Numerical classification of soil profile data using distance metrics

Quantitative grouping of soil layer descriptions into profile classes has not advanced much since the 1960s. Here we tackle the problem from pedological, utilitarian and joint points of view using an application, OSACA, that we have developed for the purpose. The program calculates the taxonomic distances between observed profiles based on layer (horizon) characteristics. Characteristics can be either observed soil properties or layer class memberships. The inter-profile distance is calculated in three ways:1 Pedological distance focuses on the sequence of layers without regard to layer thickness 2 Utilitarian distance weights the metric according to the layer thickness 3 Joint distance is like utilitarian, but with less layer thickness dependence through pre-scaling of depths OSACA either allocates profiles to existing classes, or creates a new classification of the profiles. Since the pedological distance seems to be more useful for creating classes for pedogenetic and geomorphic studies, whereas the utilitarian distance may be more useful for environmental applications, we test the three distances for soil taxonomy application and available water capacity prediction by using as input variables, soil attributes, and classifying them into new set of profiles. The methods are described for a set of soil profiles in New South Wales, Australia, leading to a conclusion on the best distance predictor and the best input variables.