Some Properties of Soils

SOME PROPERTIES OF SOILS.

BY DR. JOHN A. WIDTSOE, DIRECTOR EXPERIMENT STATION, STATE AGRICULTURAL COLLEGE, LOGAN, UTAH.

When the earth was young, as we believe today, there was no soil upon its surface. The first mountain that was lifted above the waters, was bare and bleak, and reflected upon its hard, glistening surface the first rays of the new sun. Soon, however, the face of the mountain began to bewarmed by the sun's heat; it ex- panded and probably cracked by the new warmth; and into the tiny cracks, the gases of the air, the oxygen and the carbon diox- ide, crept, and made the cracks wider and deeper. Soon the in- tersecting cracks resulted in tlie splitting off of small rock frag- ments; and before the mountain had been exposed above the waters many years, it was covered with a thin layer of rock-pieces that the sun, the water and the air had caused to crumble from the original face of the rock. Thus came the first soil. As the years wore away, this process of crumbling continued, and the soil be- came deeper and deeper. The rains came and washed the loose soil into the hollows and low-lying places. Thus it came that val- leys and hollows have deep soil, while the soil on the mountain sides is usually thin. Most of these early soils, in the process of time, were changed into rock again; indeed, many of the rocks that are exposed in the canyons are simply soils that have been hardened by various geo- logical agencies. It may be that rocks thus formed from soils were again converted into soils, and it is not impossible that this process was repeated over and over again. In any case, however,

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soils have been formed by the disintegration of rocks through the activities of the air, the water, and, in a small degree, of living things. The rocks found upon the earth, with reference to their re- lationship to soil formation, may be divided into three great classes. First, there are numerous rocks which are very rich in the substance called silica. This substance is not acted upon, to any marked extent, by the ordinary, natural agencies, and in the process of soil formation, remains undissolved as sand. Quartzites and various crystalline rocks are examples of rocks that furnish sandy soils. Another class of rocks contains but a very small amount of silica which is usually in combination with other sub- stances. When such rocks decompose, heavy clay soils result. The rocks that produce the heaviest clay soils are the shales, slates, and basic crystalline rocks. The third class of rocks, im- portant in soil formation, is limestone. The limestone may be mixed with silica or with clay, yet soils that contain a large quan- tity of limestone always possess peculiar characteristics. In classifying soils, note is first taken of the amount of clay and of sand that they contain. A soil that contains 75 per cent of sand is said to be a sandy soil; one that contains 75 per cent of clay is a clayey soil; a soil with 50 per cent clay and 50 per cent sand is called a loam. When the amount of sand is more than 50 per cent and less than 75 per cent and the remainder of the soil is clay, a sandy loam is produced. If the clay ranges be-

tween 50 per cent and 75 per cent, and the remainder is sand, the soil is said to be a clayey loam. An'ordinary clay soil, especially if it is wet, is very heavy to work. A sandy soil, on the other hand, is easily worked under all conditions. If now it happens that a heavy clay soil is mixed with a large percent (10 per cent —30 per cent) of limestone, the properties of the clay are at once changed, and it behaves in every way as an easily worked loam. It is this peculiar action of

limestone that makes necessary a special group for lime-soils in the classification of agricultural soils. Another class of soils of particular interest to all who live These are soils that contain in an arid district is the alkali soils.

a large excess of soluble materials that at times rise to the sur-

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face and make it impossible for plants to thrive. When rocks are broken down and changed into soil, a portion is so changed as to become soluble in water. In a district where much rain falls, this soluble portion is washed into the country drainage, and finds its way into the ocean. In a district of scanty rainfall, like Utah, the rains wash the alkali some few feet into the soil, whence it is again brought up as the water evaporates from the soil. Another class of soils possesses properties almost opposite to those of alkali soils. These soils have been formed on forest floors or other places where a large quantity of vegetable matter is al-

ways decaying. The characteristic property of soils formed un- der such conditions is the presence of large quantities of humus and organic matter. The vegetable mould found in our canyons is an excellent example of this class of soils. The large excess of decaying organic matter tends to make these soils sour, and thus unfit for plant growth. Mixed with a portion of mineral soil, they become exceptionally productive. In many parts of Europe, soils very rich in vegetable mould are dug out into small cubes, sometimes pressed, and sold for fuel under the name of peat. The classes of soils, of particular importance to the farmer, are therefore, —sandy soils, clay soils, loams, limestone soils, alkali

soils, and vegetable mould. Soils are of fundamental value to mankind, as it is upon them that plant life largely depends for its existence, and it is upon the vegetable kingdom that the animal kingdom and man depend for life. In every system of rational political philosophy, the wealth, health and happiness of a people are traced back to the readiness with which the soil may be made to yield products useful to man. Now, all soils are not equal in the facilities that they offer for plant growth — some need only to be stirred a little, and then have seed scattered upon them to yield well; others must be tilled ac- cording to costly and complex systems to produce only fair crops. These differences are in the soils themselves, and can not as a rule be modified to any extent by man. First, the soil is the storehouse of plant food. The plant, in order to prosper, must receive from the soil eight different sub- stances, namely: nitric acid, sulphuric acid, phosphoric acid,

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potash, lime, magnesia, oxide of iron, and water. Nearly all soils upon the earth's surface contain variable quantities of these ma- terials: but in some, the amounts are so small that the needs of the

plants are not supplied; in other cases, the essential plant foods are locked up in such insoluble forms that the plant roots cannot dissolve them quickly enough to supply the needs of the growing plant. To show the amounts of some of the essential plant foods that may be present in a fair agricultural soil, consider the follow- ing analysis. A soil from a farm yielding good crops was ex- amined, and it was found that every acre to the depth of one foot contained: Potash, 71,100 pounds; lime, 16,500 pounds; mag- nesia, 26,700 pounds; iron oxide, 150,600; phosphoric acid, 5,100. All these constituents were so combined with other substances as to be partly unavailable for plants. In fact the ^^ame soil was studied with reference to the quantities of available plant food that it contained. The result showed that one acre to a depth of one foot contained only the following amounts of available plant food materials :_ potash, 660 pounds; lime, 7,650 pounds; magnesia, 1,710 pounds; iron oxide, 3,600 pounds; phosphoric acid, 90 pounds. In other words: Of the total amount of potash in the soil, less than one-hundredth is of value to plants; of the lime, less

than one-half ; of the magnesia, about seven-hundred ths; of the iron oxide, about two-hundredths, and of the phosphoric acid, less than two-hundredths. What a farmer should know, therefore, concerning the composition of the soil of his farm is not how

much plant food it contains, but how much available plant food is found in it. This is one of the most difficult problems that the chemist has to solve. It is also a well-known fact that plants do not require the same proportion of the different plant foods. Sugar beets, for instance, feed heavily on potash and lime; lucern prefers potash; and wheat consumes a large quantity of phosphoric acid. Usually a plant which needs potash in large amounts, is able to extract potash more easily from the soil, than can a plant whose main de- pendence is phosphoric acid. Thus it happens that a soil con- tains more or less available plant food according to the crop which is grown on it.

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Utah soils, with very few exceptions, are very rich in all of the necessary plant foods; and an unusually large proportion of the plant foods is in an available condition. The soils of the state are characterized by an abundance of lime and potash, together with a sufficiency of phosphoric acid and the other necessary plant foods. They are deficient at times in nitric acid, which, by fol- lowing the results of recent science, may be added to the soil

with no outlay to the farmer. More ideal soil conditions than those we have in Utah can hardly be imagined. Now, the chemical composition of a soil is not the only im- portant consideration for crop production. Every well-tilled field is the home of countless millions of low forms of life that are busily engaged in producing a large crop of lucern, wheat or sugar beets for the farmer. In the fall, the stubble from the wheat, or the fallen leaves and stalks of the lucern, or the leaves of the beets, begin to decay and disappear. It is a familiar fact that the

high "header-stubble" on our dry farms disappears completely in one winter or at the most in two. In this process, bacteria play a very important part. As soon as the fall rains moisten the soil and the stubble, especially if fall plowing be practiced, number- and the leaves, and begin the less bacteria settle on the stubble

work of decomposition. The work is carried on until the cold of the winter compels the little workers to cease. Early in the spring the work is resumed, and soon the residues of last year's crop have been converted into a fine black humus that the farmer works into the soil by means of the plow and harrow. The humus thus produced tends to make the insoluble portions of the soil soluble and fit for plant use, and it contains in itself much avail- able plant food; it is therefore a very desirable substance to have in the soil. Other bacteria, as has been explained in an earlier article, settle on the roots of lucern, and gather nitrogen from the air, and make a large crop possible. At the same time, these nitrogen- eating bacteria furnish to our soil the only substance in which they are sometimes deficient, namely, nitric acid. Then, still other bacteria take hold of the humus, and convert the nitrogen it contains into the desirable nitric acid; others seize upon the potash and prepare that for the use of the plant. The soil must not be looked upon as a dead, inert mass. It is full of life and

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living things. Among the minute grains of soil are tiny labora- tories, with tinier workers, where wonderful, mysterious changes are wrought, which bring to man the sense of his impotency, and of the vagueness of his little store of knowledge. Sunshine, falling on the soil, is the active agent in promoting the conditions that result in proper plant growth. Sunshine, alone, could not accomplish this work \vere it not for a number of allies that are constantly active. Chief among these is the soil

water. In a country where the rainfall is slight and the sunshine is abundant, the presence or absence of water becomes the de- termining factor in the yield of a crop. Now, the water that falls upon a soil may be made to do more or less good according to the nature of the soil and the treatment which is given it. The soil is made up of small rock particles that lie close together, pretty

much like marbles in a bag. Between them are open spaces into which the water passes when the rain falls upon the ground. The force of gravity causes the water to sink downward until only a thin film of water envelopes each soil grain. When the grains are large, the amount of water so held will be small; while with small soil grains the amount will be large. Sandy soils, for example, are composed of grains that are more than .01 of an inch in diame- ter; the majority of the grains of a clay soil have a diameter less than .005 of an inch. The amount of water that may be held as a thin film around the grains of a sandy soil seldom equals more than 17 per cent of the weight of the soil; but a clay soil may easily hold 35 per cent. These water-holding properties of a soil

are of great importance to the farmer, for they determine how much water will remain in a soil after a rain, or an irrigation, and how much will drain away and be lost to the plant. The treatment that the soil receives, conditions also in part the amount of water it will take up. If the upper eight to twelve inches

are cultivated well, the water will soak into the ground easily; while, if the surface is packed hard, most of the water*will run off. This is recognized by many wise farmers, who plow their lands in the fall so that the rains and snow of the fall and winter will

have a chance to soak into the soil, and be stored there for the use of next season's crop. After a rain, or an irrigation, when the water has arranged

846 IMPROVEMENT ERA.

itself as a capillary film around the soil grains, an upward move- ment of the water begins. The sun heats the surface of the soil, and evaporates some of the water in the upper soil layers; tha water film lower down then tries to send some of the water up- ward to replace that which has been evaporated; this, in turn, is evaporated; and thus the process is repeated, over and over,. until all the water in the soil has been evaporated into the air. Soil

water, to assist in producing crops, must be taken into the struc- tures of the plants, and the evaporation of the soil moisture, just described, represents a loss to the farmer. To check evaporation he, therefore, cultivates or stirs the upper few inches of the land thoroughly. This breaks the film of soil moisture, and allows the stirred portion to dry out, but at the same time it forms a blanket through which the water, lower down, cannot escape. This fact was discovered some twenty years ago; and it is one of the far- reaching principles of soil treatment. The consideration of the relation of the soil to water is an extensive and important one, and it is not possible to deal with it thoroughly in this sketch. To deal fully with the properties of the soil, the atmosphere found among the soil grains should be considered; also, the influ- ence of color, weight, subsoil, inclination, etc., upon power of land to produce plants. These are fascinating subjects that every young man of Utali, who labors on the farm all or part of hi& time, should make it his pride to know. The soil represents a complex problem for the investigator. The changes that take place in it, are of the subtlest kind. The world is waiting for some mighty minds to unravel the mysteries that the soil has in hiding. The paths and motions of the stars that are hung in the sky are well known; but the motions of the moisture in the soil baflle the endeavors of the keenest students of the age. Much concerning the soil is known, but incompara- bly more will be known as the world advances.