Remediation of Spent Engine Oil Polluted Soil using Glycine Max (L.) (Soybean) and Vigna Unguiculata (L.) (Cowpea)
Spent engine oil is synthetic oil that contains impurities or loss of major properties thus affecting its unique purpose. In this study, an experiment was carried out at the contaminated site of Federal College of Forestry; Ibadan to investigate the remediation of spent engine oil polluted soil using soybean and cowpea. The treatments are soybean planted on polluted soil (T1), cowpea planted on nonpolluted soil (T2), cowpea planted on polluted soil (T3), soybean planted on nonpolluted soil (T4). The treatments were arranged in a complete randomized design (CRD) and replicated four times. The soil analysis before and after harvesting was carried out. The growth parameters measured for the legumes were plant height (cm), stem girth (cm), number of leaves, and number of branches. The result of this study shows that the overall growth performance of the two legumes reduced significantly (p<0.05) due to the presence of spent engine oil in the soil, which introduced heavy metals above critical level into the soil. At six weeks after planting (6 WAP), the number of leaves and number of branches was significantly reduced in soybean and cowpea polluted soil when compared with the control. The stem girth of soybean (1.37 cm) was significantly reduced (p<0.05) more than cowpea (1.94 cm) in polluted soil while the plant height of cowpea (14.86 cm) was significantly reduced more than soybean (18.59 cm). For both pre-planting and post-planting chemical properties analysis, it was observed that the level of Cd, Cr, Pb, and Ni in the pre-planting analysis reduced significantly in the post-planting chemical properties. This shows that both soybean and cowpea exhibited significant remediating ability. However, the level of Cr, Pb, and Ni in the soil cropped by soybean was higher than cowpea and level of Cr, Cd, Pb in soybean plant was higher than that of cowpea, respectively. It can be concluded that soybean is a good crop legume to remediate spent engine oil polluted soil due to its high remediating ability and is recommended that farmers should take considerable measures of cleaning up their polluted farmland with the use of leguminous crops such as soybean.
