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 upon 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 yield. Irrigation 
should only be 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: — 
