General model for N₂O and N₂ gas emissions from soils due to dentrification

TLDR

A model was developed that predicts N₂O and N₂ emissions from soil by linking denitrification rates to soil NO₃ availability, labile carbon (proxied by heterotrophic respiration), and oxygen availability, with inputs of soil respiration, texture, NO₃, and water‑filled pore space, and selecting the limiting factor between NO₃ and CO₂ to estimate daily N₂+N₂O fluxes. The model accurately predicted N₂O fluxes, with r²≈0.5 when comparing simulated and observed values in both core incubations and irrigated field soils, and the ratio of NO₃ to CO₂ reliably estimated the N₂/N₂O emission ratio.

Abstract

Observations of N gas loss from incubations of intact and disturbed soil cores were used to model N 2 O and N 2 emissions from soil as a result of denitrification. The model assumes that denitrification rates are controlled by the availability in soil of NO 3 ( e − acceptor), labile C compounds ( e − donor), and O 2 (competing e − acceptor). Heterotrophic soil respiration is used as a proxy for labile C availability while O 2 availability is a function of soil physical properties that influence gas diffusivity, soil WFPS, and O 2 demand. The potential for O 2 demand, as indicated by respiration rates, to contribute to soil anoxia varies inversely with a soil gas diffusivity coefficient which is regulated by soil porosity and pore size distribution. Model inputs include soil heterotrophic respiration rate, texture, NO 3 concentration, and WFPS. The model selects the minimum of the NO 3 and CO 2 functions to establish a maximum potential denitrification rate for particular levels of e − acceptor and C substrate and accounts for limitation of O 2 availability to estimate daily N 2 +N 2 O flux rates. The ratio of soil NO 3 concentration to CO 2 emission was found to reliably ( r 2 =0.5) model the ratio of N 2 to N 2 O gases emitted from the intact cores after accounting for differences in gas diffusivity among the soils. The output of the ratio function is combined with the estimate of total N gas flux rate to infer N 2 O emission. The model performed well when comparing observed and simulated values of N 2 O flux rates with the data used for model building ( r 2 =0.50) and when comparing observed and simulated N 2 O+N 2 gas emission rates from irrigated field soils used for model testing ( r 2 =0.47).