Synergistic remediation of oil-contaminated soil using sorghum and oil sludge-derived biochar.

Oil sludge contamination poses a significant threat to agricultural soil health and productivity. While biochar is a promising soil amendment, the synergistic potential of combining oil sludge-derived biochar with plant systems for holistic remediation remains poorly quantified. In a 60-day greenhouse study using a full-factorial design, we investigated the interactive effects of oil sludge (0-0.5% w/w) and biochar produced from the same sludge (0-1% w/w) on soil biochemistry and forage sorghum (Sorghum bicolor) growth, providing the first quantitative evidence of true synergy through combined assessment of soil biochemical recovery, polycyclic aromatic hydrocarbons (PAHs) degradation kinetics, and plant physiological resilience-surpassing previous studies that examined these factors in isolation. Biochar application at 1% (w/w) effectively counteracted oil sludge toxicity, reducing soil salinity by ~ 30% and enhancing microbial respiration and enzyme activities (e.g., dehydrogenase increased by > 60%). Crucially, the presence of sorghum amplified these benefits, creating a strong plant-microbe-biochar synergy that accelerated the degradation of total PAHs by approximately 54%-a rate substantially greater than the sum of their individual effects. In plants, biochar mitigated oxidative stress, reducing lipid peroxidation (MDA) by 73% while boosting the antioxidant system. Consequently, biochar restored sorghum growth under high contamination, increasing shoot and root biomass by 43% and 72%, respectively, and maintained nutrient uptake. Our findings demonstrate that sorghum cultivation combined with oil sludge-derived biochar creates a powerful synergistic system for soil remediation. This circular economy approach not only decontaminates soil by enhancing microbial activity but also fortifies plant health, presenting a sustainable, plant-based strategy for the management of oil-sludge impacted agricultural lands.