322 THE PRINCIPLES OF SOIL MANAGEMENT 



the elaborate experiments conducted by Lawes, Gilbert 

 and Pugh, in 1857, were required to fully demonstrate 

 the fact. Their care in conducting the experiments 

 resulted in their sterilizing the soil with which they 

 experimented, and hence their failure to discover the 

 utilization of free atmospheric nitrogen by legumes. 



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 

 introduced into Europe. The commerical fertilizer 

 industry thus dates from this time. 



188. Classes of manures. While manures are very 

 numerous as to kind, and a certain manure may have 

 a number of distinct functions, they may yet be roughly 

 divided into classes. They will accordingly be treated 

 under the following heads: (1) Commercial fertilizers. 

 (2) Farm manures. (3) Green manures. (4) Soil amend- 

 ments. 



189. 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 

 about $50,000,000 annually. Animal refuse and phos- 

 phate fertilizers are exported, while nitrate of soda and 

 potassium salts are imported. 



Of the fertilizers sold in 1899, about 70 per cent was 

 consumed in the North Atlantic and South Atlantic 

 states, in an area lying within 300 miles of the seaboard. 

 Nearly one-half of the remainder was purchased in four 

 states, Ohio, Indiana, Alabama and Louisiana. 



190. Function of commercial fertilizers. Primarily 

 the function of commercial fertilizers is to add plant 



