Organic Manure Enhanced Phytoremediation of Crude Oil Contaminated Soils in The Niger Delta: The Potentials of Cowpea (Vigna Unguiculata)

Abstract

In spite of frequent oil pollution, a cost effective, environmentally friendly and sustainable means of remediating polluted soils is yet to be discovered in the Niger Delta. This study, examined the effect of two rates of poultry manure (0 and 20 t/ha) remediating 0 and 5% oil in a 2x2x3 factorial, using cowpea (Vigna unguiculata) as possible phytoremediation plant. Two weeks after contamination, Total Petroleum Hydrocarbon (TPH) increased significantly (P<0.05) from 0.02 mgkg-1 to 125.1 mg/kg-1 and at eight weeks after remediation, TPH reduced from125.1 mgkg-1 to 91.86 mgkg-1 in the unamended contaminated soil and the poultry manure amended contaminated soil decreased significantly (P<0.05) to 73.08 mgkg-1. Soil pH increased significantly (P<0.05) from 5.34 to 5.80, two weeks after contamination and after eight-week of remediation, pH in the unamended contaminated soil increased to 5.85 and the amended contaminated soil increased to 5.97. Organic carbon increased significantly (P<0.05) from 1.15% to 2.32% after two weeks of contamination and eight weeks after remediation, increased to 2.45% in the unamended contaminated soil, and to 2.58% in the amended contaminated soil. Though oil contamination slowed germination, cowpea germination in the unamended contaminated soil recorded 60% while poultry manure amendment increased germination to only 66% indicating cowpea has phytoremediation qualities. However, poultry manure amendment increased cowpea germination energy. The study recorded no significant difference in cowpea germination percentage and growth parameters between the unamended contaminated soil and remediated oil contaminated soil indicating poultry manure application rate need to be increased.