Generalized model for N₂ and N₂O production from nitrification and denitrification

Abstract

We describe a model of N 2 and N 2 O gas fluxes from nitrification and denitrification. The model was developed using laboratory denitrification gas flux data and field‐observed N 2 O gas fluxes from different sites. Controls over nitrification N 2 O gas fluxes are soil texture, soil NH 4 , soil water‐filled pore space, soil N turnover rate, soil p H, and soil temperature. Observed data suggest that nitrification N 2 O gas fluxes are proportional to soil N turnover and that soil NH 4 levels only impact N 2 O gas fluxes with high levels of soil NH 4 (>3 μg N g −1 ). Total denitrification (N 2 plus N 2 O) gas fluxes are a function of soil heterotrophic respiration rates, soil NO 3 , soil water content, and soil texture. N 2 :N 2 O ratio is a function of soil water content, soil NO 3 , and soil heterotrophic respiration rates. The denitrification model was developed using laboratory data [ Weier et al , 1993] where soil water content, soil NO 3 , and soil C availability were varied using a full factorial design. The Weier's model simulated observed N 2 and N 2 O gas fluxes for different soils quite well with r 2 equal to 0.62 and 0.75, respectively. Comparison of simulated model results with field N 2 O data for several validation sites shows that the model results compare well with the observed data ( r 2 = 0.62). Winter denitrification events were poorly simulated by the model. This problem could have been caused by spatial and temporal variations in the observed soil water data and N 2 O fluxes. The model results and observed data suggest that approximately 14% of the N 2 O fluxes for a shortgrass steppe are a result of denitrification and that this percentage ranged from 0% to 59% for different sites.