DRY-FARMING 



action of the sun and the wind, fresh sup- 

 plies of water are lifted from the sub-soil 

 water to the exposed and rapidly evapo- 

 rating surface. In a word, we may think 

 of the sun and the wind as a mighty 

 double-acting force-pump. In a recent 

 experiment it was found that each square 

 foot of an ordinary farm soil during the 

 summer months lost 1.3 pounds of water 

 daily by evaporation from the surface of 

 the land; or, in other words, over five 

 inches in a single month. But should the 

 top layer of soil be broken up and left 

 loose upon the land by cultivation, then 

 there is no longer one continuous film 

 linking the exposed surface with the sub- 

 soil water; and consequently, surface 

 tension can only lift the water so far as 

 the film is unbroken, that is, as far as the 

 unstirred soil extends, and this layer is 

 protected from evaporation by the loose 

 soil above. Thus, when a soU-mulch is 

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