THE SOIL. 



ments, phosphorus, nitrogen, hydrogen, and oxygen 

 are largely built up into the organic compounds which 

 compose the tissue of the plant, while the remaining 

 elements are chiefly used in the plant as carriers of 

 the other elements and do not constitute a component 

 of the plant on maturity but remain in the cell sap. In 

 the case of plants which dry up as they approach ma- 

 turity the concentration of salts in this way forces a 

 considerable part of these elements out of the plant 

 and they are returned to the soil. 



Amounts of Elements Removed by Crops. In 

 order to study the influence of the removal of crops 

 from the soil we must determine the amount of these 

 essential elements which are removed by mature crops. 

 The following table from Bulletin 47 of the Minne- 

 sota Experiment Station gives the amounts of these 

 essential elements removed by average crops. 



TABLE SHOWING THE PLANT FOOD MATERIAL REMOVED 

 BY THE CROPS IN POUNDS PER ACRE. 



