260 



IRRIGATION PRACTICE 



though the total yield be slightly larger, the less the yield 

 to the unit of water. The following table, taken from the 

 Utah work, will illustrate this statement: 



YIELDS OF CORN WITH VARYING QUANTITIES OF IRRIGATION WATER 



The depth of irrigation varied from 7^2 to 55 acre- 

 inches, but the acre yield increased only from eighty to 

 ninety-seven bushels of grain, and the stover showed a 

 similarly small increase. The bushels of grain per inch 

 of irrigation water were six, when 7J^ inches of water 

 were used; and only 1.43, when 55 inches were used a 

 decrease of three-fourths. Invariably, also, as more water 

 was used, the proportion of stover to grain increased. 

 (Fig. 65.) 



Thirty acre-inches have been allowed, frequently, by 

 state engineers as the proper quantity of water to be used 

 by farmers. It may be calculated from the above table 

 that, when 30 acre-inches are applied to 1 acre, about 

 ninety-seven bushels of corn are obtained; when spread 

 over 4 acres, more than 316 bushels of corn are produced. 

 This possible crop-producing power of water must be con- 

 sidered in building irrigated empires. The best knowledge 

 of the day indicates that 12 to 15 acre-inches are ordi- 

 narily a very satisfactory depth of water for the produc- 



