A Basis for the Classification of Soil

Abstract

Summary Considering the nature of soil and the ends which a classification must serve, principles are stated whereby a soil classification may be devised for application over extensive areas of varied soil composition. Naturally occurring bodies of soil, each with a high degree of homogeneity, are apparent rather than real individuals as their properties overlap to form a continuum. This continuum is multi‐dimensional because soil is characterized by numerous properties. The procedure of devising a classification is one of subdividing the continuum such that class boundaries accommodate, as far as possible, apparent individuals rather than of grouping like apparent individuals together. A classification may be used to locate the position of a profile in the continuum and so define its relationship with other profiles. It may also be used to indicate the soil composition of land by using soil classes on a map to show differences in the soil mantle. The latter procedure may best be regarded as land classification or soil mapping rather than soil classification; a class of land or mapped area seldom contains profiles belonging exclusively to a single class, whereas a soil class never contains profiles of another class. The soil form, a specific arrangement of diagnostic horizons, is introduced as a category above the series to facilitate the identification of soil profiles. Member series of a form are defined according to property variations within the diagnostic horizons of the form. It is suggested that a binomial system of profile nomenclature, using the form and the series, would have much to commend it.

The base status criterion in South African soil classification

“…A condition for selecting differentiae is that they should possess a high information content through covariance with many other properties of interest (Van Wambeke, 1986). Properties readily changed by land-use practices should be avoided (MacVicar, 1969). The magnitude of a property used as differentia should not fluctuate with time and it should be easy to measure and to have its meaning communicated.…”

Recognition of natural soil bodies using textural properties of red freely drained soil profiles from KwaZulu-Natal and Mpumalanga

“…This is also the basis of soil classification (Mac Vicar, 1969;Soil Classification Working Group, 1991, P 1-2). The debate concerning natural soil bodies would seem to centre on creating homogenous soil groupings that generally reflect sharp changes in soil landscapes.…”

Soil Classification With Particular Reference to the Seventh Approximation

“…Attempts to accept such overlap (e.g. Macvicar, 1969) necessitate the abandonment of the hierarchy where the overlap occurs and at all the lower categoric levels included in the overlap. As Bunting (1969) has recently pointed out, however, this rigidity of class limits within a hierarchical system need not be absolute.…”