Characterisation of Soils Along a Toposequence in Plateau State, North Central Nigeria

This study characterises the morphological, physical, and chemical properties of soils along a representative toposequence in Plateau State, located in Nigeria's North Central geopolitical zone. Toposequential variation in soil properties is a fundamental concept in soil genesis and is central to understanding the distribution of soil types across the Jos Plateau landscape, where undulating terrain, variable parent materials, and diverse vegetation cover create complex soil patterns. Using a descriptive soil survey design, three pedons were excavated along a toposequence from summit to valley bottom in Barkin Ladi local government area. Each profile was described morphologically in the field following FAO guidelines, and soil samples from each horizon were collected and analysed for texture, pH, organic carbon, total nitrogen, available phosphorus, exchangeable cations, and clay mineralogy. Findings revealed systematic changes in soil properties along the slope gradient: summit soils were shallow, sandy loam, and well-drained with lower organic carbon, while valley soils were deeper, clayey, and had higher cation exchange capacity and organic matter content resulting from colluvial accumulation. The summit pedons were classified as Leptosols and the valley pedons as Gleysols under the FAO system. Differential weathering of parent material was evident from clay mineralogy, with kaolinite dominant at the summit and mixed kaolinite-smectite at valley positions. The study recommends soil-specific management strategies adapted to toposequential position for improved agricultural planning in Plateau State. Keywords: toposequence, soil characterisation, Plateau State, pedogenesis, soil classification.