NITRIFICATION 1 17 



144. Nitrous Acid Organisms. There are at least 

 two nitrifying organisms in the soil ; one produces 

 nitrates and the other nitrites or nitrous acid. It is 

 believed that the process takes place in two stages, 

 the first being performed by the nitrous organism, 

 and the process being completed by the nitric organ, 

 ism. Warington says that " both organisms are 

 present in the soil in enormous numbers, and the 

 action of the two organisms proceeds together, as the 

 conditions are favorable to both." 



145. Ammonia-producing Organisms. There are 

 also present in the soil organisms which have the 

 power of producing ammonia from proteid bodies. 

 The ammonium compounds produced are acted upon 

 by the nitrifying organisms and readily undergo nitri- 

 fication. 46 



146. Denitrification 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 form- 

 ing free nitrogen which is liberated as a gas. One of 

 the conditions for denitrification is absence of air, as 

 the organisms belong to the anaerobic class. Denitri- 

 fication readily takes place in soils saturated with 

 water, and where the soil is compacted so that air is 

 practically excluded. 47 



147. Number and Kinds of Organisms in Soils. 

 In addition to the micro-organisms which carry on the 

 work of nitrification, denitrification, and ammonifica- 

 tion, there are a great many others, some of which are 



