Effects Of Reduced Nitrogen Fertilizer Application And Population Density On Yield,Nitrogen Use And Soil Nutrients In Double-Cropping Rice

Rice is one of the main food crops in my country.The acreage and output of rice account for 25.6%of the sown area and 31.6%of the output of food crops respectively.The double-cropping rice cropping area in the middle and lower reaches of the Yangtze River is an important rice-producing area in my country,and it is also an area with more nitrogen fertilizer input.High-yield rice fields generally have excessive nitrogen fertilizer application,which will destroy soil nutrient balance and reduce nitrogen fertilizer use efficiency,which is not conducive to rice yield and quality.The improvement of rice field not only destroys the ecological environment of rice fields but also causes economic losses.Therefore,in view of the increasingly severe contradiction between environmental pollution and agricultural development,optimizing rice transplanting density and supporting fertilization technology is of great significance to sustainable agricultural development.In order to explore the effect of nitrogen fertilizer reduction combined application and population density on nitrogen utilization characteristics,yield formation and soil nutrient changes of double-cropping rice under two multi-cropping modes of rice-potato and rice-rice oil,two years of 2018-2019were used.The experiment was repeated,using early rice varieties Luliangyou 996 and Zhongjiazao 17,late rice varieties Hyou 518 and Xiangwanxian 17 as materials,a two-factor split-plot test was used,and 6 nitrogen fertilizer application modes were set:N1(no nitrogen fertilizer),N2(conventional nitrogen fertilizer),N3(slow release nitrogen fertilizer:conventional nitrogen fertilizer=1:1),N4(slow release nitrogen fertilizer and conventional nitrogen fertilizer each reduced by 30%),N5(slow release nitrogen fertilizer and conventional nitrogen fertilizer each reduced by 30%)Fertilizer),N6(30%reduction of slow-release nitrogen fertilizer and conventional nitrogen fertilizer,combined with biochar)and 3 plant spacings:D1(11cm),D2(14cm),D3(17cm).The effect of population density on the yield and soil nutrients of double-cropping rice was discussed.The nitrogen absorption and utilization characteristics and nitrogen fertilizer use efficiency of double-cropping rice were discussed,and the regulation mechanism of double-cropping rice fertilizer density under multi-cropping mode was further enriched and supplemented to achieve high yield and high efficiency of rice,green goals,in order to provide technical support for the efficient and high-quality rice cultivation technology system.The main research findings are as follows:1.Under the rice-potato and rice-oil models,the reduced N fertilizer allocation could significantly improve the yield of double-season early and late rice.From the combined data of the two years,N3D1(slow-release N fertilizer:conventional N fertilizer=1:1,machine spacing 11 cm)had the best effect on the yield of early rice Luliangyou 996,Zhong Jia Zao17and late rice Xiangwanxian17 in the two modes,while the yield of late rice Hyou518 was highest in the rice-potato mode with N5D1(30%reduction of both slow-release N fertilizer and conventional N fertilizer with organic fertilizer 4.5 t/hm~2,machine spacing 11 cm)and the highest in the rice-oil mode with N3D1.In the rice-rice oil model,N3D1 was the highest.2.Under the rice-potato and rice-oil models,the reduced N fertilizer application improved N accumulation in all organs and total plant nitrogen accumulation in double-season early and late rice.At a plant spacing of 11 cm,N3(slow-release N fertilizer:conventional N fertilizer=1:1)had the best effect on improving N accumulation in all organs and total plant N accumulation in double-season early and late rice,followed by N5(30%reduction of both slow-release N fertilizer and conventional N fertilizer with 4.5 t/hm~2of organic fertilizer).3.Under the rice-potato and rice-oil models,the reduced N fertilizer application improved the N fertilizer bias productivity,N fertilizer agronomic utilization and N fertilizer apparent utilization of double-season early and late rice,but not the N harvest index and N rice grain production efficiency.In terms of population density,N fertilizer bias productivity,N fertilizer agronomic utilization and N fertilizer apparent utilization of double-season early and late rice increased with decreasing plant spacing,while N harvest index and N grain production efficiency showed opposite performance.At 11 cm plant spacing,N3(slow-release N fertilizer:conventional N fertilizer=1:1)and N4(30%reduction in each of slow-release N fertilizer and conventional N fertilizer)were the most effective in improving N fertilizer bias productivity,N fertilizer agronomic utilization and N fertilizer apparent utilization in double-season early and late rice.4.The fertilization effect of different population densities on soil fertility varied.Under the rice-potato and rice-oil models,compared with the machine planting spacing of 11cm and 17cm,the machine planting spacing of 14cm can effectively improve the content of soil organic matter,total nitrogen,total phosphorus,total potassium,alkaline decomposition nitrogen,effective phosphorus and fast-acting potassium in double-season early and late rice,indicating that the group density is too large or too small is not conducive to the improvement of soil fertility.5.Under the rice-potato and rice-oil models,nitrogen fertilizer reduction combined with slow-release nitrogen fertilizer is beneficial to increase the content of soil organic matter,total nitrogen,total phosphorus,total potassium,alkali-hydrolyzed nitrogen,available phosphorus and available potassium,and the soil fertilization effect is better than that of conventional nitrogen fertilizer alone.When the machine planting spacing is 11cm,N3(slow-release nitrogen fertilizer:conventional nitrogen fertilizer=1:1)can significantly increase the soil total nitrogen and alkali-hydrolyzable nitrogen content in the mature stage of early and late rice,and N5(slow-release nitrogen fertilizer and conventional nitrogen fertilizer are reduced by 30%each.The application of organic fertilizer 4.5 t/hm~2)had the best effect on improving the content of soil organic matter,total potassium and available potassium in the early and late rice soil.The content of total phosphorus and available phosphorus is the best.