Soil characteristics in teak plantations and natural forests in Ashanti region, Ghana

The goal of this study to was compare soils of natural forests converted to teak (Tectona grandis Linn. F) plantations (21.3+/-5.1 years) in the Offinso and Juaso Forest Districts in the Ashanti region, Ghana. Sites selected for this study were in the moist semi-deciduous forest zone and had nearly identical physiographic characteristics. In each of three natural forest stands and three teak plantations, 16 soil pits were examined and soil samples from the 0-20 (major rooting zone) and 20-40 cm depths were analyzed for selected chemical and physical properties. In the 0-20 cm depths bulk density significantly increased (1.17 to 1.30 g cm(-3)), but soil organic matter (OM) content(13 to 11%), total nitrogen (0.3 to 0.2%), available phosphorus (4.2 to 1.2 mg kg(-1)), and exchangeable potassium (0.4 to 0.3 cmol(+)kg(-1)), calcium (17.0 to 12.4 cmol(+)kg(-1)), and magnesium (3.8 to 3.2 cmol(+)kg(-1)) significantly decreased in soils where natural forests were replaced with teak plantations. Similar results also were found for the 20-40 cm soil depths. The higher nutrient contents in soils under the natural forest may have been due to more litter contributions from understorey vegetation observed there. In the teak plantations nutrient leaching losses may have accelerated due to increased mineralization and the inability of teak to use the increase in available nutrient.