Soil properties and mineralogy in relation to land use on a sedimentary toposequence in south-eastern Nigeria

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Abstract
Summary: The mineralogy of the clay fraction (<2 μm) of nine soil samples representing three physiographic positions of a toposequence in Ochon, south-eastern Nigeria, was determined by transmission electron microscopy and X-ray diffraction.Soils in the crest and middle slopes (pedons TE1 and TE2, respectively) of the toposequence, formed over fine-grained sandstone, were coarse-textured, well-drained and acidic and had low effective cation exchange capacity and percentage base saturation. Kaolinite, mica, quartz, goethite and gibbsite were the principal minerals identified in the clay fraction of these soils. Soils in the valley bottom (pedon TE3) formed over arenaceous shale were, on the other hand, fine-textured, poorly drained and weakly acidic with higher cation exchange capacity and percentage base saturation. Their clay fraction mineralogy was similar to that of the well-drained upland soils but additionally included feldspar and smectite/vermiculite mixed layer minerals.Mixed cropping of yam, cassava, maize and other annuals under traditional methods was carried out on the drier, well-drained crest and upper slopes while sole cropping of lowland rice occurred in the poorly drained, more fertile valley-bottom site. The valley-bottom soils show greater potential for improvement in agricultural productivity under good management than the upland soils.