Evaluation of Phytoremediation Potential of Some Leguminous Crops on Crude Oil Polluted Soil in the Niger Delta Area

Since petroleum hydrocarbon contamination is a major pollution problem in the Niger Delta environment, the relative tolerance of some leguminous species to crude oil contamination and their potential in the phytoremediation of crude oil polluted soil was assessed in a greenhouse. Seeds of cowpea (Vigna unguiculata L. Walp), lablab (Dolichos lablab), mucuna (Mucuna untilis) and Soybean (Glycine max) were planted in soil polluted with 2 and 4% (v/w) crude oil and no pollution, 7 days after oil treatment in a 3x4 factorial arrangement, replicated thrice. Parameters assessed included germination percentage, plant height, leaf area, plant top and root biomass, .nodule number and plant nutrient N uptake. Whereas, at 4% pollution, germination of cowpea, lablab and soybean was depressed by 35, 40 and 60%, respectively, germination in mucuna, though delayed, was depressed by only 10%. Oil treatment significantly reduced (P<0.05) plant height, leaf area and biomass dry matter (DM) for all leguminous species except mucuna. In both oil polluted and unpolluted soils, mucuna formed more nodules and took up more soil N. At 4% pollution, mucuna produced more than 6, 4 and 3 times the biomass produced by soybean, lablab and cowpea, respectively. Therefore, at 4% pollution, if 1 ton dry matter of mucuna is turned-in as green manure, it may add 18kg/ha N to the soil compared to 11kg N for soybean. This study revealed the potentials of the legumes in the phytoremediation of crude oil contaminated soil and tolerance to oil pollution rating them in the order: mucuna>cowpea>lablab>soybean.