Local soil classification [soil association/soil slope–soil series], world reference base, and USDA soil taxonomy: roles in soil survey execution

The objective was to do a comparative assessment of the best roles of three classification systems, [the “USDA-Soil Taxonomy”; the “World Reference Base (WRB)”; and the presumably Soil Association/Soil Series Concept of Nigeria] in Soil Survey execution from Soil Mapping through to Soil Survey Report. In this instance the concern of this paper is mostly what is best applicable when mapping legend is being defined during field research and/or field activities for mapping and publication purposes. The soils used are derived from basement complex rocks (Ilero at 08.05N/03.22E) and the coastal sediments (Igbodu at 6.28’13’’N/4.19’30” E) in the sub-humid and humid parts of southwest Nigeria respectively. The soils pattern reflects the topo-sequence and/or litho-sequence concepts with a typical sequence of soils on the crest, shoulder and/or upper slope, middle slope, lower slope, fringe and/or valley bottom positions. At the mapping phase, the WRB nearly corroborates the intrinsic qualities of the Soil Association-Soil Series concept. This comparison is fully developed when the characteristics of the different classification units are compared to the morphological expression as shown in the Soil Association-Soil Series concept. However, it should be noted that the philosophy behind these two systems only slightly overlap as classification systems adaptable for soil mapping purposes [field and post field] at the level of soil management requirements – large scale ; while USDA Soil Taxonomy is best at small scale and for better understanding of soil genesis of the mapping units.