Nitrification

Nitrification is the changing of nitrogenous organic matter or ammonia compounds into nitrates. Possibly the nitrogen of the air under certain circumstances also undergoes this change in soils. Some authorities ascribe the change to 'a ferment,' 'an organised structure,' the 'micrococcus nitrificans,' &c., but it is a power possessed possibly by many micro-organisms. These nitrifying bacteroids perform their work under certain conditions. First, the temperature must be suitable, for at about $5^\backslash circ$ C. the process is stopped; but with a rise of temperature there is a proportionate increase of work—commencing at about $12^\backslash circ$ C.—until $37^\backslash circ$ is reached, which is the 'optimum' temperature, and from this onwards there is a diminution of action until the 'maximum' temperature of $55^\backslash circ$ C. is reached, when nitrification ceases. These bacteroids are annihilated at a temperature of $90^\backslash circ$ C., although the same result will follow drying even at a much lower temperature. The second condition is the presence of oxygen; and the third is the presence of a salifiable base, such as lime, potash, soda, &c., without which nitrification cannot proceed. Under these conditions nitrification goes on in every fertile soil, the atmospheric nitrogen, nitrogenous organic matter, or ammonia compounds being converted, in the presence of lime or potash, into the corresponding nitrates of lime or potash; and from these nitric compounds plants derive the most or all of their nitrogen, although some experimentalists maintain that some plants obtain part at least of their nitrogen from ammonia. See Lawes and Gilbert, Proc. Roy. Soc., vol. xlvii.; Marshall Ward, Phil. Trans., B. 1887, vol. clxxviii.