Dry-Farming | Page 5

localities, it is undoubtedly well within the truth. In comparison with the amounts of water that fall upon the land as rain, it does not seem extraordinarily large.
One inch of water over one acre of land weighs approximately 226,875 pounds. or over 113 tons. If this quantity of water could be stored in the soil and used wholly for plant production, it would produce, at the rate of 45 tons of water for each bushel, about 2-1/2 bushels of wheat. With 10 inches of rainfall, which up to the present seems to be the lower limit of successful dry-farming, there is a maximum possibility of producing 25 bushels of wheat annually.
In the subjoined table, constructed on the basis of the discussion of this chapter, the wheat-producing powers of various degrees of annual precipitation are shown:--
One acre inch of water will produce 2-1/2 bushels of wheat.
Ten acre inches of water will produce 25 bushels of wheat.
Fifteen acre inches of water will produce 37-1/2 bushels of wheat.
Twenty acre inches of water will produce 50 bushels of wheat.
It must be distinctly remembered, however, that under no known system of tillage can all the water that falls upon a soil be brought into the soil and stored there for plant use. Neither is it possible to treat a soil so that all the stored soil-moisture may be used for plant production. Some moisture, of necessity, will evaporate directly from the soil, and some may be lost in many other ways. Yet, even under a rainfall of 12 inches, if only one half of the water can be conserved, which experiments have shown to be very feasible, there is a possibility of producing 30 bushels of wheat per acre every other year, which insures an excellent interest on the money and labor invested in the production of the crop.
It is on the grounds outlined in this chapter that students of the subject believe that ultimately large areas of the "desert" may be reclaimed by means of dry-farming. The real question before the dry-farmer is not, "Is the rainfall sufficient?" but rather, "Is it possible so to conserve and use the rainfall as to make it available for the production of profitable crops?"

CHAPTER III
DRY-FARM AREAS--RAINFALL

The annual precipitation of rain and snow determines primarily the location of dry-farm areas. As the rainfall varies, the methods of dry-farming must be varied accordingly. Rainfall, alone, does not, however, furnish a complete index of the crop-producing possibilities of a country.
The distribution of the rainfall, the amount of snow, the water-holding power of the soil, and the various moisture-dissipating causes, such as winds, high temperature, abundant sunshine, and low humidity frequently combine to offset the benefits of a large annual precipitation. Nevertheless, no one climatic feature represents, on the average, so correctly dry-farming possibilities as does the annual rainfall. Experience has already demonstrated that wherever the annual precipitation is above 15 inches, there is no need of crop failures, if the soils are suitable and the methods of dry-farming are correctly employed. With an annual precipitation of 10 to 15 inches, there need be very few failures, if proper cultural precautions are taken. With our present methods, the areas that receive less than 10 inches of atmospheric precipitation per year are not safe for dry-farm purposes. What the future will show in the reclamation of these deserts, without irrigation, is yet conjectural.
Arid, semiarid, and sub-humid
Before proceeding to an examination of the areas in the United States subject to the methods of dry-farming it may be well to define somewhat more clearly the terms ordinarily used in the description of the great territory involved in the discussion.
The states lying west of the 100th meridian are loosely spoken of as arid, semiarid, or sub-humid states. For commercial purposes no state wants to be classed as arid and to suffer under the handicap of advertised aridity. The annual rainfall of these states ranges from about 3 to over 30 inches.
In order to arrive at greater definiteness, it may be well to assign definite rainfall values to the ordinarily used descriptive terms of the region in question. It is proposed, therefore, that districts receiving less than 10 inches of atmospheric precipitation annually, be designated arid; those receiving between 10 and 20 inches, semiarid; those receiving between 20 and 30 inches, sub-humid, and those receiving over 30 inches, humid. It is admitted that even such a classification is arbitrary, since aridity does not alone depend upon the rainfall, and even under such a classification there is an unavoidable overlapping. However, no one factor so fully represents varying degrees of aridity as the annual precipitation, and there is a great need for concise definitions of the terms used in describing the parts of the country that come under dry-farming discussions. In this volume, the terms "arid," "semiarid,"