The Pedon and the Polypedon

One of the great difficulties in soil classification is that soils rarely exist as discrete individuals with clear boundaries. Instead, they grade to other soils across broad transition belts and their boundaries are determined by definition. Two new concepts, the pedon and the soil individual, have been proposed to help clarify relations between the soil continuum and soil taxonomic classes. Pedons are real, natural soil volumes just large enough to show all the soil horizons present and their relationships. Boundaries of pedons do not depend on reference to any taxonomic scheme. A soil individual (polypedon) is also a real soil body; it is a parcel of contiguous pedons all of which have characteristics lying within the defined limits of a single soil series. Pedons may be considered as building blocks that make up both soil taxonomic classes and soil mapping units. Most pedons are too small to exhibit all the characteristics of a soil individual; for example, usually they do not show shape of the soil nor nature of its boundaries with other soils. Soil individuals (polypedons) are the subject of soil taxonomy; they are the real objects that are classified. They are comparable to individual pine trees, individual fish, and individual men.