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.
Several conditions must be fulfilled before nitrification can occur.
In summer, when the temperature is about 24° C. (75° F.), nitrification proceeds at a rapid rate.
The presence of a base such as lime or magnesia (or their carbonates) is also essential, as well as an adequate degree of moisture: in dry soils nitrification ceases.
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.
By their continued action the soil becomes enriched with nitrogenous material which eventually through the nitrification process becomes available to ordinary green crops.
Lime also assists in the decomposition of the organic matter or humus in the soil and promotes nitrification; hence it is of great value after green manuring or where the land contains much humus from the addition of bulky manures such as farm-yard dung.
By nitrification this substance rapidly becomes available to succeeding crops.
The growing crops should be ploughed in before flowering occurs; they should not be buried deeply, since decay and nitrification take place most rapidly and satisfactorily when there is free access of air to the decaying material.
Guano, which suggests the idea that the nitrate was formed by the nitrification of this kind of excremental matter.
As regards the ammonium carbonate accumulating in the soil from the conversion of urea and other sources, we know from Winogradsky's researches that it undergoes oxidation in two stages owing to the activity of the so-called " nitrifying " bacteria (an unfortunate term inasmuch as " nitrification " refers merely to a particular phase of the cycle of changes undergone by nitrogen).
But research showed that this process of nitrification is dependent on temperature, aeration and moisture, as is life, and that while nitre-beds can infect one another, the process is stopped by sterilization.
Mintz and others had proved that nitrification was promoted by some organism, when Winogradsky hit on the happy idea of isolating the organism by using gelatinous silica, and so avoiding the difficulties which Warington had shown to exist with the organism in presence of organic nitrogen, owing to its refusal to nitrify on gelatine or other nitrogenous media.
Nitrification; one of these, which he terms the Nitroso-bacteria., is only capable of bringing about the oxidation of the ammonia to nitrous acid, and the astonishing result was obtained that 12.42.1140, 10.01 10;3U 2.13, 2.35 2.58 4.52 3.43 :` 4.3 0 4.12 this can be done, in the dark, by bacteria to which only pure mineral salts - e.g.
Fermentation, &c.: Warington, The Chemical Action of some Micro-organisms (London, 1888); Winogradsky, " Recherches sur les organismes de la nitrification," Ann.