GENERALIZED-MODEL FOR N-2 AND N2O PRODUCTION FROM NITRIFICATION AND DENITRIFICATION

We describe a model of N-2 and N2O gas fluxes from nitrification and d enitrification. The model was developed using laboratory denitrificati on gas flux data and field-observed N2O gas fluxes from different site s. Controls over nitrification N2O gas fluxes are soil texture, soil N H4, soil water-filled pore space, soil N turnover rate, soil pH, and s oil temperature. Observed data suggest that nitrification N2O gas flux es are proportional to soil N turnover and that soil NH4 levels only i mpact N2O gas fluxes with high levels of soil NH4 (>3 mu g N g(-1)). T otal denitrification (N-2 plus N2O) gas fluxes are a function of soil heterotrophic respiration rates, soil NO3, soil water content, and soi l texture. N-2:N2O ratio is a function of soil water content, soil NO3 , and soil heterotrophic respiration rates. The denitrification model was developed using laboratory data [Weier et al., 1993] where soil wa ter content, soil NO3, and soil C availability were varied using a ful l factorial design. The Weier's model simulated observed N-2 and N2O g as fluxes for different soils quite well with r(2) equal to 0.62 and 0 .75, respectively. Comparison of simulated model results with field N2 O data for several validation sites shows that the model results compa re well with the observed data (r(2)=0.62). Winter denitrification eve nts were poorly simulated by the model. This problem could have been c aused by spatial and temporal variations in the observed soil water da ta and N2O fluxes. The model results and observed data suggest that ap proximately 14% of the N2O fluxes for a shortgrass steppe are a result of denitrification and that this percentage ranged from 0% to 59% for different sites.