ABSTRACT

Coal is a combustible black or brownish-black sedimentary rock, mostly carbon with variable amounts of other elements such as hydrogen, sulphur, oxygen and nitrogen. It is an important raw material for generating electricity, liquefied gas, diesel and coal tar (for road construction). Exploration of coal over the past years for economic improvement has led to soil degradation, loss of vegetation, general threat to existence of biota and compromising the atmosphere. The study therefore investigated the quality of soil environment for cultivation following open cast mining executed in Ugiamwen farming community.

The investigation was carried out in three phases of experiments. Experiment1 was on the analysis of physical and chemical properties of collected soil samples. Experiment 2 appraised the growth of Capsicum frutescens on the collected soil samples. While experiment 3, evaluated the growth of C. frutescens on collected soil samples inoculated with bacteria species and elucidation of possible underlying mechanism of action by soil inoculants. Six (6) soil sampling points were located each from coal mining site (CMS) and neighbourhood farmland soil (FS) from where soil samples were randomly collected at 0-15cm depth. The collected soil samples were mixed in clean plastic bucket to obtain composite soil samples and air-dried for routine laboratory analysis. Thirty nine (39) experimental pots were prepared and each experimental pot contained four kilograms (4kg) of collected soil samples. Seeds of C. frutescens were purchased from NIHORT, Ibadan. Viability test was carried out using the floatation technique. Ten (10) seeds were sown in each experimental pot. For laboratory analysis, the level of heavy metals such as cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb) and Arsenic (As) in soil were determined using Atomic Absorption Spectrophotometer (AAS). Soil physical and chemical properties were analysed by standard methods. Germination and growth assessment of C. frutescens seeds were recorded every day after sowing for twelve (12) days. Five weeks after planting (5WAP), C. frutescens plants were harvested for metal content tissue analysis. Physiological parameters like chlorophyll content, peroxidase (POX), catalase (CAT) and superoxide dismutase (SOD) were determined using spectrophotometry. Determinations of metal threshold capacity (MTC) of bacterial isolates were done using Luria – Bertani agar plate technique. Aqueous broth of selected bacteria species were prepared (106/ml) and used for seed priming and soil inoculation.

Results obtained for physical and chemical analysis showed mean pH range for coal mining site(CMS), farmland soil (FS) and control soil (CS) were 4.166 – 4.80, 7.00 – 7.066 and 4.23 – 4.77 respectively. The values for nitrogen were 0.088 – 0.366 %, 1.00 -1.006 % and 0.113 – 0.583 % respectively. The values for organic carbon for were 0.66 -2.073 %, 1. 50 – 1.573 % and 0.683 – 1.050 %. Heavy metal content showed that Pb, Cr, Cu and As were high in CMS and FS soil samples. Cadmium levels were below detection limit (BDL) in all soil samples. Tissue analyses showed that Pb and Cr were consistently higher in leaves, while Cu and As had higher values in root and stem respectively. Mean percent germination of seeds sown in soil samples was lower for CMS. Similar observations were noted for plant height and number of leaves produced. Plants grown in CMS and FS soil samples failed to flower and fruits. While plants grown in CS soil samples flowered 72 days after planting. Plants grown in CMS and FS soil samples gave lower mean values for leaf chlorophyll content. Activities of antioxidant enzymes (POX, CAT, SOD) were higher in CMS and FS than CS grown plants. Seeds inoculation with Bacillus sp. and Pseudomonas sp. before planting in CMS, CS and FS soil samples had higher percent germination. Furthermore, inoculation of CMS, CS and FS soil samples with either Bacillus sp. or Pseudomonas sp. enhanced C. frutescens growth and development. Lower mean values of POX, CAT and SOD activities were obtained for plants grown in inoculated soils. This suggests reduction in metallic stress challenge encountered by plants raised in coal-polluted/contaminated soils. The present study leads to the delivery of promising bacterial isolates that is, Bacillus and Pseudomonas species having maximum ability to produce PGP substance that helps C. frutescens plants survive metal stress conditions inherent in coal mining sites.