Preliminary Study On The Fertilizer-saving And Soil Improvement Effects Of Chinese Milk Vetch,Rice Straw And Their Combination Incorporation In Paddy Field

Chinese milk vetch(CMV,Astragalus sinicus L.)is the main green manure crop in southern China and it has a long cultivation history.CMV plays an important role in reducing the application amount of fertilizer and pesticide through biological nitrogen fixation and crop rotation.Straw returning is widely used due to the effectiveness in increasing the yield of the following crop and improving soil fertility among agricultural production.However,the combined effects of the CMV and straw returning on rice growth and paddy soil fertility are still unclear.This study was conducted in the paddy field of Taihu Lake management area of Jingzhou City,Hubei Province,from 2016 to 2018 to determine the effects of CMV,rice straw and their combination on rice yield,soil fertility,soil nitrogen management and the potential of chemical fertilizer substitution.The final goal of this study was to improve the green manure/straw returning-rice cultivating technology,enhance the combined effect of the above two most common techniques,and increase the efficiency of green rice production.The main results of this study are as follows:1)Under different nitrogen application rates,the combination of straw and CMV could increase the contents of organic matter,total nitrogen,available phosphorus,and available potassium in soil nutrients,improve soil fertility,increase nutrient uptake by rice,and then increase rice yield.According to the three-year positioning experiment,compared with a single measure,the combined application of CMV and rice straw to paddy fields did not reach significant levels in rice yield,nutrient uptake and soil fertility,but mostly showed positive interaction effects.2)The combination of CMV and rice straw could increase rice yield steadily and improve the buffering capacity to exogenous nitrogen fertilizer comparing with straw returning alone.Under different nitrogen application rates,the three-year averaged rice yield of the combined returning treatment was 5.67,6.67,7.30 and 7.33 t/ha at 0%,50%,100% and 150% N rates,respectively,while the related yield was 4.36,6.23,6.70 and 6.61 t/ha,respectively,when straw was returned alone.When nitrogen fertilizer was applied by 50% more or less,the yield of the combined returning treatment changed slightly and still maintained at a high level.3)Returning rice straw and CMV to field together performed better than returning rice straw alone in improving nutrient concentration and accumulation in rice and soil fertility.When nitrogen was applied at the same rate,the soil total nitrogen,available phosphorus,available potassium,organic matter and pH were higher with the combined returning treatment than those with straw returning only.Under different N rates,the combined returning treatment increased the content of total nitrogen by 2.76%,8.09%,5.38% and 14.29%,available phosphorus by 16.29%,14.58%,16.48% and 11.70%,available potassium by 6.49%,1.46%,2.03% and 12.52%,and organic matter by 5.72%,0.52%,3.77%and 6.84% compared with straw returning alone.4)Returning rice straw and CMV to field can effectively increase the content of ammonium-nitrogen and reduce the content of nitrate-nitrogen in soil.The combined application of straw and CMV increased the content of acid-soluble total nitrogen and decreased the content of non-acid-soluble total nitrogen.Under different N rates,the content of ammonium-nitrogen in the soil of rice straw and CMV combined returning was 1.73%,4.67%,1.01%,and 0.92% higher than that of straw returning alone,and the content of nitrate-nitrogen was 18.24%,4.48%,6.04% and 5.05% lower.Furthermore,the combination of straw and CMV(CMV+S+100% N)increased the content of Acid hydrolysable amino nitrogen and Amino sugar nitrogen in organic nitrogen components.5)CMV combined with full and half amount of straw returning could replace nitrogen fertilizer based on rice yield,rice nutrient,fertilizer utilization efficiency,and soil fertility improvement,while CMV combined with half amount of straw returning had more significant effect.In summary,the three-year positioning experiment preliminarily showed that the combination of straw and CMV could increase the content of soil organic matter,improve soil fertility,increase the content of ammonium-nitrogen and decrease the content of nitrate-nitrogen,increase the content of acid-soluble total nitrogen,decrease the content of non-acid-soluble total nitrogen,increase the content of available soil nutrients,promote the absorption of rice nutrients and increase the content of nitrate nitrogen.Utilization efficiency can improve rice yield.