Effects Of Densities And Decreasing Nitrogen Rates On Grain Yield And Quality Of Summer Maize

At present,the target of maize production in China gradually transformed from simply chasing high yield to both high yield,high quality and high efficiency.Reasonable planting density and nitrogen rate are effective cultivation measures to improve maize yield and protein quality.In this experiment,firstly,Zhengdan 958 and Suyu 41 were used as experimental materials,and then three planting densities of low,medium and high(60,000,75,000 and 90,000 plants·hm^-2)and conventional nitrogen rate,nitrogen reduction by 25%,and nitrogen reduction by 50%on the basis of conventional nitrogen rate(300,225 and 150kg·hm^-2)were set,in the end,to study the regulation effects of reduced nitrogen rate on yield and protein quality of summer maize under different densities.Combined with the accumulation and translocation of dry matter and nitrogen in different growth stages,to determine the optimal combination of density and nitrogen rate to improve protein quality and yield.We used multispectral imaging to assist in obtaining plant growth information and predicting grain yield and quality.We aimed to provide theoretical and technical support for high yield,high quality,high efficiency and precise cultivation of maize in Huaibei region.The main research results are as follows:1 Summer maize can still obtain higher grain yield with nitrogen reduction by 25%（Based on the conventional nitrogen rate）under increasing planting densitiesThe grain yield,yield components and dry matter accumulation of the two varieties were significantly reduced with nitrogen reduction by 50%under increasing densities,while the25%reduction of nitrogen at each density did not result in a significant reduction in the yield,kernel number and 1000-kernel weight of the two varieties（Except for Suyu 41 at high density in 2018）.A 25%reduction in nitrogen at each density did not significantly reduce the dry matter accumulation and harvest index,but increase the crop growth rate from tasseling stage to 14 days after anthesis and 28 days to 42 days after anthesis,and facilitate the transfer of plant nutrients to the grains,which benefit to yield formation.Under the conditions of this experiment,reducing nitrogen rate to 225 kg·hm^-2 at 90,000 plants·hm^-2 could still meet individual plant nutrition requirements and exhibit the potential for population.It is the best combination treatment to increase maize yield.2 The yield and protein quality were improved by reducing nitrogen to 225 kg·hm^-2 at high densityNitrogen reduction by 50%at different planting densities significantly reduced the total protein content,storage protein content and plant total nitrogen accumulation of the two varieties,while 25%nitrogen reduction at high density did not significantly affect the total protein content,gliadin and gluten of the two varieties.At the same condition,harvesting high Glu/Gli and lysine content,and reducing nitrogen by 25%under high density increased the nitrogen accumulation of Zhengdan 958 plant and the nitrogen translocation of vegetative organs,thus improving the nitrogen transport capacity of vegetative organs and nitrogen accumulation after tasseling stage,promoting the transport of nitrogen to the grain,which beneficial to protein formation.There is a quadratic relationship between plant nitrogen accumulation,vegetative organ translocation and protein content.Under the conditions of this experiment,reducing nitrogen to 225 kg·hm^-2 at a planting density of 90,000 plants·hm^-2 could still maintain plant nitrogen accumulation and translocation,maintain the quality of grain protein,and achieving high yields for both varieties under this combination.It is the best combination treatment to increase grain yield per unit area and feed value.3 Preliminary prediction of summer maize yield based on multispectral imagingUnder the condition of high density,the canopy vegetation indices（NDVI,RVI and DVI）of the two cultivars were significantly higher than those of the middle and low densities.A25%reduction in nitrogen at high density did not result in a significant reduction in NDVI,RVI and DVI of the two varieties,but the two varieties had different responses to nitrogen reduction.At different planting densities,nitrogen was reduced by 25%,and the vegetation index of summer maize of different varieties from 21 days to 35 days after anthesis decreased at a slower rate than that of conventional nitrogen rate,which promoted the accumulation of nutrients in plants after anthesis.There is a positive correlation between the vegetation indices and the grain yield of the two varieties.The yield prediction model based on the vegetation indices of 35 days after anthesis was as follows:Y=3.286+7.115 x₁+0.198 x₂+3.424 x₃（NDVI as x₁,RVI as x₂,DVI as x₃,and grain yield as Y）,and the prediction effect was the best（R²=0.694**）.The prediction of protein content of grains could not be presented under the experimental conditions,and further research is needed.