Influence of iron and manganese forms on pedogenesis in residual soils of the Savanna ecosystem

Soil formation in the Savanna region is a complex process influenced by various factors, with iron (Fe) and manganese (Mn) playing significant roles in pedogenesis. Understanding how these elements affect soil structure, nutrient availability, and weathering intensity is essential for improving soil management and boosting agricultural productivity. This study investigates the influence of Fe-Mn forms on pedogenesis in residual soils within this region. Soil samples were collected from various pedogenic horizons at the study sites and analyzed in the laboratory. The major methods used to assess soil formation and development included Dithionite-Citrate-Bicarbonate extractable iron and manganese (Fed and Mnd), Ammonium Oxalate-extractable iron and manganese (Feox and Mnox), and Sodium Pyrophosphate-extractable iron and manganese (Fep and Mnp). The results indicate varying values of Fed, Feox, Fep, Mnd, Mnox, Mnp, and their active ratios (Feox/Fed and Mnox/Mnd) across the pedons. Higher values obtained using the Fep method suggest that it extracted more Fe and Mn than Fed and Feox (Fep greater than Fed greater than Feox). However, higher concentrations of Mnd and Mnp were observed at the surface horizons in all pedons at Erinmope-Ekiti (Southern Guinea Savanna) compared to Ikole-Ekiti and Oye-Ekiti (Derived Savanna), indicating a greater degree of soil formation and pedogenically older soils. Therefore, higher concentrations of Fe-Mn forms accelerate pedogenesis, while lower concentrations result in slower soil development. The study also suggests that Fe-Mn forms strongly influence soil pH and nutrient availability, further shaping soil formation and development.