Microbial decomposition of fuel oil after compost addition to soil

The effects of adding straw and bark compost at different nitrogen levels to fuel oil contaminated soil was investigated using the CHCl₃ fumigation-extraction method to measure the soil microbial biomass, The addition of these substrates decreased the percentage of extractable fuel oil, increased the percentage of fuel oil mineralized to CO₂, but also increased the fraction of unrecovered fuel oil residues. The different N levels had no significant effects on fuel oil decomposition in the presence of the compost substrates. The addition of the compost substrates increased markedly the content of microbial biomass in contrast to the fuel oil addition which had no effect on the biomass level indicating toxic properties.