THEORY OF SOIL FERTILITY 



to feed us, if left to itself. They have not yet 

 taken the pains to compute the extent of the 

 mines of potash, phosphorus and calcium. 

 Why not? We have already begun to mine 

 these concentrated plant-foods in great quan- 

 tities, in response to their urgings, and en- 

 couraged, apparently, at least, by the beneficial 

 results to be obtained in the immediate crop 

 by such a system. It should be just as neces- 

 sary to know how much chemical plant food 

 will be ultimately available in the form of com- 

 mercial fertilizers as how much coal, iron or 

 gold we can extract from the earth. 



Any way one examines the hypothesis, car- 

 ried to its logical extension, it is a theory of 

 inevitable doom. Southern Illinois has enough 

 phosphorus to grow ordinary crops for seventy 

 years, we are told. The Leonardstown Loam, 

 they tell us, is already in process of active 

 abandonment. How long, then, before the 

 earth's crust will become a sterile waste, de- 

 void of living things because the means for 

 sustaining life have been consumed? 



