Organic Amendment-Mediated Recovery of Petroleum-Contaminated Agricultural Soils in Edo State, Nigeria
Abstract
Petroleum contamination degrades soil quality and limits the productivity of agricultural land, necessitating sustainable approaches to soil recovery. This study investigated the effectiveness of organic amendments in reducing total petroleum hydrocarbon (TPH) concentrations in petroleum-contaminated agricultural soil in Edo State, Nigeria. Contaminated soil was amended with poultry manure, cassava-peel biochar, or both, while unamended soil served as the control. Treatments were incubated for 42 days, with samples collected at 0, 14, 28 and 42 days to determine residual TPH and selected soil physicochemical properties. Response Surface Methodology was used to evaluate treatment effects and identify the optimum treatment condition. The initial TPH concentration was 4,286.35 ± 96.42 mg/kg. After 42 days, TPH concentrations decreased to 3,721.48 ± 83.91 mg/kg in the control, 2,486.17 ± 58.43 mg/kg following poultry-manure treatment, 2,713.54 ± 61.28 mg/kg following cassava-peel biochar treatment, and 1,864.29 ± 47.26 mg/kg in the combined treatment. Corresponding TPH reductions were 13.18%, 42.00%, 36.69% and 56.51%, respectively. The combined amendment also improved soil pH and nutrient-related properties. The response-surface model was statistically significant (p < 0.001), with R² = 0.946 and adjusted R² = 0.918. Model validation produced a prediction error of 1.00%, indicating satisfactory agreement between predicted and experimental responses. The findings demonstrate that a combined organic amendment treatment can enhance the recovery of petroleum-contaminated agricultural soil and provide a potentially practical approach for improving soil quality.