MANURES. 27 



manure is spread over a considerable number of years, its 

 nitrogen being chiefly present not as ammonia but in the 

 form of carbonaceous compounds, which decompose but 

 slowly in the soil. 



Seaweed when fresh is, on the whole, similar in value 

 to farmyard manure. It becomes more valuable as it 

 loses water. 



Guano. — This manure consists chiefly of the dried ex- 

 crements of sea fowl. When guano has been deposited in 

 the absence of rain it contains a large amount both of 

 nitrogenous matter and phosphates. If exposed to rain 

 the original nitrogenous matter is decomposed, and the 

 nitrogen volatilised in the form of carbonate of ammonium ; 

 the guano remaining is then almost purely phosphatic. 

 Ichaboe guano, for example, is a recent deposit, containing 

 about 12 per cent, of nitrogen, and 12 per cent, of phos- 

 phoric acid ; while Mejillones guano is a phosphatic guano, 

 containing 0.9 per cent, of nitrogen, and 32.5 per cent, of 

 phosphoric acid. From its great variation in composition 

 guano should always be purchased on analysis. 



In a nitrogenous guano the nitrogen is chiefly present 

 as uric acid, and as ammonium salts. The strong smell of 

 a damp guano is due to carbonate of ammonium. The 

 phosphoric acid exists principally in the form of phosphate 

 of calcium, but in nitrogenous guanos a small part exists 

 as phosphate of ammonium, a salt readily soluble in water. 

 Guano which has not suffered by washing may contain 3 to 

 4 per cent, of potash. 



Nitrogenous guano is a highly concentrated manure, 

 and may be employed with excellent effect for corn crops, 

 potatos, and roots. Phosphatic guanos may be employed 



