Chinese milk vetch and rice straw enhanced lime-induced cadmium immobilization and reduced grain Cd in paddy soil

Cadmium (Cd) contamination in paddy soil poses a serious threat to food safety and soil quality. Although organic and inorganic amendments show promise for Cd remediation, the temporal dynamics of their combined effects on soil biochemical processes and Cd bioavailability remain poorly understood. A two-year pot experiment was conducted to investigate the effects of green manure (GM), rice straw (RS), and lime (L) applied alone or in combination on Cd immobilization and rice yield in Cd-contaminated paddy soil. GM, RS, and lime combined treatment (GSL) significantly increased grain yield by 58.4% and 53.5% and reduced grain Cd concentration by 40.5% and 42.8% in 2020 and 2021, respectively, compared with chemical fertilizer application alone. GSL treatment decreased the acid-extractable Cd fraction by 25.5% and increased the residual fraction by 71.1% in 2021. Root Fe-Mn plaque increased by 52.2%-71.8% under GSL, limiting Cd translocation to aerial tissues. Partial least squares path modelling revealed a shift in the controlling mechanism between seasons: Cd fractions directly controlled grain Cd in 2020, whereas Fe-Mn plaque became dominant in 2021. The combined use of organic amendments with lime is therefore a promising strategy for strengthening lime-based remediation in Cd-contaminated paddy systems.