KOH-Enhanced Biochar As an Alternative Fertilizer Source for Plant Available Silicon.

Silicon (Si) plays an important role in the disease prevention of plants and has been increasingly recognized as an essential nutrient for crop production. Currently, common Si fertilizers are silicon slags of industrial by-products that often contain excessive heavy metals. In this study, a bio-based Si fertilizer based on pyrolysis of biomass and alkaline pretreatment was developed.  Different Si-rich feedstocks including rice, sugarcane, miscanthus, and switchgrass were pretreated by KOH at varying ratios of reagent and biomass, and pyrolyzed at 550 ^oC. The resulting biochar products were analyzed for total and plant available Si. Results showed that rice straw-derived biochar had the highest plant-available Si content based on sodium acetate extraction. Additional KOH pretreatment of feedstocks before pyrolysis also increased Si availability. SEM-EDX analysis revealed that pyrolysis conversion concentrated phytolith, the available form of Si in plant, and that KOH pretreatment promoted the breakout of dumbbell morphology of phytolith for enhanced Si dissolution. In addition, the incubation of different soils amended with KOH-enhanced Si-rich biochar significantly increased plant available Si. KOH-enhanced Si-rich biochar offers an alternative environment-friendly Si fertilizer source for crop production.