It is believed that in a dry-farm
district, where the major part of the precipitation 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.
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