Coastal Plain Soils of Southeastern Nigeria: I. Morphology, Classification, and Genetic Relationships

Abstract

AbstractFourteen pedons developed within the Coastal Plain Sands of southeastern Nigeria were investigated. Laboratory studies included particle size distributions on all pedons plus <0.2‐µm clay, pH, organic C, total N, cation exchange capacity, exchangeable bases, and extractable Al on nine of them. X‐ray analyses of selected clay samples and micromorphologic studies of thin sections of some horizons were also made. Exchangeable bases and base saturation percentages were low for these deeply weathered soils and they had low cation exchange capacities. X‐ray diffraction analyses of clay indicated the predominance of kaolinite. In most of the selected soils isotic and undulic plasmic fabrics characterized the micromorphology, indicating relatively advanced weathering stages. Ferri‐argillans were occasionally observed in the deeper horizons in accord with their higher clay and Fe2O3‐d contents (see part II, this issue). Litho‐, topo‐, climo‐ and possible chronosequences of soils were proposed. Biosequences were not clearly evident. Classification according to the U. S. Soil Taxonomy system indicated that most of the pedons were Ultisols (fine‐loamy or coarse‐loamy) with one Dystropept (coarse‐loamy) and one Tropaquod (sandy). Typic Paleustults (fine‐loamy) represented most soils on the higher (older?) physiographic surfaces. Three Typic Paleudults (fine‐loamy), an Arenic Paleudult (coarse‐loamy), a Typic Paleaquult (coarse‐loamy), and a Typic Tropaquult (fine‐loamy) were found on lower land surfaces nearer the coastline. All pedons are in siliceous, isohyperthermic families. Most of the well‐drained soils were found to be Dystric Nitosols according to the FAO/UNESCO World Soil Map legend. Gleyic Acrisols were proposed for the more poorly‐drained associates of Nitosols. A Gleyic Podzol (with a spodic B) and a Dystric Cambisol (with a cambic horizon) were also represented.