FERTILIZER MATERIALS 



41 



Some of the Sources of Chemical Fertilizers 



Percentage composition of materials used as sources of nitrogen (German Kali 

 Works, N.Y. City) 



Composition of materials used as sources of phosphoric acid (Kali Works) 



Marketed production of phosphate rock in the United States, from the beginning of 

 the industry in 1867 to 1909, in long tons (Van Horn, U.S. Geol. Surv.) 



