PHYSICAL PROPERTIES AND MAIZE PRODUCTION IN A SPENT OIL- CONTAMINATED SOIL BIOREMEDIATED WITH LEGUMES AND ORGANIC NUTRIENTS

Information on the use of plant species and organic nutrients to improve the physical properties of oil-contaminated soil, with a view to making it conducive for crop production, is very important. Three legumes (Gliricidia sepium, Leucenae leucocephala and Calapogonium caeruleam) combined or not with poultry manure were tested for their ability to improve the physical properties of a sandy soil, contaminated with 5 % (w/w) spent lubricating oil, each for two years, and its effects on the growth and yield of maize in south eastern Nigeria. Aggregate stability (MWD), saturated hydraulic conductivity, and macro-to micro-porosity ratio improved with time in all the treatments over the 5% oil contamination (A5) and control. At 12 and 18 months, the use of Gliricidia sepium with 0.5% (w/w) poultry manure (A5+Gl+PM) gave the highest improvement of 58 % and 94 % in MWD, corresponding to 136 % and 187 % improvement in saturated hydraulic conductivity, respectively over the A5. The A5+Gl+PM also enhanced soil aggregate sizes> 0.25 mm by 63.6 % and showed a 3-fold positive modification in soil macro-porosity. Positive relationships, significant at 0.01 level of probability, were observed between crusting hazard (R) and soil organic matter (r = 0.814), micro-porosity (r = 0.686) and saturated hydraulic conductivity (r = 0.787). The A5+Le+PM also increased maize growth and grain yield. Gliricidia sepium and Leucenae leucocephala combined with.0.5% (w/w) poultry manure is recommended for follow-up investigation, as it may offer a viable choice for remediation of oil-contaminated soil