Using Multivariate Geostatistics to Assess Patterns of Spatial Dependence of Apparent Soil Electrical Conductivity and Selected Soil Properties

The apparent soil electrical conductivity (EC(a)) was continuously recorded in three successive dates using electromagnetic induction in horizontal (EC(a)-H) and vertical (EC(a)-V) dipole modes at a 6 ha plot located in Northwestern Spain. One of the EC(a) data sets was used to devise an optimized sampling scheme consisting of 40 points. Soil was sampled at the 0.0–0.3 m depth, in these 40 points, and analyzed for sand, silt, and clay content; gravimetric water content; and electrical conductivity of saturated soil paste. Coefficients of correlation between EC(a) and gravimetric soil water content (0.685 for EC(a)-V and 0.649 for EC(a)-H) were higher than those between EC(a) and clay content (ranging from 0.197 to 0.495, when different EC(a) recording dates were taken into account). Ordinary and universal kriging have been used to assess the patterns of spatial variability of the EC(a) data sets recorded at successive dates and the analyzed soil properties. Ordinary and universal cokriging methods have improved the estimation of gravimetric soil water content using the data of EC(a) as secondary variable with respect to the use of ordinary kriging.