The first and most rational method of maintaining the fertility of the soil indefinitely is to return to the soil everything that is taken from it. In practice this can be done only by feeding the products of the farm to live stock and returning to the soil the manure, both solid and liquid, produced by the animals. This brings up at once the much discussed question of the relation between the live stock industry and dry-farming. While it is undoubtedly true that no system of agriculture will be wholly satisfactory to the farmer and truly beneficial to the state, unless it is connected definitely with the production of live stock, yet it must be admitted that the present prevailing dry-farm conditions do not always favor comfortable animal life. For instance, over a large portion of the central area of the dry-farm territory the dry-farms are at considerable distances from running or well water. In many cases, water is hauled eight or ten miles for the supply of the men and horses engaged in farming. Moreover, in these drier districts, only certain crops, carefully cultivated, will yield profitably, and the pasture and the kitchen garden are practical impossibilities from an economic point of view. Such conditions, though profitable dry-farming is feasible, preclude the existence of the home and the barn on or even near the farm. When feed must be hauled many miles, the profits of the live stock industry are materially reduced and the dry-farmer usually prefers to grow a crop of wheat, the straw of which may be plowed under the soil to the great advantage of the following crop. In dry-farm districts where the rainfall is higher or better distributed, or where the ground water is near the surface, there should be no reason why dry-farming and live stock should not go hand in hand. Wherever water is within reach, the homestead is also possible. The recent development of the gasoline motor for pumping purposes makes possible a small home garden wherever a little water is available. The lack of water for culinary purposes is really the problem that has stood between the joint development of dry-farming and the live stock industry. The whole matter, however, looks much more favorable to-day, for the efforts of the Federal and state governments have succeeded in discovering numerous subterranean sources of water in dry-farm districts. In addition, the development of small irrigation systems in the neighborhood of dry-farm districts is helping the cause of the live stock industry. At the present time, dry-farming and the live stock industry are rather far apart, though undoubtedly as the desert is conquered they will become more closely associated. The question concerning the best maintenance of soil-fertility remains the same; and the ideal way of maintaining fertility is to return to the soil as much as is possible of the plant-food taken from it by the crops, which can best be accomplished by the development of the business of keeping live stock in connection with dry-farming.
If live stock cannot be kept on a dry-farm, the most direct method of maintaining soil-fertility is by the application of commercial fertilizers. This practice is followed extensively in the Eastern states and in Europe. The large areas of dry-farms and the high prices of commercial fertilizers will make this method of manuring impracticable on dry-farms, and it may be dismissed from thought until such a day as conditions, especially with respect to price of nitrates and potash, are materially changed.
Nitrogen, which is the most important plant-food that may be absent from dry-farm soils, may be secured by the proper use of leguminous crops. All the pod-bearing plants commonly cultivated, such as peas, beans, vetch, clover, and lucern, are able to secure large quantities of nitrogen from the air through the activity of bacteria that live and grow on the roots of such plants. The leguminous crop should be sown in the usual way, and when it is well past the flowering stage should be plowed into the ground. Naturally, annual legumes, such as peas and beans, should be used for this purpose. The crop thus plowed under contains much nitrogen, which is gradually changed into a form suitable for plant assimilation. In addition, the acid substances produced in the decay of the plants tend to liberate the insoluble plant-foods and the organic matter is finally changed into humus. In order to maintain a proper supply of nitrogen in the soil the dry-farmer will probably soon find himself obliged to grow, every five years or oftener, a crop of legumes to be plowed under.
Non-leguminous crops may also be plowed under for the purpose of adding organic matter and humus to the soil, though this has little advantage over the present method of heading the grain and plowing under the high stubble. The header system should be generally adopted on wheat dry-farms. On farms where corn is the chief crop, perhaps more importance needs to be given to the supply of organic matter and humus than on wheat farms. The occasional plowing under of leguminous crops would he the most satisfactory method. The persistent application of the proper cultural methods of dry-farming will set free the most important plant-foods, and on well-cultivated farms nitrogen is the only element likely to be absent in serious amounts.
The rotation of crops on dry-farms is usually advocated in districts like the Great Plains area, where the annual rainfall is over fifteen inches and the major part of the precipitation comes in spring and summer. The various rotations ordinarily include one or more crops of small grains, a hoed crop like corn or potatoes, a leguminous crop, and sometimes a fallow year. The leguminous crop is grown to secure a fresh supply of nitrogen; the hoed crop, to enable the air and sunshine to act thoroughly on the soil grains and to liberate plant-food, such as potash and phosphoric acid; and the grain crops to take up plant-food not reached by the root systems of the other plants. The subject of proper rotation of crops has always been a difficult one, and very little information exists on it as practiced on dry-farms. Chilcott has done considerable work on rotations in the Great Plains district, hut he frankly admits that many years of trial will he necessary for the elucidation of trustworthy principles. Some of the best rotations found by Chilcott up to the present are:—
Corn—Wheat—Oats
Barley—Oats—Corn
Fallow—Wheat—Oats
Rosen states that rotation is very commonly practiced in the dry sections of southern Russia, usually including an occasional Summer fallow. As a type of an eight-year rotation practiced at the Poltava Station, the following is given: (1) Summer tilled and manured; (2) winter wheat; (3) hoed crop; (4) spring wheat; (5) summer fallow; (6) winter rye; (7) buckwheat or an annual legume; (8) oats. This rotation, it may be observed, includes the grain crop, hoed crop, legume, and fallow every four years.
As has been stated elsewhere, any rotation in dry-farming which does not include the summer fallow at least every third or fourth year is likely to be dangerous In years of deficient rainfall.
This review of the question of dry-farm fertility is intended merely as a forecast of coming developments. At the present time soil-fertility is not giving the dry-farmers great concern, but as in the countries of abundant rainfall the time will come when it will be equal to that of water conservation, unless indeed the dry-farmers heed the lessons of the past and adopt from the start proper practices for the maintenance of the plant-food stored in the soil. The principle explained in Chapter IX, that the amount of water required for the production of one pound of water diminishes as the fertility increases, shows the intimate relationship that exists between the soil-fertility and the soil-water and the importance of maintaining dry-farm soils at a high state of fertility.