Abstract

We describe a submodel to simulate NO x and N 2 O emissions from soils and present comparisons of simulated NO x and N 2 O fluxes from the DAYCENT ecosystem model with observations from different soils. The N gas flux submodel assumes that nitrification and denitrification both contribute to N 2 O and NO x emissions but that NO x emissions are due mainly to nitrification. N 2 O emissions from nitrification are calculated as a function of modeled soil NH 4 + concentration, water‐filled pore space (WFPS), temperature, pH, and texture. N 2 O emissions from denitrification are a function of soil NO 3 − concentration, WFPS, heterotrophic respiration, and texture. NO x emissions are calculated by multiplying total N 2 O emissions by a NO x :N 2 O equation which is calculated as a function of soil parameters (bulk density, field capacity, and WFPS) that influence gas diffusivity. The NO x submodel also simulates NO x emission pulses initiated by rain events onto dry soils. The DAYCENT model was tested by comparing observed and simulated parameters in grassland soils across a range of soil textures and fertility levels. Simulated values of soil temperature, WFPS (during the non‐winter months), and NO x gas flux agreed reasonably well with measured values ( r 2 = 0.79, 0.64, and 0.43, respectively). Winter season WFPS was poorly simulated ( r 2 = 0.27). Although the correlation between simulated and observed N 2 O flux was poor on a daily basis ( r 2 = 0.02), DAYCENT was able to reproduce soil textural and treatment differences and the observed seasonal patterns of gas flux emissions with r 2 values of 0.26 and 0.27, for monthly and NO r flux rates, respectively.