Simultaneous nitrification and diffusion in soil |
| |
| Authors: | P R DARRAH P H NYE R E WHITE |
| |
| Institution: | Department of Agricultural Science, University of Oxford, Parks Road, Oxford OX1 3PF. U.K. |
| |
| Abstract: | Darrah et al. (1985b, 1986) presented a model that predicted the distribution of ammonium and nitrate in a column of soil, following the addition of ammonium chloride as a band of fertilizer to one end of the column. Ammonification and nitrification, the inhibition of nitrification by high levels of fertilizer addition and the simultaneous diffusion of ammonium and nitrate were modelled. By simplifying algorithms concerned with the calculation of the concentration of ammonium in solution and the diffusion of solutes in the column, up to eight-fold savings in the time required to run the model could be made without significantly affecting the accuracy of the predictions. This simplified version was used to test the effect of a ±25% change in the values of the main input parameters. The distribution of ammonium was mainly influenced by parameters affecting the diffusive flux of solutes and the concentration of ammonium in the soil solution; that of nitrate was influenced by parameters affecting the growth, activity and inhibition of the nitrifiers. In general, the model was most sensitive to changes in the maximum specific growth rate of the nitrifiers, while almost no effect was observed when the affinity constant for ammonium oxidation was varied. Given the present state of knowledge of the range of parameter values in different soils, it is necessary to measure all the input parameters tested, with the possible exception of the diffusional impedance factor, in order to obtain accurate predictions from the model. |
| |
| Keywords: | |
|
|
