132 SOILS AND FERTILIZERS 



167. Ammonification. — Various intermediate products 

 occur in the breaking down of proteids, but we are concerned 

 chiefly with the product known as ammonia. This is the 

 nitrogenous substance contained in many fertilizers, and 

 it may be used by some crops directly as food material. 

 Rice, for instance, and probably other swamp plants can 

 use ammonia better than any other form of nitrogen. Even 

 some upland crops like corn, peas, barley and potatoes can 

 use it, but not as well as they can the form of nitrogen into 

 which ammonia is transformed by the next fermentation, 

 namely nitrification. 



It may be well to say, in passing, that there are some other 

 products intermediate between proteids and ammonia that 

 are directly used by plants, and it is altogether likely that 

 farm manure owes part of its great fertilizing value to some 

 of these substances that it may possess. 



168. Nitrification. — This is the final step in the prepara- 

 tion of nitrogen for use by most agricultural plants, for it is 

 in the form produced by nitrification that nitrogen is most 

 useful to most crops. This form is called nitrates. Like 

 ammonification this fermentation goes on in any normal 

 soil if the ammonia is there for it to work on, and also like 

 ammonification the conditions of temperature, air supply, 

 moisture and lime must be satisfactory or the process will 

 be so slow that plants will suffer for nitrogen. 



There has been some question as to whether heavy manur- 

 ing with organic manures results in a decreased nitrification. 

 While this may be the case where farm manure is used in 

 very heavy dressings of as high as fifty to a hundred tons 

 to the acre, as is sometimes done in truck crop gardening, 

 it is not likely to be the case in soils in which ordinary field 

 crops are grown. 



169. Effect of soil aeration on nitrate formation. — One of 

 the most important conditions that must obtain, if ammon- 



