Influence of Topography on Selected Pedological Properties of Soils Formed on Basement Complex in the Upland Areas of Rainforest Southwest Nigeria

The study investigates the impacts of topography on formation and distribution of soils within the rainforest region of southwestern Nigeria, established their taxonomic classes (USDA & FAO/UNESCO) and recommend appropriate management practices that will promote conservation. Five profile pits established and described at different physiographic positions were considered for this study. Soil samples were collected for physical, chemical and mineralogical analysis and rock samples were also collected for thin sectioning under a petrographic microscope. Fine sand fractions was separated into heavy and light minerals with bromoform. Correlation coefficients and simple regression analysis between the selected soil properties were calculated. The results revealed that the soils are derived from fined-grained biotite gneisses and schist, the clay content increased with increasing depth while sand content decreases. Organic matter and available P content was relatively low with values ranged from (0.2 – 1.35%) and (1.29 – 5.40ppm) respectively. The pH, exchangeable cations and exchangeable acidity values fluctuate across the pedons. The crystalline oxides of Fe and Al were low with no definite pattern of distribution indicating a highly weathered soil. The soils are predominantly ultisols and are placed in ustults suborder (USDA) which was equated as Luvisols (FAO-UNESCO). The correlation between slope position and chemical properties showed that no singular property consistently showed the same level of significance on the entire slope. For effective management of the soils, conservation management practices such as usage of vegetal cover of economic importance should be adopted to assist in preventing rapid soil degradation across the landscape.