426 THE SMALL GRAINS 



grain. The increased yields were more than sufficient 

 to pay for the cost of fall irrigation of these crops. 



457. The quantity of water required at each irrigation 

 depends upon the number of irrigations, the depth of 

 soil, nature of soil and subsoil, purpose for which the crop 

 is grown, climatic conditions, method of application, and 

 other factors. Usually the soil is driest at the time of 

 the first irrigation, and more water is needed than at sub- 

 sequent irrigations. Water is also plentiful always dur- 

 ing the early spring. If the first irrigation occurs when 

 the grain is in the milk, it should be the heaviest ; but if it 

 comes when the spikes are in the boot, then the heavier 

 irrigation should be at the milk stage of the grain. New 

 land requires more water than old land. 



458. Duty of water may be defined as the number of 

 acres of any crop that can be served to maturity by a 

 certain quantity of water. The unit of quantity is desig- 

 nated by several terms, of which at present the second- 

 foot is the most common. A second-foot of water is 1 

 cubic foot of water passing a given point during each 

 second of time. An acre-foot is the quantity of water 

 that will cover 1 acre to a depth of 1 foot. The miner's 

 inch, formerly employed a great deal, furnishes in the 

 same time usually about ^V as much water as the second- 

 foot, but varies in value in different states. The term 

 duty of water, however, has in practice no fixed mean- 

 ing, perhaps necessarily so, under present conditions. 

 It may become more definite as irrigation practices are 

 improved. For example, just how much of the necessary 

 losses of water is excepted or included in stating the duty 

 of water is not always clear. Losses occur in various 

 ways, but chiefly through seepage, leakage, and evapora- 

 tion. The absolute duty of water is the service of the 



