408 DRY LAND FARMING 



almost entire absence of loss by leaching, and, third, 

 because when moisture is absent the liberation of fer- 

 tility practically ceases. In humid areas the fertility 

 is continually drawn upon during the period of growth, 

 if not in growing crops in growing weeds. In dry -areas 

 growth is practically at a standstill during a consid- 

 erable portion of the growing season. The less rapid 

 loss of plant food in the soil in such dry areas is strik- 

 ingly shown in the longer period during which the 

 effects of farmyard manure are traceable when applied 

 to the soil. In many instances these are not traceable 

 in humid areas beyond three years, whereas they are 

 traceable in dry areas for at least twice as long. 



The restoration of fertility in dry areas is much 

 more difficult than in humid areas. This follows: 



(1) From the relatively small growth of vegetable mat- 

 ters produced for burial in the soil. In humid areas, 

 weed growth is more constant, and two or three crops 

 of green substance may be grown and buried in one 

 season. Such production in dry areas is much less. (2) 

 From the less extent to which legumes may be grown 

 on a given piece of land. These, of course, are the 

 most important restorers of fertility. (3) From the 

 more limited supply of the farm fertilizers that are on 

 hand, resulting from the less bulky crop production. 

 (4) From the slower action of applied commercial fer- 

 tilizers. These facts should be carefully weighed by 

 those engaged in dry farming. 



Sources of fertility. The sources of fertility in dry 

 areas include: (1) Food furnished directly by the soil; 



(2) food carried up by the subsoil ; (3) food liberated by 

 cultivation, and (4) food furnished by legumes. No 

 one of these sources is unimportant. 



The soil is beyond all comparison one of the most 

 important sources of plant food. The larger portion 

 of the food exists in the soil in the inert form, and is 



