Soils and Their Care

The following information on soils and their care comes from Five Acres and Independence by M. G. Kains. Five Acres and Independence is also available to purchase in print.

If you could start your farm on a piece of land with which man has never interfered and from the start could work as Nature does you could doubtless maintain fertility and crop production indefinitely at a high standard. The probability is, however, that the ground with which you have to deal has been so injured by man’s abuse that its ability to grow desirable plants is at a low ebb. This need not discourage you because in a surprisingly short time you may easily bring it back to its pristine condition and can even improve on this to an astonishing degree.

Soils may be classified according to their principal components—clay, sand and innumerable combinations of these with vegetable matter (humus). Clay—blue, red or yellow—though rich in various mineral elements is undesirable without modification by the presence of the other two components. It is sticky, hard to dig or plow, so dense that water and air penetrate it with difficulty and its surface bakes in dry sunny weather. Sand, the opposite extreme, contains far less actual plant food material, allows water to rush through, carrying with it and wasting soluble plant food material added by nature or man. Combinations of these extremes with vegetable matter form “loams” of many grades popularly known as heavy clay loam, light clay loam, sandy loam, etc.

Loams are more desirable for plant growing than are either clay or sand because, on the one hand, they are easier to work, more porous and less likely to bake than clay and, on the other hand, are more retentive of moisture and plant food than sand. When your soil happens to approach the characteristics of one or the other of these extremes modify it by adding the opposite extreme to it; that is, “lighten” a clay by adding sand and make a sand “heavier” by adding clay. With each class of soil it is easier to increase the water-holding capacity by adding vegetable matter through applications of manure or by plowing under green manures or cover crops. (Chapter 26.)

Clay may also be lightened by plowing under a two-horse load of fresh horse manure to each 2,500 square feet of area in late fall, leaving the clods and furrows unbroken just as turned up by the plow so frost will break them, adding a 1″ layer of sifted coal ashes during winter and, in spring, giving a surface dressing of lime (about a pound to 10 square feet, 250 to 300 pounds to the acre).

Texture is the principal characteristic that determines the value of a soil for trucking and strawberry growing. This is mainly due to the size and the quantity of sand particles. When coarse, the soil is “quick” because it drains rapidly, warms up quickly and permits early sowing. Such soils are warm all season long and thus favor early crop maturity. Because of their open texture they require large quantities of humus, lavish feeding and irrigation.

Medium sandy loams are not quite so early but retain water and plant food better and are more productive. Fine sandy loams, though later than the preceding are usually best for summer vegetables and strawberries. For latest crops silty and clayey loams are often most valuable of all. Their fertility is also more easily and economically maintained.

If your money crops are to be largely vegetables and strawberries, as they should be, you will do well to remember that sandy loams have the following merits: Earliness and warmness especially in spring, earliness of tillage in spring and lateness in autumn, earliness of tillage after rains, quickness of fertilizer action, economical cost of tillage, ease of transplanting in them, facility of root crop harvest, smoothness of root crops, ease of cleaning and preparing root crops for sale, relatively less compaction of soil during harvest, particularly when the soil is wet and adaptability to efficient overhead irrigation.

Humus is the residue of decomposed organic matter (principally vegetable) contained in the soil. It is of great importance to the fertility of soils because it increases water-absorbing and retaining power, lessens soil tenacity, increases heat absorption of the sun’s rays, seizes, holds, and develops plant food from the air and the mineral compounds of the soil, supports the life of creatures (including worms, grubs and bacteria) that live in and modify the soil, adds its elements to the supply of plant food, and on all these scores aids plant nutrition.

Nature supplies her soils with humus by the decay of fallen leaves, branches and the manures and dead bodies of animals of all kinds. When we upset her methods by cultivation we must supply humus in some other way or our soil will be so impoverished she cannot grow good plants for us. We can supply the loss of humus by liberal dressings of manure, muck, peat, leaf mold or other vegetable material or by growing green manures. (Chapter 26.)

When leaves and other forest litter decay they become “leaf mold,” a material highly valued by flower growers but, as a rule, not so much by vegetable growers and farmers. The annual deposit of leaves (“needles”) and other waste in populous pine woods is about a ton and in hardwoods probably twice as much to the acre. Not only does this gradually change to humus but it adds appreciable quantities of plant food to the soil.

In the 1928 Department of Agriculture Year Book, W. R. Mattoon gives the analysis of a ton as including 12.1 pounds of ammonia, 2.8 of phosphoric acid and 3.9 of potash. At an average of 1 pound of “dry matter” to the square foot, an acre (minus the area occupied by tree trunks) would contain at least 18 tons which, at the above figures and at prevailing prices, would be worth $39.20 for ammonia, $2.52 for phosphoric acid and $4.21 for potash, a total of $45·93.

Mr. Mattoon also reports that a farmer who applied the rakings of one acre of heavy oak woods to an acre of field crop land during 3 years secured yields of corn and cotton which increased his returns by an annual average of $ 16.15 over a similar acre not so treated.

Though these fertilizer and return figures are impressive they do not tell the whole story because leaf mold is noted for its high water-holding properties. When added to soil it acts as a sponge—absorbs rainfall, checks downward seepage, and yields moisture during long periods to plant roots. For these reasons, where it can be obtained at little or no cost but the gathering, it is valuable to use as bedding or litter in stables and poultry houses, as mulching material for strawberries and bush fruits, as a supplemental manure or as a source of humus in compost piles.

In a sketchy way the following paragraphs suggest how color may help even a novice to appraise the crop-raising value of soils.

Color has long been relied upon as an index of soil value for crop production. In a general way it proves the presence or absence of desirable and undesirable compounds and also suggests the composition of the most important soil ingredient, the clay. However, color, per se, is of small importance; though dark colored soils, especially black ones, when well drained, absorb larger proportions of sun heat than do light colored ones. (Chapter 16.) Hence, dark colored, well drained soils are earlier than light ones of otherwise similar composition and texture.

Though color differences of soils are due to differences of components it is not true that darker colored soils contain larger quantities of coloring matter than do light ones. Composition and combination account for many variations. Usually a black soil is rich and a dark soil productive in ratio to its darkness but black color is due to combinations of organic matter and lime, even in small amount (often less than 2% of lime).

Brown color generally indicates soil acidity, due to the presence of iron oxide. In such soils the organic matter, even though abundant, is not saturated with lime. When iron oxide is in the “free” state the soil is usually yellow when the quantity is small or red when it is large. However, the color is not primarily dependent upon the amount of oxide because the quantity of this material is fairly uniform in the clay of the surface soil, regardless of color. Clay, the finest divided material of soils, is formed by rock weathering. Its composition therefore varies with the nature of the original rocks. Red and brown soils are highly valued, less because of their iron oxide than because of their condition which this material (and color) indicate. For it suggests good drainage and other favorable growth conditions and proves the presence of abundant material which will both supply and retain plant food.

White and light colored soils are deficient in important components—organic matter and clay—and contain excess of sand. Hence they cannot absorb and retain water but permit such rapid drainage that the soluble components of manures and fertilizers rapidly disappear and are wasted in the drainage.

Where light colored spots appear in dark colored soils they prove that the soil there was water-logged and that the lime, organic matter, manganese, iron oxide and phosphoric acid have been leached out.

M. S. Anderson, chief chemist of the Bureau of Chemistry and Soils, has so strikingly presented certain functions of soils that I am somewhat condensing his article in the 1930 Year Book of the Department of Agriculture as follows:

Nature hoards some of her assets in an almost miserly manner. Even plant food may be kept in such closed vaults as to be only a long-time investment, bearing a very low rate of interest. Some of the coarser soil mineral grains may contain large potential supplies of fertilizing elements and yet the soil be of low fertility because of their lack of availability. Apparently little can be done to release them.

Another class or condition of plant food serves as a savings bank, whose deposits are subject to the “drafts” of a crop whether for the present or the future. The “colloidal material” (finely decomposed rock fragments combined with organic matter) appears to offer such banking facilities. It makes up the greater part of the clay in soils and differs otherwise from the coarser mineral grains than in particle size, besides its marked influence on the physical behavior of soil, its ability to serve as a plant food depository is most marked. Yet even its presence does not insure a rich plant food deposit. Its character varies widely, being the resultant of parent rock material, climate and vegetation. In the main, though sometimes badly impoverished by Nature, it is the soil’s most valuable asset. Moreover, it is the plant food asset over which the grower has the greatest control. Little can be done significantly to alter the quantity of colloid in the soil, but much can be done to maintain or improve its quality.

A bank deposit can not be indefinitely drawn upon without making deposits to the credit of the account. Colloid material is the agency through which such credit may be effectively restored to the soil. This is possible because of the great holding power of the soil colloids for mineral constituents, apparently both mineral and organic portions of the colloid. When plant foods are added as fertilizers only part of the water-soluble material added may be taken up immediately by the crop. The rest may be held by the colloids in such a way that loss by drainage is slight. Thus the crop of a later season may share in the benefits, and the balance not used may accrue to the credit of plant food.

Not all plant food of soil colloids is “subject to check” by growing plants; some is “on time deposit,” so additional requirements must be met before it is available for use. Organic matter often serves in this capacity. In addition to serving other beneficial purposes, it is a source of readily available plant food. Recent investigations have emphasized the availability of its plant-food constituents and its relatively high capacity for retaining plant food as compared with the mineral portion of the colloids of less fertile soils. Regardless of the kind of mineral colloid each load of manure added and each crop residue turned under becomes a “credit slip” to the plant-food account.

If a soil has a very low colloid content, as in the case of very sandy soils, banking facilities are not at hand, and valuable plant food may be lost. Even organic matter may be rapidly decomposed and much of its value washed away. Nitrates especially are leached out in the drainage water. Under such conditions plants must be fed in a hand-to-mouth manner without the expectancy of building a bank account for the future.

It is extremely difficult under certain conditions to build up the fertility of sandy soils, or even of some soils of finer texture containing certain kinds of colloidal material, beyond the necessities of a single season. Such soils for profitable use require frequent additions of quickly available plant food. Any attempt to treat them as store houses of plant food as in the case of most medium and heavy soils is likely to mean plant food wasted.

The loss of soil fertility due to sheet erosion is probably far greater than from gullying. Through it a thin layer of the most fertile soil is removed from the surface with each heavy rain. Because the material is thus removed gradually and because subsequent cultivation destroys all evidence of the erosion, the ill effects often go more or less unnoticed until after much damage has been done.

It has been shown by the experiments of R. I. Throckmorton and F. L. Duley of the Kansas Experiment Station (Bulletin 260) that sheet erosion is greatly reduced when the land is kept covered with a crop as much of the time as possible. By using a cropping system that provides for a crop on the land most of the time, or at least during the seasons when the greatest erosion is likely to occur, much can be done to reduce the disastrous effects of sheet erosion. Cropping systems differ widely as to the time the land is covered with a crop.

Some crops give more effective protection than do others. (Fig. 30.) Small grain crops hold the soil far better than corn or other cultivated crops. Red clover forms a sod and protects the land more effectively than a crop like soy beans and thus gives not only more efficient but more extended protection from washing. Sweet clover or alfalfa used in the cropping system gives much the same protection as red clover.

annual soil loss by treatment type

Fig. 30. Graphs to show relative annual losses of soil by sheet erosion under various treatments.

On steepest lands, permanent grass pastures or meadows should be used as much as possible since they form the most effective protection against erosion. The less sloping ground should be grown to small grain or kept in such rotations that the land will be protected by a crop at least three-fourths of the time. It is only on relatively level upland or bottom land that cultivated crops can be grown more or less constantly without serious loss from erosion. Even in such cases the land should be rotated with other crops since continuous cropping is seldom the best practice on any soil.

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Soils and Their Care

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