All in all, the undiminished crop yield and the
composition of the cultivated fields lead to the belief that
soil-fertility problems under dry-farm conditions are widely
different from the old well-known problems under humid conditions.
Reasons for dry-farming fertility
It is not really difficult to understand why the yields and,
apparently, the fertility of dry-farms have continued to increase
during the period of recorded dry-farm history--nearly half a
century.
First, the intrinsic fertility of arid as compared with humid soils
is very high. (See Chapter V.) The production and removal of many
successive bountiful crops would not have as marked an effect on
arid as on humid soils, for both yield and composition change more
slowly on fertile soils. The natural extraordinarily high fertility
of dry-farm soils explains, therefore, primarily and chiefly, the
increasing yields on dry-farm soils that receive proper cultivation.
The intrinsic fertility of arid soils is not alone sufficient to
explain the increase in plant-food which undoubtedly occurs in the
upper foot or two of cultivated dry-farm lands.
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