Mitigation of Spent Crankcase Oil-Contaminated Soil Using Organic and Inorganic Fertilizers: Microbial and Enzymatic Responses with Implications for Sustainable Agriculture and Food Production

Abstract

Spent crankcase oil contamination can disturb soil physicochemical conditions, microbial populations, and enzyme activities, thereby reducing soil quality. This study evaluated cow dung (CD), poultry droppings (PD), and NPK fertilizer for mitigating spent crankcase oil-contaminated soil at 1.5, 2.5, and 3.5% contamination levels. Soil pH, total petroleum hydrocarbons (TPH), microbial populations, and catalase, dehydrogenase, acid phosphatase, and alkaline phosphatase activities were determined. Increasing oil contamination increased TPH and reduced soil pH. Fertilizer amendment improved microbial and enzymatic recovery. Poultry droppings showed the strongest overall mitigation response, associated with higher microbial biomass, improved biochemical conditions, and reduced petroleum hydrocarbons. These findings demonstrate the potential of nutrient-rich organic amendments for bioremediation and sustainable agricultural soil management.