Deep plowing
and proper tillage, which allow the rain waters to penetrate the
soil, gradually break up and destroy the hardpan, even when it is 10
feet below the surface. Nevertheless, the farmer should make sure
whether or not the hardpan does exist in the soil and plan his
methods accordingly. If a hardpan is present, the land must be
fallowed more carefully every other year, so that a large quantity
of water may be stored in the soil to open and destroy the hardpan.
Of course, in arid as in humid countries, it often happens that a
soil is underlaid, more or less near the surface, by layers of rock,
marl deposits, and similar impervious or hurtful substances. Such
deposits are not to be classed with the hardpans that occur normally
wherever the rainfall is small.
_Leaching.--_Fully as important as any of the differences above
outlined are those which depend definitely upon the leaching power
of a heavy rainfall. In countries where the rainfall is 30 inches or
over, and in many places where the rainfall is considerably less,
the water drains through the soil into the standing ground water.
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