Abstract

An adjusted model was developed to analyse measured data of nitrous oxide and nitric oxide fluxes from an arable black earth soil. The existing models for kinetic isotope studies ignore N-trace gas fluxes. The novel model includes both N-gas production by heterotrophic and autotrophic nitrification and N-gas production and consumption by denitrification. Nitrous oxide and nitric oxide production through nitrification was simulated following the ‘hole-in-the-pipe’ model (4: M.K. Firestone et al. Microbiological basis of NO and N₂O production and consumption in soil), N-gas production by denitrification was described with first-order kinetics.

The model has been evaluated in a triplicate laboratory experiment, which involved three treatments (glycine, NH₄⁺, or NO₃^–-pool labeled) to distinguish the different sources of N₂O and NO. Heterotrophic nitrification was negligible, whereas autotrophic nitrification and denitrification occur simultaneously in soils. Nitrification was the main source of NO and N₂O in the black earth soil by field capacity (water content: 0.22 g H₂O g⁻¹ soil). The NO release was higher than the N₂O release, the N₂O/NO ratio was 0.05 in this soil.