SECTION XVII. COMMERCIAL FERTILIZERS 



SOILS have abundance of all necessary plant-food 

 materials except nitrogen, phosphates, potash, and lime, 

 which may be deficient in some lands. When one or 

 more of these valuable forms of plant-food is deficient, 

 poor crops result unless 

 something containing the 

 element wanted is added. 



The lack of even a 

 single one of these pre- 

 cious substances, or 

 forms of plant-food, will 

 cause the crop to be 



about as poor as if all FIG. 62. GRASS HAY FROM EQUAL AREAS 

 four Of them were de- O nleft > fertilized; on right, fertilized with 



nitrogen and potash. 



ficient. It is important 



to find out which of these is wanting, and to use on each 

 field a fertilizer that contains just the kind of plant-food 

 that is needed in that soil. Plants, if denied nitrogen or 

 phosphates, but given an abundance of everything else 

 needed, would die. 



Nitrogen and ammonia. Commercial fertilizers (so 



named from the word commerce, meaning trade) are those 



prepared and furnished by merchants or manufacturers. 



When they contain only nitrogen, they are called nitroge- 



H 97 



