Efficacy of untreated and treated biochar variants in environmental phosphorus management

Biochar has emerged as a promising soil amendment for mitigating phosphorus (P) losses from agricultural runoff; however, untreated biochar often exhibits limited P adsorption capacity due to inherent P content and negatively charged surface functional groups. To overcome these limitations, this study synthesized and evaluated three pinewood-derived biochar variants: untreated, Fe-modified, and DI-washed, for their P sorption–desorption behavior and soil performance. Biochar variants were characterized using XRD, SEM, FTIR, and BET analyses, and P sorption was modeled using the Langmuir isotherm. Fe-modified biochar exhibited the highest sorption maxima (S max : 1250–2000 mg kg⁻¹), followed by DI-washed (1181–1339 mg kg⁻¹) and untreated variants (310–390 mg kg⁻¹). Desorption studies revealed stark contrasts: Fe-modified biochar released