Summary
The time course of nitrate production is different in different soils; in some soils, nitrate is produced at a constant rate while in others, this rate increases with time, often exponentially. Mechanistic models, based on the Monod equations, cannot account for a constant rate of nitrification. All such mechanistic models make the implicit assumption that the nitrifying organisms are distributed uniformly as single cells throughout the soil volume, while in reality, the cells might be expected to occur in small clusters formed by repeated cell division. This paper examines the effects of allowing the ammonium oxidising cells to occur in evenly distributed clusters of cells of equal volume. One effect of clustering would be the lowering of soil pH around the cluster, caused by differences in the rates of acid production and diffusion. The effects of this pH depression were examined using a mathematical model.
In general, it was found that the effect of clustering was to reduce the rate of ammonium oxidation. In extreme cases, in which the fraction of the soil volume occupied by the cells was assumed to be small, the model predicted a constant rate of ammonium oxidation with time in contrast to the increasing rate with time predicted by a model based on a uniform single cell distribution. The clustering model was therefore capable of reproducing the different time courses of ammonium oxidation reported in the literature. The differences between the time courses of ammonium oxidation predicted using the two different assumptions was affected by the initial pH of the soil. This observation suggested a possible experimental test of the clustering hypothesis.
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References
Addiscott T M 1979 Kinetics and temperature relationships of mineralisation and nitrification in Rothamsted soils with differing histories. J. Soil Sci., 34, 343–353.
Belser L W 1979 Population ecology of nitrifying bacteria. Annu. Rev. Microb. 33, 309–334.
Buchanan R E and Gibbons N E 1974 Bergey's Manual of Determinative Bacteriology. 8th edition, Williams and Wilkins Co.
Crank J 1975 The Mathematics of Diffusion. 2nd edn. Clarendon Press, Oxford.
Darrah P R, Nye P H and White R E 1985 Modelling growth responses of soil nitrifiers to additions of ammonium sulphate and ammonium chloride. Plant and Soil 86, 425–439.
Darrah P R, Nye P H and White R E 1986 Simultaneous nitrification and diffusion in soil. V The effect of pH change, following the addition of ammonium sulphate, on the growth and activity of nitrifiers. J. Soil Sci. (In press).
Darrah P R, White R E and Nye P H 1985 Simultaneous nitrification and diffusion in soil. I The effects of the addition of a low level of ammonium chloride. J. Soil Sci. 36, 281–292.
Frissel M J and Van Veen J A (Eds.) 1981 Simulation of N behaviour in Soil Plant Systems. Centre for Agricultural Publishing and Documentation, Wageningen.
Molina J A E 1985 Components of rates of ammonium oxidation in soil. Soil Sci. Soc. Am. J., 49, 603–609.
Nye P H 1972 The measurement and mechanism of ion diffusion in soils. VIII A theory for the propagation of changes of pH in soils. J. Soil Sci. 23, 82–92.
Russell E W 1973 Soil Conditions and Plant Growth. 10th edition. Longman.
Smith G D 1978 Numerical Solution of Partial Differential Equations: Finite Difference Methods. Clarendon Press, Oxford.
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Darrah, P.R., White, R.E. & Nye, P.H. A theoretical consideration of the implications of cell clustering for the prediction of nitrification in soil. Plant Soil 99, 387–400 (1987). https://doi.org/10.1007/BF02370884
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DOI: https://doi.org/10.1007/BF02370884