Soil amendment ameliorating health of degraded soils affected by heavy metals and acidification: New insights from highly active silicon

Heavy metals (HMs) contamination and acidification lead to soil degradation, which has negative impacts on soil health and crop growth. However, high-activity silicon (Si) has been received little attention in soil for improving degraded soil health. This study elucidated the mechanism by which highly active silicon improves degraded soils through soil incubation experiments. The results showed that the application of high-activity silicon-based materials effectively supplemented the available silicon in the soil, exceeding the guideline value (95 mg/kg). After application amendment, the soil pH, dissolved organic carbon (DOC), and available nutrients of K, Ca, and Mg significantly increased; simultaneously, the available phosphorus (P) content increased, attributed to P release and soil P transformation. The activities of soil urease and catalase significantly increased, while acid phosphatase activity decreased. The application of high-activity silica-based conditioners effectively reduced the available forms of Pb and Cd. However, in short-term wet - dry cycle and one-year wet - dry cycle, the passivation performance weakened, and the longer the treatment duration, the greater the degree of weakening, indicating that the passivation performance of high-activity silica-based materials for heavy metals decreases in long-term remediation processes, which the mechanism is mainly attributed to available Si loss. Improvements in soil environmental quality and increases in nutrient availability effectively promote rice seedling growth, enhance photosynthetic capacity, and reduce malondialdehyde (MDA) accumulation in rice plants. This work contributes to the future restoration of degraded soil function and health.