THE WATER-COST OF DRY MATTER 



151 



sible area in the arid regions. However true it may be, in 

 the humid regions, that the acre-yield is the all-important 

 thing, in arid regions the yield to the acre-inch or to the 

 unit of water is equally important. For each crop and 

 given conditions, a point must be determined at which 

 the highest possible returns may be obtained from the 

 land, water and labor employed. (Figs. 25, 26.) 



103. Maximum yield with given quantity of water. 

 The relation of varying quantities of water to the yields 

 of crops may be expressed also by showing the producing 

 power of a definite quantity of water, say 30 acre-inches, 

 when spread over 1, 2, 4 or 6 acres. This is done in the 

 following table: 



POUNDS OF DRY MATTER PRODUCED BY 30 ACRE-INCHES OF WATER 



When 30 acre-inches were made to cover 4 acres 

 instead of 1 acre, the yield was increased for wheat nearly 

 three-fold, for alfalfa nearly four-fold, for sugar beets 

 nearly three-fold and for potatoes nearly three-fold. When 

 it is considered that the development of the arid regions 

 will depend upon the settlement of a dense population, 

 requiring food, clothing and shelter, it is evident that 

 irrigation water, the limiting factor of the prosperity of 

 the region, must be made to produce the largest quan- 

 tities of materials for food, clothing and shelter. The 

 acre-yield, the criterion of humid regions, will retreat 



