Effects Of Increasing Density And Reducing Nitrogen On Productivity And Nitrogen Utilization Of Maize Varieties In Different Years

In the process of maize yield improvement,the increase of planting density,nitrogen application and variety replacement all played an important role.In order to pursue high yield,excessive use of nitrogen fertilizer often leads to deterioration of farmland ecological environment.Therefore,it is an important direction to realize green maize yield increase and yield potential of different maize varieties by reasonably increasing planting density and decreasing nitrogen application rate to ensure the increase or stability of yield of maize varieties in different ages.In this study,10 maize varieties grown from 1980 s to 2010 s were used as experimental materials to study the comprehensive responses of photosynthetic physiology,plant morphological characteristics,lodging resistance,carbon and nitrogen metabolism,nitrogen utilization and grain yield to planting density and nitrogen application rate.On the premise of ensuring high and stable yield of maize,the appropriate cultivation measures of maize varieties in different years were discussed,which provided theoretical basis for green high yield,high quality and efficient cultivation of maize.The main results are as follows:1.The photosynthetic capacity of maize increased with the development of breeding years.With increasing planting density,net photosynthetic rate and leaf color value decreased significantly,while leaf area index increased significantly.Proper nitrogen application could improve photosynthetic indexes,alleviate the pressure of decreasing photosynthetic performance caused by densification,and improve photosynthetic performance of varieties under high density condition.The optimum density and nitrogen application rate of varieties in different years were different.In 2000 s and 2010 s,the photosynthetic performance under nitrogen reduction was higher than that under other nitrogen application treatments.2.Lodging resistance of maize increased with the development of breeding years.With the increase of planting density,the equilibrium point and internode length of various varieties increased,the cross-sectional area decreased,the puncture strength and bending strength of stem decreased,and the lodging resistance decreased,and the variety of 2010 s was the least affected by density.The suitable nitrogen application rate could increase the puncture strength and bending resistance of stem,and then reduce the lodging rate.Under the treatment of densification and nitrogen reduction,the plant height,spike height and internode length of2010 s varieties decreased significantly,while the stem diameter and internode cross-sectional area increased,which significantly improved the puncture strength of each stem node and ensured the stability of the flexural force.The 2010 s variety had higher suitable planting density,and the lodging rate could be significantly reduced by reducing nitrogen application rate at the same time of densification.3.With the advance of breeding years,the activities of sucrose phosphate synthase(SPS)and sucrose synthase(SS)in ear leaves increased significantly.With the increase of planting density,the contents of sucrose and soluble sugar in leaves and the activities of SPS and SS decreased.The activity of sucrose metabolizing enzyme in 2010 s variety was least affected by planting density.The content of sucrose and soluble sugar and the activity of sucrose metabolizing enzyme in leaves could be increased by appropriate nitrogen application.At silking stage and grain filling stage,the activities of sucrose metabolizing enzymes and the contents of sucrose and soluble sugar in 2010 s varieties under densification and nitrogen reduction treatment were significantly higher than those in other nitrogen application treatments.4.With the advance of breeding years,the activities of nitrate reductase(NR),glutamine synthetase(GS)and glutamate dehydrogenase(GDH)increased significantly.Increasing planting density could significantly reduce NR and GDH activities,but significantly increase GS activities;Appropriate nitrogen application rate can improve the activities of NR,GS and GDH.From silking stage to grain filling stage,2000 s and 2010 s varieties can maintain high nitrogen metabolism related enzyme activities for a longer time under the treatment of increasing density and reducing nitrogen.5.The total amount of nitrogen accumulation increased with the advance of breeding years,the increase of planting density and nitrogen application.With the advance of breeding years,the nitrogen transport of stem and leaf sheath increased,while the male spike showed the opposite performance.With the increase of planting density,the nitrogen transport capacity and nitrogen transport rate of each organ increased significantly;The appropriate nitrogen application rate can improve the nitrogen transport capacity and nitrogen transport rate of each organ.Under the treatment of increasing density and reducing nitrogen,the nitrogen transport rate of stem and leaf of 2010 s was higher than that of other treatments.6.With the advance of breeding years and the increase of planting density,nitrogen harvest index(NHI),nitrogen apparent utilization rate(NRE),Nitrogen Agronomic utilization rate(NAE),nitrogen partial productivity(PFPN)and nitrogen contribution rate(NCR)increased as a whole.With the increase of nitrogen application rate,NHI first increased and then decreased.Reducing nitrogen application rate can significantly increase NRE,NAE,PFPN and NCR.Under the treatment of increasing density and reducing nitrogen,the nitrogen harvest index and nitrogen use efficiency of 2010 s varieties were significantly higher than those of other varieties and treatments.7.With the advance of breeding years and the increase of nitrogen application,the yield,100 grain weight and dry matter accumulation per plant showed an increasing trend.With the increase of planting density,the yield increased significantly,but the 100 grain weight,grain number per panicle,grain depth and dry matter accumulation per plant decreased.Under the treatment of increasing density and reducing nitrogen,the yield and dry matter accumulation per plant of 2000 s and 2010 s varieties were not significantly lower than that of normal nitrogen application,but significantly higher than that of other treatments.