334 THE PRINCIPLES OF SOIL MANAGEMENT 



in the most available form. In fact, it produces results 

 more quickly than any other form of organic nitrogen. 

 It requires a condition of soil favorable to decomposi- 

 tion and nitrification, which prevents its exerting a 

 strong action in the early spring. It should be applied 

 to the soil before the crop is planted. The black dried 

 blood contains from 2 to 4 per cent of phosphoric acid. 



Dried meat contains a high percentage of nitrogen, 

 but does not decompose so easily, and is not so desirable 

 a form of nitrogen. It can be fed to hogs or poultry to 

 advantage, and the resulting manure is very high in 

 nitrogen. 



Hoof-meal, while high in nitrogen, decomposes slowly, 

 being less active than dried blood. It is of use in in- 

 creasing the store of nitrogen in a depleted soil. 



Ground fish is an excellent form of nitrogen, and is as 

 readily available as blood, but has a lower nitrogen 

 content. 



Tankage is highly variable in composition, and the 

 concentrated tankage, being more finely ground, under- 

 goes more readily the decomposition necessary for the 

 utilization of the nitrogen. Crushed tankage contains 

 from 3 to 12 per cent of phosphoric acid, in addition 

 to its nitrogen. 



Leather-meal and wool-and-hair waste are in such 

 a tough and undecomposable condition that they may 

 remain in the soil for years without losing their struc- 

 ture. They are not to be recommended as manures. 



198. Fertilizers used for their phosphorus. Phos- 

 phorus is generally present in combination with lime, 

 iron or alumina. Some of the phosphates also contain 



