Fuzzy classification of soil profiles and horizons from the Lockyer Valley, Queensland, Australia

Abstract This paper examines the application of fuzzy classification and ordination to the characterization of soil units recognized in the alluvial plain of the Lockyer Valley in southeast Queensland, Australia. Soil profile classes and soil stratigraphic units were recognized initially using field criteria. Data from soil profiles and horizons at 133 equally spaced sites on a 3.4 km transect were analysed. The analyses aimed to assess how similar or separate profiles and horizons were regardless of their position along the transect, and to scrutinise field assumptions of a typical alluvial soil landscape sequence. Centroids of fuzzy groups (classes) were generated together with fuzzy group memberships for each profile or horizon. Distribution of fuzzy group membership on the transect and data patterns developed using ordination procedures were found to reflect changes in landscape position, soil profile classes, soil stratigraphic units and soil factors related to internal drainage. Analysis corroborated most soil stratigraphic units and profile classes recognized in the field but some profile classes were shown to be in need of re-examination. The distribution of horizon groups generated by fuzzy classification was generally unrelated to the distribution of profile fuzzy groups. It is suggested that for these soils it would be difficult to create a fixed number of profile classes based on homologous relationships between horizons. Classification of soil by horizons appears to be more meaningful than the classification of profiles but profile fuzzy group distribution along the transect was more mappable and easily interpreted than horizon fuzzy group distribution.