SOILS 391 



agriculture are here alluded to. The important nitrifying 

 ferment is found in the superficial layers of the soil, it con- 

 sists of two distinct species, one converting the ammonia of 

 the organic matter into nitrous acid, while the other con- 

 verts nitrous into nitric acid. 



In both cases these acids unite at once with alkalies to 

 form salts ; the alkali generally selected is lime, so that 

 calcium nitrate is the final product, this is readily soluble 

 in water, and is the form in which nitrogen is taken up by 

 plants. 



This nitrifying process in soils is one of purification as 

 well as providing plants with nitrogen. The nitrogenous 

 organic matter, that is, the nitrogen combined with carbon, 

 cannot be utilized by plants until it has undergone the 

 process of nitrification ; the first step in this is the breaking 

 up under bacterial action of the nitrogen into ammonia, 

 and the carbon into carbonic acid. The ammonia is then 

 seized upon by the nitrifying ferments, and as above 

 described, converted into nitric acid. 



In this way soils get rid of both animal and vegetable 

 matter, and a process of self-purification of the utmost 

 utility occurs. It will be remembered that similar changes 

 occur in the bacterial disposal of sewage. 



In this nitrifying process, it will be observed, the 

 nitrogen for the plant begins as nitrates and ends as 

 nitrates. As soluble nitrate it is taken up by the plant 

 and converted into albumin ; in the animal body the plant 

 albumin is converted into animal albumin, its ultimate 

 decomposition product being ammonia. The ammonia in 

 the earth is seized upon by the nitrifying ferments and 

 converted into nitrites, and finally into nitrates, thus 

 completing the cycle of changes. 



Nitrification requires a porous soil, and the free access of 

 oxygen is essential to the process. A certain temperature 

 is also necessary, so that during winter it is practically in 

 abeyance, while it is active during summer. Too much 

 water in the soil is detrimental, as this means the exclusion 

 of the necessary oxygen. Nitrifying bacteria are not found 



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