Effects Of The Combination Of Green Manure Cultivation And Rice Straw Retention With Water And Nitrogen Fertilizer Management On Rice Growth And Greenhouse Gas Emissions Of Machine-Transplanted Rice

Double-cropping rice is an important agricultural production model in south China.Winter planting green manure and returning rice straw into field are effective measures to maintain the soil fertility and reduce the amount of fertilizer,however,at present,the water-fertilizer effect of their combined application is not clear enough.Therefore,this paper carried out a systematic study on the effects of water-saving irrigation and nitrogen reduction on the growth,water and nitrogen absorption,utilization and loss,greenhouse gas emissions,yield and quality of double-cropping rice under Astragalus smicus and straw returning in paddy fields in south China from 2013 to 2016.The purpose of this study was to reveal the formation basis and environmental effects of water-saving irrigation and nitrogen reduction on yield and quality of double-cropping rice,and to clarify water-fertilizer management measures in the Astragalus smicus and straw returning field.The main conclusions are as follows.（1）Under the conventional fertilizer measures,compared with the application of fertilizer（NPK）alone,the combined application of fertilizer and Astragalus sinicus and straw（NPK+GM+RS）advanced the growth process in the early growth stage,and significantly improved the number of tillers,the percentage of earring-tillers,the index of leaf area（LAI）,the dry matter accumulation and the group growth rate of early rice transplanted by machine.the NPK+GM+RS treatment promoted the absorption of N,P,and K nutrients in the early growth stage as well as the accumulation and transportation of nutrients during heading and maturity periods of early rice,and improved the chlorophyll content and photosynthetic rate of the leaves as well as the nutrients utilization efficiency in the later stage of rice.the NPK+GM+RS treatment increased the yield of early rice and late rice（5.39%and 2.56%,respectively）,and improved rice roughness,milled rice rate,whole milled rice rate and gum consistency,and reduced chalkiness,chalkiness grain rate,amylose content and alkali elimination level,thus improving the quality of machine-planted double-cropping rice.（2）Compared with W₀N₂,the NPK+GM+RS treatment optimized quality of rice groups,and significantly improved indices of high yield population quality,such as tillers,LAI,dry matter accumulation,and so on.the NPK+GM+RS treatment also enhanced the leaf net photosynthetic rate,transpiration rate,stomatal conductance and intercellular CO₂concentrations during the heading and mature stage of rice,and promoted the nutrient absorption and utilization.The results show that the nitrogen harvest index,apparent utilization rate and agronomic utilization rate of GM+RS+W₁N₁treatment increased by5.61%,39.97%and 37.45%respectively compared with that of W₀W₂treatment.Therefore,it can be said that NPK+GM+RS treatment increased the yield of rice（4.27%and 3.98%,respectively）,and improved the processing quality,appearance quality and steaming nutrition quality of double-cropping rice.（3）Compared with W₀N₂treatment,the rainfall utilization rate and water use efficiency of GM+RS+W₁N₁treatment increased by 8.73%and 15.30%,9.49%and 8.99%,respectively,and the irrigation water,runoff and water consumption decreased by 30.07%and 14.63%,72.63%and 41.44%,15.11%and 4.82%,respectively,and the average TN runoff loss decreased by 6.10 kg/hm²（by 32.34%）and 0.51 kg/hm²（by 46.79%）,respectively,during the whole growth period of early rice and late rice.（4）Under the same nitrogen application level,the cumulative CH₄emissions of early rice and late rice with intermittent irrigation decreased by 14.54%-37.37%and 16.70%-52.25%,respectively,compared with flooded irrigation,while the cumulative emissions of N₂O increased by 12.50%-35.29%and 23.08%-34.09%,respectively.Under the same irrigation method,the cumulative emissions of CH₄and N₂O in the early rice and late rice were shown as GM+RS+N₁>N₂>N₀.The CH₄emissions from early rice and late rice under different treatments were mainly concentrated in 1-2 weeks after application of basal-tiller fertilizer and the 1 week after the field drying and rehydration.while the N₂O emissions were mainly concentrated before the machine transplanting and after application of panicle fertilizer.（5）The order of GWP and GHGI in the early rice season,late rice season and double-cropping rice seasons under different treatments was GM+RS+W₀N₁>GM+RS+W₁N₁>W₀N₂>W₁N2>W₀N₀>W₁N₀.The GWP and GHGI of GM+RS+W₁N₁in double-cropping rice fields increased by 60.34%and 53.51%（2015）,34.89%and 30.46%（2016）,respectively,compared with that of W₀N₂.Water and fertilizer were important factors affecting the comprehensive greenhouse effect of double-cropping paddy fields.Both water management and fertilizer management had a significant impact on the cumulative emissions of CH₄and N₂O,GWP and GHGI of early rice and late rice.Among them,fertilizer management was the dominant factor determining the greenhouse effect of double-cropping paddy fields,and water management was the secondary determinantIn conclusion,under water-saving irrigation and nitrogen reduction,the GM+RS+W₁N₁treatment had a significant effect on saving water and increasing crop production,but it also had a greenhouse effect in the paddy field.Even if nitrogen application of early rice and late rice reduced by 30%and 15%respectively,the GM+RS+W₁N₁treatment was still able to promote the growth and development of rice,reduce the loss of runoff and nitrogen in the paddy field,and improve the absorption and utilization of water and nitrogen,so as to realize water saving,fertilizer saving,yield increasing and high quality of double-cropping rice.