PROFILE DISTRIBUTION OF SESQUIOXIDES IN THE INLAND VALLEY SOILS OF CENTRAL CROSS RIVER STATE, NIGERIA.

The morphological properties (colour, structure, texture, consistence, miscellaneous features and horizon boundary conditions) of inland valley soils in central Cross River State were described. The soils were sampled from pedogenic horizons and analyzed for physico-chemical properties. They were specially analyzed for pedogenic forms of iron (Fe) and manganese (Mn), namely, acid (pH 3) oxalate extractible and citrate-bicarbonate-dithionite (CBD) extractable forms The soils were deep, gleyed/mottled acid loams and clays, with low (3%) orgaic matter contents. The contents of CBD extractible Fe (FeD) in the surface horizons of soils range from 6255.00 mg kg-1 to 8131 mg kg-1 with a mean of 7100.0 mg kg-1 while the subsoil horizon values range from 5421.0 mg kg-1 to 8131 mg kg-1 with a mean of 6500 mg kg-1. Amorphous iron (Feox) in the surface soil ranged between 959.0 mg kg-1 and 5838 mg kg-1 with a mean of 4000.00 mg kg-1; and the subsoil horizon values ranged from 1084 mg kg-1 to 5838.0 mg kg-1 with a mean of 3500 mg kg-1. Active iron ratio of the surface horizons was in the range of 0.15 and 0.85 with a mean of 0.55. The extractable manganese oxides for the surface horizons ranged between 83.3 mg kg-1 and 550.0 mg kg-1 with a mean of 250.0 mg kg-1 while the subsoil values ranged from 25.0 mg kg-1 to 3392.7 mg kg-1 with a mean of 570.0 mg kg-1. The surface amorphous manganese oxide values ranged from 41.70 mg kg-1 to 325.0 mg kg-1 with a mean of 261.0 mg kg-1. The subsoil results ranged between 20.8 mg kg-1 and 1583.3 mg kg-1 to give a mean of 378.0 mg kg-1. With these concentrations of manganese and iron oxides in these soils, supplemental phosphorus especially after liming during cultivation is recommended for optimum crop yield. Nigerian Journal of Soil Science Vol.4 2003: 41-49