252 



IRRIGATION PRACTICE 



The quantity of water which produces the largest 

 yield of grain to the acre is seldom the most economical 

 quantity to apply. In the irrigated region, the acre of 

 land and the acre-foot of water must both be given atten- 

 tion; and, since the acre-foot of water usually has a higher 

 value than the acre of land, the emphasis should be 

 placed upon the producing power of a given volume of 

 water. The possibility of wheat-production with 30 

 acre-inches of water the quantity often assigned by 

 irrigation engineers based on the preceding table, may 

 be shown as follows: 



By spreading 30 acre-inches over 6 acres instead of 

 over 1, the total yield of wheat was increased from forty- 

 seven bushels to 226 bushels. In the final establishment 

 of empires on irrigated soils this fundamental relation- 

 ship between water and crop-yield, must of necessity be 

 taken into consideration. (Fig. 64.) 



The best knowledge of the day makes it safe to say 

 that, on deep soils, 7^ inches of water in two good irriga- 

 tions, should be ample for the production of a crop of 

 wheat. On shallow, gravelly soils, as high as 18 inches 

 may be used in four or five irrigations. On many soils 

 one good irrigation of 4 to 5 inches would be sufficient to 

 carry the crop to a large yield of grain of higher quality 

 than if more water were used. Everything considered, 

 an average of 1 acre-foot should be ample for the pro- 

 duction of wheat on fertile, well-tilled soils. 



