Experience in the arid section of America,
in Egypt, India, and other desert-like regions has further proved
that the sands of the deserts produce excellent crops whenever water
is applied to them. The prospective dry-farmer, therefore, need not
be afraid of a somewhat sandy soil, provided it has been formed
under arid conditions. In truth, a degree of sandiness is
characteristic of dry-farm soils.
The _humus _content forms another characteristic difference between
arid and humid soils. In humid regions plants cover the soil
thickly; in arid regions they are bunched scantily over the surface;
in the former case the decayed remnants of generations of plants
form a large percentage of humus in the upper soil; in the latter,
the scarcity of plant life makes the humus content low. Further,
under an abundant rainfall the organic matter in the soil rots
slowly; whereas in dry warm climates the decay is very complete. The
prevailing forces in all countries of deficient rainfall therefore
tend to yield soils low in humus.
While the total amount of humus in arid soils is very much lower
than in humid soils, repeated investigation has shown that it
contains about 3-1/2 times more nitrogen than is found in humus
formed under an abundant rainfall.
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