Analysis Of Yield Gap And Approach Of Narrowing The Gap And Increasing Nitrogen Utilization Efficiency Of Summer Maize In Huang-Huai-Hai Plain

Narrowing the yield gap is essential to improve crop grain yield and ensure national food security.Quantitative analysis of yield gap can clarify the potential for yield increase,explore the limiting factors of yield,and provide theoretical support for sustainable improvement of maize yield.In order to better understand the current situation of summer maize production in Huang-Huai-Hai Plain,evaluate the potential of yield increase,clarify the limiting factors of yield,and explore the ways of increasing yield,this study combined farmer survey and field experiment,and used the theoretical potential yield of crop model simulation as a reference to analyze the yield gap of summer maize.This study quantified the grain yield gaps of summer maize at different levels in the Huang-Huai-Hai Plain,clarified the agronomic factors restricting the improvement of grain yield and nitrogen utilization efficiency of summer maize,and explored the technical ways to synergistically improve the grain yield and nitrogen utilization efficiency of summer maize in the Huang-Huai-Hai Plain,which provided a theoretical basis for the high-yield and high-efficiency production of summer maize in the Huang-Huai-Hai Plain.The main results are as follows:1.Grain yield and nitrogen utilization efficiency gap of summer maize in the Huang-Huai-Hai PlainThe average actual yield of farmers’summer maize in the Huang-Huai-Hai Plain was8.4 t hm^-2,only achieving 63%of the potential yield,and the total yield gap was 4.9 t hm^-2.The average attainable yield of farmers was 10.3 t hm^-2,and the average exploitable yield gap was1.9 t hm^-2.The average N partial factor productivity（NPFP）of farmers’summer maize was 42kg kg^-1,and the average attainable NPFP was 65 kg kg^-1.Farmers’summer maize only achieved65%of the attainable NPFP,and the average exploitable NPFP gap was 23 kg kg^-1.2.Limiting factors of summer maize yield at different levels in the Huang-Huai-Hai PlainThe yield limiting factors considered by farmers mainly include unreasonable water and fertilizer input,unreasonable planting density and poor quality of plough layer.Low N uptake and LAI,short duration of LAI high value and low net photosynthetic rate limit the radiation interception and utilization efficiency of the population,resulting in low dry matter production capacity.Low planting density leads to insufficient number of harvested ears per unit area,which is the main reason for the exploitable yield gap.The low conversion efficiency of intercepted resources and the distribution of dry matter to grains restrict the further improvement of high-yield and high-efficiency summer maize yield.3.Effects of tillage method,planting density and nitrogen management on grain yield and nitrogen utilization efficiency of summer maizeBased on the current cultivation and management mode of farmers,the optimized tillage method improved the root morphology index,LAI,N and dry matter accumulation during the whole growth period,grain yield and N utilization efficiency of summer maize.Optimized N fertilizer management reduced LAI,N and dry matter accumulation before R1,increased N accumulation at R6 stage,and increased grain yield and N utilization efficiency.Optimized planting density increased LAI,N and dry matter accumulation during the whole growth period,number of harvested spikes,grain yield and N utilization efficiency,and decreased grain number per spike.The yield contribution rates of optimized tillage methods,N fertilizer management and planting density were 10.4%,7.6%and 11.1%,and the contribution rates of NPFP were 10.4%,15.2%and 11.1%,respectively.The yield contribution rates of synergistic optimization of N fertilizer management and planting density,N fertilizer management and tillage methods,planting density and tillage methods were 21.0%,18.6%and 21.4%,and the contribution rates of NPFP were 29.6%,27.1%and 21.4%,respectively.The yield contribution rate of synergistic optimization of N fertilizer management,planting density and tillage methods was 31.2%,and the NPFP contribution rate was 40.6%.4.Effects of cultivation patterns on grain yield and nitrogen utilization efficiency of summer maizeCompared with the farmer cultivation mode,the high-yield and high-efficiency cultivation mode can significantly increase the root length density,root surface area density and root dry weight density of summer maize,and increase N accumulation by 20%.The LAI and radiation interception rate increased by 14%and 15%,respectively,and the dry matter accumulation increased by 14%.The number of harvested spikes was increased by 22%,thereby increasing grain yield by 30%.In addition,the high-yield and high-efficiency cultivation mode also increased the nitrogen recovery efficiency by 43%and reduced the nitrogen loss rate by 17%.NAE and NPFP were increased by 51%and 39%,respectively.Therefore,the high-yield and high-efficiency cultivation mode can effectively overcome the obstacle factors that restrict the improvement of grain yield and N utilization efficiency of summer maize,and is an effective technical way to improve the grain yield and N utilization efficiency of summer maize in the Huang-Huai-Hai Plain.