Abstract: A 28?day laboratory incubation experiment was conducted to explore the environmental impacts of incorporating Chinese milk vetch into paddy soil. Chinese milk vetch was incorporated into soil at rates of 0 (CK), 15000, 30000, and 45000 kg?ha (M1, M2, and M3, respectively), and the dynamic changes in reducing substances and greenhouse gas emissions in paddy soil were monitored. Incorporation of Chinese milk vetch significantly increased the total soil reducing substances, active reductive material, and the concentrations of iron and manganese ions (Fe2+ and Mn2+) in paddy soil, but decreased the soil redox potential (Eh). Compared with CK, the M1, M2, M3 treatments increased total soil reducing substances by 0.34, 0.80, 1.16 cmol?kg-1, respectively; increased the active reductive material content by 0.14, 0.35, and 0.52 cmol?kg-1, respectively; increased the average Fe2+ content by 87.91, 182.91, and 280.61 mg?kg-1, respectively; increased the average Mn2+ content by 10.12, 12.77, and 15.73 mg?kg-1, respectively, and decreased the average Eh by 32.88, 47.98, and 57.26 mV, respectively. The total reducing substances content peaked after 0.5 months of incubation. The Fe2+ content in the M3 treatment increased to >400 mg?kg-1, which may result in poisoning of rice seedlings. Incorporation of Chinese milk vetch significantly increased CO2 and CH4 emissions, but decreased N2O emissions, and ultimately increased the global warming potential. Compared with CK, the M1, M2, M3 treatments increased the average CO2 emission rate by 7.67, 12.48, and 20.54 mg?kg-1?d-1, respectively; increased the average accumulative emission of CO2 by 171.63, 293.42, and 498.45 mg?kg-1, respectively; increased the average CH4 emission rate by 0.04, 0.09, and 0.21 mg?kg-1?d-1, respectively; increased the average accumulative emission of CH4 by 0.36, 0.69, and 1.77 mg?kg-1, respectively; decreased the average N2O emission rate by 0.46, 0.64, and 0.72 μg?kg-1?d-1, respectively; and decreased the average accumulative emission of N2O by 10.00, 13.02, and 14.36 μg?kg-1, respectively. The global warming potential of the M1, M2, and M3 treatment was 1.59?times, 2.04?times, and 2.93?times higher, respectively, than that of CK. The CO2 and N2O emissions were mainly concentrated in the earlier period of incubation, while CH4 emissions were concentrated in the later period of incubation. The reducing substances content was positively correlated with CO2 and CH4 emissions, but negative correlated with N2O emissions. The results showed that incorporating Chinese milk vetch significantly increased the reducing substances content, enhanced CO2 and CH4 emissions, and decreased N2O emissions. Importantly, Chinese milk vetch incorporation increased the rice yield. Therefore, there is potential value in incorporating Chinese milk vetch into soil to maintain rice yield, but it should be incorporated at appropriate rates to reduce environmental impacts. Appropriate incorporation rates should be verified through pot and field experiments.

Key words: Astragalus sinicus (Chinese milk vetch), reducing substance, greenhouse gas