Spatial Dependence and Interpolation of Soil Properties in West Sumatra, Indonesia: II. Co-regionalization and Co-kriging1
- B. B. Trangmar,
- R. S. Yost and
- G. Uehara2
Co-kriging was used to interpolate values of topsoil 0.5 M NaHCO3-extractable P at 234 locations in West Sumatra, Indonesia, by exploiting its spatial covariance with a more densely sampled property, 25% HCl-extractable P. NaHCO3-P and HCl-P had been sampled at 52 and 107 locations, respectively, in a nongeometric pattern across the 106 650 has region. Isotropic semivariograms of NaHCO3-P and HCl-P and their cross semivariogram showed spatial dependence over 6.3, 4.2, and 10.4 km, respectively, at the sampling scale used. The map of co-kriged values for NaHCO3-P showed a similar regional pattern but more local detail than that achieved by kriging from NaHCO3-P samples alone. Co-kriging reduced estimation variances (relative to kriging) by up to 40% in areas where sampling density of NaHCO3-P was lowest. Co-kriging variances exceeded those of kriging by up to 10% in areas where sampling density of NaHCO3-P was high. In such areas, the covariate HCl-P had little effect on the interpolated value but still added a component to the estimation variance. Co-kriging could not be used to interpolate values for extreme locations where there were no NaHCO3-P samples within the radius of the kriging neighborhood. Despite local improvement in estimation precision the full benefits of co-kriging interpolation are not universally obtained from nongeometric variate-covariate sampling patterns.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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