2l6 



SOILS AND FERTILIZERS 



to the soil of all elements removed in the crop. Ex- 

 periments have shown that this view is incorrect. 

 The composition of plants cannot be taken as the 

 PI^ANT FOOD REMOVED BY CROPS 37 



basis for their manuring. For example an acre of 

 wheat contains 35 pounds of nitrogen while an acre 

 of clover contains 70 pounds. If 70 pounds of nitro- 

 gen were applied to an acre of clover and 35 pounds 

 to an acre of wheat, poor results would follow, be- 

 cause clover can obtain its own nitrogen while wheat 



