Objective The aim was to explore the effect of incorporating Chinese milk vetch with sulfur fertilizer application on cadmium（Cd） uptake by rice and the changes in Cd forms in soil.

Methods A pot experiment was conducted to investigate the effects of combined application of Chinese milk vetch and sulfur fertilizer on Cd absorption by rice and its transformation in soil speciation in Cd-contaminated paddy soil.

Results The soil solution exhibited Eh and pH ranges of 20 - 252 mV and 5.7 - 6.7 during the rice growth periods. The incorporation of Chinese milk vetch and sulfur fertilizer application significantly increased soil pH while decreasing Eh. Both Chinese milk vetch incorporation and sulfur fertilizer application alleviated Cd toxicity in rice, significantly increased the dry matter weight of the above-ground parts of rice, and the interactive effect of them was even better. Compared to the control (CK), the individual or combined application of Chinese milk vetch and sulfur fertilizer significantly reduced Cd fractions in rice stems, leaves, and grains by 30.32% - 77.06% and 77.99% - 157.96%. The exchangeable Cd fraction progressively decreased, while carbonate-bound, Fe-Mn oxide-bound, and residual Cd fractions gradually increased throughout the growth periods. The organic-bound Cd fraction exhibited an initial decrease followed by an increase. Both individual and combined applications effectively decreased exchangeable Cd contents while increasing residual Cd contents in soil.

Conclusion The combined application of Chinese milk vetch and sulfur fertilizer in Cd-contaminated paddy fields significantly enhanced rice dry matter production, decreased Cd accumulation in aboveground tissues and Cd bioavailability in soil.