Immobilization of Cd in a paddy soil using moisture management and amendment

• Moisture management and amendment had impacts on Fe in root of plant.
• Gradual increase of Fe2+ in soil was reason for low Cd bioavailability.
• Competition for adsorption sites in root between Fe2+ and Cd2+ caused low plant Cd.

To offer basis for remediation of Cd-polluted paddy soil under reasonable water condition, pot experiment was conducted to study the effects of moisture management and amendment on the immobilization of Cd in paddy soil. Application of sepiolite in combination with phosphate fertilizer reduced exchangeable Cd by 18.2%, 13.7% and 12.5%, brown rice Cd by 52.3%, 46.0% and 46.8%, under continuous flooding, conventional irrigation and wetting irrigation, respectively, compared to the control groups. Under no amendments, the content of Fe(II) in root coating in the continuous flooding treatment was 2.3 and 3.6 times of that in the conventional and wetting irrigation treatments, but Cd content in root coating in the continuous flooding treatment was only 82.6% and 73.8% of that in the conventional and wetting irrigation treatments. Amendments application increased Fe(II) in root coating by 40.1%, 70.2% and 78.0%, but reduced the Cd content in root coating by 35.3%, 42.4% and 38.6% under continuous flooding, conventional irrigation and wetting irrigation, respectively. The lower availability of Cd in soil and the competition for adsorption sites in root coating of rice plant between Cd2+ and Fe2+ etc. reduced form bivalent ions in paddy soil resulted in lower Cd concentrations in brown rice in amended soil treatments.