Profile Distribution of Forms of Iron and Aluminium Oxides in Wetland Soils Formed Over Recent Alluvium

Abstract

Iron (Fe) and aluminium (Al) forms are important properties for understanding soil-forming processes and serve as helpful markers in identifying the horizon where secondary oxides accumulate. This study evaluated the physical, chemical, and extractable forms of Fe and Al in Eriti wetlands, Ogun State, Nigeria. The wetlands were mapped, and three soil pedons were dug and sampled across genetic horizons for laboratory analyses. The data were subjected to descriptive statistics, correlation analysis, and principal component analysis (PCA). Results showed that the soils were predominantly sandy, with sand (478-698 g kg⁻¹) and clay (192-352 g kg⁻¹) in this range. Soil reaction was strongly to moderately acidic (4.58 to 5.80). The organic carbon (1.22-6.69 g kg⁻¹), total nitrogen (0.06-0.64 g kg⁻¹), and available phosphorus (1.47-24.73 mg kg⁻¹) were generally higher in the surface horizons and decreased with depth. Dithionite-extractable Fe (Fed) and oxalate-extractable Fe (Feo) ranged from 11.33–18.78 mg kg⁻¹ and 5.92–11.19 mg kg⁻¹, respectively. Similar trends were observed for extractable Al fractions. Correlation analysis revealed significant positive relationships among pH, OC, TN, and Fe and Al fractions. The PCA identified four components explaining 96.16% of the total variance, with the first component accounting for 62.70%. The study revealed that the wetland soils are moderately weathered and characterised by appreciable accumulation of Fe and Al oxides, which significantly influence nutrient dynamics and soil development.