Soil Taxonomy and Soil Survey

Soil taxonomy was developed primarily for the practical purpose of supporting the National Cooperative Soil Survey (NCSS) Program in the United States. It was adopted nearly 40 years ago by all of the NCSS partners, and is recognized as one of our most important standards. The adoption of the classification system had several important impacts on the soil survey program. The emphasis on observable diagnostic horizons and features for defining classes tended to make all competent soil scientists, regardless of experience and rank, equally capable of accurately and consistently classifying soils. By focusing attention on qualitative class differentiae, the quantity of field data collection has increased and the quality has improved. Property ranges of soil series and their geographic distribution have generally been narrowed over time, allowing us to make more precise interpretations. Soil Taxonomy has benefited the soil correlation process by grouping the nearly 22,000 series currently established in the United States in ways that allow us to efficiently compare and differentiate competing soil series, and coordinate their use among survey areas. One area that has presented difficulty and confusion from the beginning of Soil Taxonomy’s use has been reconciling the difference between map units and taxonomic units. Our soil maps are an attempt to depict our understanding of how natural soil bodies occur within the landscape. The 222 delineated boundaries reflect the constraints of map scale and the conceptual landscape model of the surveyor ( Hudson, 1992 ). We do not attempt to map taxonomic concepts. Rather, we use the taxonomy to classify the soil bodies we have mapped. Concepts such as pedons, polypedons, series, taxadjuncts, ranges in characteristics, map unit components, similar soils, dissimilar soils, and multi-taxa map units take significant effort to be mastered by soil surveyors, and are little understood outside of our profession. We must always remember that the taxonomy is simply a tool to help us organize our knowledge and transfer our experience and technology from place to place in the landscape. Our primary goal is to help individuals and society understand the soil resource by showing them where the soils are and interpreting, in as simple a manner as possible, their suitability and limitations for intended uses.