A study was conducted in the teaching and research farm of the University of Nigeria, Nsukka to evaluate the applicability
of some organic materials as bio-stimulation agents. Spent engine oil (Sp) was the main plot treatment applied at 0 (control), 10,000, 20,000 and 30,000 mg/Kg (‘Sp’/soil) in a single dose whereas sub-plot treatments were control (No Amendment = NA), Palm Oil Mill Effluent (PE), Palm Bunch Refuse (PR) and Cassava Peels (CP) applied at 12 Mg/ha each, per year. Treatments were arranged in a split-plot format in Randomized Complete Block Design (RCBD) with three replications. Results indicated that microbial population in amended plots followed the order PE > CP > PR > NA. The PE amended soils reached a peak of 11-fold reduction in total hydrocarbon content relative to un-amended equivalents. Bio-remediation efficiency reached 111.3 % (highest) in PE treatment compared to 51.3% (least) in PR treatment. Increased ‘Sp’ contamination inhibited maize germination.