Potential Of Straw Return Modes On The Net Emission Mitigation And Its Extension Policy Suggestions In A Rice-wheat Rotation System Of Yangtze Delta Plain

China is a large agricultural country with abundant crop straws.Returning straw to the field is one of the important ways to treat straw.It can not only improve soil fertility,increase crop yield,but also alleviate environmental problems caused by straw burning.However,in the existing research,the effects of different straw returning methods on the ecological environment are different.Therefore,it is very important to explore a straw returning method that can realize a large amount of straw,ecology and safety.In this study,the Yangtze River Delta region of China is used as the research area,and the rice-wheat rotation method is used as the farming condition.Based on the published literature on soil carbon sequestration and greenhouse gas emissions under the different returning methods of straw before 2018,the Meta-analysis method system is applied.Evaluated soil organic carbon and greenhouse gas emission under different straw returning methods(conventional tillage straw returning,CTS;no-tillage straw returning,NTS;rotary tillage returning,RTS)in China’s Yangtze River Delta rice-wheat cropland(The changes and effects of CH4 and N2O)were used to analyze the net emission reduction potential of different straw returning methods in the Yangtze River Delta Region of China.The research on the behavior of farmers’ straw returning was studied by using the meta-analysis method.The main influencing factors,the combination of the two to explore the most suitable straw returning method for the rice-wheat rotation system in the Yangtze River Delta region of China,and put forward relevant policy recommendations.The conclusions of the study are as follows:1.The average soil organic carbon content of farmland under three different straw returning methods(CTS,NTS and RTS)in the Yangtze River Delta region of China is 12.3g·kg-1,11.18g·kg-1 and 17.31g·kg-1,the average soil carbon sequestration is 449.89kg·hm-2,333.71kg·hm-2 and 594.03kg·hm-2,and the relative annual variation of soil organic carbon content was 0.31g·kg-1·a-1,0.26g·kg-1·a-1 and 0.34g·kg-1·a-1.The carbon sequestration time of farmland soil under the three returning methods is 23 years,42 years and 28 years,the organic carbon content increased during the carbon sequestration cycle was 18.58%,21.01%and 27.45%,respectively.Compared with the three straw returning methods,RTS treatment can increase the soil organic carbon content.Therefore,the Yangtze River Delta region in China can enhance the carbon sequestration potential of the farmland soil by rotary tillage.2.The cumulative CH4 seasonal emissions of farmland soil under three different straw returning methods(CTS、NTS、RTS)in the Yangtze River Delta region in China were 341.03 kg·hm-2,253.07 kg·hm-2 and 315.14 kg·hm-2,respectively.The cumulative N2O seasonal emissions were 1.43 kg·hm-2 and 1.42 kg·hm-2and 1.76kg·hm-2.The cumulative CH4 annul emissions are 495.5kg·hm-2,370.86kg·hm-2 and 652.61kg·hm-2.The cumulative annual emissions of N2O are 1.98kg·hm-2,1.63 kg·hm-2 and 3.53kg·hm-2.On the scale of 20 years,the comprehensive warming potentials of greenhouse gases under CTS,NTS and RTS treatments were 36247.25,27174.51 and 48007.72kg CO2-equivalent·hm-2,respectively.The net warming potentials were 34597.66,25950.90 and 45829.60kg CO2-equivalent·hm-2.On the 100-year time scale,the global warming potential of greenhouse gases under each treatment is 12976.48,9758.74 and 17366.60kg CO2-equivalent·hm-2,respectively.The net warming potential is 11326.89,8535.11 and 15188.47 kg CO2-equivalent·hm-2.Therefore,most suitable crop straw returning method in the Yangtze River Delta region of China is no-still straw returning to the field.3.The research results of related papers on the behavior of farmers returning straw to the field indicate that the key factors affecting farmers’ straw returning behavior are not completely homogeneous,age,total annual household income and subsidies for straw returning to the field,which all of them have significant heterogeneity.Under the condition of allowing heterogeneity to exist,the key factors affecting farmers’ straw returning behavior are the gender,cultural level,subsidies for straw returning behavior,punishment for straw burning and farmers to participate in straw returning,which can be seen that the external condition factors have obvious effects on the decision-making of farmers’ straw returning behavior,especially the subsidies and punishments for different treatments of straw treaments adopted by farmers.In addition,compared with the external conditions,due to the current urbanization background in China and the reality of rural "ageing" and"commercialization of farmers",in addition to the gender factors of farmers,this study did not find individual characteristics of farmers.Family characteristics have a significant impact on the choice of straw returning behavior.Based on the above,this study concluded that no-tillage straw returning is most suitable method for straw returning in the Yangtze River Delta region in China.The policy recommendations are as follows:(1)Improve the government policy system and increase administrative rewards and punishments;(2)Strengthen use and promotion of the technology about straw returning to the field;(3)Improve farmers’ awareness of the benefits of straw returning to the field.