TEMPORAL AND VECTORIAL REACTIONS OF NITROGEN IN SOIL: A REVIEW

Some features of enzyme activities and microbial growth kinetics are reviewed and applied to sequential biochemical reactions in soil. Transformations of some soluble nitrogen compounds are discussed in terms of time of fluid flow downward in soil and a mathematical model is analyzed in such a way as to predict concentration-depth profiles of urea, ammonium, nitrite and nitrate. The intermediate compounds tend to reach maximal amounts in the profile whereas urea declines and nitrate, in the absence of denitrification, accumulates with depth. Although the model is general, it is limited to fallow soils or to laboratory soil columns. Nevertheless, the model suggests that much more needs to be learned about the influence of microenvironments on soil microbes and soil metabolism before any realistic analysis of dynamic profiles can be achieved.