Soil chemical properties and heterotrophic bacterial population in the rhizosphere of oil palm plantations under different ages

Abstract

This study was carried out to determine the soil chemical properties and heterotrophic bacterial population and species that are predominant in the rhizosphere of oil palms (Elaeis guineensis. jack) and to compare the bacteria population in the rhizosphere of matured (10 years and above) fruit bearing palms with those present in young (3 – 6 years) palms that are just bearing fruits for the first few years. Four plantations of different ages were sampled at the Nigerian Institute for Oil Palm Research (NIFOR) main station located in Ovia North Local Government Area of Edo State at soil depth of; 0 – 15 cm, 15 – 30 cm, 30 – 45 cm and 45 – 60 cm. The soil samples obtained were analyzed for their physical, chemical and microbial compositions and the bacteria counts found in the various oil palm plantations were tested for significant differences (p ≤ 0.05) using Duncan multiple range test in a Completely Randomized Design. The soil texture of Field 52 (3 – 6 years) was sandy in both top and sub soil (0 – 60 cm) while the older plantations had sandy-loam and loamy-sand at some depth. The nitrogen, phosphorus and organic carbon content of the soil were also observed to increase with age. The investigation further showed a high presence of bacteria at the top soil (0 – 15 cm and 15 – 30 cm) than in the sub soils (30 – 45 cm and 45 – 60 cm). This was in close relationship with the high presence of carbon and other primary nutrients that were also more at the top soils. On the basis of plant age, the heterotrophic bacteria populations were greater in the older plantations than found in the young (3 - 6 years) plantations. The specific bacteria isolated from the rhizosphere soils were Pseudomonas aeroginosa, Micrococcus cereus, Staphylococcus aureus, and Coryrubacteria spp.