Characterization and identification of contemporary diagnostic (B) horizons of some soils in Ideato North local government area of Imo state Southeastern Nigeria

Abstract

Most soils in Nigeria have not been characterized and classified based on diagnostic B horizon and identification of diagnostic B horizon is essential in the study of soils. As a result, this study was carried out to characterize and classify these soils with special emphasis on the identification of diagnostic B- horizons. A free survey method was employed to locate the representative profiles. Ten profile pits were dug, studied macromorphologically, georeferenced and sampled based on identified horizons. Results were presented using descriptive statistics. Soil textural classes consisted of sand, loamy sand, sandy loam and sandy clay loam. Soil bulk density was low to high ranging from 1.23g/cm3 to 1.94g/cm3. Soil pH values were extremely acidic (pH 4.4) to slightly acidic (pH 6.1). Exchangeable calcium and magnesium were low to high, ranging from 0.20cmol/kg to 6.20cmol/kg for calcium and from trace to 30.20cmol/kg for magnesium while that of sodium and potassium were very low ranging from 0.005 to 0.052cmol/kg for sodium and from 0.003cmol/kg to 0.016cmol kg-1 for potassium. Cation exchange capacity was low to high ranging from 5.20cmol kg-1 to 51.20cmol kg-1. Exchangeable acidity was trace to low; soil organic matter was low to high ranging from 0.07 g/kg to 5.00 g/kg. Percentage base saturation was low to very high ranging from 2.32% to 82.20%. Effective cation exchange capacity were low (1.457cmol kg-1) to high (35.56cmol kg-1). The available phosphorus is low ranging from 0.004cmol/kg to 0.013cmol/kg. Water dispersible clay values range d from 4.32% - 20.32%. The diagnostic criteria such as clay coatings/cutans, subsurface to surface clay ratio of 1.2, lithologic discontinuity, abrupt textural changes, artefacts, CEC. ECEC, etc. were identified. The two diagnostic B- horizons identified in the study areas were Kandic horizon and Argillic horizon (USDA) which correlate with Argic horizon (FAO/UNESCO (WRB).