150 TRANSFORMATION OF NITROGEN BY SOIL MICROBES 



TABLE 34 



Amounts (Percentages) of Ammoni.\ or Gaseous Nitrogen Formed 



FROM Nitrate by Bacteria Using Different Carbohydrates as Food 



(from Stoklasa and Vitek) 



gases represents a definite disappearance of nitrogen from the soil. 

 This reduction of nitrate to gaseous nitrogen or nitrous oxide is the 

 change referred to as denitrification. These various reactions 

 are considered as processes of nitrate reduction. The forma- 

 tion of nitrite and ammonia does not necessarily result in losses 

 of nitrogen from the soil, since, under favorable conditions, these 

 substances may be oxidized to nitrate again. The reaction (pH) of 

 the material in which the reductions are taking place will, of course, 

 affect the loss of ammoniacal nitrogen ; under alkaline conditions, 

 considerable amounts of ammonia may be lost by volatilization. 



Importance of Denitrification in Soil. — Since nitrate plays 

 such an important part in plant nutrition, the discovery of denit- 

 rifying organisms in soils suggested that denitrification might be 

 responsible for the limitation of plant growth by depletion of the 



