Direct sunshine promotes plant growth, but at the same time it
accelerates the evaporation of water from the soil. The whole
dry-farm territory receives more sunshine than do the humid
sections. In fact, the amount of sunshine may roughly be said to
increase as the annual rainfall decreases. Over the larger part of
the arid and semiarid sections the sun shines over 70 per cent of
the time.
Winds
The winds of any locality, owing to their moisture-dissipating
power play an important part in the success of dry-farming. A
persistent wind will offset much of the benefit of a heavy rainfall
and careful cultivation. While great general laws have been
formulated regarding the movements of the atmosphere, they are of
minor value in judging the effect of wind on any farming district.
Local observations, however, may enable the farmer to estimate the
probable effect of the winds and thus to formulate proper cultural
means of protection. In general, those living in a district are able
to describe it without special observations as windy or quiet. In
the dry-farm territory of the United States the one great region of
relatively high and persistent winds is the Great Plains region east
of the Rocky Mountains.
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