Preparation of Sodium Silicon-Modified Maize Stalk Biochar-Based Fertilizer and Its Impacts on Foxtail Millet Growth and Soil Properties

There exist multiple conflicting challenges in dryland agricultural production: excessive chemical fertilizer input contrasts with low utilization efficiency of maize straw resources, and long-term over-fertilization triggers continuous degradation of farmland soil fertility. To explore the soil improvement and growth-promoting potential of silicon-modified biochar-based fertilizers, this study conducted relevant preparation and pot experiments. This study used maize stover as feedstock to investigate the effects of pyrolysis temperature and silica modification on the structural characteristics of biochar. Raw biochar was pyrolyzed at 400–600 °C and subsequently modified with sodium silicate. Biochar-based fertilizers were then produced using modified biochar as the carrier, and their influences on soil physicochemical properties, soil enzyme activities, and foxtail millet growth were analyzed via pot experiments. The results indicate that 500 °C is the optimal pyrolysis temperature for maize straw biochar. After sodium silicate modification, the specific surface area of modified biochar increased by 18.84% relative to unmodified raw biochar, accompanied by a more developed surface pore structure. The application of biochar-based fertilizers significantly reduced soil pH and increased soil carbon stocks and available nutrient content. All biochar-based fertilizer treatments significantly improved foxtail millet growth, among which the BF3 treatment showed the strongest growth-promoting performance. Compared with the sole chemical fertilizer (CF), BF3 increased plant height by 63.72% and total biomass by 54.27%, while stem diameter decreased by 11.41%. In summary, sodium silicate-modified biochar-based fertilizer pyrolyzed at 500 °C can effectively improve soil quality and promote millet growth, with a biochar-to-fertilizer ratio of 1:3 being the optimal formulation for dryland millet cultivation. This study provides a direct basis for the compatibility evaluation of biochar-based fertilizers in dryland foxtail millet cultivation.