QUANTITY OF WATER IN IRRIGATION 345 



much higher than when water is obtained from grav- 

 ity canals. It is, therefore, important that the costly 

 water so obtained be used in the most economical 

 manner. This is doubly important in view of the 

 fact that the water supply obtained on dry-farms 

 is always small and insufficient for all that the farmer 

 would like to do. Indeed, the profit in storing and 

 pumping water rests largely uiDon the economical 

 application of water to crops. This necessitates the 

 statement of one of the first principles of scientific 

 irrigation practices, namely, that the yield of a crop 

 under irrigation is not proportional to the amount 

 of water applied in the form of irrigation water. In 

 other words, the water stored in the soil by the 

 natural precipitation and the water that falls during 

 the spring and summer can either mature a small 

 crop or bring a crop near maturity. A small amount 

 of water added in the form of irrigation water at the 

 right time will usually complete the work and pro- 

 duce a well-matured crop of large 3deld. Irrigation 

 should only he supplemented to the natural precip- 

 itation. As more irrigation water is added, the 

 increase in yield becomes smaller in proportion to 

 the amount of water employed. This is clearly 

 shown by the following table, which is taken from 

 some of the irrigation experiments carried on at the 

 Utah Station : — 



