NITROGEN, NITRIFICATION, NITROGENOUS MANURES 



organism and changed into nitrates. Nitrites exist in 

 soils as transition products, the amount present in fer- 

 tile soils being less than one part per million of soil. 



156. Ammonia-producing Organisms. There are also 

 present in the soil organisms which have the power 

 of producing ammonia from proteid bodies. The am- 

 monium compounds produced are acted upon by the 

 nitrifying organisms and readily undergo nitrifica- 

 tion. 46 ' 68 When oxidation of the protein is rapid, nitro- 

 gen may be liberated and lost. 



157. Denitfification is just the reverse of the nitri- 

 fication process, and is the result of the workings of 

 a class of organisms which feed upon the nitrates, 

 forming free nitrogen which is liberated as a gas. One 

 of the conditions for denitrification is absence of air, 

 as these organisms belong to the anaerobic class. De- 

 nitrification occurs in soils saturated with water, -and 

 where the soil is compacted so that air is practically 

 excluded. 47 ' 68 



158. Number and Kinds of Organisms in Soils. In 



addition to the micro-organisms which carry on the 

 work of nitrification, denitrification, and ammonification, 

 there are a great many others, some of which are bene- 

 ficial while others are injurious to crop growth. It has 

 been estimated that in a gram of an average sample of 

 soil there are from 60,000 to 500,000 beneficial and 

 injurious micro-organisms. 48 There are produced from 



