Influence of Clay Application and Water Management on Ability of Rice to Resist Cadmium Stress

A high percentage of available Cadmium (Cd) in acid rice fields in south China promoted Cd accumulation in rice plant and caused a grain Cd content above the national standard GB 2762-2012 guideline of 0.20 mg/kg. In this study, an in-situ field-scale demonstration was conducted under continuous flooding and conventional and wetting irrigation to establish the optimal remediation mode for reducing the Cd concentration in rice plant grown in polluted soils. The Cd assimilation by plant, pH, and Cd chemical fraction in soils, and the physiological response of plant were observed to illuminate the influences of palygorskite on Cd immobilization and the antioxidant capacity of plant. The results showed that continuous flooding promoted Cd conversion from exchangeable to Fe/Mn oxide bound and residual. The pH in clay-treated soils increased by 0.58–1.34 U under continuous flooding, 0.52–1.39 U under conventional irrigation, and 0.44–1.37 U under wetting irrigation (p < 0.05). The palygorskite application decreased the exchangeable Cd by 8.1–16.2%, 4.7–14.0%, and 1.8–9.1%, respectively (p < 0.05). The concentrations of Cd in brown rice in clay-treated soils were reduced by 28.6–61.9%, 24.2–51.5%, and 25.0–54.5% (p < 0.05). Under continuous flooding, the Cd concentration of brown rice was lower than national standard GB 2762-2012 guideline of 0.20 mg/kg only after 0.5% clay addition. The antioxidant activities in leaves were enhanced after clay addition. Palygorskite application combined with continuous flooding was proposed as a strategy for the remediation of metal-polluted rice fields to realize the safe production of rice.