332 THE PRINCIPLES OF SOIL MANAGEMENT 



air-tight casks. The fertilizer thus prepared contains 



11 to 13 per cent nitrogen. 



Calcium nitrate contains its nitrogen in a form 

 directly available to plants. It resembles sodium nitrate 

 in its solubility, availability, and lack of absorption by 

 the soil. It may be spread upon the surface of the ground, 

 as it exerts no poisonous action, and does not tend to 

 form a crust, as does sodium nitrate. 



The relative values of the different soluble nitrogen 

 fertilizers vary with a great many conditions and can 

 be accurately judged only by a large number of tests. 

 At present, both the calcium nitrate and the cyanamid 

 are being produced at less cost per pound of nitrogen 

 than is sodium nitrate, when laid down in the neighbor- 

 hood of the factories in Europe. It seems quite certain 

 that, when the processes have been further improved, 

 the result will be to greatly reduce the cost of the avail- 

 able nitrogen. 



197. Organic nitrogen in fertilizers. The commercial 

 fertilizers containing organic nitrogen include cotton- 

 seed-meal, which contains 7 per cent nitrogen, when 

 free from hulls; linseed-meal, with 5.5 per cent nitrogen; 

 castor pomace, having 6 per cent nitrogen; and a number 

 of refuse products from packing-houses, among which 

 there are red-dried blood and black-dried blood, the 

 former having about 13 per cent nitrogen, and the latter 

 6 to 12 per cent; dried meat and hoof meal, carrying 



12 to 13 per cent nitrogen; ground fish containing 8 per 

 cent nitrogen; and tankage, of which the concentrated 

 product has a nitrogen content of 10 to 12 per cent, and 

 the crushed tankage, 4 to 9 per cent; also leather-meal 



