148 DRY-FARMING 
It is an important fact that very dry soil furnishes 
a very effective protection against the capillary 
movement of water. 
In accordance with the principle above established, 
if the surface soil could be dried to the point where 
capiliarity is very slow, the evaporation would be 
diminished or almost wholly stopped. More than a 
quarter of a century ago, Eser showed experimentally 
that soil-water may be saved by drying the surface 
soil rapidiy. Under dry-farm conditions it frequently 
occurs that the draft upon the water of the soil is 
so great that nearly ail the water is quickly and so 
completely abstracted from the upper few inches of 
soil that they are left as an effective protection against 
further evaporation. For instance, in localities 
where hot dry winds are of common occurrence, the 
upper layer of soil is sometimes completely dried be- 
fore the water in the lower layers can by slow capil- 
lary movement reach the top. The dry soil layer 
then prevents further loss of water, and the wind 
because of its intensity has helped to conserve the 
soil-moisture. Similarly in localities where the rela- 
tive humidity is low, the sunshine abundant, and 
the temperature high, evaporation may go on so 
rapidly that the lower soil layers cannot supply the 
demands made, and the topsoil then dries out so 
completely as to form a protective covering against 
further evaporation. It is on this principle that the 
native desert soils of the United States, untouched 
