Morphogenetic and geochemical assessment of wetland soils developed over Abeokuta formation of Ogun State Nigeria

Abstract

Morphogenetic properties and geochemical compositions were analyzed and assessed to improve our understanding of pedogenesis and geochemistry of wetland soils on the Abeokuta formation of Ogun State, Nigeria. Three profiles were dug to a depth of 1.2 m except where the water table is high, and examined for their morphological, physical, chemical, and geochemical compositions using standard laboratory techniques. Gleying (mottles) were present in some of the subsurface horizons, and dark greyish colour dominates the soil matrix. The particle size is dominated by sand fractions and the clay fraction increases with depth. The soil pH was moderately acid to neutral (4.6–6.8) and the organic carbon contents were low to high (4.9–43.1 g/kg). The exchange site was dominated by Ca and Mg, while Fe and Mn contents were higher among the micronutrients. Kaolinite, quartz, and degraded mica were the dominant minerals in the clay fractions. The geochemical results reveal that the order of abundance of major oxides is SiO₂ > Al₂O₃ > Fe₂O₃ > CaO > MgO > Na₂O > TiO₂ ≥ K₂O. Geochemical indices point to a moderate degree of weathering and pedogenesis. Higher contents of SiO₂ and Al₂O₃ and calcium in the surface layers indicate relative enrichment of minerals during weathering and nutrient cycling by vegetation.