THE POTENTIAL PLANT FOOD 8/ 



Potential plant food is large. We may be certain, 

 therefore, that the potential supply of food is large, that 

 the stores of available plant food are more or less con- 

 stantly reenforced from other sources and that, this being 

 the case, the following conclusions are correct : 



1. Soils are able to produce crops indefinitely with 

 proper treatment. 



2. Soils are never exhausted of their potential plant 

 food. 



3. Soils are often depleted in producing power, but only 

 temporarily. 



4. \Yorn-out soils are not exhausted chemically but 

 physically. Their humus has been used up. 



5. Soils, once productive, but now unproductive, may 

 be restored to their former state through the rejuvenation 

 of the physical life. 



6. Physical improvement is the first step necessary for 

 restoring the producing power of soils. 



7. A fertile soil, wisely managed, maintains its fertility. 



8. A fertile soil, unwisely managed, loses its fertility 

 producing power but not its chemical constituents : 

 these are present in the tightly secured storehouses of the 

 land. 



9. Crop production bears a close relation to the physi- 

 cal nature of the soil the humus content, the texture, 

 the air and water circulation, the nature of the earthy 

 material, the previous treatment given it; but no correct 

 estimate can be made from the chemical analysis of the 

 soil alone. 



10. Chemical analysis can be interpreted only in con- 

 nection with group or type surveys, reenforced by broad 

 observations in the field, and modified by climatic condi- 

 tions, commercial opportunities, and the temperament of 

 the operator. 



