REGULATING THE TRANSPIRATION 191 



cultivation are sufficient to set free an abundance of 

 plant-food, it may be necessary to apply manures or 

 commercial fertilizers to the soil. While the question 

 of restoring soil fertility has not j'et come to be a lead- 

 ing one in dry-farming, yet in view of what has been 

 said in this chapter it is not impossible that the time 

 will come when the farmers must give primary atten- 

 tion to soil fertility in addition to the storing and 

 conservation of soil-moisture. The fertilizing of lands 

 with proper plant-foods, as shown in the last sections, 

 tends to check transpiration and makes possible the 

 production of dry matter at the lowest water-cost. 



The recent ]3ractice in practically all dry-farm 

 districts, at least in the intermountain and far West, 

 to use the header for harvesting bears directly upon 

 the subject considered in this chaj)ter. The high 

 stubble which remains contains much valuable plant- 

 food, often gathered many feet below the surface by 

 the plant roots. When this stubble is plowed under 

 there is a valuable addition of the plant-food to the 

 upper soil. Further, as the stubble decays, acid 

 substances are produced that act upon the soil grains 

 to set free the plant-food locked up in them. The 

 plowing under of stubble is therefore of great value 

 to the dry-farmer. The plowing under of any other 

 organic substance has the same effect. In both cases 

 fertility is concentrated near the surface, which dis- 

 solves in the soil-water and enables the crop to ma- 

 ture with the least quantity of water. 



