Evaluation of soil additives for stabilizing cadmium-contaminated paddy soil and its effect on the soil bacterial community.

Abstract

Given the significant contribution of contaminated rice to higher dietary Cd intake, agricultural scientists are concerned about reducing Cd contamination of paddy soils. A pot experiment was conducted to evaluate the influence of different soil additives (biochar, Fe-biochar, oyster shell, zeolite, yirang, and sepiolite) on Cd bioavailability and bacterial community in paddy soils. Application of 1% and 2% (w/w) soil additives significantly (p < 0.05) increased soil pH by 0.54-1.92 units and reduced DTPA-extractable Cd by 32, 29-60.84%, with biochar and oyster shell treatments having the highest effects. After adding soil additives, the geochemical fraction of Cd partially shifted to a more stable form, with the exchangeable fraction decreasing by 29.54-49.88% and the residual fraction increasing by 48.55-69.44%. The biochar and oyster shell treatments showed the greatest effectiveness of Cd stabilization, with the DTPA-extractable Cd content decreasing by 48.50-53.40% and 58.3-60.42%, respectively. Biochar and oyster shell treatments also significantly increased bacterial community diversity (p < 0.05), specifically increasing the relative abundance of Proteobacteria and Firmicutes while decreasing the abundance of Acidobacteria. The RDA analysis revealed that Cd bioavailability, pH, SOM, and CEC were the most influential factors on the soil bacterial community. The results of this study suggest that the use of biochar and oyster shells has the potential to minimize Cd bioavailability and improve the microecosystem of Cd-contaminated rice soils.