Abstract: Soybean yield in Jilin Province has increased approximately 1.12% per year since early 1920. Our objective was to investigate the changes in agronomic traits associated with yield increase in the selection of historical cultivars using 30 soybean cultivars cultivated and genetically improved from 1923 to 2005. The experiments were performed with randomized complete block design with at least three replicates in Changchun (43.53°N, 125.10°E), Jilin Province in 2005–2006. The results indicated that according to the regression equation, soybean yield exhibited a linear increase with genetic improvement, from 1 197.80 kg ha^-1 in 1923 to 2 305.54 kg ha^-1 in 2005, with average increase of 14.60 kg ha^-1(1.12%) per year. With the increasing of soybean yield, plant height and branches shortened; stem diameter and number of pods and seeds increased. Yield was positively correlated with number of pods and seeds per plant, stem diameter, leaf area per plant, leaf area index (LAI), and the number of leaves (P<0.05) while negatively correlated with plant height, number of branches, and lodging index (P<0.05). This study demonstrated that genetic improvement enhances the resistance to lodging, the sink capability and the assimilation ability which results in a consecutive yield increase in soybean.

Key words: Soybean [Glycine max (L.) Merr.], Genetic improvement, Agronomic trait, Yield