Spatial structure of soil physicochemical properties and implications for site-specific management in the semi-deciduous forest zone of Ghana

Understanding within-field soil variability is important for improving land management and supporting more efficient input use. In Ghana, fertiliser is often applied at fixed rates despite substantial variation in soil conditions within the same field. This can reduce input-use efficiency and limit productivity. This study assessed the spatial variability of selected soil physicochemical properties within a 169.6-ha farm block in Ghana’s semi-deciduous forest zone. A total of 290 georeferenced topsoil samples (0–20 cm) were collected using a systematic transect-based design. The samples were analysed for pH, organic carbon (OC), total nitrogen (N), available phosphorus (P), effective cation exchange capacity (ECEC), exchangeable bases, bulk density (BD), and particle-size fractions. Descriptive statistics, Spearman rank correlation, principal component analysis (PCA), terrain-based regression, geostatistical interpolation, and exploratory k-means clustering were used to characterise soil variability and its management implications. The soils were generally acidic and low in organic carbon, total nitrogen, and available phosphorus, although substantial variation occurred across the field. The PCA identified three dominant gradients of variability: a texture-soil matrix gradient, an acidity gradient, and a chemical fertility gradient. Terrain-based modelling showed that available P, OC, and ECEC were more responsive to terrain than pH and bulk density. Ordinary kriging of directly measured soil properties revealed clear within-field heterogeneity in pH, available P, OC, ECEC, total N, clay, and bulk density. Exploratory clustering further identified management-relevant zones with contrasting soil conditions. These findings show that the field is not a homogeneous management unit and suggest that spatially differentiated soil management may improve input-use efficiency and support more sustainable land management in Ghana and similar agroecological settings.