Exogenous silicon facilitates safe crop production in cadmium-contaminated soils: A comprehensive meta-analysis

Soil contamination by cadmium (Cd) is an increasing environmental concern that potentially jeopardizes both crop productivity and human health. Silicon (Si), the Earth's second most abundant element, has shown a significant potential in reducing Cd uptake by crops. However, there is still a lack of quantitative data on the beneficial effects of Si in reducing Cd toxicity, thereby making it more difficult to ensure safe crop production. We conducted a comprehensive meta-analysis of 105 studies to assess the impact of exogenous Si on Cd accumulation in three major cereal crops (wheat, maize, and rice) and elucidate the key factors governing the Si effects. We found that Si supplementation significantly mitigated Cd toxicity in crops, reducing Cd accumulation in maize, rice, and wheat by 37 %, 30 %, and 45 %, respectively. This reduction was most pronounced in all three crop grains (reductions reaching 40-51 %). The four different forms of Si applied all increased crop yield, with nano-silicon resulting in an average yield increase of 19 %, surpassing silicate, Si-based fertilizer, and other silica-based materials. The effects of Si were primarily influenced by application rate and methods, soil pH, Cd concentration, and the effects of foliar and field application. Based on Cd inhibition levels and overall economic benefits, we recommend a Si application rate of ≤ 250 mg/kg, preferably using nano-silicon or silicate. Overall, our study provides valuable globally relevant guidance on Si amendments selection and application thereby ensuring safer and higher crop production in Cd-contaminated soils.