Abstract: Two soybean varieties, Nandou12 (ND₁₂) and Nandou25 (ND₂₅), with different 100-seed weight and growth characteristics were used in field experiment to investigate the maturation rate, stem growth characteristics and yield at different sowing rates. It was found that seedling density of ND₁₂ was higher than that of ND₂₅ with the same sowing rate, but the mature plant number of ND₁₂ was lower and the maturation rate was slower than for ND₂₅. The variety×sowing rate interaction effect for mature plant number was significant. With increased sowing rate, stem diameter decreased significantly. However, stem height, height of the stem center of gravity and internode length increased significantly. Elongation growth of the stem was promoted, but increase in stem diameter was restrained. ND₂₅ was more sensitive to increase in plant density than ND₁₂. ND₁₂ had a higher reduction in seed number per plant with increased plant density than ND₂₅, but a lower reduction in 100-seed weight. The plant density response of various yield components differed between varieties. As the sowing rate and mature plant number increased, the stem mechanical strength and lodging resistance index decreased, while yield increased initially and then decreased. There was no significant difference between varieties for plant seed weight while the effect of density on yield formation was more important than that of lodging. ND₁₂ and ND₂₅ have the highest yield at 90 and 120 kg·ha^-1, respectively.

Key words: sowing quantity, stem characteristics, mechanical strength, lodging, yield