366 DRY FARMING 



related' to, the content of plant food materials in the soil. 



Soils do not become literally "depleted" or "exhausted" 

 of the plant food elements they contain, although the 

 amount may 'be seriously lessened, but the land may be- 

 come depleted or exhausted of its "productiveness". 

 These so-called "depleted' soils may at any time be made 

 productive, but the trouble is they cannot be made to 

 produce a profit until such time as the pressure of popu- 

 lation or some other economic condition increases the 

 price of soil products or lowers the cost of production. 

 And if this does not happen, such soils remain unprofit- 

 able and unproductive. In any case they seldom redeem 

 themselves. They generally have to be built up by capital 

 brought from some other source. Such soils become not 

 only a source of loss to the man who operates them but 

 also a burden to the state which indirectly has to bear, 

 not only the loss from their inefficient use, but also the 

 cost of their redemption. 



327. Factors that Affect Permanence. The chief factors 

 that affect the maintenance of productiveness in any com- 

 munity have already been mentioned, but will bear re- 

 peating. They are : 



1. The maintenance of soil tilth, which in practice 

 generally means the maintenance of organic matter. 



2. The maintenance of soil health, or the prevention 

 or control of plant diseases that live in the soil. 



3. The maintenance of soil purity, or weed control, and 

 last but by far the most important in the long run 



4. The maintenance of a sufficient amount of available 

 plant food. 



In addition to being productive, a permanent agricul- 

 ture must also ~be a profitable agriculture. 

 And now, having considered this many-sided problem 



