Effects of dose nitrogen on yield and global warming potential in a typical rice-wheat rotation system in China

A three-year field experiment was carried out to investigate the methane (CH4) and nitrous oxide (N2O) emissions and calculate the global warming potential (GWP) according to all energy input in response to the nitrogen (N) rate in the typical rice-wheat rotation system in Jiangsu, China. Four N treatments, including R220W180 (local practice), R220W140 (cutting 10% total N in wheat season), R180W180 (cutting 10% total N in rice season) and R180W140 (cutting 20% total N in rice and wheat seasons separately), were designed in the study. Results showed that annual CH4 emission was decreased by 25.7% in response to cutting 20% N, which was ascribed to the 24.6% reduction of CH4 emission in rice season (P < 0.05) compared to local practice. The mitigation of N2O emissions in R220W140 and R180R180 treatments contributed to the 8.5% and 15.7% decrease in annual N2O emission, which was the 23.5% decrease in cutting 20% N treatment compared to local practice, respectively. Specifically, under the same amount of N rate condition (10% N cutting), the transfer N from rice season (R220W140) to wheat season (R180W180) led to the 8.5% increase in N2O emission (P < 0.05). In the end, the cutting of 20% N decreased GWP and yield-scale GWP by 19% and 17%, which mainly originated from CH4 and N2O emissions. However, cutting N did not significantly decrease grain yield (P > 0.05). These results suggested that the 180 kg N/ha for rice and 140 kg N/ha for wheat in one rotation season were the beneficial N rate to achieve the co-benefit of yield and GWP in the typical rice-wheat rotation system in Jiangsu, China.