Abstract: To explore the effects of different amendments on selenium bioavailability in the soil-soybean system, a field experiment was conducted on selenium-containing soil in Longzhou Village, Jingzhou District, Jingzhou City, Hubei Province, in which five organic materials including rice straw biochar, mineral-derived potassium fulvate, decomposed organic chicken manure, mineral-derived humic acid and Aspergillus niger agent, as well as a compound amendment, were selected, and the available selenium content in soil and the selenium content in various organs of soybean were measured. The results showed that the grain selenium content was highest under the treatments of application of rice straw biochar at the maturity stage and topdressing of mineral-derived humic acid at the branching stage only, reaching 0.434 mg/kg and 0.403 mg/kg, respectively. The compound amendment at three times the normal dosage was beneficial for increasing the available selenium content in soil, but most treatments with three times the dosage of amendments did not promote selenium content accumulation in soybean grains.Selenium showed an obvious enrichment characteristic toward grains within the soybean plant, and amendments mainly affected the accumulation by regulating distribution efficiency. Reasonable selection of amendment types, control of dosage, and matching the critical period of soybean selenium demand (branching stage or seed-filling stage) effectively improved soil selenium bioavailability and the selenium content in soybean grains, whereas excessive application exerted an inhibitory effect.

Key words: amendments, soil-soybean system, selenium bioavailability, field experiment