To determine whether or not the natural winter precipitation, upon
which the crops of a large portion of the dry-farm territory depend,
penetrates the soil to any great depth a series of tests were
undertaken. At the close of the harvest in August or September the
soil was carefully sampled to a depth of 8 feet, and in the
following spring similar samples were taken on the same soils to the
same depth. In every case, it was found that the winter
precipitation had caused moisture changes to the full depth reached
by the soil auger. Moreover, these changes were so great as to lead
the investigators to believe that moisture changes had occurred to
greater depths.
In districts where the major part of the precipitation occurs during
the summer the same law is undoubtedly in operation; but, since
evaporation is most active in the summer, it is probable that a
smaller proportion reaches the greater soil depths. In the Great
Plains district, therefore, greater care will have to be exercised
during the summer in securing proper water storage than in the Great
Basin, for instance. The principle is, nevertheless, the same.
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