Comparison of Soil Properties Under Teak Plantation and Natural Forest in Ondo State, South West Nigeria

This study compares selected soil properties under Tectona grandis (teak) plantation and adjacent natural forest in Ondo State, located in Nigeria's South West geopolitical zone. Teak plantations have expanded significantly in Ondo State as a commercial forestry investment, but concerns exist about their effects on soil properties relative to the diverse natural forest systems they replace, particularly regarding soil organic matter, nutrient cycling, and biological activity. Using a comparative design, surface (0 to 15 cm) and subsurface (15 to 30 cm) soil samples were collected from three teak plantation blocks of different ages (5-year, 12-year, and 20-year-old stands) and three adjacent natural forest sites in Akure South and Owo local government areas. Soil properties analysed included pH, organic carbon, total nitrogen, available phosphorus, exchangeable cations, cation exchange capacity, bulk density, and microbial biomass carbon. Litter mass and decomposition rates were also measured. Findings revealed that teak plantations had significantly lower soil pH, organic carbon, and cation exchange capacity than natural forest, with differences increasing with plantation age. Litter decomposition under teak was slower due to the high lignin content of teak leaves, reducing nutrient return to soil. Microbial biomass carbon was 29 to 47 percent lower in teak plantations than in natural forest, indicating reduced biological activity. The study recommends mixed-species plantation designs that incorporate indigenous trees with teak to sustain soil biological quality and nutrient cycling in Ondo State commercial forestry systems. Keywords: teak plantation, natural forest, soil properties, Ondo State, microbial biomass.