Mineral Nutrients 



153 



soil the value of using, about once in twelve or fifteen years, 

 a lime with high magnesia content. Finally, of all the 

 important elements furnished by the soil, nitrogen, phos- 

 phorus, and potassium are less abundant, relatively more 

 in demand by the growing crop, and accordingly to be 

 conserved and consistently restored. 



83. Nutrients removed by farm crops. In order to 

 appreciate properly the relation of cropping to the fertility 

 of the land it is necessary first to note the amounts of the 

 more important soil nutrients nitrogen, phosphorus, 

 and potassium which may be removed by various 

 crops annually. The table below is adapted from data 

 given by Hopkins : 1 



1 Hopkins, C. G., "The Fertility in Illinois Soils." 111. Agl. Exp., BuL 

 123 : p. 189. 



