410 DRY LAND FARMING 



The limit of root penetration in the crop, therefore, 

 is an important factor when conducting experiments in 

 dry areas. But the upward movement of the natural 

 precipitation in the soil is also an important factor 

 in determining its producing power. The plant food 

 dissolved in the downward movement of soil moisture 



* 



is again carried upward to the domain where it may be 

 utilized by growing plants. In this way the fertility of 

 the surface soil is continually reinforced by plant food 

 carried up from the subsoil. In humid areas much of 

 the food thus dissolved and carried down to the surface 

 soil goes out in the drainage water. 



The proper cultivation of the soil tends to liberate 

 plant food in the same. The frequency with which the 

 soil is stirred in the summer-fallow and in growing a 

 cultivated crop favors such liberation of fertility. It 

 greatly facilitates growth in the crop sown on such land, 

 but this influence is secondary to that exerted by the 

 moisture conserved. In humid areas much of the fer- 

 tility thus liberated may be carried down and out into 

 the drainage water, but in dry areas this very seldom 

 occurs. 



The growing of legumes is one of the most effective 

 methods by which fertility may be increased in dry 

 soils. The supply of available fertility may be increased 

 by cultivation, by the amount carried in solution through 

 capillarity, and from the action of certain bacteria work- 

 ing in the organic matter in the soil, but such increase 

 relates almost entirely to temporary increase, which 

 means a reduction of the total amount left in the soil. 

 The increase through growing legumes is a positive 

 addition to the fertility of the soil, at least with refer- 

 ence to its nitrogen content. 



How to increase fertility. Fertility in dry areas 

 may be increased: (1) by growing legumes; (2) by ap- 

 plying farm manures, and (3) by applying artificial fer- 



