| The purpose of this study was to explore the substitution of Chinese milk vetch?Astragalus sinicus L.?to nitrogen fertilizer,to provide scientific theoretical basis for rational reduction of fertilizer application in paddy fields,and to make rational use of light,temperature,water and heat in winter in the middle and lower reaches of the Yangtze River.The experiment was carried out from October 2015 to November 2017 in the Science and Technology Park of Jiangxi Agricultural University.First,the experiment adopted a split plot design with no application of Chinese milk vetch or nitrogen as control one,the conventional nitrogen application level(180 kg·hm-2)as control two.The application of Chinese milk vetch included two levels:27000 and 45000 kg·hm-2?designated M1 and M2respectively?,and the application of nitrogen fertilizer included four levels:0,60,120 and180 kg·hm-2?designated N0,N1,N2,N3 respectively?.The best fertilization ratio of coupling different amounts of Chinese milk vetch and nitrogen of rice were examined.Based on the results of pot experiment,three gradients of Chinese milk vetch were set up in the field experiment in the following year,and the corresponding reduced nitrogen fertilizer was applied,and the conventional fertilization was used as the control.The effects of reducing nitrogen fertilizer with different amount of Chinese milk vetch application on rice yield,growth dynamics,dry matter accumulation,nitrogen accumulation and soil nutrients in paddy field were analyzed.Finally,a mathematical model of the relationship among the pure N-Chinese milk vetch-yield was established.The purpose of this study was to find out the optimal model of reducing nitrogen fertilizer application by returning Chinese milk vetch to the field.The main findings are as follows:1.In the pot experiment,under the condition of different Chinese milk vetch quantity,the applications of 27000 kg·hm-2of Chinese milk vetch+N 120 kg·hm-2and 45000kg·hm-22 of Chinese milk vetch+N 60 kg·hm-22 could ensure the rice yield and growth,and the utilization rate of nitrogen fertilizer was higher.In the field experiment,the applications of 27000 kg·hm-2of Chinese milk vetch+N 120 kg·hm-2had a tendency to increase the yield of early rice,the applications of 45000 kg·hm-22 of Chinese milk vetch+N 60 kg·hm-22 had the highest late rice yield,and according to the annual yield,the applications of 36000 kg·hm-2of Chinese milk vetch+N 90 kg·hm-2was the best.2.Returning Chinese milk vetch to the field could delay the early rice to the tiller exuberant stage and increase the tiller peak value,but that had no obvious effect on the effective tiller.Under the condition of no excess nitrogen fertilizer,the accumulation of dry matter in rice and the SPAD value of leaves in the middle and late stage of early rice could be increased effectively by returning Chinese milk vetch to the field.That also increased dry matter accumulation ratio at the middle and late stage of early rice,nitrogen accumulation amount and nitrogen harvest index of early rice.3.In a year's trial,Returning Chinese milk vetch to the field could increase the soil total nitrogen,alkali-hydrolyzed nitrogen,organic matter content and soil pH.Compared with the control treatment,the alkali-hydrolyzed nitrogen,organic matter content and soil pH increased by 4.39%,6.91%and 1.47%respectively.That also can promote the transformation of total phosphorus and potassium into available nutrients.4.Based on the mathematical relationship between nitrogen application rate and rice yield,a model of the relationship among the yield of rice,the amount of pure nitrogen and the amount of Chinese milk vetch returning to the field was established.According to the change of substitution coefficient of Chinese milk vetch,it can be found that under the condition that the nitrogen supply is sufficient of early rice,with the increase of the ratio of Chinese milk vetch to the total fertilization,the ability of Chinese milk vetch to replace nitrogen fertilizer was gradually weakened. |
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