constituents, 76; sandy,
description of, 82; clayey, 83;
chemical composition of, 84, 85,
86, 87 ; kinds, 99 ; warm and cold,
99 ; amount of nitrogen in, 107 ;
distribution of nitrogen in, 115;
absorbs ammonia from the air,
122; capillary rise of water in,
139, 141 ; water capacity, 157,
159; rate of capillary rise in,
174, 176.

Soil air, movements of soil water
due to, 178; producing diurnal
oscillations of soil water, 180.

Soil grains, size of, 72 ; influence
of size on water capacity, 72,
157, 160; smallest not individu-
ally invested by water films, 73 ;
influence of size on rate of solu-
tion, 72 ; compound structure of,
75 ; in varieties of soil, 100; influ-
ence of size on percolation,
171.

Soil moisture, part played in soil
fertility, 154; best amount of,
161 ; conservation of, 177.

Soil temperature, 218.

Soil texture, 70; influence of, on
water capacity, 72 ; influence of,
on food supply, 74 ; influenced by
drainage, 76; influence of, on
capillary movement, 176, 177

Soil water, movements of, 170, 173 ;
movements due to soil air, 178;
diurnal oscillations of, 180.

Solution, 142; I'elouze and K<;gers,
experiments on rate f)f, 74 ; intlu-
ence of size of soil particles on
rate of , 74 ; nature of, 142 ; iiitlu-
ence of temperatur(! on, 144 ; j)art
played by root hairs in, IKJ.

Sphagnum moss, 66.

Springs, flow of, influenced by
barometric changes, 18C.

Spring plowing, 188.

Starch, movements oi, in plants,
151.

Storer, amount of nitrogen in soil,
107 ; dry-earth closets, 133.

Storer, quoted, 269.

Sub-irrigation, 260; natural, 171.

Subsoil, 29; chemical composition,
84, 85, 86, 87; compared with
soil, 92.

Sulfur in soil, 78, 97.

Sulfuric acid, amount in soil, 102;
in rain water, 121.

Sun, work done by, 6.

Sunshine and its work, 3; nature
of, 3; causing evaporation, 4;
stored in the soil, 5 ; part played
in plant growth, 5; velocity of,
6 ; measured in horse power, 6 ;
absorbed by bisulfid of carbon,
8 ; snow and ice opaque to dark
rays of, 8; solution and move-
ment of plant food, 144 ; in capil-
larity, 146.

Surface drainage, 262.

Surface tension, 136; magnitude
of, 138; distance over which it
acts, 139; part played in solu-
tion, 143; modified by dissolved
salts, 177.

Swamp soils, 64; formation by
rivers, 65; in lakes, 66; by the
sea, 66 ; by eel-grass, 67 ; chemi-
cal composition, 84, 85, 86, 87.

Symbiosis, 128, 134.

302

Index,

Temperature of soils, 218.

Temperature of the earth without
an atmosphere, 1.'3; changes of,
in soil formation, 39; influence
on solution, 144; influence on
water capacity, 160; diurnal os-
cillations of soil water due to
changes of, 183.

Texture of soil, 70; influenced by
drainage, 70.

Texture of soils influenced by fer-
tilizers, 285.

Tidal friction, 17.

Tillage and moisture, 192.

Tillage, deep, and moisture, 202.

Tillage, physical effects of, 276.

Tilth, importance of, 277; to se-
cure, 279.

Timothy, roots of, 212.

Translocation of moisture, 195.

Tripe de Roche, 34.

Tubercles on roots of leguminous
plants, 124, 125.

Tull, Jethro, 293.

U.

Underdraining, 257.
Underdraining and aeration, 248.
Underdraining and temperature,
225.

V.

Van't Hoff, nature of solution, 145.
Velocity of ether waves, 6.
Ventilation of soils, 239.
Voeleker, composition of farmyard
manure, 74.

W.

Wagner, P., fixation of nitrogen by
peas, 127 ; importance of nitric
nitrogen, 129.

Waring, Col., dry-eiarth -clotjets,
133.

Warington, nitrogen removed from
soil by wlieat, 107; amount of
nitric acid in soil, 114; produc-
tion of nitrous acid, 123 ; produc-
tion of nitric acid, 123; denitrifi-
cation in water-logged soils, 132.

Warmth of soils, 220.

Water in soils, 184.

Water, opaque to dark rays, 8 ;
and its work, 16; cooling the
earth, 16; retards earth's rota-
tion, 17; dissolving and trans-
porting power, 17, 19 ; importance
in life processes, 18 ; magnitude
of movement of, 24 ; absorbed by
rocks, 39 ; freezing of, in soil for-
mation, 39 ; solvent action of, 39 ;
running, in soil formation, 45;
amount used by plants, 155 ; ca-
pacity of soils for, 155 ; retained
by sand, 157; capacity of field
soils for, 159; yielded to plants
by kinds of soil, 161 ; contamina-
tion of, in wells, 167 ; percolation
into wells, 168; rate of capillary
rise in soil, 174, 176.

Water capacity, influence of size of
soil grains on, 72 ; of field soils,
159.

Water films, on soil grains, 72.

Water table, 163; influence on
water capacity of soils, 160,- po-
sition influences land values, 162;
altitude of , 163 ; height variable,
163 ; wells most affected by sea-
sonal changes, 166.

Waves, ether, 6; velocity of, 6;
complex character of, 7; kinds
of, 7 ; absorbed by water, 8. "

Weight of soils, 185.

Wells, 162, 167 ; relation to water
table, 163; conditions to be ob-
served in digging, 166; most
affected by seasonal changes of
the water table, 166; depth below

Index.

303

water table iiiflnences capacity,
1(57; ('onlamiiiation of water in,
167; niovemeiits of water in, due
to soil air, 179,

Wheat, amount of water used by,
155.

Wheat, roots of, 212.

Whitney, mechanical analyses of
soils, 91.

Wiley, mechanical analyses of soils,

Wilson, H. M., quoted, 273.

Wilson, John, quoted, 270.

Windmill.s for irrigatinfc, 274.

Winds and soil moisture, 204.

Winds, systems of, 23 ; soils formed
by, (58; caused by sunshine, 4;
maintain uniform composition of
air, 23.

Wolff, ash ingredients of jdants,
101.

Wollny, observations uu percola-
tion, 172.

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