Nodulation response of Leucaena leucocephala to different levels of crude oil contamination in soil

Abstract

The effects of crude oil pollution in soil on the nodulation of Leucaena leucocephala seedlings were studied for ten weeks at the arboretum of the Department of Forestry and Wildlife, Faculty of Agriculture, University of Benin, Benin City. The experiment was laid out in a completely randomized design with four levels of soil contamination and three replicates, each replicate consisting of three seedlings. Seedlings were grown on topsoil of known physico-chemical properties contaminated with crude oil (specific gravity 0.78) from Ologbo flow station at 0, 5, 10 and 15 ml/kg soil. Results showed that plant height, number of leaves and leaflets, leaf and root lengths, dry weight, nodulation and stem girth of seedlings in the control soil were significantly higher (P = 0.05) than those grown in polluted soils. Nodulation percentages were 48%, 26%, 18% and 8% for 0, 5, 10 and 15 ml/kg treatments respectively. After 10 weeks, soil pH, organic carbon, available phosphorus and residual nitrogen increased, while aluminum decreased and calcium and magnesium  increased. Heavy metal concentrations in soil declined after harvest, but manganese, zinc and copper accumulated in plants, especially
at 15 ml/kg. Plants grown at 5 and 10 ml/kg, with lower metal accumulation, may serve as phytoremediation crops in crude oil-polluted soils.