Q6 WILSON & TOOMKR FERTILIZER COMPANY 



not at hand the nitrifying bacteria will soon be killed by 

 their own product. Van Slyke says: "Each pound of 

 nitric acid formed, calls for nearly a pound of calcium 

 carbonate." "Nitrification cannot . . . take place 

 in acid or sour soils. In order that there may be no 

 accumulation of free nitric or other acids in soils, it is 

 absolutely necessary that there shall be an abundance 

 of some basic compound w r hich can unite with the free 

 acids and form salts that do not act injuriously on 

 nitrifying organisms." 



It has been seen that the change from ammonia to 

 nitrous and nitric acids consists of combining oxygen 

 with the nitrogen, hence it is evident that the nitrifying 

 bacteria must have an abundance of air. "Water-satu- 

 rated soils prevent nitrification by shutting off the air. 

 Limited air supply is one of the important factors which 

 explains the slow nitrification on heavy sod land and 

 in clay soils." Temperature also affects bacterial ac- 

 tivity. Crops start earlier on open, well-drained soil, 

 especially if they have a southerly slope, because of the 

 warmth inducing a more rapid formation of nitrates. 



Denitrifying Bacteria These are the enemies which 

 flourish when by ill-advised cultivation we have dis- 

 couraged the presence of the nitrifying bacteria. Nitri- 

 fying bacteria can take oxygen only from the air, but 

 denitrifying bacteria can break down nitrogen com- 

 pounds to secure the oxygen needed for their develop- 

 ment. They change nitrates to nitrites, then nitrites to 

 free nitrogen wrhich escapes into the air and leaves the 



