CHAPTER VIII 



THE EVIDENCE OF HISTORY AND 

 RESEARCH 



GRANTING, for the purpose of argument, 

 that the mineral plant food in the soil is avail- 

 able at all times to plants in optimum quan- 

 tities, and that, generally speaking, the rate of 

 solution cannot be hastened or retarded, we 

 are still face to face with the proposition that 

 there is an end to the supply of these minerals. 



Doctor Hopkins, as we have seen, states 

 that the earth's crust contains about 49,200 

 pounds of potassium and 2,200 pounds of 

 phosphorus to 2,000,000 pounds. 



It is estimated that an acre one foot deep 

 of soil in New York State contains 35,000 

 pounds of potassium and 2,500 pounds of 

 phosphorus, and 20,000 pounds of lime. 



Does not this constitute a definite bank ac- 

 count of mineral fertility, paying interest to 

 the farmer in the form of crops out of its 



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