Abstract

We assessed the effects of long-term organic fertilizer application on the culturable resident bacterial and fungal communities of a typical tropical soil of the Niger delta. The total viable bacterial counts ranged from 5.8 × 10⁵ cfu/g to 1.6 ×10⁶ cfu/g, while the fungal density varied from 3.5 × 10⁵ cfu/g to 5.5 × 10⁵ cfu/g. The highest bacterial and fungal counts were recorded during 21 – 52 weeks (S2) of fertilizer application, while the lowest counts were recorded during the 0 – 4 and 104 – 260 weeks of fertilizer application. Several bacteria isolated belonging to six genera including Bacillus, Erwinia, Pseudomonas, Micrococcus, Proteus, and Klebsiellawere observed in this study, while the fungal isolates included members of the genera Aspergillus, Penicillium, Rhizopus and Fusarium. Bacillus, Proteus andAspergillus and were observed to have increased in number within the period of the different treatments, in comparison with Erwinia, Klebsiella, Micrococcus andFusarium genera which decreased in population. We conclude that the organic fertilizer used in the present study was well tolerated by the native soil micro flora since there were no discernable changes in the overall population of the resident soil bacteria and fungi. Besides their value in restoring soil nutrient and structure, incorporation of organic fertilizer could lead to the control of some soil borne bacterial and fungal pathogens.