Effects of crude oil spillage on growth and yield of maize (Zea mays L.) in soils of midwestern Nigeria.

The effect of crude oil spillage on growth, productivity and nutrient uptake of maize (Zea mays L.) was assessed in a pot experiment using an Evwreni manifold sample of a petroleum development company, which had a specific gravity of 0.8778. The Suwan 1 variety of maize was used in the experiment. In crude oil polluted soils, germination was delayed and the germination percentage was significantly affected by oil pollution. Growth was poor in polluted soils using parameters such as plant height, stem girth, ear height, leaf area at four weeks after planting, leaf area at maturity and average length of primary roots as growth indicators. Grain yield was significantly reduced at 95% level of probability with yield (when compared with the control) reduced by as much as 98.6%, 96.5% and 58.3% for preplant, five weeks after planting (5 WAP) and seven weeks after planting (7 WAP) treatments, respectively. Leaf analysis of the maize plants grown in soils contaminated with crude oil a week before planting (preplant treatment) revealed mean levels of heavy metals (6.18 ppm Zn2+, 0.62 ppm Cu2+, 26.24 ppm Fe2+, 10.84 ppm Mn2+, 2.96 ppm Pb2+ and 3.88 ppm Co2+) which are higher than the maximum permissible levels (MPL) for maize in tropical soils. Maize plants that were polluted at other time intervals showed no significant (p > 0.05) variation in heavy metal concentrations when compared with the control, and were considered potentially safe for human consumption.