WHAT IS BECOMING OF OUR SOILS? 209 



has been removed with the crops. Every harvest takes 

 from the field a certain quantity of its blood. There 

 is carried away with the crop, no matter what it is, 

 more or less of the vital principles on which the growth 

 of vegetation, that is, of future crops, depends. There 

 are removed with the crops certain quantities of phos- 

 phoric acid, potash, nitrogen and lime. The ingre- 

 dients removed which are principally of value are the 

 first three named. It follows that there must be a 

 gradual impoverishment of the soil, no matter how rich 

 it may have been originally, if this drain continues in- 

 definitely. 



NATURE AVOIDS BANKRUPTCY. 



It is true that there is present in most soils large 

 quantities of phosphoric acid and potash, which, if they 

 could be unlocked in the proportions in which they are 

 needed, might supply the wants of the crop for a hun- 

 dred or even a thousand years. The greater part of 

 this material, however, is locked up wisely by nature, 

 so that spendthrift man cannot break the bank. If na- 

 ture had made all its treasures of plant food readily 

 available, starvation would long since have overtaken 

 humanity. It is the nature of man to exploit the soil 

 to the last degree, hence it was a wise invention of 

 nature to make the soil self -protective. 



There is a certain limit to what we can get out of 

 the soil. Beyond that it holds its treasures with a firm 

 grip and refuses to part with them. Long years of ex- 

 perience at the Rothamsted Station have shown that the 

 yield of wheat on properly cultivated soil, which will 

 produce from thirty to thirty-five bushels per acre, rap- 

 idly declines when crop after crop of wheat and straw 

 are removed from the field and nothing is returned. In 



