Spatial Variability and Delineation of Soil Physical and Chemical Properties of the Vellar Basin Using Geospatial Techniques

Understanding the spatial variability of soil physical and chemical properties is critical for sustainable land management and precision agriculture. This study assessed the spatial variability of selected soil properties, including pH (1:2.5), electrical conductivity (EC, dS m⁻¹), soil organic carbon (SOC %), available nitrogen (N, kg ha⁻¹), phosphorus (P, kg ha⁻¹), potassium (K, kg ha⁻¹), and texture across 280 sampling sites in the Vellar River Basin, Tamil Nadu, India, at 0–30 cm soil depth. Soil data were analyzed using both classical statistics and geostatistical techniques, including semivariogram modelling and ordinary kriging interpolation. The results indicated that pH, OC, and macronutrients exhibited strong spatial dependence (nugget/sill ratio = 0.05–0.24), whereas EC and texture fractions showed moderate spatial dependence, reflecting the combined influence of intrinsic soil factors and local heterogeneity. Kriging based spatial prediction maps revealed clear patterns of variability, identifying zones with higher and lower nutrient and organic carbon concentrations. The study demonstrates that geostatistical approaches, particularly semivariogram modeling and kriging, provide reliable tools for characterizing soil spatial variability and can support site-specific nutrient management and sustainable soil management practices in river basin.