114 SOILS AND FERTILIZERS 



In order to allow nitrification to proceed, all of these 

 conditions must be satisfied. The process is fre- 

 quently checked because some of the conditions, as 

 presence of a basic compound, are unfulfilled. 



138. Food for the Nitrifying Organisms. All liv- 

 ing organisms require food, and one of the food re- 

 quirements of the nitrifying organism is a supply of 

 phosphates. In the absence of phosphoric acid, 

 nitrification cannot take place. The change which 

 the phosphoric acid undergoes in serving 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 nitrifying 

 organism is the organic matter of the soil. Organic 

 matter, only when incorporated with soil, 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. The process 

 can take place only when the organic matter is largely 

 diluted with soil. Under favorable conditions nitrify- 

 ing organisms may take all of their food in inorganic 

 forms ; that is, nitrification may take place in the ab- 

 sence of organic matter provided the proper mineral 

 food be supplied. When growth under such condi- 

 tions takes place the organisms assimilate carbon 

 from the combined carbon of the air, and produce 

 organic carbon compounds. An organism, working 

 in the absence of sunlight and unprovided with 

 chlorophyl, may construct organic carbon com- 

 pounds. 44 The nitrification which takes place in the 

 absence of nitrogeneous organic matter is of too 



