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 environmental problems in oil-rich countries. Bioremediation processes usually exploit the ability of microorganisms to degrade and/or detoxify organic contaminants. A widely used bioremediation strategy is bio-stimulation of the soil’s indigenous microbes by the addition of nutrients, as crude oil contamination tends to result in the rapid depletion of the available pools of major inorganic nutrients such as nitrogen and phosphorus. This study examined the bio-stimulation effect of diammonium phosphate and urea fertilizers on crude oil-contaminated soil 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 results indicated that the activity of laccase for all the treated soils was significantly higher than the untreated group on days 18, 24, and 30, while those of peroxidase and catalase peaked at day 12, with a sharp decline on days 18 to 30 when compared to the untreated soil. However, the activity of lipase continued to increase until the 30th day in all the treated soils, and the increase was higher in contaminated soils treated with DAP and urea. The decreased activities of peroxidase and catalase in the treated soils may be related to a decrease in the microbial load of the soil. Furthermore, the increase in the activities of soil enzymes, especially in the treated soils, suggested that the treatments contributed to enhancing the activities of the enzymes, and hence may help in the bioremediation process through bio-stimulation of the soil enzymes that function in the breakdown of environmental contaminants.