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 yet 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 practice 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 chapter. 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. 
