Kinetic formulation of oxygen consumption and denitrification processes in soil

A kinetic expression for oxygen, nitrate, nitrite and nitrous oxide reduction in soil was developed. The formulation was based on competitive Michaelis-Menten kinetics for a steady microbial population whose respiratory activity was assumed to be constant so that the number of electrons produced per unit of time was constant. Competition among the electron accepters was characterized by their affinity toward the electron and by their concentration. Several different Values for the affinity coefficients were used to simulate the concentration of O-2, NO3-, NO2-, N2O and N-2 at various times. When relative magnitudes of affinity 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 showed that the disappearance of O-2 and NO3- was zero order. The accumulation 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 disappeared. With these competition parameters NO3- was stable in the presence 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 of O-2, and it was further reduced to N2O. With the relative magnitude of the chosen affinity coefficients, the kinetic formulation effectively simulated the ''inhibitory'' effect of O-2 upon the denitrification process, and the ''inhibitory'' effect of NO3- and NO2- upon the reduction of N2O to N-2.