Soil quality assessment of an oil-contaminated tropical Alfisol amended with organic wastes using image analysis of pore space

Petroleum products are the most common source of pollution in Nigeria. We studied changes of the pore space of a soil contaminated with petroleum products by image analysis; and also assessed the applicability of fractal scaling of the pore surfaces to estimate soil degradation. The main-plot treatments include control (C), cow dung (CD), poultry manure (PM), and pig waste (PW) each applied at 10 Mg/ha; sub-plot treatments were control (0%), 0.5%, 2.5% and 5% spent oil (SP) applied at 10, 50 and 100 Mg/ha respectively with four replications. The results show that treatment with waste-lubricating oil (spent oil) led to increases in pore space parameters, viz. area, perimeter, count number (hole count), equivalent cylindrical diameter and shape. However, treatment with only organic wastes shows that PM increased these parameters and percent macroporosity over CD and PW. At the 0.5% oil level, the order of this increase was CD > PM > PW while at the 2.5% and 5% oil contamination levels the sequence was PM > PW > CD. This indicates that addition of CD had a greater effect on increasing void space at low oil concentrations, whilst PM was better at high contamination levels. The calculated pore surface dimension ( D s D s) was between 2.30 and 2.80, showing that the pore outlines exhibit fractal behaviour. Oil contaminated soil supplemented with organic wastes showed that the D s followed 0.5%SP > 2.5%SP > 5%SP, indicating increases in irregularity of the soil pores with decrease in oil concentrations. This study demonstrates the applicability of fractal scaling for evaluating pore space of soils amended with cow dung, poultry manure, and pig waste.