Abstract:

To quantitatively analyze the effects of increased planting density on the growth, lodging resistance, and yield of summer soybeans, field experiments were conducted using ‘Qihuang 34’ as the material during the 2022 and 2024 summer soybean growing seasons. Through systematic analysis of the effects of different planting densities on summer soybean canopy growth indicators, lodging resistance trait indicators, yield composition indicators, and the intrinsic relationship between lodging resistance index and lodging resistance trait indicators, the impact of increased planting density on summer soybean growth, lodging resistance, and yield was clarified. The results showed that within a certain range, increasing planting density reduced the SPAD value of the top three leaves of summer soybean plants, with a maximum SPAD value 0.12%-6.47% higher than other density treatments, promoting the construction of plant canopy functional structure. However, excessive density can inhibit the accumulation of nitrogen in soybean plant canopy and the formation of leaf area index. The leaf layer nitrogen content, leaf layer nitrogen accumulation, RVI value, NDVI value, and LAI were 3.70%-5.49%, 10.94%-22.26%, 7.20%-11.87%, 3.84%-7.60%, and 7.51%-11.70% higher than other planting density treatments, respectively. The larger the stem bending resistance and stem thickness, the shorter the main stem length and the stronger the plant's ability to resist lodging. Increasing density reduced the plant's lodging resistance index, which is not conducive to improving the plant's lodging resistance. Overall, when the planting density was 240000 plants/hm², the various lodging resistance traits of soybean plants were relatively reasonable. In this study, soybean grain yield was highest when the planting density was 200000 plants/hm², but showed better production potential when the density reached 240000 plants/hm².

Key words: summer soybean, increasing density, growth, lodging resistance, yield