Contingency and generalization in pedology, as exemplified by texture-contrast soils

Soils and landscapes are subject to historical and spatial contingency, leading to locally unique pedologic features. This can make broad-scale generalizations difficult, impractical, or even impossible. The development of vertical texture-contrast soils with argillic horizons, for example, is potentially subject to all general forms of spatial and historical contingency. A case study in east Texas shows evidence both supporting and refuting five general classes of explanation for the formation of vertical textural contrasts. Multiple causality is likely, and attempts to apply any single explanation to a county-size area (and sometimes to a pedon) are not likely to be successful. The implication is not that pedologists should abandon the search for generalizations, but that the context in which laws and generalizations are developed needs rethinking. Explanatory constructs should be formulated not with the notion that a single explanation is likely to be applicable to most soils, but with the idea that multiple causality and polygenesis are likely, and that location-specific characteristics cannot be ignored. The search is directed not toward a single principle to explain the majority of cases and against which exceptions can be judged, but toward a set of principles that define the possibilities (or probabilities). Two analogies that may be useful in addressing historical and spatial contingency in soils are proposed, based on demographic and synoptic metaphors.