Oil bioremediation in a high and a low phosphorus soil

Phosphorus (P) content may influence bioremediation of soils contaminated with crude oil. A soil testing high in plant available P (Weswood, 194 mg P kg^?1 soil) and one testing low in plant available P (Lufkin, 2 mg P kg^?1 soil) were selected for laboratory experiments on oil biodegradation. Plant available P content was determined using acidified ammonium acetate at pH 4.2 as the soil extractant. Soils were amended with 3, 6, and 9% crude oil by weight and incubated for 120 d at 25°C. Treatments consisted of a factorial arrangement, with soil, N, P, and oil concentration as factors. Addition of P without N generally did not enhance biodegradation. Addition of N without P approximately tripled the quantity of oil degraded. Addition of P and N together did not increase biodegradation of oil more than addition of N alone when oil concentration was 3%. At 6 and 9% oil concentrations, CO₂ evolution increased for both soils by adding P and N together in comparison to adding N alone, and total petroleum hydrocarbon (TPH) bio‐degradation increased by 30% for the Weswood soil by 60 d and at least 25% for the Lufkin soil by 30 d. The quantity of plant‐available P or total P in soil was not very useful in predicting need for supplemental P. Addition of P to soil to enhance oil degradation was only beneficial for oil concentrations above 3% and the positive effect for higher concentrations was transitory.