Various amendments differ in decreasing cadmium and raising selenium accumulation in rice in high geological background soils.

Selenium biofortification of staple crops in naturally selenium-rich regions offers a safe and effective approach to mitigating global selenium deficiency. However, the simultaneous presence of high cadmium (Cd) concentrations and low selenium (Se) bioavailability in seleniferous paddy soils constrains the production of Se-enriched rice. Preventing excessive Cd accumulation while increasing Se content in rice grains is therefore essential. This field study assessed the effectiveness of four soil amendments-hydrated lime (HL), mixed soil conditioner (MSC), biochar (BC), and humic acid (HA)-in modifying Se and Cd bioavailability and their accumulation in local rice cultivars grown on Se-enriched, Cd-contaminated paddy soils at three sites. HL and MSC were more effective in reducing CaCl2-extractable Cd in acidic soils, while BC and HA promoted Se mobilization in soils with near-neutral pH and higher soil organic carbon content. HL and MSC treatments increased grain Se by 35-39 % in rice with high Se uptake or translocation capacity and reduced grain Cd by 45-76 % in high-Cd-accumulating rice varieties. Notably, for the rice cultivar Xiushui 519, which has a relatively low bioconcentration factor for Cd/Se, all amendments failed to further decrease grain Cd and increase root/shoot Se, but significantly reduced grain Se (29-47 %). The study underscores the importance of soil properties and rice physiological traits in achieving safe and effective selenium biofortification, and provides a scientific basis for managing Se and Cd bioavailability in the soil-rice system through targeted soil amendments and cultivar selection.