CHEMICAL CHANGES 



21 



(4) Absence of Strong Light. Light suspends the action of 

 the organisms and finally destroys them. 



(6) Freedom from Excess of Salts. Ammonia chloride, car- 

 bonate, calcium chloride, or other salts in excessive amounts 

 inhibit its action. 



Physical Conditions. The three most important physical con- 

 dition which affect nitrification are, looseness of the soil, tempera- 

 ture, and water content. 



A loose and porous condition of the soil is more favorable to 

 nitrification than a compact condition. Thus, a soil under cul- 

 tivation allows more nitrification than the same soil in pasture. 

 Stirring a soil also favors nitrification. For example. King 

 obtained the following results in 285 days : 



The temperature also has a decided effect upon nitrification, as 

 is shown by the figures of King and Bertz obtained in 27 days, 

 expressed as nitric nitrogen in parts per million of soil. 



Temperature 

 degrees F. 



34 

 50 

 70 

 9 



Parts 

 per million 



... 6.5 

 7-7 

 ." 14.3 

 ... 29.1 



Nitrifying organisms, like other living things, have a minimum, 

 maximum, and optimum temperature of existance. The mini- 

 mum seems to be about the freezing point of water, and the 

 maximum about 45 C., the optimum about 35 C. 



Production of Ammonia and Nitrates in the Soil. The produc- 

 tion of active nitrogen in the soil depends upon the nature of the 



