250 



IRRIGATION PRACTICE 



steadily to a limit, beyond which there is an actual 

 decrease; but, as the increase goes on, there is a steady 

 diminution in the yield per unit of water applied. This is 

 shown in the following table, taken from the Utah results: 



YIELDS OF WHEAT WITH VARYING QUANTITIES OF IRRIGATION 



WATER 



The quantity of water applied to wheat varied from 

 5 to 50 inches, but the yield varied from about thirty- 

 eight bushels to a little over forty-nine bushels an 

 increase of not quite twelve bushels of wheat for an 

 increase of nearly 45 inches of water. In the last column 

 of the table, it is shown that the yield per inch of irriga- 

 tion water fell from about seven and one-half bushels with 

 5 inches of water, to about one bushel with 50 inches 

 of water. This variation in yield, due to increasing applica- 

 tions of water, has been confirmed by practically every 

 investigator who has carried on accurate work under 

 field conditions. Moreover, the greater the quantity of 

 water used, the smaller the proportion of seed in the whole 

 plant. See the fourth column of the above table. (Fig. 63.) 



Not only is it possible to diminish beyond serious con- 

 sideration the acre-inch yield by increasing irrigations, 

 but it is possible by excessive irrigation to cause an actual 



