Mathematical modelling of nitrous oxide evolution during nitrification

Abstract

There is a need for a process-based model of N 2O evolution during nitrification as part of larger models used to study trace gas exchange between terrestrial ecosystems and the atmosphere. The model proposed here for N 2O evolution is based on the hypothesis that NO 2 − is used as an alternative acceptor for electrons not accepted by O 2 during C oxidation for growth by NH 3 oxidizers. Rates of N 2O evolution simulated using this hypothesis are thereby sensitive to any physical or biological attribute of the soil that controls the demand for, or the supply of, O 2 during nitrification, such as substrate concentration, temperature ( T) or water content (θ). These rates were compared under a common range of T (10, 20 and 30°C) and θ (0.10, 0.20 and 0.30 m 3m −3) to ones reported in the literature that were measured during incubation of an NH 4 + amended soil. Simulated rates of N 2O evolution reproduced a sensitivity to T and θ that increased with both T and θ, although these rates were overestimated at θ = 0.20 m 3m −3. This overestimation is probably caused by uncertainty in parameterizing the model equation in which rates of gas transfer between gaseous and aqueous phases are calculated. Ratios of simulated N 2O evolution to NO 2 − + NO 3 − production increased with both T and θ through a range of 1–5 × 10 −3 μg N 2ON μg −1 NO 2 − + NO 3 −N in a way that was consistent with ratios of measured evolution to production reported from the NH 4 + amended soil as well as with those reported from other soils and pure cultures. As part of the larger ecosystem model ecosys, this model hypothesis will make a useful contribution towards the estimation of N 2O evolution from terrestrial ecosystems under different climates and fertilizer managements.