Physico-chemical, morphological, and clay mineralogica properties of soils overlying basement complex rocks in Ogoja, northern cross river state of Nigeria

Three soil profiles located along a toposequence in a sub-humid climatic zone of southeastern Nigeria were examined and described. Fifteen soil samples collected from them were characterized in order to evaluate their agricultural potentials. The soils were moderately weathered, with strong to medium acidity. Effective cation exchange capacity (eCEC) varied from low to medium. Total N, available P, and organic C were low. Pedons 1 and 2, sited at the crest and middle slope respectively, were well-drained, with dark brown to brown surface/sub-soil colors while profile 3 in the valley bottom was poorly drained, with light brownish grey to light grey colors. The soils showed a mixed mineralogical composition consisting of kaolinite (predominant), mica, goethite, and quartz. Smectite occurred in small amounts in pedon 3. Under the U.S. Soil Taxonomy, the soils were classified as Orthic plinthustalf, coarse, loamy, mixed, isohyperthermic (crest and middle slope), and Typic tropaqualf, coarse, loamy, mixed isohyperthermic (valley bottom). Constraints to higher crop productivity identified included high sub-surface quartz gravel concentrations, presence of argillic horizons, low organic matter, total N, and available P contents. The principal pedogenic processes affecting the properties of these soils were ferrugination, leaching, and lessivage.