Effect of Different Levels of Crude Oil Contamination on Germination and Chemical Properties of Soil Grown with Maize and Okra

This study was carried out to determine the effect of different levels of crude oil contamination on a sandy loam soil grown with maize (Zea mays L.) and okra (Abelmoschus esculentus L.) in pots. The experiment was arranged in a Completely Randomised Design (CRD) with four replicates. The factors comprised of four levels of crude oil contamination (0%, 0.5%, 2% and 5% v/w) and two test crops (maize and okra). The soil was treated with different levels of crude oil. The control samples were not contaminated. It was observed that maize emerged and grew in 5% crude oil concentration, which was high enough to cause mortality in okra. Crude oil at a level of 5% increased germination time in maize by 24h but germination of okra seeds was totally inhibited. On the contrary, germination of maize seeds occurred at all levels of crude oil pollution although at different rates. The germination time was 5 days in soils with 5% oil concentration. Even though maize germinated and grew in all concentrations of crude oil tested, significant (p<0.05) shoot growth retardation still occurred in both cereal and vegetable consequent on crude oil toxicity. The ability of maize to grow in crude oil level that was harmful to okra make it better suited for growth in oil-contaminated soils and consequently a promising and potential candidate for phytoremediation of such soils than other crops. The results also showed that crude oil contaminations have negative impacts on the soil pH, mineral elements such as nitrogen, phosphorus and potassium contents, organic content, exchangeable bases and acids, and heavy metals. The observable changes in composition of the mineral elements in the soil could be attributed to the toxic nature of the petroleum products. This study has demonstrated that soil contamination with different crude oil levels has a highly significant effect of retarding the germination of some crops, and mineral composition of soils and creating imbalance in the health status of the soil leading to infertility of the soil. Key words: Maize; Okra; Crude Oil; Soil Chemical Properties; Germination; Hydrocarbon