Biostimulation Potentials of Vigna Species (L.) in Hydrocarbon Impacted Soil

Contamination of soil with hydrocarbons is gradually increasing since oil explorations began in Nigeria. With claims of new exploration sites, widespread contamination is possible in many parts of the country in the near future. In view of that, this study aimed to evaluate the growth and phytoremediation potentials of Vigna unguiculata (Cowpea) and Vigna subterrenean (Bambara nut) in hydrocarbon contaminated soil. The study involved a field experiment conducted in a botanical garden under irrigation. The plants were grown on 0%, 5%, and 10% (v/w) used engine oil contaminated soil in plastic bowls. Percentage emergence of V. unguiculata was between 20% and 100%, while that of V. subterrenean was between 50% and 60%. Phytotoxicity studies showed that the oil was toxic to both plants especially at 10% oil concentration and V. unguiculata was more tolerant than V. subterranean. Microbial analyses revealed more bacterial cells as period of treatment increased presumably due to root exudation in the rhizosphere. Eighteen bacterial isolates were identified to belong to Bacillus, Acinetobacter, Klebsiella, Pseudomonas, Enterobacter, Micrococcus, Serratia, Proteus and Staphylococcus genera. All the isolates were found to utilize used engine oil as sole carbon and energy source. The plants and associated bacterial consortium therefore, could be used as important tools in reclaiming soil contaminated with low levels of used engine oil