A new study from the University of Duhok compared compost, sheep manure, chicken manure, aeration, and no treatment for cleaning crude-oil-contaminated calcareous soil in Iraqi Kurdistan. After 60 days, mature compost removed 75.5% of total petroleum hydrocarbons, outperforming sheep manure (67.9%), biostimulation (31%), and intrinsic bioremediation (22.4%). The key difference was nutrient retention. Compost kept the soil's carbon-to-nitrogen ratio in the optimal 15:1 to 30:1 range and lost only 37.6% of its nitrogen, while chicken manure lost 76.5% and ended with a C/N ratio near 60. The authors report a strong negative correlation between final C/N ratio and hydrocarbon removal, meaning nitrogen availability drove the cleanup. For regions like the Kwashe industrial area, where small refineries leak an estimated 15,000 to 20,000 tons of oil into the ground each year, the finding points to mature compost as a practical, low-cost bioremediation amendment. It also suggests that cheap, nitrogen-rich manures may work better as short-term boosts than as long-term soil restoration tools.
