Effects On Rice Yield And Function Assessment On Ecological Environment Of Paddy Fields Under Incorporation Of Chinese Milk Vetch And Rice Straw Combined With Reduced Nitrogen Fertilizer

Chemical fertilizer has been playing an important role in sustaining soil fertility and rice yield.However,the environmental risks and the side effects on soil caused by excessive application of chemical fertilizer promote people to refocus attention on organic fertilizer sources.Chinese milk vetch（Astragalus sinicus L.,CMV）and rice straw are the main organic fertilizers in South China,which can increase rice yield and soil nutrients,improve physical,chemical and biological properties of paddy soil,but also have a certain impact on greenhouse gas emissions.Due to the carbon and nitrogen ration of rice straw and green manure,there are some limitations when they are returned to the field alone.Therefore,under the premise of maintaining high rice yield,how to optimize the three farmland management measures of chemical fertilizer,green manure and straw retention,improve nitrogen utilization efficiency and reduce greenhouse gas emissions has become the focus of attention and the key problem to be solved.In order to explore the effects of the above three kinds of farmland measures on rice production,nitrogen use efficiency,soil characteristics and greenhouse gas emissions,a field experiment was conducted in Dengjiabu,Yujiang County,Yingtan City,Jiangxi Province as the research object.7 treatments were set up:CK(winter fallow,without organic fertilizer,120 kg·hm^-2N fertilizer for each rice season),treatments with full retention of Chinese milk vetch named MRN1（-0%N fertilizer for each rice season）,MRN2（-12.5%N fertilizer for each rice season）MRN3（-25%N fertilizer for each rice season）and treatments with incorporation of Chinese milk vetch and rice straw names SRN1（-15%N fertilizer for each rice season）,SRN2（-27.5%fertilizer for each rice season）and SRN3（-40%N fertilizer for each rice season）.By monitoring crop production and greenhouse gas emissions,the effects of nitrogen fertilizer,green manure and straw retention as well as their interaction on crop yield composition,nitrogen use efficiency,soil fertilization,soil carbon and nitrogen transformation,soil microbial community,greenhouse gas emissions and related functional genes were systematically analyzed to provide theoretical basis for high yield of rice,carbon sequestration,emission reduction,and sustainable development of agriculture in southern China.The main results are as follows:（1）Milk vetch retention or incorporation of Chinese milk vetch and rice straw with reduced chemical fertilizer is helpful to improve yield components,such as panicle length,effective panicle number,effective tillers,grain number per panicle and 1000-grain weigh,thus increasing rice yield.Seed setting rate and actual yield increased by 1.20%～3.96%and 10.57%～14.53%,and the yield difference between them and control CK was significant（P<0.05）.Chinese milk vetch retention or incorporation of Chinese milk vetch and rice straw with reduced nitrogen fertilizer also increased dry matter,nitrogen uptake and utilization of rice,dry matter productivity and nitrogen partial productivity of early and late rice.Treatments SRN1 and SRN2 had the best effect on yield increasing.（2）Chinese milk vetch retention or incorporation of Chinese milk vetch and rice straw with reduced nitrogen fertilizer improved the physical and chemical properties of soil.The soil bulk density,soil total porosity,soil aeration porosity,the content of large aggregates,soil organic matter content,soil total nitrogen,alkaline hydrolysis nitrogen,available phosphorus and available potassium were enhanced.Moreover,Chinese milk vetch retention or incorporation of Chinese milk vetch and rice straw with reduced nitrogen fertilizer could improve soil carbon compositions and soil carbon management index,such as the total organic carbon,active organic carbon,readily oxidization organic carbon and microbial carbon.The range of soil microbial entropy was 1.67%～2.12%.The results of the correlation study indicated that a significant positive correlation exist between soil active organic carbon and carbon sink activity and carbon sink activity index（P<0.05）,a very significant positive correlation between soil active organic carbon and carbon sink management index（P<0.01）,and a significant negative correlation between microbial entropy and carbon sink index（P<0.05）.Treatment SRN2 had the best effect on improving soil physical and chemical properties and maintaining soil fertility.（3）Chinese milk vetch retention or incorporation of Chinese milk vetch and rice straw plus reduced nitrogen fertilizer significantly improved the OTU number of soil bacteria,the abundance and diversity indexes of bacterial community in paddy soil.The average relative abundance of proteobacteria,acidobacteria,nitrospirae and chloroflexi accounted for more than 80%.Soil urease activity,soil invertase activity,soil catalase activity were improved.（4）Chinese milk vetch retention or incorporation of Chinese milk vetch and rice straw plus reduced nitrogen fertilizer reduced N₂O emission,but increased CH₄and CO₂emission.Annual cumulative CH₄and CO₂emissions as well as the greenhouse gas emissions intensity（except SRN2）was significantly enhanced（P<0.05）;the net global warming potential were higher 4.20%～9.79%than that of control CK.The number of functional genes associated with greenhouse gas emissions also increased significantly,such as,the population number of soil ammonia-oxidizing bacteria（amo A）,methane-oxidizing bacteria（pmoA）and soil methanogens（mcr A）.Treatment SRN2 had the best effect on mitigating cumulative N₂O emissions and its CH₄cumulative emissions increased least.（5）Chinese milk vetch retention or incorporation of Chinese milk vetch and rice straw with reduced nitrogen fertilizer increased the total value of ecosystem services in paddy field.Agricultural products output increased by 6.01%～17.45%,and the gas regulating function value increased by 6.45%and 16.37%,and soil nutrient accumulation function value of treatment SRN2 was the highest,followed by treatment MRN2,while treatment SRN3 was the least,-1728.42 yuan/hm^-2.The total value of agricultural products,the value of gas regulation,the value of soil nutrient accumulation and the r yield to input ration of treatment SRN2 was the highest.