288 DRY-FARMING 



mit a deeper penetration of the natural precipitation 

 and a freer movement of the soil-water result in a 

 larger quantity of plant-food reaching the upper 

 two or three feet from the lower soil depths. Such 

 concentration near the surface, when it is not exces- 

 sive, favors the production of increased yields of 

 crops. 



The characteristic high fertility and great depth 

 of arid soils are prol^ably the two main factors 

 explaining the apparent increase of the fertility of 

 dry-farms under a system of agriculture which does 

 not include the practice of manuring. Yet, there 

 are other conditions that contribute largely to the 

 result. For instance, every cultural method accepted 

 in dry-farming, such as deep plowing, fallowing, and 

 frequent cultivation, enables the weathering forces 

 to act upon the soil particles. Especially is it made 

 easy for the air to enter the soil. Under such condi- 

 tions, the plant-food unavailable to ])lants because 

 of its insoluble condition is lilx'ratcd and made avail- 

 able. The practice of dry-farming is of itself more 

 conducive to such accumulation of available plant- 

 food than are the methods of humid agriculture. 



Further, the annual yield of any crop under con- 

 ditions of dry-farming is smaller than under condi- 

 tions of high rainfall. Less fertility is, therefore, 

 removed by each crop and a given amount of avail- 

 able fertility is sufficient to produce a large number 

 of crops without showing signs of deficiency. The 



