Water Management Strategies Modulate Cadmium Dynamics and Phytotoxicity in Direct-Seeded Rice (Oryza sativa L.) Grown in Contaminated Soil

Abstract

Cadmium (Cd) contamination in paddy soils poses a significant threat to rice productivity and food safety. With water scarcity driving a shift from traditional transplanting to direct-seeded rice (DSR), understanding the interaction between water management and Cd dynamics is crucial. A pot study was conducted to investigate the impact of three water management practices—continuous flooding (CF), alternate wetting and drying (AWD), and maintenance at 70% water holding capacity (70% WHC)—on the growth, yield, and cadmium accumulation in DSR under four levels of soil Cd contamination (0, 1, 3, and 6 mg kg⁻¹). The results demonstrated that water regime significantly influenced Cd phytotoxicity and bioavailability. Continuous flooding was most effective in mitigating the adverse effects of Cd on plant growth, resulting in the highest values for plant height, fresh and dry biomass, and grain yield. Conversely, the aerobic 70% WHC treatment exacerbated Cd stress, leading to severe reductions in all growth and yield parameters. Paradoxically, despite supporting better growth, the CF treatment resulted in the highest Cd accumulation in plant shoots and roots, a phenomenon attributed to the role of iron plaque as a reservoir for Cd under reducing conditions. The AWD treatment presented an intermediate compromise, showing moderate growth reduction and Cd accumulation. Soil analysis confirmed higher residual Cd concentrations under CF, indicating reduced leaching and transformation into less soluble forms. The study elucidates a critical trade-off: while continuous flooding optimizes growth in contaminated soils by suppressing Cd bioavailability, it poses a higher risk of plant Cd uptake. Conversely, water-saving aerobic conditions inflict severe phytotoxicity. These findings underscore that the choice of water management in DSR is a critical determinant for balancing crop productivity, water conservation, and food safety in Cd-affected regions.