SIMULATION OF ECOLOGICAL CONTROLS ON NITRIFICATION

The accurate representation of nitrification in mathematical models is necessary to account for N distribution and transport through simulated ecosystems. Because of the complexity with which environmental factors interact to control nitrification, these representations should be based upon the kinetics of the limiting reactions mediated by microbial nitrifiers, rather than upon those of NO3- formation as is currently done. In the nitrification model proposed here, algorithms for autotrophic nitrifier activity and growth are coupled to ones for substrate production and transport under dynamic conditions of water, temperature and NH4+ concentration. This model is used to reproduce the time course of nitrifier biomass and activity following different NH4+ amendments under different CO2 concentrations, temperatures and water contents in a manner consistent with literature reports. Rates of NO3- formation arising from simulated nitrifier activity are comparable to those measured during incubations of NH4+-amended soil under common conditions of temperature and water content. However, the rigour of comparison is limited by the detail with which soil conditions are reported, and by the temporal resolution with which NO3- formation is measured, from most nitrification experiments.