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.
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