ABSTRACT:

Tree crop plantations enhance the fertility of soil on which they grow by providing favourable micro-climate, massive organic litter and protection against erosion. Detailed quantitative scientific information on the soils under different tree species plantations are needed to guide management of the plantation to ensure soil conservation. This study investigated the effects of plantation crops on microbiological properties of soils of Uyo and Ibecikpo Asutan Local Government Areas in Akwa Ibom State. Soil samples were collected at 0 -15 cm depth in three plantations – oil palm (OPP), cashew (CAS) and Gmelina (GME). Total heterotrophic 5 bacteria count (THBC) and total heterotrophic fungi count (THFC) were 14.58 x 10 cfug and 8.51 x 10-1-1 5 -1 5 5 cfug during the wet seasonwhile during the dry season they were 17.50 x 10 cfug and 5.92 x 10 cfug respectively. THBC and THFC showed no significant difference (p>0.05) between seasons and plantations. THBC and THFC showed no significant (p>0.05) effect of plantation crop type and there was no significant difference between the seasons. The soils contained Bacillus, Achromobacter, Enterobacter, Clostridium perfringers, Microccocus, Flavobacteria sp, Penicillium, Aspergillus, candida, monilia, Mould sp, and 5-1 5 5-1 Fusarium sp. THBC was found as 17.25 x 10 , 18.63 x 10 , and 12.25 x 10 cfug , while THFC was 6.94 x 10 , 5 5 5 -1 5.58 x 10 , and 9.13 x 10 cfug , respectively for OPP, CAS and GME. It was concluded that the relative abundance and diversity of the microorganisms encountered in the different plantation sites was an indication that the seasonal fluctuations of microbial population are due to moisture content of the soils which affect the total number of microorganisms in the soils. The higher population of microorganisms during rainy season can be attributed to favorable moisture contents of the soils which favors rapid multiplication and growth of microorganisms.