NITRIFICATION. 



It has been said already that though plants can make use 

 of sulphate of ammonia and other ammonia compounds, 

 yet they can use nitric nitrogen more easily, and do, in fact, 

 take up most of their nitrogen in that form. Nitrification, 

 or the process by which organic and ammoniacal nitrogen is 

 changed into the nitric form in the soil, must therefore 

 next be considered. 



In a general way, nitrification may be described as a series 

 of changes in which nitrogen is taken from its various com- 

 pounds in the soil, and made to combine with oxygen obtained 

 from the air to form nitric acid. Like other acids, this com- 

 bines with any of the substances which the chemist calls 

 bases, to form compounds called nitrates. 



CONDITIONS NECESSARY FOR NITRIFICATION. 



These reactions depend on the presence and activity of 

 micro-organisms or bacteria in the soil. It has been shown 

 by Warington* that there are two different organisms con- 

 cerned in this action, one of which converts the ammonia 

 into nitrites compounds in which the nitrogen is combined 

 with a smaller proportion of oxygen than in nitrates and 

 the other acts on the nitrites, causing their further oxidation, 

 with the formation of nitrates. From a practical point of 

 view, we may consider their actions as a single process ; for, 

 under the conditions existing in the soil, the two organisms 

 are equally active. If, however, they are to cause free 

 nitrification, the soil must be suitable for them. 



In the first place, it must contain nitrogen for the organisms 

 to convert into nitric acid. This nitrogen may be in the 

 form of either organic matter or compounds of ammonia, the 

 latter being more readily acted upon. 



If the nitrogen is present as ammonia, there must also be 

 organic matter in the soil to act as food for the organisms ; 

 for like other living things both animals and plants they 

 only thrive when they have enough food. If the nitrogen is 

 in the form of organic matter, the latter will, of course, serve 

 the double purpose of supplying nitrogen and feeding the 

 organisms. 



A supply of oxygen is also necessary to enter into com- 

 bination with the nitrogen, for it must be remembered that 

 the process of nitrification consists essentially of the oxida- 

 tion of nitrogen in the soil. This oxygen is, of course, derived 

 from the air ; and from this point of view the texture of the 

 soil, and the freedom or otherwise with which the air per- 

 meates it, are highly important, by influencing the facility 

 with which nitrification can take place. 



Moisture is also essential fgr nitrification. Provided the 

 soil is not water-logged, a large amount of water in the soil 



* Journal of the Chemical Society," 1891. 



