LOCAL DISJUNCTIVE KRIGING OF SOIL PROPERTIES WITH CHANGE OF SUPPORT

Disjunctive kriging estimates from a set of measurements the conditional probability that true values of a regionalized variable such as a soil property exceed, or are less than critical thresholds. Estimates can be for sites equal in size to the supports of the samples and, by changing the support of the variogram, for larger blocks. The method also estimates the block averages and their associated variances. The underlying theory and steps in the analysis are described. They are illustrated using a case study from south-east Scotland where the aim is to estimate the likelihood of copper and cobalt deficiency over whole farms or 1 km2 blocks of land using data from individual fields of 5 to 10 ha only. Maps show the conditional probabilities for 1 km2 squares that the available copper in the soil is less than 1 mg kg-1 and that cobalt is less than 0.25 mg kg-1.