346 



DRY-FARMING 



Effect of Vahying Irrigations on Crop Yields per 



Acre 



The soil was a typical arid soil of great depth and 

 liad been so cultivated as to contain a large C{uantity 

 of the natural precij)itation. The first five inches 

 of water added to the precipitation already stored 

 in the soil produced forty l)ushels of wheat. Dou- 

 bling this amount of irrigation water produced only 

 fort3'-one bushels of wheat. Even with an irrigation 

 of fifty inches, or ten times that which produced forty 

 bushels, only sixty bushels of wheat, or an increase 

 of one half, were produced. A similar variation 

 may be observed in the case of the other crops. The 

 first lesson to be drawn from this important princij^le 

 of irrigation is that if the soil be so treated as to 

 contain at planting time the largest proportion of 

 the natural precipitation, — that is, if the ordinary 

 methods of dry-famiing be employed, — crops will be 



