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 estabhshed, 

 if the surface soil could be dried to the point where 

 capillarity 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 rapidl}'. Under dry -farm conditions it frequently 

 occurs that the draft upon the water of the soil is 

 so great that nearly all the water is quickl}' 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 A\'inds 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 to}). 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 temj^erature 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 



