Since the average field capacity of soils for water is about 2.5
inches per foot, it follows that it is possible to store 25 inches
of water in 10 feet of soil. This is from two to one and a half
times one year's rainfall over the better dry-farming sections.
Theoretically, therefore, there is no reason why the rainfall of one
season or more could not be stored in the soil. Careful
investigations have borne out this theory. Atkinson found, for
example, at the Montana Station, that soil, which to a depth of 9
feet contained 7.7 per cent of moisture in the fall contained 11.5
per cent in the spring and, after carrying it through the summer by
proper methods of cultivation, 11 per cent.
It may certainly be concluded from this experiment that it is
possible to carry over the soil moisture from season to season. The
elaborate investigations at the Utah Station have demonstrated that
the winter precipitation, that is, the precipitation that comes
during the wettest period of the year, may be retained in a large
measure in the soil. Naturally, the amount of the natural
precipitation accounted for in the upper eight feet will depend upon
the dryness of the soil at the time the investigation commenced.
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