492 SOILS: PROPEUTim AND MANAGMMBNT 



Between 1840 and 1850, Sir John Lawes began the 

 manufacture of bone superphosphate, and about the 

 same time Peruvian guano and nitrate of soda were intro- 

 duced into Europe. The commercial fertilizer industry 

 thus dates from that time. 



412. Classes of manures. — While manures are very 

 numerous as to kind and while a certain manure may have 

 a number of distinct functions, they may yet be roughly 

 divided into classes. They will accordingly be treated 

 here under the following heads : (1) commercial fertilizers ; 

 (2) soil amendments; (3) farm manures; (4) green 

 manures. 



413. Commercial fertilizers. — Although the commer- 

 cial fertilizer industry is little more than half a century 

 old, the sale of fertilizers in this country amounts to more 

 than $110,000,000 annually. Animal refuse and phos- 

 phate fertilizers are exported, while nitrate of soda and 

 potassium salts are imported. 



Of the fertilizers sold in the United States in 1909, 

 about fifty per cent was consumed in the South Atlantic 

 States, in an area lying within three hundred miles of 

 the seaboard. Nearly one-half of the remainder was pur- 

 chased in the Middle Atlantic and New England States, 

 Only five per cent was purchased west of the Mississippi 

 River.^ 



Primarily the function of commercial fertilizers is to 

 add plant nutrients to the soil, usually in a form more 

 readily soluble than those already present in large quan- 

 tity. While other beneficial effects may be produced by 

 certain fertilizers, these are usually of secondary impor- 

 tance as compared with the addition of the plant nutrients. 



^Statistics from THrteentli Census of the United States* 

 Abstract of tke Census, p. 372. WasMngton. 1913. 



