Farm science; a foundation textbook on agriculture

Front matter

SPILLMAN

WORLD BOOK COMPANY

Class ^ ^ ^ 5

Preface

The aim of this book is to explain to the farm boy the facts about farming that have puzzled him. There are many mysteries that are not mysteries to the average boy, for the simple reason that he has never recognized their existence. No attempt is made in these pages to introduce the student to new mysteries except such as are necessary in connection with a proper explanation of those he has actually met in his experience on the farm. The primary idea underlying the book is to enable the farm boy to understand the reasons for the things he has observed but does not understand.

Many of the schools in which it is hoped this book will be used have no special laboratory equipment. For this reason the experiments outlined at the end of the various chapters require no apparatus and, for the most part, no materials not readily obtainable on the farm. It is believed such experiments will convey to the student the lessons intended, more certainly than those that must be conducted with apparatus of a pattern unfamiliar to him. They do not require the student to think in a new and strange language.

No attempt has been made to make the book "practical" in the sense of teaching those things the farmer usually learns by experience. The aim has been rather to enable the student to understand why things are as he knows them to be. It therefore deals with fundamental principles, which are the same everywhere, and which are valuable guides in ail the work of the farm. It is thus adapted to one locality about as well as to another. A book intended to give practical directions for doing things on the farm might be valuable in a particular locality ij written with special reference to that locality, but would be of little value for classroom use elsewhere. The author believes that when agriculture is put in proper pedagogical form, the textbook will deal with prinvi Preface

ciples rather than with the details of practice, and this ideal has been adhered to in preparing the text. The teaching of farm practice requires a manual, or a series of manuals, to be used as guides in actual farm work.

The attempt has been made to put the subject matter in a form suitable for classroom use. In this matter the author has followed closely the structure of those textbooks which in his seventeen years' experience as a teacher he has found most satisfactory for this purpose. The degree of success attained in this respect can be determined only by experience. The author would welcome any criticisms or suggestions that would enable him to make the book more useful to the farm boys of America, for whom it has been written.

The illustrations used in the text have been obtained to a large extent from the files of government bureaus. Acknowledgment is here made of the author's indebtedness to the many individuals who have so generously permitted the use of material of this character, or who have given helpful suggestions as to choice of illustrations; also to Mr. M. B. Waite and Professor C. V. Piper, for suggestions as to treatment of fungi, to Professor C. F. Marbut, for suggestions concerning the chapters dealing with soils, and to my colleague, Professor J. W. Ritchie, for many helpful suggestions. For the original drawings which have been made of a number of subjects, expressions of appreciation are due the artists, Messrs. J. M. Shull and R. C. Steadman, for their cooperation with the author in carrying his suggestions through to completion.

Part One — The Soil Chapter One

The four layers of the earth. The outermost portion of the earth is the atmosphere. We Hve at the bottom of an ocean of air. We are to learn that air is all-important to life, both plant and animal.

The second layer of the earth consists of water, but this layer covers only about three fourths of the earth's surface. Water plays as important a part in the maintenance of life as does air.

The third layer consists of the loose material we call earth, dirt, or soil. It covers the whole earth except in steep or exposed places where rain washes it away and leaves the underlying rocks bare. It extends under all the oceans. In reality only a few inches of the surface of the loose dirt layer, and that only on dry land, is properly called soil. The thickness of the loose dirt layer varies from almost nothing to many hundreds of feet.

The fourth layer consists of solid rock, which extends downward as far as we know anything about the structure of the earth.

The soil is the foundation of agriculture, and it is fitting that we should begin our study of this important and interesting subject by learning what we can about the soil.

FACTS FROM OTHER SCIENCES

Before we can understand some of the processes concerned in the making of soil material, we need to learn a few facts from other sciences. Such of these facts as are necessary are given below.

The magnet. Nearly every one knows that a magnet will pick up small pieces of iron. It is not so wejl known that the quantity of iron a magnet will thus pick up and hold is quite limited, and that when this quantity has been brought in contact with the magnet, the latter appears to lose all power of magnetic attraction for additional iron. We say its magnetism has been " saturated." A knowledge of this property of magnets will help us to understand the principles of chemistry.

The atom. All substances are composed of small particles called atoms. These are so small that they cannot be seen even with the best microscope ever made. How we know of the existence of atoms, and of their exceedingly small size, is a story much too long to tell here. It is told in the science of chemistry.

So far as we know, there are only about 90 different kinds of atoms in the entire universe. The spectroscope tells us that the distant stars have, for the most part, the same kinds of atoms in them as those that compose substances here on the earth. All the numerous substances known are composed of these 90 odd kinds of atoms united in various proportions. There is some uncertainty as to the exact number of kinds of atoms, for some of them occur only in rare substances, and chemists have not yet fully proved the existence of some of the kinds that are believed, but not certainly known, to exist.

Most kinds of atoms have strong attractions for each other, but the attraction between some kinds is stronger than that between others. Atoms are, in fact, small magnets, and like magnets, their attractions can be saturated. This means that an atom may be so united with other atoms that its attraction for additional atoms disappears. But with very few exceptions, an atom which has been torn loose from all combination with other atoms will attach itself to almost any kind of atom it can find.

Molecules. When two or more atoms join into a group in which the attracting power of each is satisfied, the group is called a molecule, a word meaning " little body." Such a body can exist alone indefinitely unless the group of atoms constituting it is violently broken apart.

The atoms of quicksilver have a peculiarity possessed by few, if any, other kinds of atoms. They will unite readily enough with several other kinds to form molecules, but they do not unite with each other, so that when this substance is obtained in a pure form, its atoms remain apart as if their attractions were satisfied. We do not know why this is, but it is probably due to some peculiarity in the structure of these atoms which enables them actually to satisfy their own attractions. If we define the molecule of a substance as the smallest particle of that substance that can exist alone indefinitely, then we may say that the molecules of quicksilver consist of a single atom. The molecules of other substances consist of two or more atoms so united that the attracting power of each atom is satisfied.

Elementary and compound substances. When the atoms in a molecule are all of the same kind, the substance composed of such molecules is said to be an elementary substance — it consists of a single chemical element. Iron is an elementary substance. Copper and sulfur are others.

If the molecules of a substance are made up of two or more kinds of atoms, the substance is said to be compound. Such a substance is composed of two or more chemical elements. Common table salt is a compound substance. Its molecules are made up of two atoms, - — one atom of the element sodium and one of the element chlorin. When sodium atoms are united with each other, they form the molecules of the metal sodium, an elementary substance. When chlorin atoms are united with each other, they form the elementary substance chlorin, which is a yellowish, very offensivesmelling gas. But when an atom of sodium unites with one of chlorin, they form a molecule of the compound which we call salt.

The molecules of some compound substances contain many atoms of several different kinds.

There can be, of course, only as many different kinds of elementary substances as there are kinds of atoms, while the number of compound substances is practically unlimited.

Chemical symbols. Chemists have invented a simple and convenient set of symbols for the various elementary substances. The symbol for an element is usually the first letter of its name. Thus C is the symbol for carbon, O for oxygen, H for hydrogen, I for iodin, etc. In some cases the names of several elements begin with the same letter. In such cases the symbol may consist of two letters of the name, usually the first two, or of one or more letters of the Latin name. Examples : calcium, Ca ; chlorin, CI ; iron, Fe (Latin, Jerruni) ; sodium, Na (Latin, natrium). Some of the elements of which we shall see a great deal in this book are, with their symbols, nitrogen, N ; phosphorus, P ; and potassium, K (Latin, kalium)..

Meaning of chemical symbols. Chemical symbols are used in two ways. First, they are often used merely as abbreviations for the names of the elements, to save time in writing and speaking. The second and more important use is to represent a single atom of an element. Thus " CaO " represents a molecule of quicklime, composed, as its symbol indicates, of one atom of calcium and one of oxygen. Some kinds of molecules have two or more atoms of the same kind in them. Thus a molecule of oxygen consists of two atoms of oxygen, and its molecular symbol is Oo. A molecule of water consists of two atoms of hydrogen and one of oxygen ; its symbol is HoO. The molecular symbol of limestone is CaCOa, which means that a limestone molecule consists of one atom of calcium, one of carbon, and three of oxygen. The molecular symbol of carbonic acid gas is CO2.

Chemical reactions. When limestone is heated, the change that occurs is represented as follows :

CaCOg -> CaO + COo

limestone — ^ quicklime + cart)onic acid gas

This means that the molecule of limestone breaks up and the atoms rearrange themselves into one molecule of quicklime and one of carbonic acid gas. This formation of new molecules from old ones is called a chemical reaction. In such reactions the atoms rearrange themselves so that in each case every atom has its power of attraction satisfied.

When we add water to quicklime, as is done in slaking it, the following reaction occurs :

CaO + HoO -^ CaOoHz

quicklime + water — ^ slaked lime

a new arrangement of atoms by which a molecule of quicklime and a molecule of water unite to form a molecule of slaked lime. The molecular symbol Ca02H2 is usually written Ca(0H)2, for reasons which we need not explain here.

Experiments

1. Get at a lumberyard, or elsewhere, a chunk of quicklime. Place it on a board or in a shallow box. Pour water on it, a little at a time, till it has completely crumbled. The water unites molecule by molecule with the quicklime, forming slaked lime. Since the newly formed molecules are larger than the molecules of quicklime, they cannot occupy the same space ; hence the crumbling.

The quicklime may become very hot in this experiment. Take care not to set anything on fire with it. What would happen if a hard rain should fall on a wagon box full of quicklime?

2. Blow the breath through a straw into a glass of clean drinking water. Nothing happens. Now take a fresh glass of the same water and put some of the slaked lime in it — say, a tablespoonful. Stir up the slaked lime in the water and then let it settle. Pour off the clear liquid into another glass, being careful not to get any of the sediment. Now blow the breath into this clear liquid (limewater). The cloudiness that follows is due to chemical reaction between the carbonic acid gas in the breath and the slaked Hme dissolved in the water, as follows :

CaOsHs + CO2 -^ CaCOs + HoO

In this reaction the atoms of a molecule of slaked lime and a molecule of carbonic acid gas rearrange themselves so as to form a molecule of limestone and a molecule of water. While slaked lime is somewhat soluble in water, limestone is not, or at least very slightly so. Hence the newly formed molecules of limestone collect into small particles that appear as a fine white powder suspended in the water. A solid thus formed in a liquid in which it is not soluble is called a precipitate.

Continue to blow the breath into the cloudy water for several minutes, and suddenly the liquid will become perfectly clear again. The reason is as follows : the slaked lime in solution is finally all used up in forming limestone. As soon as this occurs, the additional carbonic acid gas in the breath becomes dissolved in the water, and the following reaction occurs :

CaCOg + COo + H2O -> CaH2(C03)2

This means that one molecule of limestone, one of carbonic acid gas, and one of water unite to form a molecule of acid calcium carbonate. This latter substance is readily soluble in water, and dissolves as fast as it is formed. When the limestone is all used up in the reaction, the liquid becomes clear again.

HOW SOIL MATERIAL ORIGINATES

Chemical action. We are now equipped with sufhcient knowledge of chemistry to understand some of the most important processes in soil formation.

The original rocks of the earth's crust are at all times subjected more or less to the action of water, air, and numerous substances found in the soil. Chemical reactions are going on continually in the soil, and between the underlying solid rocks and substances in solution in the soil water that comes in contact with them. In this way the rocks are slowly broken down and converted into fine soil material, much as quicklime crumbles when slaked.

Most of the rocks of the earth's crust contain grains of quartz and other materials not easily affected by chemical agents, along with materials that are easily attacked. The more resistant grains remain to form the bulk of the soil after the more soluble ones have been dissolved by soil water and carried away. The soil is thus composed mainly of small rock particles of many sizes and kinds, though quartz grains make up the greater part of all ordinary soils.

In most parts of the country you can find stones that, when broken, show plainly in their outer portions that they have been changed by the action of water, air, or other substances, and are not so hard as in their inner portions. In time all such stones will fall to pieces and form soil.

It is mainly by processes like those described above that by far the greater part of the material composing the soil was derived from the solid rocks of the earth's crust. These processes are going on now just as they have always gone on. This is why the surface of the earth is nearly everywhere covered with dirt. It is only in exposed places where the dirt washes away as fast as it is formed that we find the bare rocks that extend down into the depths of the earth.

How ice aids in soil formation. Those who live in cold climates know that when the water in a water pipe

Fig. I. The Great Stone Face in the White Mountains of New Hampshire. Water creeps into the crevice behind and underneath the " cap," and freezes. The force of expansion is so great that the cap stone, weighing thousands of tons, is moved outward each winter. It is now being put back in position, and the crevice closed with cement.

freezes, it bursts the pipe. Because of this the pipes that bring water into the house are buried deep in the ground to keep them from freezing. The reason for the bursting is that water expands while freezing, and thus the ice occupies more space than did the water from which it was formed. This is because the molecules of ice are arranged in needlelike crystals, with more or less open space between the crystals, while in water the molecules have no particular arrangement, but move freely about among each other.

Figure i shows the enormous expansive force exerted by freezing water. Every time the water freezes in the crevice behind and under the " cap " of the Great Stone Face, the huge cap, which weighs several thousand tons, is moved outward a little. Engineers have recently been at work moving this cap back into place and filling the crevice with cement to keep the water out.

lo Farm Science

Nearly all stones or rocks have crevices in them that get full of water. When the water freezes, the expansion breaks the stones, or at least chips off pieces of them. The repeated freezing and thawing of water in the crevices of rocks thus helps in the process of breaking up the rocks to form soil material.

How rolling stones form soil. In a freshet the stones lying in the bed of a stream are rolled considerable distances. Every time one of these stones strikes another, pieces are chipped from both. Every one has seen rounded stones, like those shown in Figure 2, that are found in stream beds or in places where they were left by flood waters. Each of these stones was sharp-cornered when it was first split from a larger stone. What has become of the sharp corners? They have been worn off piece by piece, and these pieces now constitute part of the soil, especially in river and creek bottoms. However, there are in some regions rounded stones not formed in this manner.

A little figuring will show that a good deal of soil comes from this source. (See problem at end of this chapter.) If we grind off the corners of a cubical stone till it is perfectly round, we take off nearly half of it. From the number of water-worn stones found in most parts of the country, it is clear that no small part of the fine material we now call soil must have originated in this manner, though not nearly so much as was formed by the action of air, water, etc., in causing stones to fall to pieces.

The part played by glaciers. Both the north and the south pole of the earth are covered by thick layers of ir

Office of Farm Management Fig. 2. Water-worn stones in the bed of a stream. Each of these stones was sharp-cornered at one time. What has been worn off from them is now soil.

snow, compacted more or less into solid ice. These are called the " polar ice caps." Through the telescope we can see caps of this kind on the poles of the planet Mars.

Several times in the distant past the climate of the earth became much colder than it is now. During these long periods of low temperature, sometimes lasting for thousands of years, the polar ice caps spread out till they covered a large part of the earth. The north polar cap at one time came down to about where the Ohio River now is. In places the ice was several thousand feet thick, being thicker northward, of course. While ice is solid, it is not so solid as iron, for it will flow a little, just as very thick molasses does.^ The ice cap slowly spread out (flowed) from the north, where it was thick-

^ By subjecting a block of ice to very gradual pressure, it can be bent into any shape desired; but if subjected to sudden pressure, ice is very brittle.

U . S. Cieologiciil Survey Fig. 3. Bed rock marked by rocks embedded in glaciers flowing ovcr it during the glacial period. Such rocks are found in many parts of the northern states.

est, toward the south. Its enormous weight pressed into its lower surface much of the loose dirt and stones beneath it. These were dragged along the surface of the earth, grinding against everything they touched.

Many rocks were thus ground into fine powder, and much soil material was formed in this manner. Figure 3 shows a rock surface that was ground and scratched by the stones embedded in glacial ice moving slowly over it. In Figure 4 are shown stones that were embedded in the ice and were scratched by the rocks over which they were dragged. Such stones may be seen in any geological museum.

In its flow, a glacier would frequently meet with obstacles, causing it to buckle up here and there, turn this way and that, and thus frequently bring what was formerly the bottom ice to the top. In this way the stones and dirt became well distributed throughout the mass of the glacier, as is seen to be the case with the modern mountain glacier shown in Figure 5, page 14.

Finally, when the climate changed again, and it became warmer on the earth, the southern edge of the northern ice cap melted, and the millions of tons of rocks and dirt embedded in it were left on the earth's surface (Fig. 6, page 15). In some places the layer of earth thus deposited is a hundred feet or more in thickness. The surface soil of most of the region lying north of the Ohio and Missouri rivers is of this character. Much of it is merely dirt that the ice picked up and carried along with it as it flowed slowly southward. In some places there are four or five layers of this material, indicating that what is described above took place several times.

How so-called limestone soils are formed. In some large areas in this country the rocks seen in the bluffs

U. S. Geological Survey

Fig. 4. Rocks once embedded in glaciers and scratched by being dragged over bed rock.

Harry Fielding Reid

Fig. 5. End of a modern mountain glacier, showing rocks and dirt embedded

in the ice.

along the streams are limestone. This is the case in part of the Ozark Region of southern Missouri and northern Arkansas, and in a large part of Kentucky and Tennessee. (See map facing page 32.) Now the atmosphere contains a small percentage of carbonic acid gas, and this gas is readily soluble in water. Rain therefore carries into the soil considerable quantities of this gas. More of it is formed in the soil as the result of the decay of plant and animal remains. We have already learned that water containing carbonic acid gas in solution will dissolve limestone. Because of the small amount of this gas in soil water, the action of water in dissolving limestone is very slow ; but in areas where the rock underneath the soil is limestone, the upper surface of the stone is at all times being slowly dissolved away and carried back to the ocean, whence it originally came. But all limestone has embedded in it small particles of other kinds of rock that are not so easily dissolved and carried away. In some cases it contains large masses of flint, as well as many other kinds of mineral substances. When the limestone is dissolved away, these less soluble mineral particles are left as soil. Soils formed in this manner are usually called limestone soils, but where the rainfall is heavy, and especially if the resulting soil is rather porous, they may be very poor in lime, even where the limerock is only a few feet below the surface.

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U. S. Geolo(.ical Suney Fig. 6. Soil material once embedded in a glacier, and deposited on the surface when the glacial ice melted. The gravelly character of this soil is characteristic of most glacial soils.

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Q^ce of Farm Managevient Fig. 7. Flint rock once embedded in limestone, which was dissolved away. Smaller particles of soil washed to foot of hill, leaving rocky hillside.

In Figure 7 is shown a rocky soil that originated in the manner here described. In this case the original limestone contained a great deal of flint, often in large masses, though these masses had nearly always been broken into relatively small pieces by the forces that everywhere cause large rock masses to become cracked and broken. Figure 7 shows a hillside from which the rain has washed all the finer soil particles, leaving only the larger rocks to form the surface. Part of the fine dirt that was originally formed here is now lying in the valley at the foot of the hill.

The soils of the famous Bluegrass Region of Kentucky and of the Central Basin of Tennessee are derived from limestone that had much less flint in it, and they are not rocky like the soil shown in Figure 7. There is also a large area of soil in western Texas that was formed from limestone in the manner here outlined. Smaller areas occur elsewhere. Look up these areas on the map facing page 32.

The part played by plants and animals in forming soils. In the preceding paragraphs we have seen how the httle rock particles that form by far the greater part of the soil came to be little particles instead of large stones. A good soil, however, contains something besides little pieces of stone. Plant roots rot in the soil. Leaves and stems fall to the surface, become mixed with dirt, and soon fall to pieces by decay. Uncounted millions of worms and bugs, mice, gophers, etc., die in the soil or on its surface. All these decaying remains of plants and animals are part of what we call the soil. Although they form only a small part of the substance of the soil, they are highly important to its fertility, as we shall see presently.

Chemical changes going on in the soil. You have noticed what happens to a piece of old iron that lies in contact with the damp soil for a few years. In the presence of moisture and air it is attacked by the oxygen of the air, with which it unites chemically to form iron rust. In time it is completely converted into ironoxygen compounds, and crumbles away much as lime does in slaking. The soil contains a great many substances, some of mineral origin, others derived from the decaying remains of plants and animals, that act on each other and on the rocks of the soil in much the same manner that air and moisture act on iron, though usually much more slowly. Such changes are always going on in the soil. The surface of almost every rock particle in the soil is more or less stained and discolored by gummy substances that form in the soil as the result of these chemical activities. The soil is thus an exceedingly complex thing, and hardly any two samples of it are exactly alike. This makes it difficult to lay down any hard and fast rules for improving the soil. What is good for one soil is not always good for another. We shall find, however, that much can be learned about how to make the soil yield abundant crops.

WHAT A CUBIC INCH OF SOIL WOULD LOOK LIKE IF MAGNIFIED INTO A CUBIC MILE

Let US imagine, if we can, what a cubic inch of soil would look like if we could enlarge it to a cubic mile, or if we could reduce ourselves to small creatures that could crawl in and out between the particles that constitute the soil. Some of the little rock particles that form most of the bulk of the soil would then appear to us to be stones several feet through. Others would be no larger than a pea, while there would be still others of every size between these extremes. Most of the particles would look like the common flint stones seen in stream beds and in many regions beside the road, for they are indeed only small pieces of flint. But there would be an occasional crystal of some beautiful mineral that most of us have never seen before, though scientists who study minerals could immediately tell what each crystal is.