Abstract: A pot experiment was conducted at the Shaoyang University test base in May 2020, with Xudou 18 as the research object. We investigated the growth and development as well as the agronomic traits and nutrient content across a gradient of 0 (CK), 5, 10, 20, and 40 g·kg^-1 of biochar addition. The results showed that compared with CK, the biochar application significantly affected growth dynamic, plant height, number of effective pods per plant, 100-grain weight, and leaf and stem dry weights of soybean plants, and the contents of protein, crude fat and isoflavone in soybean seeds. At the application rate of 20 g·kg^-1, the germination rate of soybean was the highest, the growth period was the shortest, the number of effective pods per plant was the highest, the 100-grain weight was the largest, and the contents of protein, crude fat, and isoflavone were the highest in the seeds. When biochar application reached 40 g·kg^-1, the plant height of soybean was the highest with extended vegetative growth and delayed maturity, whereas the effective pods per plant and 100-grain weight was reduced compared to that with 20 g·kg^-1 application. In conclusion, the effects of biochar addition on agronomic traits and nutrient content of soybean varied with application amount, with 20 g·kg^-1 being the optimal under the test condition.

Key words: biochar, soybean, yield, agronomic trait, nutrient content