Genotypic Differences In Shoot,Root Growth And Lodging Resistance In Response To Nitrogen Rate And Increasing Planting Density Of Field-grown Maize

In this study,a field experiment was conducted to investigate the interaction between N application and planting density on the crown-root characteristics of different maize genotypes,as well as on seed yield,N efficiency and plant failure resistance,using a split-zone treatment with planting densities of60,000 plants/ha(D6)and 80,000 plants/ha(D8)in the main zone and three different N application levels in the secondary zone: no N application(0 kg N/ha,N0),suitable N supply(120 kg N/ha,N120)and suitable N supply(240 kg N/ha,N240).The secondary zones were three maize varieties,XY335,JNK728 and YNY10,and the responses of maize crown-root growth and N efficiency,stalk strength and maize yield to increased planting and N fertilization were systematically analyzed.The main conclusions were as follows:1.When planting density was increased from 60,000 to 80,000 plants/ha,canopy spike leaf SPAD values and canopy vegetation index NDVI did not decrease significantly;leaf area index increased by12.8%-98.0%.Maize root-related indicators of high density planting were not significantly different from low density planting.2.Planting density increased from 60,000 to 80,000 plants/ha,and N accumulation increased by26.6%-105.7% in XY335 and JNK728 at late reproductive stage,and decreased by 28.5% in YNY10 at maturity.The efficiency of nutrient organ nitrogen contribution to the seed increased with increasing density,and the physiological efficiency of nitrogen use increased by 4.99%-55.8% in the fertilizer treatments,except for JNK728,which decreased,and XY335 and YNY10.Nitrogen fertilizer agronomic efficiency increased by 7.7%-85.9%,N fertilizer bias productivity by 8.3%-23.5% and N harvest index by 0.5%-35.6%.3.Under denser planting conditions,the above-ground population dry matter accumulation of XY335 and JNK728 increased significantly by 12.5%-50.2% at maturity,while the dry matter accumulation of YNY10 decreased by 43.7% and 9.9% in the D8N0 and D8N240 treatments respectively.The yield of the three varieties increased by 2.6%-42.6% in the fertiliser treatments.4.Under the condition of additional N fertilizer,the three varieties of N240 treatment compared to N120 and N0 treatment: the SPAD value of spike position leaves increased by 2.7%-95.9% at the spatulation stage,the NDVI value of canopy vegetation index differed significantly in the early stage of fertility,and the fertilizer treatment differed insignificantly in the late stage of fertility,which was significantly higher than the treatment without fertilizer.Leaf area index increased by 1.3%-243.8% in the N240 treatment and by 8.76%-497.2% in the N120 treatment compared to the N0 treatment at all times.Root biomass and root length at spatulation increased by 33.5%-146.3% and 12.9%-65.9% in the N240 treatment compared to the N120 treatment.The number of nodal roots at the spatulation stage increased by 7.2%-163.1% in the N240 treatment compared to the N120 and N0 treatments.5.Under the condition of additional N fertilizer,the N accumulation of the three varieties at maturity increased by 11.4%-128.5% in the N240 treatment and 186.0%-467.8% in the N120 treatment compared to the N0 treatment.Nitrogen fertilizer agronomic efficiency and N fertilizer bias productivity decreased with increasing N fertilizer,by 39.4%-112.9% and 53.2%-84.6% respectively.6.The above-ground dry matter accumulation of the three varieties increased by 9.7%-291.9% at maturity in the N240 treatment compared to the N120 and N0 treatments.Seed yield increased by 8.3%-973.1% in the N240 treatment compared to the N120 and N0 treatments.Dry matter weight per unit stem length increased by 2.7%-70.5% at the first three nodes above ground.The crushing strength of the five above-ground nodes was significantly increased.Under the D8N240 treatment,XY335,JNK728 and YNY10 maize varieties were compared and XY335 had the best canopy index values,root growth traits and N efficiency,and the highest seed yield;XY335 had the best stalk strength and resistance to overturning.In other words,the selection of dense varieties,the optimisation of N fertiliser input and the moderate increase in densities contributed to the increase in yield and efficiency.