Spatial prediction of two soil properties using topographic information

The objective of this study was to determine whether the use of the co-regionalization of the distanceto- river topographic variable with the soil properties topsoil clay and sand can improve their mapping. The interpolation techniques: ordinary kriging, kriging combined with regression (two models) and heterotopic co-kriging were applied to data from 153 observation points. The two models of kriging combined with regression involve: (a) linear regression of the two soil variables with the distance-toriver variable on the 153 observation points followed by kriging and (b) summation of the kriged regression values and kriged regression residuals. For co-kriging 350 additional observations for the distanceto- river-variable were employed. The distance-to-river data were easily obtained from the map of the area which was stored in a Geographical Information System (GIS). The performances of the methods were evaluated and compared using the cross-validation method. The mean error of prediction indicates reasonably small bias of prediction for the two soil variables by almost all the methods. The mean square error showed that heterotopic co-kriging produced better estimates of the soil variables than kriging but there was a clear advantage in using the first model of kriging combined with linear regression technique. The second model of kriging combined with regression does not show any particular advantage over the other methods.