Effects of Chinese milk vetch(Astragalus sinicus L.)and nitrogen fertilizer reduction combined with biochar on soil physical and chemical properties and rice yield
[Objective]In order to reduce the use of chemical nitrogen fertilizer,pot experiment was conducted to explore the effects of nitrogen(N)reduction combined with different ratios of biochar on improvement of soil nutrient and increase of rice yield under the condition of returning milk vetch to the field.The aim is to clarify the optimal nitrogen reduction and biochar addition ratio that are more conducive to fertilization and yield increase on the basis of replacing part of nitrogen fertilizer with Chinese milk vetch.The results could be used to provide scientific basis for production.[Method]A two-factor rice pot experiment was conducted,and four(0.25%,0.5%,1%,2%)biochar addition ratios and three(10%,20%,30%)N reduction ratios during topdressing were set.A total of 13 treatment combinations were set,and each treatment was repeated four times.A total of 52 pots were grown for 120 days.The effects of each treatment on soil physicochemical properties,rice yield and characters were compared after rice ripening.[Result]The soil pH(P＜0.01)was significantly increased by 12.02%compared with that of CK in the field with 30%N reduction combined with 2.0%biochar.The contents of soil organic matter(SOM),available phosphorus(AP)and available potassium(AK)were significantly increased by 20%N reduction combined with 2.0%biochar(P＜0.01),and the contents of soil total N(P＜0.05)were significantly increased by 38.8%,107.2%,25.4%and 24.9%compared with that of CK.The content of alkali N was significantly increased by 49.6%when 20%N reduction was combined with 0.5%biochar(P＜0.01).The highest yield was obtained when 30%N reduction 30%was combined with 1.0%biochar,which was significantly increased by 18.7%(P＜0.01)compared with that of CK.However,the application of low biochar(0.25%biochar)was more beneficial to above-mentioned biomass accumulation,which was significantly increased by 90.04%compared with that of CK(P＜0.01).Correlation analysis showed that soil organic matter,available phosphorus and available potassium in this study were the main soil environmental factors(P＜0.05,r＞0.5)to improve rice yield.[Conclusion]Combined application of milk vetch,N reduction and biochar has a significant effect on fertilizer cultivation and yield increase.The application of 20%nitrogen reduction combined with 2.0%biochar under Chinese milk vetch returning to the field is more conducive to improving the nutrient content of paddy soil.It can reduce N loss and promote rice growth and yield increase,but excessive application of biochar has a certain inhibitory effect on rice yield and biomass.30%N reduction combined with 1.0%biochar in topdressing had the optimal effect on rice yield.
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