Spatial dependence and classification of the soil along a transect in northeast Scotland

Abstract This paper analyses a problem common to almost all general-purpose soil surveys, namely how to classify the soil of a region so that each class is both reasonably homogeneous with respect to soil profile and occurs as reasonably large parcels of land. A spatial analysis and a classification have been made of the soil along a transect in northeast Scotland. Semi-variograms of subsoil properties were computed from sample data at 20 m intervals. They showed spatial dependence extending to about 360 m for some properties, in particular, colour and pH, and little or no spatial dependence in others, notably the particle-size fractions and organic-matter content. The form of the first group of semi-variograms suggested that there were several discontinuities on the transect, i.e., boundaries between distinct soil types. These were identified by two segmentation techniques, thereby providing a spatial classification. The results were then compared with an optimal classification of the same data irrespective of position on the ground. There was close agreement between the two classifications in some parts of the transect, particularly where the soil was strongly gleyed. Elsewhere segments contained mixtures of non-spatial classes.