Enhancement and inhibition of soil petroleum biodegradation through the use of fertilizer nitrogen: An approach to determining optimum levels

Laboratory studies were conducted to evaluate the relationship between soil water content and microbial response to soil nitrogen (N) in petroleum-contaminated soils. Various levels of N were added to a sand, a sandy loam, and a silt loam. Measurements of the extent of biodegradation in each soil (petroleum loss or CO₂ production) indicated that biodegradation was related to soil N expressed as a function of soil water (mg N/kg soil H₂O or mg N/l) better than N expressed as a function of soil dry matter (mg N/kg soil). A loamy sand was treated with four levels of N (0, 250, 500, 750 mg N/kg soil) and incubated at three water contents (5.0, 7.5, and 10.0% on a dry soil weight basis). Soil water potential and O₂ consumption were best related to N expressed on the basis of soil water. It is concluded that expressing N in units of mg N/kg soil H₂O (easily obtained by dividing [mg N/kg dry soil] by [soil moisture content]) can be used to determine fertilization rates for bioremediation processes. On this basis, an optimum N level of approximately 2000 mg N/kg H₂O is tentatively identified for the range of soils and conditions tested.