164 SOILS AND FERTILIZERS 



a nitrogen content of from 10 to 12 percent, and crushed 

 tankage, that has from 4 to 9 percent nitrogen. Leather 

 meal and wool and hair waste may also be mentioned but 

 they have only a small fertilizer value. Ground fish or fish 

 waste is also sold as a fertilizer and usually contains about 

 8 percent of nitrogen. 



Dried blood is the most readily decomposed of these 

 products, and its nitrogen is in the most available form. 

 It also contains a small quantity of phosphoric acid. It is 

 slower in its action than either nitrate of soda or sulfate of 

 ammonia. With this, as with all the animal products, the 

 soil should be in a condition favorable to decomposition of 

 organic matter and to the formation of nitrates. 



Dried meat contains a high percentage of nitrogen, but 

 does not decompose so easily as does dried blood, and is not so 

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

 to advantage, and the resulting manure is very high in nitro- 

 gen. 



Hoof-and-horn meal is high in nitrogen, but decomposes 

 slowly. Its nitrogen is less active than dried blood or meat. 

 It is useful to increase the store of nitrogen in a depleted soil. 



Tankage is highly variable in composition. The concen- 

 trated tankage, being more finely ground, undergoes more 

 readily the decomposition necessary for the utilization of its 

 nitrogen. 



Leather meal and wool and hair waste when untreated 

 are in such a tough and undecomposable condition that they 

 may remain in the soil for years without losing their structure. 

 They are not to be recommended as manures. 



215. Fish waste. — The material sold under this name is 

 usually waste from canning factories, and consists of the 

 heads, tails, bones, entrails and all other discarded portions 

 of the fish that are canned. As a fertilizer it acts very slowly 

 and is not at all adapted to crops that make their growth in 



