Short communication Using a modified DNDC model to estimate N2O fluxes from semi-arid grassland in China

Field measurement results showed that approximately 40% of the annual N2O losses occurred during the non-growing season and confirmed the importance of spring and autumn periods for assessment of total N2O losses from semi-arid temperate grassland in China. In the previous study, we found that the 7.2 version of Denitrification–Decomposition (DNDC) model had significantly lower estimates of N2O losses in spring and autumn time. In this study, three modifications, which mainly focus on the nitrification sub-model, the impact of soil frost and snow cover on gas production and emission, had been made to the model code. Based on field measurement, we concluded that modified version of DNDC model is more suitable for estimating the magnitude and seasonal trends of N2O losses from this region on a plot scale. By extrapolating the field data with our modified model, we estimated that the annual N2O emission rates for natural temperate grasslands of northern China is ca. 0:056Tg N2O–N y , i.e. ca. 40% lower than the estimate based only on field measurements (ca. 0:092Tg N2O–N y ). q 2003 Elsevier Science Ltd. All rights reserved.