During the fallow season the disk and
smoothing harrows are run along the hillsides for the same purpose
and with results that are nearly always advantageous to the
dry-farmer. Of necessity, each man must study his own farm in order
to devise methods that will prevent the run-off.
The structure of soils
Before examining more closely the possibility of storing water in
soils a brief review of the structure of soils is desirable. As
previously explained, soil is essentially a mixture of disintegrated
rock and the decomposing remains of plants. The rock particles which
constitute the major portion of soils vary greatly in size. The
largest ones are often 500 times the sizes of the smallest. It would
take 50 of the coarsest sand particles, and 25,000 of the finest
silt particles, to form one lineal inch. The clay particles are
often smaller and of such a nature that they cannot be accurately
measured. The total number of soil particles in even a small
quantity of cultivated soil is far beyond the ordinary limits of
thought, ranging from 125,000 particles of coarse sand to
15,625,000,000,000 particles of the finest silt in one cubic inch.
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