Effects Of Soil Fertility And Nitrogen Rates On Yield And Nitrogen Use Efficiency In A Double-rice Cropping System

As the country with the largest population and the largest consumption of chemical fertilizers in the world,ensuring food security and improving nitrogen efficiency has always been a major challenge for China’s agricultural production.Previous studies mainly focus on improving rice fertility,but there are few studies on the utilization efficiency and direction of fertilizer nitrogen by paddy soil fertility.For this reason,in this experiment,three soils with different fertility levels（denoted as F_L,F_M and F_H,respectively）were selected and four N application rates(0,90,150 and 210 kg·hm^-2,denoted as N₀,N₉₀,N₁₅₀ and N₂₁₀,respectively)were set,and a split zone design was adopted.On the one hand,the effects of soil fertility,nitrogen application rate and their interaction on yield and nitrogen use efficiency of double cropping rice were studied.On the other hand,the use of ¹⁵N tracer technology was used to clarify the location of nitrogen fertilizer and the utilization of residual nitrogen fertilizer in the soil.The aim of this study was to clarify the effects of different nitrogen application rates on the yield and nitrogen use efficiency of double cropping rice under different soil fertility,so as to provide scientific basis and technical support for the high yield and efficiency of rice,the improvement of nitrogen use efficiency,the reduction of production cost and the reduction of agricultural non-point source pollution.The main research results are as follows:1.With the increase of soil fertility and nitrogen application rate,rice yield increased significantly in early and late season.In early rice season,compared with N₀treatment,N₉₀,N₁₅₀ and N₂₁₀ treatments increased yield by 96%,134%and 160%on low fertility soil,respectively.In medium fertility soil,they were 93%,125%and 148%,respectively.In high fertility soils,the rates were 82%,98%and 100%,respectively.In late rice season,compared with N0 treatment,the yield in low fertility soil increased by84%,98%and 123%,respectively.In medium fertility soil,40%,57%and 64%,respectively.In high fertility soils,the rates were 36%,50%and 52%,respectively.The yield increasing effect of increasing nitrogen application rate decreased gradually with the increase of soil fertility.In terms of yield composition,the increase of soil fertility and nitrogen application rate mainly increased the number of effective panicles.2.The results of difference subtraction method showed that the nitrogen apparent use efficiency increased significantly with the increase of soil fertility in early and late rice seasons.In early rice season,N apparent use efficiency under N₉₀,N₁₅₀ and N₂₁₀treatments was increased by 6.1%,12.1%and 12.9%in medium-fertility soil compared with low-fertility soil,respectively.In high fertility soil,the increase was 12.4%,17.2%and 17.9%,respectively.In late rice season,N apparent use efficiency under N₉₀,N₁₅₀and N₂₁₀ treatments was increased by 4.0%,8.0%and 8.3%in medium-fertility soil compared with low-fertility soil,respectively.In high fertility soil,the increase was13.2%,21.3%and 16.1%,respectively.With the increase of soil fertility,nitrogen partial productivity increased significantly in early and late rice seasons.The physiological use efficiency of nitrogen fertilizers decreased significantly.N agronomic use efficiency increased first and then decreased in early rice season,and significantly decreased in late rice season.3.The ¹⁵N tracer showed that the N recovery rate decreased significantly with the increase of soil fertility in early rice season.Compared with low fertility soils,N recovery rates of N₉₀,N₁₅₀ and N₂₁₀ treatments were decreased by 5.2%,1.9%and 2.7%in medium fertility soils,respectively.In the high-fertility soil,they decreased by 16.2%,8.2%and 6.9%,respectively.With the increase of soil fertility,the nitrogen loss rate decreased significantly and the nitrogen residual rate increased significantly in early rice season.In the late rice season,the nitrogen recovery rate increased significantly with the increase of soil fertility.Compared with low fertility soils,N recovery rates of N₉₀,N₁₅₀ and N₂₁₀ treatments were increased by 20.4%,15.2%and 22.7%in medium fertility soils,respectively.They increased by 31.0%,26.0%and 27.7%in high fertility soils,respectively.With the increase of soil fertility,the residual rate of nitrogen fertilizer increased significantly,and the loss rate of nitrogen fertilizer decreased significantly.The increase of nitrogen application rate significantly increased the nitrogen loss rate in early and late rice seasons,and the nitrogen residual rate and recovery rate were significantly decreased.4.With the increase of soil fertility,nitrogen uptake by early rice plants to soil increased significantly.The increase of nitrogen application rate significantly increased the nitrogen absorption of early rice.In the late rice season,the uptake of soil nitrogen and fertilizer nitrogen by plants increased significantly with the increase of soil fertility and nitrogen application rate.5.With the increase of soil fertility,the recovery and residual rate of residual nitrogen fertilizer increased significantly,while the loss rate of residual nitrogen fertilizer decreased significantly.The recovery rate and loss rate of residual nitrogen were significantly increased with the increase of nitrogen application rate,but the residual rate of residual nitrogen was significantly decreased.Compared with low fertility soil,N₉₀,N₁₅₀ and N₂₁₀ treatments increased the recovery of residual nitrogen fertilizer by 39.2%,14.1%and 3.8%in medium fertility soil,respectively.In the high-fertility soil,they increased by 46.4%,14.8%and 6.3%,respectively.Therefore,on soils with low fertility,N application could be appropriately increased to maintain high rice yield.On soils with high fertility,it is advisable to reduce the amount of N fertilizer input to improve N fertilizer utilization while ensuring high rice yield.