EFFECTS OF CRUDE PETROLEUM OIL ON THE MORPHOLOGY, GROWTH AND HEAVY METAL CONTENT OF MAIZE (Zea mays Linn.).

Abstract

Nigeria being a major exporter of crude oil has experienced several oil spills which affected agricultural lands as well as plant growth and development in the affected areas. Oil makes the soil conditions unsatisfactory for plant growth, due to the reduction in the level of available plant nutrients or rise in the amounts of certain elements such as iron and zinc to toxic levels. A field study was conducted to demonstrate the effect of crude petroleum on the morphology, growth and heavy metal content of maize (Zea mays L.). Four different volumes of crude oil: 00 ml (control), 50 ml, 100 ml and 150 ml were thoroughly mixed with 10 kg of loamy soil (dry weight) in plastic bowls which served as the experimental pots. The soil was well drained, slightly acidic (pH 6.7), high in phosphorus but low in organic carbon. Seedlings of Zea mays of three weeks old were transplanted into polluted and unpolluted soil in perforated experimental pots and watered. Each treatment had five replicates and was in Completely Randomized Design (CRD). Growth parameters (plant height, stem girth, number of leaves and leaf area) were determined. Soil used was analysed for PH, nitrogen, total organic carbon, phosphorus and heavy metals using standard procedures. Plant parts (root, stem and leaves) were examined for the presence of heavy metals due to the pollution by crude oil. All the growth parameters of Zea mays planted in the polluted soil were adversely affected by crude oil pollution. The highest mean height for treatments 50 ml, 100 ml and 150 ml were 33.54 cm, 31.34 cm and 27.44 cm respectively while that of the control was 87.58 cm. It was observed in this research that polluted soil became harden thus hindering the penetration of water and this may be responsible for the poor growth of maize seedlings planted in polluted soil. The pH of the soil increased as the volume of the crude oil increased. Chlorophyll content of the Zea mays leaves reduced with increase in the volume of crude petroleum. It was generally observed that in the Zea mays plant parts examined, root had the highest content of chromium (Cr) with 0.22 ppm (150 ml), nickel (Ni) with 0.46 ppm (150 ml), lead with 0.06 ppm (150 ml) and cadmium (Cd) with 0.02 ppm (150 ml) while the highest copper (Cu) value of 0.28 ppm (150 ml) was recorded in the leaves (150 ml). Also, the concentration of heavy metals were significantly increased (P < 0.05) with the increase in volume of crude oil pollution. There were no significant differences (P > 0.05) in the quantity of cadmium (Cd) and nickel (Ni) in the soil, in all treatment levels using Duncan’s New Multiple Range Test (DMRT). This study has shown that crude oil polluted soil has high significant effect of reducing the growth, yield and increasing the heavy metal concentration in maize, thus this could lead to scarcity of maize for man and animal consumption in areas where there is soil or environmental pollution by crude oil.