Characterization and land evaluation of three tropical rainforest soils derived from the coastal plain sands of southeastern Nigeria

Soils on coastal plain sands of southeastern Nigeria have hitherto been referred to as fragile sandy and acidic soils of low base saturation, cation exchange capacity (CEC) and fertility, as evidenced by the extensive land degradation evident in the region. This underscores the need for the characterization of the soils for sustainable use. Three profile pits were therefore dug on the upper, middle and bottom slopes of three towns in the rainforest belt underlain by the coastal plain sands. The results showed that the topsoil of the soils was generally sandy, with relatively more clayey subsoil. The pH ranged from extremely acidic (< 4.4) to slightly acidic (6.1- 6.5). They had low organic matter, low total nitrogen, low effective CEC, low Al saturation and moderate base saturation. The soils of the upper and the middle slopes were classified as Arenic Kandiudult by the United States Department of Agriculture’s (USDA) Soil Taxonomy or as Chromic Acrisols by the World Reference Base (WRB) for Soil Resources classification system, while that of the bottom slope was classified as a TypicDystrudept (USDA Soil Taxonomy) / Dystric Cambisol (WRB classification system). The upper slope had a USDA land capability class of IIes and a United States Bureau for Reclamation (USBR) land capability class of 2v/C. The middle slope and the bottom slope both had USDA and USBR capability class of IVs and 3v/C, respectively. Though moderately to marginally irrigable, the soils can still produce increased and sustainable agricultural yield if the appropriate land use and husbandry practices are adopted. Key words: Coastal plain sands, land use planning, soil characterization, toposequence, tropical rainforest