The effect of soil physical conditions on the nitrification of NH4

Abstract

SUMMARYThe purpose of the present paper is to elucidate the effect of the amount of NH4-N applied (30, 61, 122, 406 and 1016 ppm) on the nitrification process of a chernozem soil at 5 levels of bulk density (between t. 15 and 1.67 g.cm-a). The experiments were performed at two moisture contents :-15 and 26 per cent.The experimental results indicated that there is a direct relationstlips between the amounts of NH4-N applied to the soil and the accumulation of nitrate, at all levels of NH4-N applied. The greater the quantity of NH4-N applied, the greater the decrease in the productivity ratio (NO3-N accumulating/Ntte-N applied.In the case of soils having a high moisture content (26%) the nitrification depends on the amount of NH4-N applied and on the degree of aeration.The NHe-N remaining after incubation under conditions of inadequate aeration cannot be subsequently recovered as NO3, eren if the soil is subsequently made less tightly packed.It is well known that a close relationship exists between the ammonium content of a soff and the rate of nitrification. This is the basis of the differing fertility of soils to which differing quantities of mineral nitrogen have been added.On the other hand, in earlier papers 4 5 6 it was shown that the rate of nitrification greatly depends on the soil air/water ratio. Information on the relative influence of the chemical, physical and microbiological factors of the soll on nitrification is not yet available; the amount of oxidizable substrate, the conditions governing the oxidation reaction and the population of micro-organisms responsible for the NH4--> NO3 transformation are not yet sufficently known.