CHAPTER XXI 



CONTROL OF MOISTURE 

 IV. IRRIGATION 



IRRIGATION may be practiced in any region where the normal 

 rainfall is not sufficient to grow maximum crops or where the 

 rainfall is deficient during any part of the season. The profit 

 realized will depend upon the crop grown, the increase in yield over 

 no irrigation, the cost of applying water, and the price of the crop. 

 The practice is usually confined to arid regions because irrigation is 

 absolutely necessary under those conditions to produce any crop 

 whatever, or to semi-arid regions where irrigation will give larger 

 yields and in some very dry years would insure a crop where other- 

 wise there would be none. Irrigation is practiced to a very limited 

 extent in humid climates, even in Florida with from fifty to sixty 

 inches of rainfall and in other states with thirty to forty inches. 

 In these regions water is applied in a very intensive form of agri- 

 culture or to special crops which command a high price, thus jus- 

 tifying the expense. In some European countries sewage is some- 

 times applied to soils, thus furnishing both water and plant food. 

 In China and Japan irrigation is an almost universal practice, even 

 where much of the land receives a fair natural supply of water in a 

 well distributed rainfall. 



Some Irrigation Projects in Western United States 



Salt River, Arizona 



Yuma, Arizona-California 



Uncompahgre, Colorado 



Boise, Idaho 



Minidoka, Idaho 



Flathead, Montana 



Milk River, Montana 



Sun River, Montana 



North Platte, Nebraska-Wyoming. 

 Shoshone, Wyoming. . 



Approximate 



$10,000,000 

 7,(XX),000 



"1,000. (XX) 



S,7(X),0<)0 

 4,400.000 

 1.2." 0,000 



i.ono.ooo 



1. (XX). 000 

 ir>.200.000 



:t.xw.(xx) 



Aero* to ho 

 irrigated 



219.000 



140.000 

 243,000 

 11S.OOO 

 1.72,000 

 210,000 



2i(i.noo 



1 29,000 

 HVi.OOO 



17 



