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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 <0.1% of sorbed P, DI-washed released ~10%, and untreated released ~63%, indicating strong retention in Fe-modified samples. An incubation experiment mimicking field conditions in high-P coastal plain sandy soil confirmed that Fe-modified biochar reduced cumulative water-extractable P by up to 34% compared to the control, while DI-washed biochar provided moderate retention and controlled release, offering agronomic benefits. These findings demonstrate that Fe modification substantially enhances P immobilization, whereas DI washing offers a cost-effective alternative for balancing environmental protection and agronomic nutrient availability. The novelty of the study lies in systematically comparing Fe-modified and DI-washed biochars derived from the same feedstock across multiple production batches, thereby linking sorption–desorption dynamics with soil incubation performance to simulate real-world conditions. Overall, biochar modification strategies can be tailored to mitigate P losses from high-risk soil and improve water quality in agricultural landscapes.
Popoola et al. (Sat,) studied this question.