Optimizing fertilizer management mitigated net greenhouse gas emissions in a paddy rice-upland wheat rotation system: A ten-year in situ observation of the Yangtze River Delta, China

Optimizing the type and rate of nitrogen (N) fertilizer is an effective approach for achieving food security and minimizing environmental impacts. In this study, a ten-year in situ field experiment was conducted to evaluate the interannual responses of crop yields and greenhouse gas (GHG) emissions to the continuous application of chemical fertilizer (CF) and partial manure application (30 %, CFM) in a paddy rice-upland wheat rotation system. The results indicated that the trends of crop yields and GHG emissions were stable over ten years, and an appropriate N rate (200/150 kg N ha-1 for rice/wheat) in the rice-wheat system had greater potential for maintaining crop yields (9.25/3.32 t ha-1 for rice/wheat) and reducing their net GHG emissions by 20.8-38.7 % in contrast to the high rate (300/225 kg N ha-1 for rice/wheat). Among CF treatments, CH4 emissions had a negative correlation with the N rate, while N2O emissions were positively correlated. The CFM treatments significantly increased CH4 emissions (37.5-112.2 %) compared to the CF treatments during the rice season, but mitigated N2O emissions during both the rice (55.7-58.2 %) and wheat season (32.0-48.2 %). In a comprehensive assessment of the CH4 and N2O emissions in rice-wheat system, 81 % of the net GHG emissions was occurred in the rice season, and there was no significant difference between the CF and CFM at rate of 200/150 kg N ha-1. The study suggests that partial manure application at an optimum rate can effectively mitigate GHG emissions and be beneficial for the sustainability of rice and wheat production in a paddy rice-upland wheat rotation system.