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Estimation of the Spatial Distribution of Soil Chemicals Using Pseudo-Cross-Variograms

U.S. Salinity Lab. USDA-ARS, 4500 Glenwood Dr., Riverside, CA 92501

D. E. Myers

Mathematics Dep.

A. W. Warrick

Dep. of Soil and Water Science, Univ. of Arizona, Tuscon, AZ 85721

* Corresponding author.

ABSTRACT

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.

Received for publication August 2, 1991.

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