Effect Of Different Reducing Nitrogen Fertilization On Soil Environment In Double Rice Cropping System

In the view of the low utilization rate of N fertilization,problem of rich straw resource but low effective return rate in the middle and lower reaches of the Yangtze river and problem of serious agricultural non-point source pollution,a consecutive field experiment of the double-rice system was conducted in JiangXi province,south of China to investigate the optional models of high-efficient and sustainable nitrogen(N)fertilization.We applied four different fertilizer treatments::farmers' fertilization practices using normal nitrogen(FP);FP with a 20%reducing in total nitrogen fertilizer,and the remaining with 20%replacement of organic nitrogen(T1);T1 supplemented with micro-element fertilizer(T2);T2 with 20%slow-release inorganic nitrogen replacement of normal inorganic N.Based on the estimations of different impacts of fertilization models on the efficiency of N agronomy,soil fertility and microbial community structure,the optional models was selected.The results were shown as follows:(1)From 2014 to 2015,compare with FP treatment,the three reducing nitrogen fertilization model significantly increased the nitrogen agronomic efficiency by 19.41%-32.23%,enhanced the apparent utilization rate of nitrogen by 23.29%-47.43%,reduced nitrogen loss by 74.88%-95.19%and prevented and controlled the agricultural non-point source pollution effectively.In addition,compared with FP treatment,the total rice yield of T1,T2 and T3 treatment increased by 0.79%,3.14%and 0.25%respectively,while the seed setting rate,panicle number,grain weight and the grain number per panicle had no significant difference between each treatment.The result invested that the three reduction of nitrogen fertilization mode could effectively protect and improve rice yield and significantly improve the nitrogen agronomic efficiency,moreover,T2 treatment had an obvious advantage in improving nitrogen agronomic efficiency and rice yield,reducing nitrogen loss and preventing and controlling agricultural non-point source pollution.(2)Compared with FP treatment,T1,T2 and T3 treatment could enhanced soil organic matter 0.26%-8.62%,increase total nitrogen 0.35%-8.80%,improve soil microbial organic carbon 0.32%-6.33%,increase soil microbial organic nitrogen 12.42%-43.39%,improve ammonium nitrogen 9.68%-19.27%,enhance nitrate nitrogen 73.73%-106.78%,enhance urease 2.54%-11.16%,improve invertase 9.52%-27.21%and increase acid phosphatase 5.56%-11.40%.Compared with the initial value,the soil pH of each treatment showed a decreasing trend.The result showed that the three reducing nitrogen models could effectively improve the soil nutrient and soil enzyme activities,what's more,T3 treatment had an obvious advantage in improving soil fertility and soil enzyme activity.(3)After different fertilization treatments,the soil microbial community structure of all treatments changed inordinately,and the three reducing nitrogen fertilization could improve the diversity of microbial community structure.In the RDA analysis,the content of soil organic matter was the largest contribution to the soil microbial community structure,followed by nitrate nitrogen and ammonium,which invested that soil nutrient contents had dominant effect on soil microbial community structure when soil pH had no significant difference.(4)In the grey correlation evaluation,the correlation coefficient of FP treatment was the lowest,while the T2 treatment was the highest and followed by the T3 treatment in 2014,and the T3 treatment was the highest and followed by the T2 treatment in 2015.In the sustainability index evaluation,the sustainability index of FP treatment was less than 1.30 from 2014-2015,indicating that the fertilization model was not sustainable,while the sustainability index of T1?T2 and T3 treatment were more than 1.30,indicating that these models were sustainable.The order of sustainability index in 2014 as followed:T2>T3>T1>FP,while the order of sustainability index in 2015 as followed:T3>T2>T1>FP.The sustainability index of T2 and T3 treatment were higher than that in 2014,and the microbial index of T3 treatment was better than that of T2 treatment while the crop index of T2 treatment was better than T3 treatment which indicating that T2 treatment was better at improving rice yield and T3 treatment was better at improving soil microbial biomass and enzyme activity.The results showed that the three kinds of nitrogen reducing fertilization models were better than FP treatment,and T2 and T3 treatment were better.In the summary,in the comprehensive analysis,including rice yield,soil fertrility,efficiency of nitrogen agronomic and microbial community structure,T1?T2 and T3 treatments could effectively improve the pollution from the source,improve soil quality,improve soil microbial community structure,compared with FP treatment.While,T2 and T3 treatment were better,and T2 treatment was superior in ensuring rice yield and improving agronic efficiency of nitrogen while T3 treatment was superior in increasing soil microbial community quantity and soil enzyme activity,T2 and T3 treatments could be used as the optimized model of red paddy soil double rice cropping system in JiangXi Province,providing scientific theory basis on solving the problem of unreasonable nitrogen fertilizer,improving the efficiency of nitrogen fertilization,enhancing the soil fertility and advancing soil microbial community structure,reducing risk of agricultural non-point source pollution from the source and provide technical guidance to the practice of agricultural production in the region.