The process by which bacteria in soil and water oxidize ammonia and ammonium ions and form nitrites and nitrates. Because the nitrates can be absorbed by more complex organisms, as by the roots of green plants, nitrification is an important step in the nitrogen cycle.
Several conditions must be fulfilled before nitrification can occur.
This result is partly due to their period of accumulation and growth extending even months after the period of collection by the ripening cereals has terminated, and at the season when nitrification within the soil is most active, and the accumulation of nitrates in it is the greatest.
In summer, when the temperature is about 24° C. (75° F.), nitrification proceeds at a rapid rate.
It is only when these conditions are attended to that decay and nitrification of dung, guano, fish-meal, sulphate of ammonia and other manures take place, and the constituents which they contain become available to the crops for whose benefit they have been applied to the land.
They are, however, very readily absorbed by growing plants, so that in summer, when nitrification is most active, the nitrates produced are usually made use of by crops before loss by drainage takes place.