IRRIGATION 131 



IRRIGATION 



This name is given to a number of different methods of supply- 

 ing water to soils used for agricultural purposes. Every one is 

 familiar with the needs for irrigation in regions having low annual 

 rainfall. The purpose is to supply water at a time when the 

 growing crops most need it, thus securing increased yields suffi- 

 cient to give ample returns for the cost of irrigation. Not only is 

 irrigation needed in arid regions, but it is often found profitable 

 even where the annual rainfall is abundant. This is because 

 water may be artificially supplied during dry, hot weather when 

 the rainfall is not enough to produce maximum crops. Recent 

 trials made on light soils in the east have shown that yields of 



Fia. 87. A dam of wood and earth erected by private capital to irrigate land to be sold to 

 users. The water "shares" go with the land. 



potatoes and truck crops can be increased many fold and that the 

 profit from such irrigation is very great. 



About twelve million acres of land are irrigated in the United 

 States. This is only a small fraction of the arid region which 

 could be improved by irrigation. There is also a very extensive 

 area which can never be profitably irrigated because of the diffi- 

 culty and enormous expense of conducting water to the land. 



The United States Government has under construction a 

 number of irrigation projects which will irrigate many thousands 

 of acres (Fig. 86). As soon as the land watered by this means 

 becomes available for use it may be sold to actual users and the 

 money reinvested in other irrigation projects. Extensive areas 



