Updated classification of Southwestern Nigeria soils

Abstract

Seven pedons from the uplands of the Ife, Ondo and Shagamu areas representing humid parts of southwestern Nigeria were classified in the local classification system of Smyth and Montgomery; Moss; the FAO/UNESCO legend and Soil Taxonomy. The pedons from the Shagamu area derived from sedimentary parent material and belong to the Agege, Iju and Owode series. The pedons from the Bagment Complex area belong to the Iwo, Balogun and Ondo series. In the FAO/UNESCO legend, all pedons belong to either Ferric Acrisols or Orthic Acrisols. All seven pedons also belong to the Ultisols of Soil Taxonomy. These soils are further divided into Oxic Paleustults, Typic Rhodustults and Oxic Haplustults. In these soils when soil pH values are below 5.8 or base saturation values are below 50% by neutral aceatate methods, base saturation by sum of cations are likely to be below 35%. Such relationships will be useful in the identification of Ultisols and Alfisols in the absence of laboratory data for sum of cations. Even though the upland soils of southwestern Nigeria were traditionally considered Alfisols, the present study suggests the probable occurrence of Ultisols in the more humid areas