Datensatz

Zusammenfassung

We describe a submodel to simulate NO_x and N₂O emissions from soils and present comparisons of simulated NO_x and N₂O fluxes from the DAYCENT ecosystem model with observations from different soils. The N gas flux submodel assumes that nitrification and denitrification both contribute to N₂O and NO_x emissions but that NO_x emissions are due mainly to nitrification. N₂O emissions from nitrification are calculated as a function of modeled soil NH4+ concentration, water-filled pore space (WFPS), temperature, pH, and texture. N₂O emissions from denitrification are a function of soil NO₃- concentration, WFPS, heterotrophic respiration, and texture. NO_x emissions are calculated by multiplying total N₂O emissions by a NOx:N₂O 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 N₂O 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_x flux rates, respectively. [References: 71]