Effects of simulated crude oil contamination on the physicochemical properties and bacterial population of rhizosphere of sorghum vulgare pers

Thesis Abstract

This study has been undertaken to investigate the physicochemical properties and the bacterial population of the rhizosphere of Sorghum vulgare. In order to simulate spillage, 0.2, 0.9 and 5.0 % v/w concentrations of crude oil were used to contaminate soil sown with seeds of Sorghum vulgare, while the control had no crude oil contamination. 0ne hundred and twenty days after contamination, the physicochemical properties and bacterial population of the rhizosphere were analyzed using standard techniques. Results showed that 5.0 % v/w of crude oil used in this study caused significant (P<0.05) increase in soil pH, soil temperature, bulk density and total petroleum hydrocarbon while moisture content, sand particle, exchangeable cations and total organic matter were significantly (P< 0.05) reduced when compared with all the other treatments. These physicochemical conditions may suggest low fertility and could have been as a result of 5.0 % v/w concentration of crude oil used to simulate pollution. Soil treated with 0.9 %v/w concentration of crude oil gave highest increase in soil electrical conductivity, silt particle, exchangeable bases such as Na+, Ca2+, Mg2+ and K+, total nitrogen and bacterial population when compared with all the other treatments and significant decrease in total petroleum hydrocarbon when compared with all the crude oil treated samples. This suggests that there was synergistic cooperation between roots of Sorghum vulgare and rhiztospheric bacteria which may have facilitated removal of petroleum hydrocarbon and improved the physicochemical conditions and bacterial population of the soil treated with 0.9 % v/w concentration of crude oil. Hydrocarbon-utilizing bacteria isolated from the crude oil contaminated rhizosphere of Sorghum vulgare were Pseudomonas sp., Bacillus sp., Klebsiella sp. and Streptomyces sp.