Development of Soil Taxonomy in the United States of America

Soil Taxonomy was developed primarily for the practical purpose of supporting the National Cooperative Soil Survey Program in the United States. The previous system of classification was limited in its usefulness and could not be applied consistently by a large cadre of soil scientists with diverse levels of skill and experience. The first edition of Soil Taxonomy, published in 1975, was developed under the leadership of Dr. Guy Smith over a period of about 25 years. The magnitude and complexity of the information favored the use of a hierarchical system presented as a key for consistent application. Operational definitions were used to identify taxonomic limits and diagnostic horizons and features, so that each taxon conveyed the same meaning to every user. The application of Soil Taxonomy had several important impacts on the soil survey program in the United States. The emphasis on objective, measurable diagnostic horizons and features to define classes made all competent soil scientists, regardless of experience and rank, equally capable of accurately and consistently classifying soils. The use of quantitative class differentia improved the quantity and quality of the field data collection. The property ranges of soil series and their geographic distribution have generally been narrowed over time, thus, allowing more precise interpretations to be made. 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 coordinates their use among survey areas. After publication in 1975, Soil Taxonomy was further refined through the work of nine international committees and many individuals. This work culminated in the publication of the second edition in 1999 and, most recently, the 9th edition of the Keys to Soil Taxonomy in 2003. Today, two international committees are considering revisions to the moisture and temperature regimes and improvements to the classification of anthropogenic soils.