ABSTRACT:

This study was conducted to characterize and classify soils along a toposequence at Obio Akpa in Oruk Anam Area of Akwa Ibom State, Nigeria. Five soil profiles sited at the summit, upper slope, middle slope, lower slope and valley bottom positions of the toposequence were described, while twenty disturbed and twenty undisturbed soil samples were obtained and routinely analyzed to determine some physical and chemical properties of the soils. Results showed that the surface horizons were light grey at the summit and middle slope and pinkish white at the valley bottom; whereas the subsoil horizons were generally pink and reddish brown at the summit and valley bottom respectively. Surface horizons were loamy sand except at the valley bottom, where it was sandy loam; whereas subsoil horizons were generally sandy clay loam. Bulk density ranged from 3 3 1.36 g/cm in the surface horizon of valley bottom soil to 1.58 g/cm in the Bt2 horizon of summit soil. pH varied in the order: valley bottom (5.3) > lower slope (5.0) > middle slope/summit (4.9) > upper slope (4.8). Organic carbon ranged from 0.12% at the upper slope to 2.45% at the valley bottom. Exchangeable Ca and K concentrations increased down the slope ranging from 1.11 to 2.46 cmol/kg and 0.41to 0.75 cmol/kg respectively. Mean ECEC and base saturation increased down the slope -1 ranging from 5.12 to 5.77 cmolkg and 66.88to 71.38% respectively. All the soils were classified as Ultisols under the USDA Taxonomy, except the valley bottom soil which was classified as an Inceptisol. Effective erosion control, regular applications of manure, liming and conservation tillage are strategies recommended to help improve the quality and productivity of the soils.