comes during winter, the early springtime, before the spring rains come, is the best time for determining the maximum water capacity of a soil.  At that season the water-dissipating influences, such as sunshine and high temperature, are at a minimum, and a sufficient time has elapsed to permit the rains of fall and winter to distribute themselves uniformly throughout the soil.  In districts of high summer precipitation, the late fall after a fallow season will probably be the best time for the determination of the field-water capacity.

Experiments on this subject have been conducted at the Utah Station.  As a result of several thousand trials it was found that, in the spring, a uniform, sandy loam soil of true arid properties contained, from year to year, an average of nearly 16-1/2 per cent of water to a depth of 8 feet.  This appeared to be practically the maximum water capacity of that soil under field conditions, and it may be called the field capacity of that soil for capillary water.  Other experiments on dry-farms showed the field capacity of a clay soil to a depth of 8 feet to be 19 per cent; of a clay loam, to be 18 per cent; of a loam, 17 per cent; of another loam somewhat more sandy, 16 per cent; of a sandy loam, 14-1/2 per cent; and of a very sandy loam, 14 per cent.  Leather found that in the calcareous arid soil of India the upper 5 feet contained 18 per cent of water at the close of the wet season.

It may be concluded, therefore, that the field-water capacities of ordinary dry-farm soils are not very high, ranging from 15 to 20 per cent, with an average for ordinary dry-farm soils in the neighborhood of 16 or 17 per cent.  Expressed in another way this means that a layer of water from 2 to 3 inches deep can be stored in the soil to a depth of 12 inches.  Sandy soils will hold less water than clayey ones.  It must not be forgotten that in the dry-farm region are numerous types of soils, among them some consisting chiefly of very fine soil grains and which would; consequently, possess field-water capacities above the average here stated.  The first endeavor of the dry-farmer should be to have the soil filled to its full field-water capacity before a crop is planted.

Downward movement of soil-moisture

One of the chief considerations in a discussion of the storing of water in soils is the depth to which water may move under ordinary dry-farm conditions.  In humid regions, where the water table is near the surface and where the rainfall is very abundant, no question has been raised concerning the possibility of the descent of water through the soil to the standing water.  Considerable objection, however, has been offered to the doctrine that the rainfall of arid districts penetrates the soil to any great extent.  Numerous writers on the subject intimate that the rainfall under dry-farm conditions reaches at the best the upper 3 or 4 feet of soil.  This cannot be true, for the deep rich soils of the arid region, which never have been disturbed by the husbandman, are moist to very great depths.  In the deserts of the Great Basin, where vegetation is very scanty, soil borings made almost anywhere will reveal the fact that moisture exists in considerable quantities to the full depth of the ordinary soil auger, usually 10 feet.  The same is true for practically every district of the arid region.