Effects of silicon fertilizers application and water management on soil bioavailability and cadmium uptake by rice in cadmium contaminated farmland

To investigate the effects of water management and silicon application on cadmium (Cd) uptake by rice plants and the bioavailability of Cd in paddy soil, a pot experiment was conducted. The experiment included different water management practices and silicon fertilizer treatments: conventional water management (CK), alternating wet and dry conditions (IF), and long-term flooding (CF), each combined with silicon fertilizer (CK+Si, IF+Si, and CF+Si). The results showed that, compared to CK, Cd content in roots, stems, leaves, and brown rice under CF+Si treatment decreased by 61.6% (P < 0.05), 82.6% (P < 0.05), and 60.5% (P < 0.05), respectively. Under the same water management conditions, silicon fertilizer application reduced Cd content in roots, stems, and brown rice by an average of 43.1%, 38.7%, and 15.1%, respectively. Compared to conventional water management, alternating wet and dry conditions increased soil available silicon and available Cd, while long-term flooding reduced both. The application of silicon fertilizer increased soil available Si content while reducing soil available Cd, soil pore water Cd, and exchangeable Cd (Exc-Cd). Under the same water management conditions, silicon fertilizer application decreased Exc-Cd and carbonate-bound Cd (Carb-Cd) while increasing residual Cd (Res-Cd). In terms of water management, Cd content in roots, stems, leaves, and brown rice showed a significant positive correlation with soil pore water Cd and Exc-Cd. Moreover, Cd content in all plant parts was significantly positively correlated with soil available Cd, pore water Cd, and Exc-Cd across all treatments. The combination of silicon fertilizer and water management significantly altered soil available Cd, pore water Cd, and Exc-Cd content, thereby affecting Cd uptake by rice plants. In conclusion, long-term flooding combined with silicon fertilizer is a recommended agronomic management strategy for cadmium-contaminated farmland.