CHAPTER XIX 

 DENITRIFICA TION 



Denitrification is the reverse of nitrification. The 

 latter process has been defined as the gradual changing 

 of the nitrogen of vegetable and animal substances 

 (organic nitrogen) into nitrates. It is therefore, an 

 oxidation process, involving the addition of oxygen 

 to the nitrogen through the activities of the nitrifying 

 bacteria. Denitrification is a reducing process whereby 

 the nitrate is made to part with some or all of its oxygen, 

 and is changed to a nitrite, to ammonia, or to nitrogen 

 gas. A distinction should be drawn, therefore, between 

 the complete destruction of nitrates with the formation 

 of nitrogen gas, and the partial decomposition in which 

 a nitrite or ammonia is formed. The first instance, 

 which represents denitrification proper, is -of much 

 greater importance from the economic standpoint, 

 since the nitrogen, once returned to the air, is lost to 

 the soil and crops. On the other hand, the reduction 

 to nitrite, or ammonia, does not remove the nitrogen 

 from the soil. It is still there, though in a changed form, 

 and may ,again be oxidized -to nitrate. 



Early idea of denitrification. -^-The earlier observers 

 who noted the reduction of nitrates ascribed it to re- 

 actions purely chemical. In the sixties of the last cen- 



(183) 



