430 THE SMALL GRAINS 



with and without irrigation, Widtsoe (1912, pp. 15-25) 

 found that with 7.5 inches of water applied the percent- 

 age of the dry matter due to rain and the soil water, al- 

 ready present, was 85.5 per cent in the case of wheat, and 

 86.2 per cent for oats. In Utah, with 12 \ inches of rain 

 and soil water economically utilized, 1\ inches of irriga- 

 tion water added, or 20 inches in all, will make a good 

 crop of grain; and, therefore, in an average year very 

 little added above the 1\ inches can be utilized, but is 

 wasted. 



465. The yield to an acre-foot of water is much more 

 important in irrigation than the acre-yield. As already 

 intimated, water becomes less efficient the more there is 

 applied. That is, the more water a soil contains to a 

 given depth, the larger the quantity that will be absorbed 

 by the plant and evaporated by the sun in proportion 

 to dry matter produced. The principle as stated by 

 Widtsoe (1912, p. 239) is that " the rate of loss of water 

 from soils increases as the initial percentage of moisture 

 in the soil increases." Briefly, the problem is to secure 

 the maximum yield of dry matter with a given quantity 

 of water, at the least cost. Under irrigation, water is 

 often worth more than the land, and it is important to 

 know what the water will produce. The acre-foot yield 

 is largest with the smallest quantity of water, and least 

 with the largest quantity. Thirty acre-inches of water 

 will produce about 7000 pounds of the dry matter of wheat 

 on 1 acre, but will produce 22,000 pounds, over 3 times as 

 much, if applied over 4 acres. Of course the cost is 

 greater in tilling the 4 acres, but even so, the conditions 

 might be such that 30 inches on 4 acres would give greater 

 net profit than on one acre, considering the relative value 

 of land and water. In experiments with Siberian oats at 



