| Planting density and nitrogen application are important measures affecting maize production.With the mechanized harvest of maize and the change of suitable varieties,the suitable planting density and nitrogen application rate still need to be further discussed.In this study,two maize varieties were selected,including the newly approved variety Denghai 618(DH618)and the conventional extension variety Zhengdan 958(ZD958).Four nitrogen application rates were set,including conventional nitrogen rate(300 kg/hm2,N300),reduction 25% in N rate(225 kg/hm2,N225),reduction 50% in N rate(150kg/hm2,N150)and no nitrogen application(N0).Three planting densities were used,including 60000 plants/hm2(conventional planting density,D1),75000 plants/hm2(D2)and 90000 plants/hm2(D3).Field experiments were carried out in Huanggang and Jingmen of Hubei Province from 2017 to 2018 to study the effects of planting density,nitrogen application rate and their interaction on maize population structure,yield and nitrogen utilization,then to provide basis for high-yield and high-efficiency production of spring maize in Hubei Province.The main results are as follows:1.Under the experimental conditions,the canopy structure of maize was significantly affected by planting density.LAI increased significantly with the increase of density.Compared with D1,LAI at silking stage of D2 and D3 treatments increased by20.33% and 36.28% respectively.At the same time,the light transmittance at the bottom of the population was significantly reduced.With the increase in density,ear-bearing height increased significantly,stem diameter decreased significantly,and the compressive force decreased significantly.Comparing with D1,the average compressive force of D2 and D3 decreased by 11.73% and 18.08%,respectively.However,three nitrogen treatments had no significant effect on maize canopy structure and had no interaction with planting density.The ear-bearing height and ear position coefficient of Denghai 618 were significantly lower than those of Zhengdan958 by 15.92% and 16.98%,respectively.2.Compared with nitrogen application,planting density had a more significant effect on dry matter accumulation in maize population.The accumulation of dry matter in different periods increased significantly with the increase of density.Compared with D1,D2 and D3 treatments increased dry matter accumulation by 11.09% and 22.95%respectively at maturity stage of maize.At the same time,the increase of density significantly increased the dry matter distribution ratio before silking.The dry matter accumulation of Denghai 618 after silking was significantly higher than that of Zhengdan 958,especially by 8.20% increase at maturity stage.The interaction of nitrogen fertilizer and density in the second insitu experiment year(2018 Huanggang site)had a significant effect on the dry matter accumulation at the maturity stage.Under 225 kg/hm2 nitrogen application rate and 90000 plants/hm2 density,dry matter accumulation reached 24.3 t/hm2,which was 18.26% higher than the conventional nitrogen-density combination.3.Compared with nitrogen application rate,planting density had more significant effect on maize yield and its components.The number of grains per ear(GN)and 100-grain weight(GW)decreased significantly with the increase of density.Compared with D1,GN decreased by 5.82% and 10.56% respectively in D2 and D3 treatments,and GW decreased by 2.55% and 3.46% respectively.Compared with D1,the yield at D2 and D3 plots increased by 12.02% and 20.41% respectively.Compared with Zhengdan958,the yield and GW of Denghai 618 were 11.47% and 7.39% higher,and there was no significant difference in GN.There was no significant difference in maize yield and its components among three nitrogen fertilizer treatments.The interaction between density and nitrogen rate had significant effects on GN and yield in the second year of insitu experiment(Huanggang site,2018).Under 225 kg/hm2 N application and 90000 plant/hm2 density,GN was more and the yield was the highest,reaching 12.7 t/hm2.The net income of this nitrogen-density combination is better,with 4365 yuan/hm2 higher than that of the conventional nitrogen-density combination.4.Nitrogen accumulation in two cultivars had different responses to planting density and nitrogen application rate,but the interaction effect between the two cultivars was not consistent between years.Compared with D1,D2 and D3 treatments increased9.24% and 22.25% in N accumulation,respectively,at maturity stage.Nitrogen application could significantly increase nitrogen accumulation,but there was no significant difference between N225 and N300 treatments.On average,Denghai 618 had higher nitrogen accumulation at Huanggang experimental site than Zhengdan 958,and the average nitrogen accumulation was 20.04% and 7.11% higher in silking stage and maturity stage,respectively.The interaction of nitrogen fertilizer and density in the second insitu experimental year(2018 Huanggang site)had a significant effect on the nitrogen accumulation at maturity stage.Under 225 kg/hm2 nitrogen application rate and 90000 plant/hmdensity combination plots,it reached 239.7 kg N/hm.5.Planting density had a significant effect on partial productivity of nitrogen fertilizer of the two varieties,but had no significant effect on other nitrogen utilization indicators.Compared with D1,partial productivity of nitrogen fertilizer under D2 and D3 treatments increased by 14.26% and 25.17% respectively.Nitrogen application rate had a significant impact on nitrogen utilization indexes.Nitrogen agronomic use efficiency,partial productivity of nitrogen fertilizer and nitrogen use efficiency decreased significantly with the increase of nitrogen application rate.The agronomic utilization efficiency and partial productivity of nitrogen fertilizer of Denghai 618 at Huanggang site in 2018 were significantly higher than that of Zhengdan 958,which increased by 21.20% and 7.34% respectively,but there was no significant difference in nitrogen use efficiency and nitrogen harvest index between the two varieties.The interaction effect of nitrogen density had no significant effect on nitrogen utilization index.Under the experimental conditions,increasing density had obvious effect on reducing nitrogen.The best performance in yield and net income were under the combination of 225 kg N/hm2 of nitrogen fertilizer and 90000 plants/hm2 of planting density.Under this treatment,the canopy structure was more reasonable,with higher LAI,higher light radiation interception rate and high SPAD value,which were beneficial to dry matter accumulation and nitrogen uptake and accumulation.At the same time,the N agronomic utilization efficiency,partial productivity and nitrogen use efficiency of nitrogen fertilizer were all higher.Compared with Zhengdan 958,Denghai 618 has low ear position,high mechanical strength of stem,rapid decrease in grain moisture,and grain moisture content can be reduced to 27% at maturity.It is suitable for mechanized harvesting.The recommended planting density for spring maize in Hubei Province is75000 plants/hm2-90000 plants/hm2,and nitrogen application rate is about 225 kg/hm2. |
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