NITRIFICATION 12 1 



tions nitrifying organisms may take all of their food 

 as 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 assim- 

 ilate carbon from the combined carbon of the air, and 

 produce organic carbon compounds. That is, an 

 organism, working in the absence of sunlight and un- 

 provided with chlorophyl, may construct organic car- 

 bon compounds. 43 The nitrification which takes place 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 produc- 

 tion the organic matter of the soil is the source of the 

 nitrogen which undergoes the nitrification process, 

 and which furnishes food for the nitrifying organisms. 



136. Oxygen Necessary for Nitrification. — The 



second requirement for nitrification is an adequate 

 supply of oxygen. The nitrification organism belongs 

 to that class of ferments (aerobic) which requires oxy- 

 gen for existence. Oxygen is present as one of the ele- 

 ments in the final product of nitrification as in calcium 

 nitrate, Ca(NO ) 2 . In the absence of oxygen the nitri- 

 fication process is checked. When soils are saturated 

 with water, the process cannot go on for want of oxygen. 

 In well-cultivated soils, particularly clay soils, the con- 

 ditions for nitrification are improved by aeration be- 

 cause the supply of oxygen in the soil spaces is increased. 



