138 SOILS AND FERTILIZERS 



may secure all of their food in inorganic forms ; that is, 

 nitrification may take place in the absence of organic 

 matter, provided the proper mineral food be supplied. 

 When growth under such conditions 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 un- 

 provided with chlorophyll, may construct organic com- 

 pounds containing nitrogen and designated bacterial 

 protein. 44 Nitrification in the absence of nitrogenous 

 organic matter is of too limited a character to supply 

 growing crops with all of their available nitrogen. For 

 general crop production the organic matter of the soil 

 is the source of the nitrogen which undergoes the nitri- 

 fication process, and which furnishes food for the nitrify- 

 ing organisms. 



150. Oxygen Necessary for Nitrification. The second 

 requirement for nitrification is an adequate supply of 

 oxygen. The nitrifying organism belongs to that class 

 of ferments (aerobic) which requires oxygen for exist- 

 ence. Oxygen is present as one of the elements in the 

 final product of nitrification as calcium nitrate, Ca(NO 3 ) 2 . 

 In the absence of oxygen, nitrification is checked. 

 When soils are saturated with water, the process can- 

 not go on for want of oxygen. The formation of a 

 hard, dry crust in soils also checks nitrification. Cultiva- 

 tion, particularly of clay soils, favors nitrification by 

 increasing the supply of oxygen in the soil. 



