Greenhouse gases emission under different cropping systems in the Jianghan Plain based on DNDC model

Increased greenhouse gases emission contributes to global warming. Paddy field is considered to be one of the main sources of greenhouse gas CH₄ and N₂O emissions. The rice planting area in the Jianghan Plain is about 8×10⁵ hm², accounting for about 40% of the total rice planting area in Hubei Province. Studies on characteristics of greenhouse gases emission in the Jianghan Plain are important for evaluation and reduction of regional greenhouse gases emission. So far, several models, such as DNDC model, have been used for simulating the greenhouse gases emission, which in conjunction with ArcGIS may be used for simulating the regional greenhouse gas emission. In this study, we used DNDC model to simulate the greenhouse gases emission in the Jianghan Plain. The field experiment was carried out for investigating the characteristics of CH₄ and N₂O emissions under rice-wheat (RW), rice-rape (RR) and rice-fallow (RF) cropping systems. Meteorologic, soil, crop and field management data were obtained for DNDC-stimulating CH₄ and N₂O emissions under different cropping systems in the Jianghan Plain. The results of field experiment showed that the CH₄ fluxes were from -2.80 mg·m^-2·h^-1 to 55.64 mg·m^-2·h^-1, and the N₂O fluxes were from 0 to 1.90 mg·m^-2·h^-1 in the Jianghan Plain. CH₄ emission was mainly concentrated in rice season, and the peaks occurred at rice heading and tillering stages. N₂O emission in rice season was higher than in non-rice season. And the peaks occurred after wheat or rape sowing in non-rice season and during field drying period in rice season. CH₄ emission under RW and RR systems were significantly higher than that under RF system, while N₂O emission was significantly higher under RF system than under RW and RR systems. The DNDC model stimulating results were verified by comparing the observed values with the stimulated values. The R² and RAE between the observed and the stimulated values under different cropping systems were form 0.85 to 0.98 and from 8.29% to 16.42%, respectively. The high R² and the low RAE suggested that the stimulated values of CH₄ and N₂O emissions with DNDC model were in good agreement with the observed values. According to the simulation results, the annual emissions of CH₄ and N₂O were 0.292 9 Tg C and 0.009 2 Tg N in the Jianghan Plain from 2010 to 2016, respectively. For different crop systems, CH₄ and N₂O emissions were presented as RW > RR > RF and RW > RF > RR, respectively, and the global warming potential (GWP) was RW > RR > RF. The CH₄ and N₂O emissions were also different for different regions. The annual average CH₄ emission from 2010 to 2016 was in the order of Jianli > Jingmen > Gong'an > Tianmen > Xiantao > Honghu > Songzi > Hanchuan > Qianjiang > Shishou > Jingzhou > Jiangling > Chibi > Jiayu. And the annual average N₂O emission from 2010 to 2016 was in the order of Jianli > Jingmen > Gong'an > Honghu > Xiantao > Tianmen > Hanchuan > Qianjiang > Songzi > Jingzhou > Jiangling > Chibi > Shishou > Jiayu. The results of our study indicated that the DNDC model could preferably stimulate the greenhouse gases emissions in the Jianghan Plain. And RR and RF could reduce CH₄ and N₂O emissions compared with RW.