DENITRIFICATION AND FLUXES OF NITROGENOUS GASES FROM SOIL UNDER STEADY OXYGEN DISTRIBUTION

Transport equations for O-2, NO3-, NO2-, N2O and N-2 were formulated t o investigate NO - stability, denitrification and formation of gaseous nitrogen compounds in a soil profile under different moisture and tem perature conditions. The source-sink terms of the transport equations, including those for O-2, Were based upon competitive Michaelis-Menten type kinetics of denitrification. The equations were solved under Var ious soil and seasonal temperature conditions typical of the Prairie R egion of Canada in order to explore the effects of these parameters up on predicted NO3- stability, denitrification product distribution in a soil profile and gaseous N fluxes from the soil surface. The depth to the aerobic-anaerobic interface from the soil surface was controlled by temperature, moisture and microbial activity distributions in the s oil. The kinetic expressions predicted that NO3- was generally stable under aerobic conditions since the affinity coefficient of O-2 for ele ctrons is much greater than that of NO3-. However, nitrate in the anae robic zone was subject to denitrification to produce N2O and N-2. The N2O produced in the anaerobic zone diffused into the aerobic zone wher e it was stable and eventually emitted to the atmosphere. As the NO3- concentration decreased, a greater proportion of N was emitted to the atmosphere as N-2. Thus, the ratio of N2O to N-2 emitted from the soil decreased with decreased NO3-. We found that the potential for denitr ification to take place in a soil profile was actually greater in late summer than in mid-summer since subsoil temperatures were higher late r on in the season. The ratio of fluxes of N2O to N-2 was a function o f time, moisture content distribution, the depth at which the maximum reduction of NO3- took place, and NO3- concentration.