Improving the Chemical Nature of the Soil 87 



a large amount of salt, but when prepared for commerce 

 it is quite pure nitrate of soda. This is the form most 

 used on quick-growing truck crops. It is readily soluble 

 and, therefore, easily washed out of the soil. (See f 127, 

 Nitrification.) 



Sulphate of ammonia is obtained as a by-product 

 in the manufacture of illuminating gas from coal, and 

 from the distillation of bone in the manufacture of bone- 

 black. It is a very concentrated fertilizer, containing 

 about twenty per cent nitrogen. Ammonia salts may 

 be absorbed by some plants, but they are readily con- 

 verted into the nitrates by the nitrifying bacteria and 

 are usually absorbed in this form. 



122. Guano, obtained from the habitation of flesh- 

 eating birds roosting in caves and sea islands, has long 

 been used as a fertilizer. Dried fish, blood, hair, leather, 

 and various other substances of animal origin, are fre- 

 quently used for fertilizing purposes. The nitrogen of 

 both animal and vegetable origin must first be decom- 

 posed and converted into nitrates before it can be used 

 by plants. This takes time, and hence such substances 

 are slow-acting fertilizers. The meal, or pomace, 

 obtained as a by-product in the extraction of vege- 

 table oils, all contain large quantities of nitrogen, 

 such as cottonseed meal, castor pomace, germ meal 

 obtained from corn, etc. These substances are very 

 valuable as feeds for stock. This does not preclude 

 their use for fertilizing, for, in fact, they are almost 

 as valuable for fertilizing purposes, after passing 

 through the cattle, as before. 



123. Composted manures are the most economical and, 

 in general, the most desirable fertilizers. Besides sup- 

 plying large amounts of nitrogen, they contain consid- 



