Regulation Effects Of Nitrogen Fertilizer And Density On Stem Lodging And Grain Filling Of Maize

In recent years,maize yield has increased year by year,and thus becoming the main food crop in China.As the main production area of maize,Heilongjiang Province accounts for more than 1/3of the country's total planting area,and the total yield accounts for 40%of the country's total,which contributes to ensuring China's food security.Since 2017,the country has called for the development of green ecological agriculture to get rid of the current situation of excessive inputs in agricultural production.Therefore,in response to the national call for the current situation of excessive application of maize fertilizer and insufficient density in Heilongjiang,this study takes nitrogen fertilizer and density as the starting point.We used‘Nonghua 101'as the material,and carried out this field experiment at Xiangyang Farm,a trial site of Northeast Agricultural University from 2017to 2018.The test used three nitrogen fertilizers(100 kg?ha^-1,200 kg?ha^-1,300 kg?ha^-1)and three densities(67500 plants?ha^-1,82500 plants?ha^-1 and 97500 plants?ha^-1)to explore the effects of nitrogen fertilizer application rates and densities on leaf canopy photosynthesis characteristics,leaf carbon and nitrogen metabolism,stem lodging characteristics,root bleed characteristics,grain filling dynamics,yield and quality of Heilongjiang spring maize.The main findings are as follows:1.Under the interaction of different application rates of nitrogen fertilizer and densities,D2N2treatment of intermediate-density and intermediate-application rates of nitrogen fertilizer improved leaf photosynthesis and aboveground dry matter accumulation.The leaf area index?LAI?and the content of chlorophyll SPAD value were the largest in D2N2 treatment,and the maximum enzyme activity of RUBPCase and PEPCase were respectively obtained in D3N1 treatment and D1N2treatment.The difference of average leaf inclination angle and PAR interception rate in the upper layer was significant.Correlation analysis showed that the chlorophyll SPAD value and PEPCase enzyme were significantly correlated with yield at each growth stage,while RUBPCase enzyme had a very significant correlation with yield only at the early filling stage.2.Under the interaction of different application rates of nitrogen fertilizer and densities,D2N2treatment enhanced the nitrogen metabolism of leaves and delayed leaf senescence.As the growth progress moving forwards,the activities of nitrogen metabolism key enzymes?NR,GS,GOGAT,GDH?increased firstly and then decreased.In tasseling stage and early filling stage,the NR activity was the highest in D1N2 treatment.Except for the tasseling stage,the GS activity was highest under low density.In each growth period,GOGAT and GDH activities were the highest in D2N2 treatment.3.Under the interaction of different application rates of nitrogen fertilizer and densities,D2N2treatment could significantly improve the lodging resistance of stalks and reduce the lodging rate of maize.D2N2 treatment increased maize plant height,stem thickness,internode length,puncture strength,bending strength,and increased stalk cellulose,hemicellulose,lignin content and lignin synthesis related enzymes phenylalanine aminotransferase?PAL?,tyrosine ammonia lyase?TAL?,cinnamyl alcohol dehydrogenase?CAD?,4-coumaric:Co A ligase?4CL?activity.When the application rate of nitrogen fertilizer reached 300 kg?ha^-1,all indicators showed no upward or downward trend.Correlation analysis showed that in addition to plant height,the other maize stalk lodging indices were significantly negatively correlated with lodging rate,among which the stem thickness,internode length,puncture strength,bending strength were extremely negatively correlated with lodging rate.4.Under the interaction of different application rates of nitrogen fertilizer and densities,the injury indices of D1N1 and D3N3 treatments were significantly lower than those of D2N2 treatment.D2N2 could significantly increase the root injury flow,the flow of metal ions,amino acids,and endogenous hormones in the injury fluid,and promote the aboveground growth and development.Correlation analysis showed that IAA and ABA had a significant correlation with stem fiber traits.The flow of amino acids,metal ions,IAA and CTK in the root bleed fluid were significantly positively correlated with yield.5.Compared with D1N1 and D3N3 treatments,D2N2 treatment increased the maximum filling rate?V_m?and the growth amount at the maximum filling rate?W_m?,extended the time when the maximum filling rate?T_m?appeared.The difference of each treatment on the average grouting rate?G_m?was not significant.As the filling stage moving forward,auxin?IAA?,gibberellin?GA?and cytokinin?CTK?gradually decreased,and abscisic acid?ABA?increased firstly and then decreased.6.D2N2 increased the maize grain weight and yield.Different application rates of nitrogen fertilizer and densities had no obvious effects on ear thickness and the number of ear rows,but had significant effects on number of grains,number of ears and bald tips.It shows that the greater the density,the smaller the number of rows and the longer the bald tips.The maximum yield was obtained at D2N2 treatment,which was 9321.21 kg?ha^-1,which was higher than D1N1 treatment and D3N3 treatment for 5.14%and 59.01%,respectively,indicating that proper application of nitrogen fertilizer and density could increase maize yield.