Optimization of Crop Straw Biochar Physicochemical Properties and Facilitating Plant Growth and Shaping Rhizospheric Microbial Community

Abstract Sustainable development is imperative amid increasing energy crises and fossil fuel pollution. Crop straw, a common agricultural waste, can be converted into high‐value biochar through thermal carbonization. In this study, corn, cotton, rice, and sorghum straws were pyrolyzed at 300–500 °C, and the resulting biochars were characterized for morphology, elemental composition (C/H/N), pore distribution, and surface chemistry. Thermogravimetry indicated that 450 °C was optimal for retaining maximal residual mass. Higher temperatures increased aromatization and surface smoothness. Sorghum‐derived biochar exhibited the largest specific surface area (442.71 m 2 /g) and the highest N/C ratio (0.031), whereas rice biochar showed the lowest N/C ratio (0.019). All crop straw biochar pore sizes were predominantly 2–10 nm (average size ≈ 4 nm). Germination assays with rapeseed revealed significant enhancement (86.11%–91.67% germination) across all biochar types relative to the control. Microbial cultivation confirmed that biochar fosters a beneficial microenvironment. These findings demonstrate the agronomic potential of straw biochar and provide a reference for optimizing feedstock selection and pyrolysis parameters for plant growth and soil amendment.