Effects Of Straw Return Modes On Carbon Sequestration And Emission Mitigation And Its Extension Policy Suggestions In Paddy Fields Of South China

Crop straw is a multipurpose and renewable biological resource.Since the 20C 80's,with the rapid development of China's agricultural production,the yields of crop straw have increased quickly,and it appeared the regional,structural and seasonal surplus.The proportion of the straw directly as fuel and feed reduced largely.The majority of farmers wanted to grab the farming season and sowing.There were a lot of wheat,corn and rice straw directly burned in the field,despite repeated prohibitions.Straw burned in the field is not only a waste of valuable resources,but also pollutes the atmospheric environment,threatens traffic safety,influences the life of urban and rural residents.It is an urgent problem to deal with crop straw reasonably and effectively in the sustainable development of agriculture in China.In this study,we choose the South China as the study area.In order to determine the net mitigation potentials of different straw return modes,a quantitative study from macroscopic regional angle is conducted to estimate the accumulation enhancement of soil organic carbon sequestration and greenhouse gases emission under different straw return modes by the method of Meta-analysis.Through the questionnaire survey and farmer interview from a microscopic perspective,the current situation of straw returning in this region and the main factors influencing the farmers' behavior decision of straw return will be determined.Based on the combination of regional research from macro angle and farmers' behavior from micro angle,we can find a suitable straw return mode under the net emission reduction conditions,put forward the extension policy recommendations for the paddy fields in South China.Through regional integration analysis and empirical research in the study,the main conclusions are as follows:1.It showed that conventional tillage with straw return(CTS),no tillage with straw return(NTS)and rotary tillage with straw return(RTS)could significantly increase the topsoil organic carbon content in paddy fields in South China,and the relative annual change of topsoil organic carbon content(RM)under CTS,NTS and RTS were 0.42,0.37 and 0.64 g·kg-1·a-1,respectively.The average RM in double cropping system and triple cropping system under straw return treatments were 0.40 g·kg-1·a-1 and 0.61 g·kg-1·a-1,respectively.The soil organic carbon sequestration duration of CTS,NTS and RTS were about 27,44 and 30 years,respectively.Accumulation enhancement rates of soil organic carbon for CTS,NTS and RTS over the whole soil organic carbon sequestration period were about 15.8%,23.3%and 27.3%,respectively.Compared with other two kinds of straw return modes,rotary tillage with straw return could maximize the soil organic carbon content.In order to improve the ability of soil carbon sequestration we should promote rotary tillage with straw return in paddy fields in South China.2.Conventional tillage with straw return(CTS),no tillage with straw return(NTS)and rotary tillage with straw return(RTS)could increase the greenhouse gas emissions in cropland in South China.The CH4 seasonal cumulative emissions under CTS,NTS and RTS were 326.84,265.69 and 313.78 kg·hm-2,respectively.The N2O seasonal cumulative emissions under CTS,NTS and RTS were 1.55,1.40 and 1.73 kg·hm-2,respectively.In condition of the same straw return mode,the seasonal cumulative emissions of greenhouse gas in triple cropping system was higher than that in double cropping system.The types of straw returned to the soil influence farmland greenhouse gas emissions.The CH4 seasonal cumulative emissions under different straw return modes in rice season wheat straw returned to soil were higher than that in wheat season rice straw returned,and the N2O seasonal cumulative emissions were on the contrary.Rotary tillage with straw return on soil carbon sequestration showed the maximum offset effect on slowing down the global warming,but no tillage with straw return showed the minimum effect.3.The willingness in straw burnt of the farmers was significantly affected by the cognition of straw return,understanding the goodness of straw return,education level,understanding the harm of straw burnt in cropland and enforcement of prohibition burning policy.And the cognition of no-till straw return and the area of the largest piece of land were the two distinct factors of farmers' willingness in no-till with straw return.Therefore,this study showed that no-till with straw return should be promoted in paddy fields in South China.Firstly,the government should increase the publicity of no-till with straw return,subsidies of farmers used no-till with straw return,and improve the economic benefit of straw return.Secondly,the government ought to actively organize agro-technician to study the technology of straw return,breaking through the problem of seeding emergence,plant diseases and insect pests.