Microbiological Status, Physico-chemistry and Plant Performance in Spent Lubricating Oil (SLO) Polluted Soils Amended with Spiked Organic Fertilizer

Soil contaminations by spent lubricating oil (SLO) have been reported to be threatening as it can negatively impact soil macro/micro-flora, destroy the food chains, disrupt biogeochemical cycling of elements, thus reducing soil fertility/productivity, with attendant economic implications. This study evaluated the changes in microbial population and performance of plant in SLO polluted soils amended with different organic fertilizers. The fertilizers were produced from organic waste materials using aerobic composting technique; pollution was simulated in potted soils; soil toxicity were determined using Zea mays L. as test crop; microbial counts and physicochemical properties of the test soils were determined using standard microbiological and chemical protocols respectively. Apart from significant (P˂0.05) decrease in population of total heterotrophic bacteria (THB) and total fungal counts (TFC) (2.6×108 to 6.1×107 cfu/g and 2.3×105 to 1.7×105 cfu/g respectively), and increase in populations of hydrocarbon utilizing bacteria (HUB) and hydrocarbon utilizing fungi (HUF) (7.3×103 to 4.6×104 cfu/g and 8.0×103 to 1.7×104 cfu/g respectively) following contamination of soil with SLO at pollution level., results also revealed increase (improvements) in counts of all microbial groups at the end of remediation treatments. Mean microbial count in soils amended with different levels of fertilizer treatments (5%, 10%, and 15%) reflected a dose-dependent increase as follows: Ft2 ˃ Ft0 ˃ Ft4 for the 5% (3.7×108 cfu/g), 10% (9.2×107 cfu/g) and 15% (6.9×107 cfu/g) respectively. At 5% application, post remediation pH increased following the order: Ft0 ˃ Ft2 ˃ Ft4 (6.00, 5.34, and 4.90 respectively). The test crop, Zea mays L. recorded 100% and 62.5% germination in amended and unamended soils respectively. Leave length and chlorophyll index of Z. mays L. grown on remediated soils ranged between 35.10±0.40 – 52.85±0.05 (at 5% treatments); 32.60±0.10 – 56.55±0.35 (at 10% treatments); and 35.35±0.15 – 42.45±0.25 (at 15% treatments), compared with 30.30±0.80 – 50.55±0.75 (for PS) and 18.05±0.85 – 25.50±0.70 (for unamended CS). All test crops yielded except those grown on unamended soils. Conclusively, application of organic fertilizers to SLO polluted soils increased population of different groups of soil microbes, leading to increased breakdown of the pollutant and reduced soil toxicity.