386 



IRRIGATION PRACTICE 



The process has gone on in nature for many ages; the 

 salts have each year been washed down to a depth ordi- 

 narily reached by the rainfall and returned to the surface 

 during the warmer season. Arid soils are often underlaid 

 at a certain depth by layers of salts which indicate the 



UOOO 



FIG. 113. Structure of an alkali spot. 



annual penetration of the rainfall throughout the ages 

 before man began to cultivate the soil. (Fig. 113.) 



Upward leaching may be prevented by preventing 

 evaporation from the soil surface. The tillage methods 

 recommended for the conservation of water are those 

 that will prevent the accumulation of alkali at the soil 

 surface. 



