SOIL FERTILITY AND 

 PERMANENT AGRICULTURE 



BY 

 CYRIL G. HOPKINS, PH.D. 



PROFESSOR OF AGRONOMY IN THE UNIVERSITY OF ILLINOIS, CHIEF IN 



AGRONOMY AND CHEMISTRY AND VICE DIRECTOR OF THE 



ILLINOIS AGRICULTURAL EXPERIMENT STATION 



V 

 GINN AND COMPANY 



BOSTON NEW YORK CHICAGO LONDON 



