Ebermayer showed in 1873 that the
shading due to the forest cover reduced evaporation 62 per cent, and
many experiments since that day have confirmed this conclusion. At
the Utah Station, under arid conditions, it was found that shading a
pot of soil, which otherwise was subjected to water-dissipating
influences, saved 29 per cent of the loss due to evaporation from a
pot which was not shaded. This principle cannot be applied very
greatly in practice, but it points to a somewhat thick planting,
proportioned to the water held by the soil. It also shows a possible
benefit to be derived from the high header straw which is allowed to
stand for several weeks in dry-farm sections where the harvest comes
early and the fall plowing is done late, as in the mountain states.
The high header stubble shades the ground very thoroughly. Thus the
stubble may be made to conserve the soil-moisture in dry-farm
sections, where grain is harvested by the "header" method.
A special case of shading is the mulching of land with straw or
other barnyard litter, or with leaves, as in the forest. Such
mulching reduces evaporation, but only in part, because of its
shading action, since it acts also as a loose top layer of soil
matter breaking communication with the lower soil layers.
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