SAVING WATER BY CULTIVATION 49 



The temperature cannot be controlled, effectively, by the 

 farmer; neither can the relative humidity; and, if the land 

 is to produce the largest and best crops, there must be in 

 the soil a fair abundance of water. To diminish the rate 

 of evaporation by controlling these three factors seems, 

 therefore, almost hopeless. The control must come from 

 the proper treatment of the top soil. (Fig. 11.) 



36. Mulching to check evaporation. It was observed 

 many years ago, that evaporation of water from soils 

 may be quite effectively stopped by covering the soil 

 loosely with straw, manure, litter of any kind or loose 

 soil. This method has been tried out practically in so 

 many countries and by so many investigators that there 

 can be no question about its effectiveness. 



Fortier recently re-examined the matter, under the 

 climatic conditions of the irrigated sections of the United 

 States, and found that a covering of sand, if of proper 

 depth, applied to the soil immediately after irrigation, 

 could be made to reduce the evaporation to less than 2 

 per cent of the water applied. In earlier days, it was 

 advocated rather largely that straw and other litters be 

 placed upon the soil to prevent evaporation. This method, 

 however, is too expensive to be of wide application. 



The method of today is to stir the top soil with proper 

 implements. The process is called cultivation. The 

 layer of loose dirt which is thus left upon the soil hinders 

 very effectively the movement of soil water into the 

 atmosphere. In the Utah work it was found that, by 

 cultivation, an infertile clay soil lost only 63 per cent of 

 the quantity lost by the non-cultivated soil; a fertile 

 clay loam, 13 per cent, and a loose sandy soil, 34 per cent. 

 Fortier found that by thorough cultivation of a southern 

 California soil the loss by evaporation could be reduced 

 D 



