| Chinese milk vetch is a natural organic fertilizer source.Planting Chinese milk vetch in paddy field can add a large amount of biological nitrogen fixation and improve soil fertility to the rice field ecosystem,which is conducive to stable rice production and increase yield,thereby reducing the input of mineral nitrogen fertilizer.Therefore,as an organic fertilizer source in rice fields,Chinese milk vetch is of great significance to the reduction of nitrogen fertilizer and the improvement of soil fertility in rice production.Field experiments were carried out from 2017 to 2019 in Jingzhou,Hubei Province,using the rice-Chinese milk vetch rotation planting pattern,by monitoring the dynamic changes of rice growth,soil nutrients and rice nutrient uptake under the conditions of Chinese milk vetch,chemical fertilizer and their combined application.The purpose of this study was to explore the optimum amount of nitrogen fertilizer and the effect of Chinese milk vetch on the nitrogen supply capacity of rice field,and to provide basis for optimizing the application of chemical fertilizer under the condition of planting Chinese milk vetch.The main conclusions are as follows:(1)The return of Chinese milk vetch could significantly reduce the application of nitrogen fertilizer.In the first and second years,the reduction of 20%and 40%of nitrogen fertilizer will not affect the absorption of rice nutrients,thus ensuring stable rice yields.With the increase in the years of Chinese milk vetch planting and utilization,the proportion of alternative fertilizers has increased and the soil fertility could be improved by returning to the field of Chinese milk vetch.Chinese milk vetch combined with reduced nitrogen fertilizer obviously increased the total nitrogen and organic matter content in the soil during the rice maturity period,and decreased the soil p H.(2)It is possible to give full play to the potential of rice production and increase the replacement rate of chemical fertilizer by increasing the return amount of Chinese milk vetch.Under the condition of recommended application of nitrogen fertilizer,the yield of rice treated with ultra-high content(67.5 t/ha)of Chinese milk vetch was the highest,increasing by 3.67%and 18.14%respectively in two years;without application of nitrogen fertilizer,the yield of rice treated with ultra-high content of Chinese milk vetch was the highest,increasing by 48.99%and 71.60%respectively in two years,and the effect of the model to increase production is significantly higher than the former.(3)Proper increase of the return amount of Chinese milk vetch can promote the absorption of plant nutrients.Under constant N application,the accumulation of N,P and K in rice growth period was 13.21%-120.53%,19.57%-118.09%,8.12%-48.41%higher than that in winter fallow treatment.When no nitrogen fertilizer was applied,the accumulation of N,P and K in the rice growth period was 40.20%-191.89%,28.17%-226.26%,41.85%-197.14%higher than that in the winter fallow treatment.The content of total nitrogen,organic matter,available phosphorus and available potassium in the soil with high turnover pressure and conventional fertilization was at a high level in the whole growth period,while that of winter fallow treatment was at a low level.At the rice maturity stage,the highest content of ammonium nitrogen was found in the soil treated with the recommended amount of nitrogen and no application of nitrogen,which increased by 29.38%-90.83%and 54.99%-64.74%respectively.(4)Nitrogen fertilizer with 20%-40%reduction combined with appropriate amount of turning over pressure of Chinese milk vetch can promote the absorption of nutrients by rice,increase the content of organic matter,total nitrogen,available phosphorus and available potassium in the soil,so as to maintain the yield of rice.When the yield of Chinese milk vetch was 30.0 t/ha,the effect of increasing yield of rice was the best(reducing nitrogen fertilizer by 20%nitrogen fertilizer for two years increased rice yield by 6.58%and 13.70%respectively,and reducing 40%nitrogen fertilizer by two years increased yield by 2.78%and 16.83%respectively).(5)Nitrogen fertilizer with 20%-40%reduction combined with appropriate amount of turning over pressure of Chinese milk vetch can improve N use efficiency.Turning over30.0 t/ha Chinese milk vetch and reducing the application of 20%-40%nitrogen fertilizer can significantly improve RE_N and PFP_NAccording to the results of the two-year located experiment of green manure-rice planting system,it was found that the application of Chinese milk vetch could replace 20%-40%of nitrogen fertilizer and keep rice yield not reduced,and under the condition of reducing nitrogen fertilizer by 20%-40%,the optimum yield of green manure is 30 t/ha,and the yield can reach 2.78%-16.83%.It is possible to create a better soil environment for rice growth by increasing the incorporation amounts of Chinese milk vetch properly without reducing the amount of nitrogen fertilizer,giving full play to the potential of increasing rice yield.The main reasons why green manure could replace part of nitrogen fertilizer,stabilize and increase rice yield were to improve soil fertility,increase utilization rate of fertilizer and maintain soil fertility. |
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