International Journal of Petroleum and Gas Engineering ISSN 5675-0715 Vol. 2 (9), pp. 001-008, September, 2015. © International Scholars Journals
Full Length Research Paper
Nitrogen fixing capacity of legumes and their Rhizospheral microflora in diesel oil polluted soil in the tropics
M. A. Ekpo* and A. J. Nkanang
Department of Microbiology, University of Uyo, Uyo, Akwa Ibom State, Nigeria.
Accepted 15 March, 2015
Abstract
The nitrogen fixing capacity of legumes cowpea (Vigna unguiculata) and groundnut (Arachis hypogea) and their micrflora grown in diesel oil simulated utisol was investigated. Result revealed that concentration as low as 1% v/w of diesel oil significantly affected the densities of nitrogen fixing bacteria, bacteriods, actinomycetes and fungi associated with the legumes. The heterotrophic bacteria count in the rhizosphere of cowpea reduced from 2.46 ± 0.72 × 107 to 1.5 ± 0.37 × 107 cfu/g after a growth duration of 12 weeks while it reduced from 3.4 ± 1.25 × 107 to 1.52 ± 0.36 × 107 cfu/g for groundnut in the same growth period. Nitrifying bacteria count reduced from 3.25 ± 1.19 × 104 to 4.5 ± 0.18 × 103 cfu/g for cowpea and 3.43 ± 1.23 × 104 to 2.7 ± 0.21 × 103 cfu/g for groundnut. Bacteriods count also significantly (P > 0.05) reduced from 3.85 ± 2.30 × 105 cfu/g for the control treatment to 1.25 ± 2.23 × 105 cfu/g in 1% level of pollution with no bacteriod formed in both 4 and 8% pollution due to inhibition of nodule formation by the diesel oil. Significant reduction (P > 0.05) was also observed in fungal and actinomycetes counts. Generally, organisms in the rhizosphere of groundnut exhibited more tolerance to diesel oil pollution than those found in the rhizosphere of cowpea. This study revealed that diesel oil adversely affected nitrogen fixing bacteria and bacteriods and consequently the nitrogen fixation in the soil.
Key words: Vigna unguiculata, Arachis hypogea, bacteriods, rhizosphere, actinomycetes.