Geophysical Mapping of Agricultural Soil Variability Using Electromagnetic Induction in Benue River Floodplain, North Central Nigeria

The Benue River floodplain in Benue State, often referred to as the food basket of Nigeria, supports extensive irrigated and rainfed agriculture, yet soil spatial variability within floodplain fields is poorly characterised, leading to suboptimal fertiliser application and variable crop yields. This study employs electromagnetic induction to map the spatial distribution of apparent soil electrical conductivity as a proxy for soil texture, salinity, and organic matter across two 50-hectare agricultural plots in Guma Local Government Area. A Geonics EM38 instrument was operated in both vertical and horizontal dipole modes along parallel transects at 20-metre spacing to provide depth-sensitive conductivity measurements. Apparent conductivity data were georeferenced using GPS coordinates and interpolated using ordinary kriging to produce two spatial conductivity maps for each field. Statistical clustering of the conductivity data identified three soil management zones characterised by distinct combinations of conductivity values at two depths. Soil sampling at 36 points stratified across the management zones confirmed significant differences in clay content, cation exchange capacity, and available phosphorus between zones. The management zone map provides a basis for variable-rate fertiliser application trials to be conducted in subsequent cropping seasons. The study demonstrates that EM induction is a practical and rapid tool for precision agriculture applications in Nigerian floodplain farming systems. Keywords: electromagnetic induction, soil variability, precision agriculture, Benue floodplain, apparent conductivity