| Aiming at the problems of unreasonable nitrogen density allocation,serious lodging phenomenon and low nitrogen use efficiency in summer maize harvest period in Guanzhong area.The experiment was conducted in the pilot trial（exhibition）base of new crop varieties in Yangling,Shaanxi Province from 2021 to 2022.The maize varieties Zhengdan 958 was used as experimental material.With nitrogen application rate as the main area and planting density as the secondary area.Three nitrogen application levels are set:Low nitrogen N0(0kg hm-2),medium nitrogen N1(225kg hm-2),high nitrogen N2(300kg hm-2);Three planting density treatments:low density D1(52500 plants hm-2),medium density D2(67,500plants hm-2)and high density D3(87,500plants hm-2).The canopy structure,photosynthetic synthesis,nitrogen metabolism level,nitrogen accumulation and utilization,and stem agronomy and physicochemical characteristics of summer maize were analyzed and compared.The internal reasons of stabilizing yield,improving lodging resistance and nitrogen use efficiency under optimal nitrogen density allocation was clarified,which provided reference for efficient and stable summer maize cultivation in Guanzhong area.The results are as follows:1.The optimal nitrogen density configuration could increase corn yield,but the yield difference was not significant when the middle nitrogen level was higher.In 2021,the maximum production will be 12026.74 kg hm-2under the N1D2 configuration;In 2022,the maximum yield of 11033.69 kg hm-2under N2D3 configuration has no significant difference from the stable yield of 10888.42 kg hm-2under N1D3 configuration.When low-density D1was densified to high-density D3 level,the effective ear number of N0,N1 and N2treatments increased by 29.65%,38.52%and 32.61%,respectively.Under medium density D2 and high density D3,the average 100 grain weight under N1 was 34.45g and 31.50g,respectively,and that under N2 was 34.42g and 31.24g,respectively,and there was no significant difference between N1 and N2.Compared with N2,the number of grains per ear in N1 decreased by 9.36 grains and 13.55 grains,respectively.2.The optimal nitrogen density configuration can adjust the population structure,improve the canopy light environment,and stabilize the synthesis of photosynthetic substances.With the increase of nitrogen application rate and planting density,the leaf area index increased significantly.Compared with the level of middle nitrogen N1,high nitrogen N2 had no significant effect on the light transmittance of the upper canopy of the population,but decreased the light transmittance of the middle canopy at D2 and D3 densities by 9.6%,14.8%and 24.8%at D1,D2 and D3 densities,respectively.In terms of photosynthetic characters,nitrogen application significantly reduced the decline of relative chlorophyll content after anthesis.There was no significant difference in relative chlorophyll content between N1 and N2 at low and medium density,while high nitrogen level had better relative chlorophyll content at D3 density.There was a relatively stable net photosynthetic rate between N1 and N2,which stabilized the synthesis of photosynthetic materials.3.The optimal nitrogen density configuration stabilized nitrogen metabolism,promoted nitrogen transport rate and adjusted nitrogen allocation ratio.Nitrogen application significantly increased the activities of enzymes related to leaf nitrogen metabolism.High nitrogen N2 level had better NR activity than medium nitrogen N1 level,but there was no significant difference in the activities of GS and GOGAT after flowering.Denser planting promoted the population N accumulation.The average N accumulation of D3 increased by31.69%compared with D1,and the N accumulation of N2 was 3.69%higher than that of N1,with no significant difference.The post-flowering transfer rates of leaves and stems under N1 were 10.04%and 12.19%higher than that under N2.At physiological maturity stage,the average nitrogen allocation ratio of leaves,culms and grains at N1 level was 18.23%,14.19%and 60.04%,which were 11.79%,18.57%and 10.00%higher than N2 level,respectively.The higher N allocation ratio of grain at N1 level ensured the material basis of grain growth and development.4.The optimal nitrogen density configuration improved lodging resistance and decreased lodging rate.The lodging rate increased with the increase of planting density,and the lodging rate was higher at both low and high nitrogen levels.Compared with high nitrogen N2,light environment in the middle and lower canopy was improved and plant height and ear height were decreased under medium nitrogen N1 level.The number of small internode vascular bundle,cortical thickness,stem cross-sectional area increased by 10.90%,7.88%and 9.93%,respectively,and stem length decreased by 4.82%.The endogenous lignin content was increased by 10.23%,which ensured the internode filling degree,achieved strong stem strength during harvest,and stabilized lodging rate.In conclusion,optimized nitrogen-dense N1D2 configuration can stabilize or improve crop yield while coordinating low lodging and high nitrogen use.The higher nitrogen dense planting optimized the population structure,realized better light transmission in the lower canopy,stabilized the formation of stem lignin,vascular bundle and other material structures,reduced lodging,and then increased the effective panicle number of the population.At the same time,balanced photosynthetic matter and nitrogen accumulation were maintained,which coordinated post-anthesis vegetative growth and reproductive growth,ensured nitrogen distribution and stabilized grain weight. |
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