508 SOILS: PROPERTIES AND MANAGEMENT 



phorus — the nitrogen and potassium having been largely 

 leached out. In a dry guano the nitrogen exists as uric 

 acid, urates, and, in small quantities, ammonium salts. 

 A damp guano contains more ammonia. The phosphorus 

 is present as calcium phosphate, ammonium phosphate 4 , 

 and the phosphates of other alkalies. A portion of 

 the phosphate is readily soluble in water. Thus all 

 the plant-food either is directly soluble or becomes so 

 soon after admixture with the soil. The composition 

 is extremely variable. The best Peruvian guano con- 

 tains from 10 to 12 per cent of nitrogen, from 12 to 15 

 per cent of phosphoric acid, and from 3 to 4 per cent of 

 potash. 



Guano was formerly a very important fertilizing ma- 

 terial, but the supply has become so nearly exhausted 

 that it is relatively unimportant at the present time. 



Of the abattoir products, dried blood is the most readily 

 decomposed, and therefore has its nitrogen 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 decomposition and nitrifica- 

 tion, which prevents its exerting a strong action in 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 as dried blood, 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 slowlv, 

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

 ing the store of nitrogen in a depleted soil. 



