Effects Of Nitrogen Topdressing Stage And Light Quality On Canopy Light Environment And Stem Lodging Resistance Of Winter Wheat

Nitrogen fertilizer is an important guarantee for stable and high yield of wheat.In order to improve the yield of wheat,a large amount of nitrogen fertilizer is often applied in wheat cultivation.Excessive nitrogen application exacerbates the contradiction between individuals and populations,leading to a decrease in the quality of individual stem development and resulting in lodging and reduced yield.A reasonable nitrogen application period can promote wheat population growth,optimize population structure,improve light quality and quantity within the canopy,and increase yield and nitrogen fertilizer utilization efficiency.This experiment selected two wheat varieties with different lodging resistance,Shannong23（SN23,lodging resistant variety）and Shannong16（SN16,lodging sensitive variety）,as the research materials.The total nitrogen application was 240 kg ha^-1,and 80 kg ha^-1 of pure nitrogen（1/3of total nitrogen fertilizer）was applied before sowing,with the remaining 2/3 being applied later.Set four nitrogen application periods:starting fertilizer and booting fertilizer 1:1（T1）,jointing fertilizer fully applied（T2）,jointing fertilizer and flowering fertilizer 1:1（T3）,and booting fertilizer fully applied（T4）,while setting two light qualities:red light treatment and far red light treatment,with natural light as the control.Study the canopy light environment of wheat under different nitrogen application stages,explore the cultivation measures for coordinated regulation of wheat lodging resistance and high yield under different nitrogen application stages and canopy light environment,and further analyze the effects of wheat plant morphological characteristics,mechanical characteristics,stem chemical components and other indicators on stem strength and nitrogen response under different populations.The main research findings are as follows:1.The mechanism of lodging resistance in wheat affected by nitrogen application period and light quality（1）In terms of stem morphology and mechanical characteristics,plant height and center of gravity height are negatively correlated with bending resistance,while stem thickness,wall thickness,and plumpness are positively correlated with bending resistance.Under the irradiation of red light,the stem thickness,wall thickness,and plumpness of the stem were significantly improved.Compared with other treatments,the quality of the stem is higher and the lodging resistance is stronger.（2）In terms of the chemical components of the stem,the content of gibberellin（GA₇）in the stem is negatively correlated with the bending strength,the content of cellulose and lignin is positively correlated with the bending strength,and the content of GA₇ is negatively correlated with the content of cellulose and lignin.Exposure to red light significantly reduced the content of GA₇ in the stem,while the content of cellulose and lignin in the stem increased significantly.Light quality significantly affects the morphological characteristics and chemical components of wheat stems.Compared with natural light and far red light treatments,red light treatment increases the ratio of red light to far red light at the base of the wheat population,reduces the content of GA₇ in the stems,weakens the GA-mediated shading effect,increases the stem diameter,wall thickness,and plumpness of the stems,decreases plant height and center of gravity height,and significantly increases the lignin and cellulose content of the stems,The bending resistance of stems increased by an average of 12.14%and 22.34%compared to natural light and far red light,respectively.2.Effects of nitrogen application period and light quality on wheat yieldThere are certain differences in grain yield among different treatments,and a reasonable nitrogen application period can promote the improvement of wheat yield.Optimizing the nitrogen application period mode can ensure the effective number of panicles in the population,which is conducive to the formation of grain number and weight per spike in wheat.Compared with other treatments,the number of wheat ears and thousand grain weight increased with the ratio of starting fertilizer and booting fertilizer 1:1（T1）,but the difference in grain number per ear was not significant.The total application of booting fertilizer significantly increased the thousand grain weight compared to other treatments,but the difference in grain number per ear was not significant,and the number of ears was significantly lower than other treatments.Moreover,the red light treatment enhanced the lodging resistance of stem with a 1:1（T1）ratio of starting fertilizer and booting fertilizer.In summary,under red light irradiation,the content of GA₇ in the stem is significantly reduced,the content of cellulose and lignin in the stem is increased,and the bending resistance of the stem is improved;On the other hand,in the ratio of starting fertilizer and booting fertilizer 1:1（T1）,starting fertilizer can ensure the number of wheat populations,increase the number of ears per unit area,and increase the weight of 1000 grains in the later stage of growth.Therefore,under the conditions of this experiment,applying nitrogen fertilizer at a ratio of 1:1（T1）during the starting and booting stages and irradiating with red light is beneficial for the synergistic improvement of wheat stem lodging resistance and yield.