COLLATERAL READING 153 



Conservation of Soil Resources. Farmers' Bulletin, No. 342, pp. 

 5-10. 



The Maintenance of Fertility. Ohio Bulletin, No. 182. 



The Maintenance of Fertility (Barnyard Manure). Ohio Bulletin 

 No. 183. 



How to Determine the Fertilizer Requirements of Ohio Soils. 

 Ohio Circular No. 79. 



The Fertility in Illinois Soils. Illinois Bulletin No. 123. 



Cyclopedia of American Agriculture. Vol. I, pp. 454-513 



Soils, by S. W. Fletcher. 



Ths Fertility of the Land, by I. P. Roberts 



Soils and Fertilizers, by Harry Snyder. 



Fertilizers, by E. B. Voorhees. 



