Bio-Stimulation of Soil Enzymes Using Diammonium Phosphate and Urea Fertilizer on Crude Oil Contaminated Sandy-Loam Soil

Pollution caused by crude oil is one of the most prevalent environmentalproblems in oil-rich countries. bioremediation processes usually exploit theability of microorganisms to degrade and/or detoxify organic contaminants. awidely used bioremediation strategy is bio-stimulation of the soil’s indigenousmicrobes by the addition of nutrients, as crude oil contamination tends toresult in the rapid depletion of the available pools of major inorganic nutrientssuch as nitrogen and phosphorus. this study examined the bio-stimulationeffect of diammonium phosphate and urea fertilizers on crude oilcontaminatedsoil enzymes. soils were artificially contaminated with 3000,5000, or 8000 ppm of crude oil and treated with diammonium phosphate(dap) and urea fertilizers. the activities of soil enzymes such as laccase, lipase,catalase, and peroxidase were analyzed every 6th day for 30 days. the resultsindicated that the activity of laccase for all the treated soils was significantlyhigher than the untreated group on days 18, 24, and 30, while those ofperoxidase and catalase peaked at day 12, with a sharp decline on days 18 to30 when compared to the untreated soil. however, the activity of lipasecontinued to increase until the 30th day in all the treated soils, and the increasewas higher in contaminated soils treated with dap and urea. the decreasedactivities of peroxidase and catalase in the treated soils may be related to adecrease in the microbial load of the soil. furthermore, the increase in theactivities of soil enzymes, especially in the treated soils, suggested that thetreatments contributed to enhancing the activities of the enzymes, and hencemay help in the bioremediation process through bio-stimulation of the soilenzymes that function in the breakdown of environmental contaminants.