332 MAN'S USE AND CONSERVATION OF SOILS 



companies have spent millions of dollars in putting in irriga- 

 tion plants. By this means thousands of acres of land which 

 would otherwise have been valueless for agriculture have 

 been made exceedingly productive. 



Alkali Soils. In dry regions where the rainfall all 

 sinks into the ground and after remaining for a time rises 

 to the surface and is evaporated, large areas are found 

 upon which almost nothing can be made to grow even 



ALKALI SOIL 

 Few plants can grow here because of the excess of alkaline salts. 



when sufficient water is provided. Often in the dry sea- 

 son white or brown crusts appear scattered over the sur- 

 face in large patches. The white crust usually tastes like 

 Epsom salts and the brown like sal soda. The salts form- 

 ing these patches have been dissolved out of the soil by the 

 soil water and left on the surface when it evaporated. 



Such substances are not found in wet regions because 

 they are carried away by the water which runs into the 

 streams. About the only way soil of this kind can be treated 

 to make it productive is to irrigate and drain it, thus washing 

 the salts out of the soil. This is just what is done by nature 



