Whenever the soil is carefully stirred, as will be described, the
value of shading as a means or checking evaporation disappears
almost entirely. It is only with soils which are tolerably moist at
the surface that shading acts beneficially.
Alfalfa in cultivated rows. This practice is employed to make
possible the growth of alfalfa and other perennial crops on arid
lands without irrigation.
The effect of tillage
Capillary soil-moisture moves from particle to particle until the
surface is reached. The closer the soil grains are packed together,
the greater the number of points or contact, and the more easily
will the movement of the soil-moisture proceed. If by any means a
layer of the soil is so loosened as to reduce the number of points
of contact, the movement of the soil-moisture is correspondingly
hindered. The process is somewhat similar to the experience in large
r airway stations. Just before train time a great crowd of people is
gathered outside or the gates ready to show their tickets. If one
gate is opened, a certain number of passengers can pass through each
minute; if two are opened, nearly twice as many may be admitted in
the same time; if more gates are opened, the passengers will be able
to enter the train more rapidly.
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