ESTIMATION OF THE SPATIAL-DISTRIBUTION OF SOIL CHEMICALS USING PSEUDO-CROSS-VARIOGRAMS

In using cokriging to study soil spatial variability, a key step is to determine cross-variograms. A recently developed approach was utilized to compute pseudo-cross-variograms, from which cross-variograms can be formulated. The approach does not require a large number of common locations where data are available for all variables used in the cokriging modeling and estimation processes. In this study, with only one-thirteenth of the original data for NO3 and Ca, valid cross-variograms, each with the electrical conductivity (EC), were obtained by using pseudo-cross-variograms. Based on the cross-variograms, cokriging with EC improved the estimation of NO3 and Ca significantly. Cokriging yielded a smaller mean squared error (MSE) and kriging variance, and a higher correlation between estimates and measurements. Using 20 points of NO3 and 130 points of EC, cokriging provided a similar distribution pattern for NO3 as that generated with 100 points of NO3. Cokriging with EC reduced MSE and the mean kriging variance of the estimated Ca up to 78 and 85%, respectively, compared with kriging.