Immobilization of Lead in a Pb‐Contaminated Soil Under Triticale (X Triticosecale wittmack) Cultivation Through Simultaneous Application of Biochar and Silicon

It is often advantageous to employ a combined application of soil amendments to attain enhanced performance in the stabilization of potentially toxic elements; however, there have been no investigations that have studied how Silicon (Si) and biochars together affect the distribution and release kinetics of Pb in calcareous soils where triticale ( X Triticosecale wittmack ) is grown. Thus, the aim of this study was to investigate the interaction between biochars and Si to mitigate the bioavailability of Pb in soil and accumulation in triticale grain. A factorial greenhouse pot trial study was conducted where Si was applied at 0 (K 0 ), 200 (K 1 ), and 400 (K 2 ) mg kg −1 soil supplied as sodium metasilicate and three different biochars (rice husk (R500), sheep manure (S500), and municipal solid waste (M500)) were applied at 3% wt. to a Pb‐contaminated, calcareous, loamy sand soil, and then triticale was grown to maturity. After harvest, the grain yields and Pb concentration were determined, and the soil was sequentially extracted into different chemical fractions, and the soil Pb release kinetics were determined. Among the applied biochars and Si levels, both individually and combined, the S500 + K 2 treatment had the most significant positive impact in reducing soil Pb content in the soluble and exchangeable fraction by 55.8%, lowering the P 1 kinetics parameter by 41.2%, and decreasing the soil Pb mobility factor by 20.0%. This effect is likely attributed to the increased soil pH resulting from the combined use of S500 and K 2 , which promotes Pb precipitation and adsorption. Application of Si and biochar shifted the mobile fraction of soil Pb (soluble and exchangeable) into fractions with reduced (Pb bound to organic materials and iron‐manganese oxides) or negligible (residual) bioavailability. The application of S500 in combination with Si at the K 1 level was the best treatment to increase triticale grain yields (68.1%) and reduce grain‐Pb concentration (52.0%). In contrast, the highest Si level (K 2 ) reduced grain yields, possibly due to suppressed nutrient uptake. In conclusion, the combined application of S500 and K 1 proved to be the most effective stabilizing treatment for achieving optimal triticale grain yields in Pb‐contaminated calcareous soil.