KINETIC FORMULATION OF OXYGEN-CONSUMPTION AND DENITRIFICATION PROCESSES IN SOIL

A kinetic expression for oxygen, nitrate, nitrite and nitrous oxide re duction in soil was developed. The formulation was based on competitiv e Michaelis-Menten kinetics for a steady microbial population whose re spiratory activity was assumed to be constant so that the number of el ectrons produced per unit of time was constant. Competition among the electron accepters was characterized by their affinity toward the elec tron and by their concentration. Several different Values for the affi nity coefficients were used to simulate the concentration of O-2, NO3- , NO2-, N2O and N-2 at various times. When relative magnitudes of affi nity coefficients were chosen to be 100 000, 1, 100 and 0.1, for O-2, NO3-, NO2- and N2O, respectively, the temporal plot of concentration s howed that the disappearance of O-2 and NO3- was zero order. The accum ulation of NO2- was very small and it was rapidly reduced to N2O. The production rate of N2O was nearly zero order but the magnitude of the rate was rather small as opposed to the rate of disappearance of NO3-. The reduction of N2O to N-2 took place only after NO3- had almost dis appeared. With these competition parameters NO3- was stable in the pre sence of O-2. The reduction of N2O was also very much retarded in the presence of NO3-. NO2- was relatively unstable, even in the presence o f O-2, and it was further reduced to N2O. With the relative magnitude of the chosen affinity coefficients, the kinetic formulation effective ly simulated the ''inhibitory'' effect of O-2 upon the denitrification process, and the ''inhibitory'' effect of NO3- and NO2- upon the redu ction of N2O to N-2.