Crop Management Practices To Improve Nitrogen Use Efficiency In Rice And The Underlying Mechanisms

Low nitrogen use efficiency has always been an urgent problem to be solved in rice production.Nitrogen uptake efficiency and nitrogen loss in the environment are important factors affecting nitrogen use efficiency after nitrogen fertilizer is applied to paddy fields.Under the condition of high yield and high nitrogen input in modern agriculture,how to reduce nitrogen loss through cultivation measures and promote high yield,high efficiency and high quality of rice is worthy of further study.In this study,two experiments were set up.In the first experiment,Wuyunjing 24,Yangdao 6 and Jinxiangyu 1 were used as the research objects,and the local farmers’ practise(LFP)were used as the control.Five cultivation measures were set up,including nitrogen blank area(ON),increasing density and reducing nitrogen(integrative crop management 1,ICM1),precise irrigation(integrative crop management 2,ICM2)and increasing cake fertilizer(integrative crop management 3,ICM3).The 15N marker tracer analysis method was used to analyze the nitrogen fate of base fertilizer and nitrogen distribution in plants,and the root activity and soil enzyme activity of rice were analyzed.The effects of different cultivation measures on rice yield and nitrogen use efficiency and their physiological mechanisms were studied.In experiment 2,Yongyou 2640 and Jinxiangyu 1 were used as the research objects,and conventional available nitrogen fertilizer(T2)was used as the control.Nitrogen blank area(T1)and conventional controlled release nitrogen fertilizer(T3)were set up.Quick-acting fertilizer nitrogen reduction(T4);controlled release fertilizer nitrogen reduction(T5);controlled release nitrogen+available nitrogen once application(T6);the effects of different controlled release nitrogen fertilizer treatments on rice yield and its physiological mechanism were studied by seven treatments of controlled release nitrogen+available nitrogen(T7).The main results are as follows:1.In Experiment 1,compared with LFP cultivation measures,ICM1,ICM2 and ICM3 treatments significantly increased yield.Among them,compared with LFP treatment,ICM3 treatment increased by 17.79%-22.89%,the largest increase.The number of tillers in rice reached the peak at panicle differentiation stage.Compared with the control,the number of tillers in ICM1,ICM2 and ICM3 treatments of Yangdao 6 increased by 9.20%-16.52%,and Jinxiangyu 1 increased by 6.68%-12.20%.By analyzing the nitrogen utilization rate of each fertilization period,it was found that compared with the control,the optimization of comprehensive cultivation measures significantly improved the nitrogen utilization rate of base fertilizer.Compared with the control,the nitrogen uptake of ICM1,ICM2 and ICM3 increased by 0.3%-16.11%,the residual nitrogen content in soil decreased by 34.07%-45.83%,and the nitrogen loss in the environment decreased by 28.50%-41.02%.Further analysis of nitrogen distribution in plants found that with the optimization of various cultivation measures,the distribution of nitrogen in roots and leaves gradually increased,while the proportion showed a downward trend.The distribution amount of nitrogen in plant stems increased gradually,but the distribution ratio increased first and then decreased,and reached the highest in ICM2 treatment.The distribution amount and proportion of nitrogen in plant panicles showed an upward trend.The optimized cultivation measures had little effect on the distribution of nitrogen in roots,stems and leaves,and mainly increased the transfer of nitrogen to grains.These results suggest that optimized integrated cultivation practices can significantly improve plant nitrogen accumulation and translocation,reduce nitrogen residues in the soil and environmental losses,thereby improving nitrogen use efficiency and increasing rice yield.Compared with LFP,ICM1,ICM2 and ICM3 increased soil nitrate nitrogen content by 4.55%-40.81%,and decreased soil ammonium nitrogen content by 8.94%-26.83%.The optimization of cultivation measures also significantly increased soil urease and invertase activities.Compared with the control,the urease activity of ICM2 and ICM3 treatments increased by 0.56%-9.97%,and the invertase activity increased by 3.61%-29.17%.These results showed that the optimization of comprehensive cultivation measures can effectively improve the soil environment,improve the absorption and utilization of nitrogen,and effectively improve the ability of plants to absorb nutrients,thus promoting high yield.Compared with LFP,ICM1,ICM2 and ICM3 increased root redox capacity by 1.9%-11.39%,root active absorption surface area by 1.3%-41.34%,and root total absorption surface area by 2.1%-35.48%.The above results show that the optimized comprehensive cultivation measures can effectively improve the root activity,promote root development,improve root elongation in the soil,and provide the basis for plant growth to absorb nutrients.2.In Experiment 2,compared with T2,the treatments with slow and controlled release fertilizers significantly increased the yield.Among them,the treatments with the ratio of available fertilizer+controlled release fertilizer(T6,T7)performed best.Compared with T2,the yields of T6 and T7 increased by 6.67%-11.11%and 5.79%-10.22%,respectively.The analysis of yield components found that the increase in yield was related to the total number of spikelets.Compared with T2,the total spikelet number of T6 and T7 treatments increased by 13.64%-14.92%and 4.67%-14.92%,respectively.By analyzing the agronomic traits,it was found that compared with the control,the controlled-release fertilizer treatment increased the tiller spike rate,leaf area index and dry matter accumulation.Compared with the control,the leaf area index of T6 and T7 treatments increased by 4.03%-6.16%and 1.84%-3.65%respectively at heading stage.Analysis of dry matter accumulation showed that compared with the control,T6 increased by 18.37%-28.84%,and T7 treatment increased by 23.47%-29.33%.These results showed that the release rule of slow-release fertilizer was synchronized with the nutrient demand of rice plants.In the later stage of rice growth,the nitrogen supply was guaranteed,and the utilization efficiency of nitrogen fertilizer was improved on the basis of reducing the number and amount of fertilization,so as to improve the yield.Compared with the control,the application of controlled release fertilizer significantly increased soil nitrate nitrogen content,soil ammonium nitrogen content and urease activity.Among them,the treatment with the ratio of quick-acting fertilizer+controlled-release fertilizer was the most significant,indicating that reasonable nitrogen release rate and sufficient nutrient supply can reduce nitrogen residue in the soil,thereby reducing nitrogen loss and improving soil enzyme activity and nitrogen use efficiency.Compared with the control,the root length,root diameter,root redox force and total root absorption surface area of the treatment with controlled release fertilizer were significantly increased,and the treatment with the ratio of quick-acting fertilizer+controlled release fertilizer was the most significant.Compared with the control and conventional controlled-release nitrogen fertilizer,T6 treatment has a higher proportion of aerenchyma area and root porosity,indicating that the application of controlled-release nitrogen+available nitrogen can promote the formation of root aerenchyma and improve root activity.These results show that slow-release fertilizer can meet the needs of crop growth through slow release rate,effectively improve root activity,promote the absorption and utilization of nitrogen by rice roots,and provide nutrient basis for plant reproductive growth.The application of available fertilizer+controlled release fertilizer can save time and labor,further promote the development of root aerenchyma,increase the ability of root to absorb nutrients,effectively improve the utilization rate of nitrogen,and then increase the yield.In this study,integrative crop management measures can increase soil oxygen uptake and supply conditions,reduce nitrogen loss,improve microbial communities and inter-root environment,adjust the relationship between nitrogen nutrient release and rice nutrient demand,and promote nitrogen uptake by rice roots,which is important for improving nitrogen use efficiency,reducing agricultural production costs,reducing environmental pollution,improving crop yield and quality,and promoting sustainable agricultural development.This is important for improving the efficiency of nitrogen fertilizer use,reducing agricultural production costs,reducing environmental pollution,improving crop yield and quality and promoting sustainable agricultural development.