230 NITRIFICATION 



Mn is written for per cent, of water for maximum nitrification, 

 C for moisture capacity as defined by Hilgard, W for wilting co- 

 efficient, E for moisture equivalent, and H for hygroscopic 

 coefficient. 



Temperature. The temperature is a factor which controls in a 

 great measure the quantity of nitrates produced in unit time. 

 Schlosing found nitrification very slow at 7.5 C., quite marked at 

 11, reached its maximum at 37, and ceased entirely at 55. 

 Deherain found nitrification almost ceased at 5 C. and begins very 

 slowly in soils which have been frozen, yet Conn found the freezing 

 of soil increases its nitrifying powers. These temperatures are 

 questioned by some, for example Warington states that he was 

 unable to start nitrification at 40 C. 



Hutchinson gives the optimum temperature for nitrification in 

 Pusa soil at 35 C. No nitrates were formed at 40, nor did nitri- 

 fication take place in soil which had been kept at 40 C. when its 

 temperature was afterward reduced to 30 C. These apparent 

 contradictions may be due to different strains of the organisms 

 varying in sensitiveness to heat. Beddies isolated four stable 

 forms of nitric and three of nitrous ferments. One of the nitric 

 forms was capable of resisting the action of steam at 100 C. for 

 two minutes and one of the nitrous bacteria lived for one minute 

 in steam at the same temperature. The other two nitrous ferments 

 could not withstand steam but survived for several minutes in a 

 dry heat of 80 to 100 C. Moreover, Bazarewski found the most 

 favorable temperature for nitrification in soils to be between 25 and 

 27 C., or about 10 C. lower than in pure cultures in artificial 

 media. 



King, in his work, found that there was 1.26 times as much 

 nitric nitrogen formed at 9 C. as at 1 C., 2.76 times as much at 

 20, and 6.24 times as much at 35, as at 1. The significance of 

 these figures is brought out more fully when we examine the amounts 

 of nitric nitrogen obtained in some cases. At 1 C. there were 

 formed 120 pounds per acre; at 9, 150 pounds per acre; at 20, 329 

 pounds per acre; while at 35 there were formed 747 pounds per acre. 



Light Rays. The nitrifying organisms are heat-loving and light- 

 avoiding. They are dependent on the heat of the earth or of the 

 sun, but they carry on their activities best in the absence of sunlight. 

 Direct sunlight, partly due to the coagulation of the bacterial col- 

 loids by the rays of the ultraviolet light, soon proves fatal to them. 



Aeration and Cultivation. The nitrifying bacteria are all aerobic; 

 hence, nitrification is best other things being equal in a well- 

 aerated soil. This is illustrated by the work of Schlosing who 

 exposed soil for four months to an atmosphere containing different 

 percentages of oxygen. Soil which contained 1.5 per cent, of 

 oxygen yielded 45.7 mg. of nitric nitrogen, that containing 6 per 



