Spatial interpolation of soil salinity and sodicity for a saline soil in Southern Alberta

Abstract

Soil salinity and sodicity data are usually represented as contour maps based on spatially interpolated data. This study was conducted to assess two commonly used spatial interpolation methods (moving average and weighted moving average) and three forms of two-dimensional (2D) and three-dimensional (3D) kriging. Soil was sampled from two depths on a 25-m grid at 40 sites in a saline and sodic soil of Southern Alberta. Samples were analyzed for electrical conductivity (ECe) and sodium absorption ratio (SARe) of saturation paste extracts. Methods were compared by cross-validation using the mean absolute difference (MAD) between estimated and observed values. Values of MAD resulting from 3D kriging were inferior to those obtained from moving averages. Moving average methods were very sensitive to the number of neighbors used in the estimation. For kriging methods, however, precision remained stable for more than about 10–12 neighbors. Three-dimensional ordinary kriging was the most precise and robust interpolator with a MAD value of 9.74 dS m−1 for ECe. For SARe the lowest MAD value of 10.55 was obtained with 3D ordinary co-kriging. Data representation produced by 3D kriging allowed easy identification of ECe spatial structure. Key words: Spatial interpolation, kriging, moving average, soil, salinity, sodicity