Spatial Distribution of Major Soil Fertility Indicators in Ussa Local Government Area, Taraba State, Nigeria

Spatial variability of soil fertility indicators influences nutrient availability and the effectiveness of soil management practices. This study assessed the spatial distribution of major soil fertility indicators in Ussa Local Government Area (LGA), Taraba State, Nigeria. A base map of the study area showing sampling points was generated in ArcGIS using georeferenced coordinates to stratified coverage. The coordinates were uploaded into a GPS and used as waypoints for field sampling. A randomized sub-sampling approach, following the Soils4Africa configuration, was adopted to capture site variability. Soil samples were collected at two depths (0 - 25 cm and 25 - 50 cm), composited to obtain representative samples, yielding 64 samples. Soil pH, total nitrogen (TN), available phosphorus (AvP), and exchangeable potassium (K⁺) were determined using standard laboratory procedures. Ordinary kriging interpolation in ArcGIS 10.5 was used to assess spatial variability and generate nutrient maps. The results revealed considerable spatial variability in the distribution of the investigated soil fertility indicators. Soil pH ranged from 5.56 to 7.50, indicating predominantly slightly acidic to neutral conditions, TN was generally low across the study area, while AvP occurred mainly at medium concentrations with localized low-concentration zones and K+ was predominantly high and relatively uniform across the area. Nutrient concentration maps delineated distinct zones of nutrient sufficiency and deficiency, highlighting areas requiring targeted fertility interventions. The study demonstrates the effectiveness of geostatistical techniques for characterizing soil fertility variability and provides spatial information for site-specific nutrient management, fertilizer optimization, and sustainable agricultural planning in Ussa LGA.