Bedrock Geology, Physical and Physico-Chemical Properties of Teak Plantation Soil in Southwest Nigeria

The high rate of demand for this exotic timber product all over the world might have led to the over exploitation which has equally led to the current decline in the soil nutrient. This study therefore examined the differences in the soil physico-chemical properties of Teak plantations under basement and sedimentary rocks in south western Nigeria. 72 soil samples were collected; 36 from each of the two plantations underlying by Sedimentary and Basement complex of Ilaro and Olokemeji respectively. 12 Soil samples each from 3 quadrants each of 30m2 were selected from each age i.e. 1970, 1972 and 1975 within a site respectively across the two sites. Bulked soil samples were collected each from horizon A and B of topsoil and subsoil with depth of 0-15cm and 15-30cm respectively. Also, 18 soil samples 9 from each site were collected from 3 profiles section from their A, B and C-Horizons. All these samples were analysed for their physico-chemical parameters such as Electrical Conductivity (EC), pH, Total Dissoved Solid (TDS) and Temperature. Results of the physico-chemical parameters revealed higher values of EC and TDS in the top soil of the plantation underlain by basement complex rock while that underlain by sedimentary rock showed higher values in the subsoil. This is attributed to higher porosity in the sedimentary rock which encourage leaching of nutrients and minerals to the subsoil while fine grains soil of the residual soil of the basement rocks accommodate nutriens and mineral entrapments on the top soil. On the other hand pH in soil of both bedrocks geology revealed low values. The low values in Olokemeji plantations could be attributed to the weathering of granitic rocks which are acidic while that of Ilaro could be attributed to acid rain from nearby industial and automobile exhaust from Agbara and ewekoro.