IDEA!- FERTILIZERS 65 



kinds of bacteria present. When green vegetation is 

 turned under or a soil is saturated with water, "putrefac- 

 tion" and its poisonous products occur in place of the 

 "decomposition" which attends dead vegetation in an 

 aerated soil. However, there are some forms of organic 

 matter, which, under the most favorable conditions, pro- 

 duce enough of these poisons to affect citrus trees seri- 

 ously, for the citrus family is especially sensitive to the 

 action of such compounds. 



Ammonifying Bacteria The change from organic ni- 

 trogen to ammonia "is accomplished by many kinds of 

 bacteria, . . . some of them are aerobic, others an- 

 aerobic. . . . The formation of ammonia from or- 

 ganic nitrogen compounds in soils depends upon a variety 

 of conditions, such as the kind of protein, the kind of 

 soil bacteria, and all the physical and chemical condi- 

 tions that modify or influence their activity." It is 

 during these processes that the above-mentioned enzymes 

 and their products occur. 



Nitrifying Bacteria Though the change from organic 

 nitrogen to ammonia is so varied and complex, "the 

 conversion of ammonia into nitric acid takes place as the 

 result of two distinct bacterial chemical operations, one 

 kind of bacteria being responsible for the first operation 

 and another for the second;" these two chemical opera- 

 tions being the change of ammonia into nitrous acid and 

 of the nitrous acid into nitric acid, in each instance by 

 an addition of oxygen. These acids are immediately neu- 

 tralized when there is free base present. If such base is 



