How Red Mud-Induced Enhancement of Iron Plaque Formation Reduces Cadmium Accumulation in Rice with Different Radial Oxygen Loss

In situ stabilization of cadmium (Cd) in soil by the addition of Fe-rich amendments (e.g., red mud or RM) has been suggested as an effective and low-cost method. A combined soil-sand pot experiment was conducted to investigate the influence of the addition of RM on iron plaque formation and Cd accumulation in rice plants. Two experiments were conducted: 1. A hydroponic trial with 20 cultivars for screening the rice cultivars with different radial oxygen loss (ROL). 2. A rhizobag trial using the three selected rice cultivars (Zheyou12, Qianyou 1, Chunjiangnuo 2) with different ROL at 2 and 5 mg Cd kg(-1) exposures amended by three rates of RM application (0, 0.5%, 1%). The results indicated that the three rice cultivars with different ROLs on average showed better growth performance, less Cd uptake, and more iron (Fe) plaque on root surface and in the rhizosphere under RM treatments. In addition, the rice cultivar with higher ROL tended to have higher Fe plaque and Cd adsorption on the roots and in their rhizosphere with increasing RM additions. These results suggested that rice plants (especially high ROL-ability cultivars) amended by Fe-rich amendments tend to possess a high ability to increase Fe plaque on root surface and in the rhizosphere, as well as decrease Cd uptake and translocate from root to grain.