Tobacco straw biochar enhances pak choi growth and quality: Lead/cadmium immobilization and soil fertility improvement

To address heavy metal contamination in farmland and promote tobacco straw waste utilization, this pot experiment compared three application rates (1%, 3%, 5%) of tobacco straw biochar on pak choi growth, quality, nutrient and heavy metal uptake, and soil properties and bacterial communities. The results showed that, compared to the control, the addition of biochar increased shoot fresh weight by 15.56–18.97%, and contents of soluble sugar, soluble protein, and vitamin C by up to 109.82%, 62.03%, and 153.36%, respectively. Biochar addition reduced soil bulk density, increased pH, organic matter, alkali-hydrolyzable nitrogen, and available potassium, and reduced Cd and Pb contents in pak choi shoots by 30.76% and 38.98%, respectively. Furthermore, biochar addition significantly increased the Shannon index of the soil bacterial community and the relative abundances of Gemmatimonadota, Myxococcota, and norank_Saprospiraceae. Based on a comprehensive evaluation, the 3% application rate was the most effective.