Ammonification. 187 



Ammonification. When organic matter containing 

 nitrogen is decomposed by bacterial action, a part of the 

 nitrogen is returned to the air as free nitrogen. This is- 

 of course lost so far as the soil is concerned. The larger 

 part of the nitrogen is changed to ammonia after pass- 

 ing through a complex series of changes. The presence 

 of ammonia can often be noted about heaps of decompos- 

 ing matter, especially piles of horse manure. The pro- 

 duction of ammonia from organic matter is due to the 

 work of many classes of bacteria widely distributed in 

 the soil. These bacteria belong to both the aerobic and 

 anaerobic classes, thus making possible the process of am- 

 monification under widely diverse conditions as to pres- 

 ence or absence of oxygen. There is usually no lack of 

 some of the various kinds of ammonifying bacteria in the 

 soil, and the conditions under which they work are so 

 varied that the farmer does not have to consider means 

 of favoring their action. The work which they do is ab- 

 solutely essential to the fertility of the soil, since it is 

 one of the steps in the transformation of the nitrogen to 

 an available form for the plant. Soils have been studied 

 in which it was thought that the cause of the low fer- 

 tility was the lack of ammonifying bacteria. 



Nitrification. Under the action of these bacteria the 

 nitrogen of decomposing matter is rapidly changed to 

 ammonia. Plants can not use nitrogen in this form to 

 advantage. Some kinds of plants can cover part of their 

 need for nitrogen from this source, others can not use 

 ammonia at all. It is therefore necessary for the nitro- 

 gen to be still farther changed by the action of specific 

 organisms, the nitrifying bacteria. There are to be found 

 in nearly every soil two classes of the nitrifying organ- 

 isms, one which changes the nitrogen of ammonia to ni- 



