NITROGEN, NITRIFICATION, NITROGENOUS MANURES 137 



149. Food for the Nitrifying Organisms. All living 

 organisms require food, and one of the food require- 

 ments of the nitrifying organism is a supply of phos- 

 phates and other minerals. In the absence of phos- 

 phoric acid, nitrification cannot take place. The 

 change which the phosphoric acid undergoes in serving 



FlG. 33. Nitric Acid Organism. (After Winogradsky.) 



as food for the nitrifying organism is unknown, but it 

 doubtless makes the phosphoric acid more available as 

 plant food. 91 The principal organic food of the nitrify- 

 ing organism is the organic matter of the soil, and it is 

 only when organic matter is incorporated with soil that 

 it can serve as food for the nitrifying organism. In the 

 presence of a large amount of organic matter, as in a 

 manure pile, nitrification does not take place. It occurs 

 only when the organic matter is largely diluted with 

 soil. Under favorable conditions, nitrifying organisms 



