Ageing characteristics and mechanism of straw-based biochar in heavy metal passivation for vegetable facilities soil

Using corn stover as raw material, 0～20 cm surface from vegetable facilities soil was selected as test soil, with four treatments based on MBC application rates（0%, 1%, 2%, and 4%）．Cultivation was conducted at a constant temperature of 25 °C for 180 days．Samples were collected at 1, 30, 60, 90, and 180 days．Heavy metal speciation, soil physicochemical properties, MBC adsorption capacity, and stability were measured．Differences were analyzed by one-way analysis of variance（ANOVA）with SPSS 26.0．Results has indicated that MBC passivation exhibited dose-dependent and time-dependent effect．Treatment with 4% MBC at 60 days achieved cadmium passivation efficiency of 66.67%, which remained at 64.15% after 180 days．Treatment with 4% MBC at 180 days achieved 30.19% lead passivation efficiency, while 4% treatment yielded 28.50% zinc passivation efficiency．Treatment with 4% MBC at 180 days increased CEC and SOM by 53.14% and 35.18% compared to CK, respectively．MBC has passivated heavy metals through synergistic adsorption complexation and chemical precipitation, with strong stability．Straw-based biochar has shown long-term stable passivation effects on heavy metals in vegetable facilities soil while simultaneously increasing soil fertility．