The study investigated the effects of Jatropha curcas (JC) and Vetiveria zizanioides (VZ) on hydrocarbon concentration levels in mine spoils. A 2 × 2 × 3 factorial arrangement of treatments in a completely randomized design with 3 replications was adopted. With compost amendments, JC caused 78.8 and 82.2% and VZ caused 51.1 and 39.7% decline in soil TPH and TOG concentrations, respectively after 16 weeks. Compost amendments significantly reduced TOG and TPH concentrations compared to the other treatments in both JC and VZ (p < 0.0001). However, the effect of species on TOG and TPH concentrations were marginally significant (p = 0.081 and p < 0.006, respectively). Growth in height, collar diameter and number of leaves in JC were significantly higher in the compost amendment compared to the fertilizer and control treatments (p < 0.0001). Number of leaves (p = 0.009) and collar diameter growth (p = 0.010) were significantly lower in contaminated soils compared to non-contaminated soils. Furthermore, only the number of tillers in Vetiver was significantly influenced by the soil amendments (p = 0.003) and the soil hydrocarbon levels (p = 0.048). It is concluded that phytoremediation particularly with JC is an alternate means to reducing soil hydrocarbon concentration levels. However, soils must be amended with compost for effective remediation and rapid, vigorous, early growth of plants.
Keywords: Amendments; collar diameter; compost; contamination; oil and grease; soil.