Changes in yield and agronomic traits of soybean cultivars released in China in the last 60 years

Breeding and cultivar improvement are important for increasing crop yields. In this study, 1472 soybean cultivars released in the last 60 years and 683 landrace cultivars from three regions of China (North spring soybean region, Yellow-Huai-Hai summer soybean region, and South soybean region) were collated to examine changes in agronomic characters and plant density that might be associated with yield improvement. The yield and 100-seed weight of the soybean cultivars increased significantly over time in all three regions. Planting density decreased significantly in the Yellow-Huai-Hai summer and South soybean regions but did not significantly change in the North spring soybean region. The increased soybean yields were mainly due to increased 100-seed weight and seed number per plant. Seed protein content has not significantly changed in 60 years, but oil content has increased in all three regions. The North spring soybean region had the highest oil content, whereas the South soybean region had the highest protein content. Future increases in soybean yield in China may occur by improving seed number per plant without reducing 100-seed weight. The North spring region should focus on breeding soybean with high oil content, and the Yellow-Huai-Hai summer and South regions should focus on high protein and low oil contents.