COMMERCIAL FERTILIZERS 507 



accurately judged only by a large number of tests. At 

 present, both calcium nitrate and cyanamid are being 

 produced at less cost per pound of nitrogen than is sodium 

 nitrate, when laid down in the neighborhood of the fac- 

 tories in Europe. It seems fairly certain that, when the 

 processes have been further improved, the result will be 

 to greatly reduce the cost of available nitrogen. 



428. Organic nitrogen in fertilizers. — The commercial 

 fertilizers containing organic nitrogen include cottonseed 

 meal, which contains 7 per cent of nitrogen when free 

 from hulls; linseed meal, with 5.5 per cent of nitrogen; 

 castor pomace, with 6 per cent of nitrogen; and a num- 

 ber of refuse products from packing houses, among which 

 are red dried blood and black dried blood, the former 

 having about 13 per cent of nitrogen and the latter from 

 6 to 12 per cent_; dried meat and hoof meal, with 12 to 

 13 per cent of nitrogen ; ground fish, with 8 per cent of 

 nitrogen ; and tankage, of which the concentrated product 

 has a nitrogen content of from 10 to 12 per cent and the 

 crushed tankage from 4 to 9 per cent ; also leather meal 

 and wool-and-hair waste, but these, because of their 

 mechanical condition, are of very little value. 



The meals made from seeds are primarily stock foods 

 but are sometimes used as manures. They decompose 

 rather slowly in the soil, owing to their high oil content, 

 and are much more profitably fed to live stock than ap- 

 plied as farm manure. They contain some phosphorus 

 and potash as well as nitrogen. 



Guano consists of the excrement and carcasses of sea 

 fowl. The composition of guano depends on the climate 

 of the region in which it is found. Guano from an arid 

 region contains nitrogen, phosphorus, and potassium, while 

 that from a region where rains occur contains only phos- 



