EFFECTS OF CRUDE OIL ON SOME BACTERIA AND MINERAL CONSTITUENTS OF RHIZOSPHERE OF DELONIX REGIA HOOK.

ABSTRACT

Crude oil spill is hazardous to soil and subsequently affects food production. Certain plants however tolerate and/or improve the mineral deficiency imposed by crude oil. Also, due to the ability of bacteria to degrade crude oil, plants that enhance the abundance of soil bacteria under pollution have been under investigation. The effects of crude oil on the bacterial count and mineral constituents of soil rhizosphere of Delonixregia were investigated. The effects of D. regia on total bacterial count and mineral constituents were tested. A total of 96 polythene bags were filled, each with 18 kg of soil. Four soil bags each containing a seedling of D. regia and four without seedlingwere polluted with 30 ml of crude oil. This was repeated using 150 ml and 750 ml of crude oilwhile the control was not polluted. The experiment was set up in 3 replicates in a completely randomized design. After one month, the soil bacterial count and mineral composition were analyzed using standard techniques. Bacterial analysis was repeated after the second and third month of pollution. Some vegetative parameters were taken before and after pollution. The results of the 1st and 2nd bacterial counts revealed a significant (P<0.05) increase in soils treated with 750 ml of crude oil but a rdecrease in bacterial count of soil treated with 30 ml and 150 ml crude oil compared with the control. The results of the 3rd count revealed significant (P<0.05) decrease in polluted soils compared to the control. Identified bacteria include Pseudomonas, Bacillus, Proteus and Micrococcus species. Bacterial count was slightly higher in unvegetated soil than in the vegetated one. Polluted soil depicted a significant (P<0.05) increase in cation exchange capacity, carbon and organic matter contents but a decrease in pH, available phosphorus and % nitrogen compared to the control. Carbon and organic matter contents as well as % nitrogen were reduced in vegetated soils compared to the unvegetated soil. There were significant differences in sodium, potassium, calcium, and magnesium among different treatments and between the unvegetated and vegetated soils at different levels of significance. The bacterial count was influenced by crude oil concentration, duration of the pollutant, presence of D. regia and some mineral constituents in the soil.