Spatial Variability of Soil Nutrients in a Rice-Growing Area in Kebbi State, North West Nigeria

This study investigates the spatial variability of selected soil nutrients across a rice-growing irrigation scheme in Kebbi State, located in Nigeria's North West geopolitical zone. Understanding within-field spatial variability of soil nutrients is essential for precision fertiliser management, reducing input waste, and improving rice yields in the Kainji Lake basin irrigation systems where Kebbi State holds a major share of Nigeria's paddy rice production. Using a systematic grid sampling design with a 50 by 50 metre grid spacing, 80 surface soil samples were collected from a 20-hectare rice paddock in Augie local government area. Samples were analysed for pH, organic carbon, total nitrogen, available phosphorus, exchangeable potassium, and exchangeable sodium. Spatial analysis was conducted using geostatistical methods including semi-variogram modelling and ordinary kriging interpolation to produce spatial distribution maps of each nutrient. Findings revealed moderate to strong spatial dependence for all measured nutrients, with available phosphorus and exchangeable potassium showing the greatest variability coefficients. Areas of low pH and potassium deficiency were concentrated in the upper portions of the paddock, likely reflecting irrigation water distribution patterns. Nitrogen was most uniformly distributed, suggesting predominantly atmospheric nitrogen inputs from flooding and decomposition. The study provides a site-specific nutrient management map for the study paddock and recommends adoption of variable-rate fertiliser application informed by spatial analysis for improved efficiency in Kebbi State paddy rice production. Keywords: spatial variability, soil nutrients, rice farming, Kebbi State, geostatistics.