USDA soil taxonomy

USDA soil taxonomy
Name	USDA soil taxonomy
Type	Soil classification system
Country	United States
Established	1960s–1970s
Authority	United States Department of Agriculture

USDA soil taxonomy is a hierarchical system for classifying soils used primarily in the United States and internationally by scientists, land managers, and policymakers. It organizes soils into orders, suborders, great groups, subgroups, families, and series to facilitate communication among practitioners in agriculture, ecology, forestry, and engineering. Developed through collaboration among federal agencies, universities, and international partners, the system integrates field observations, laboratory analyses, and mapping practices.

Overview

USDA soil taxonomy provides a standardized framework for describing pedons, pedological profiles, and landscape variability across regions such as the Great Plains (United States), Appalachian Mountains, and Pacific Northwest. It interfaces with initiatives at the United States Department of Agriculture, programs at the Natural Resources Conservation Service, and research at land-grant institutions including Iowa State University, University of California, Davis, and University of Minnesota. The taxonomy supports conservation planning tied to statutes like the Soil and Water Resources Conservation Act and environmental assessments under laws such as the National Environmental Policy Act.

Classification System

The classification follows a six-level hierarchy used by practitioners in agencies like the Soil Science Society of America and by researchers at organizations such as the United States Geological Survey. At the top level, soils are sorted into orders based on diagnostic horizons and processes recognized in international forums including the Food and Agriculture Organization meetings and collaborations with the International Union of Soil Sciences. Further levels—suborders, great groups, subgroups, families, and series—incorporate criteria used by mapping projects from the Natural Resources Conservation Service and applied research at institutions such as Cornell University and Texas A&M University.

Soil Orders and Suborders

There are multiple soil orders that reflect major pedogenic regimes observed across biomes like the Great Basin (United States), Mississippi River Delta, and Sierra Nevada (United States). Examples include orders characterized by accumulation of organic matter found in peatlands studied by scientists at the Brookhaven National Laboratory and orders dominated by carbonate accumulation relevant to rangelands in Nevada. Suborders refine distinctions for climatic, hydrologic, and vegetative controls familiar to ecologists at the Smithsonian Institution and range managers at the Bureau of Land Management.

Diagnostic Horizons and Characteristics

Diagnostic horizons and properties such as mollic, argillic, spodic, and oxic horizons are fundamental to assigning soils to orders and suborders; these features are emphasized in technical guidance from the Natural Resources Conservation Service and in curricula at universities like Michigan State University and Pennsylvania State University. Soil color, structure, texture, and chemical indicators such as pH and base saturation are measured using protocols developed in concert with laboratories at the United States Department of Agriculture and research centers like the Agricultural Research Service. Hydric and gleyed features recognized under wetland delineation guidance intersect with work by the Environmental Protection Agency and conservation projects of the The Nature Conservancy.

Applications and Uses

Practitioners apply the taxonomy in land-use planning, precision agriculture projects led by firms in Silicon Valley, forestry management in regions administered by the United States Forest Service, and infrastructure siting analyzed by engineers working with departments such as the Federal Highway Administration. It underpins soil surveys used by county offices collaborating with state agencies like the California Natural Resources Agency and informs carbon accounting in climate initiatives aligned with entities including the Intergovernmental Panel on Climate Change. Educational programs at institutions such as Colorado State University use the taxonomy to teach mapping, sampling, and interpretation.

History and Development

The taxonomy evolved from early twentieth-century classification efforts by scientists associated with the United States Department of Agriculture and universities such as University of Wisconsin–Madison and Rutgers University. Major revisions were produced through cooperative work involving the International Soil Science Congress and advisory input from professional societies including the American Society of Agronomy. Advances in pedology, mineralogy, and geochemistry from laboratories at the Argonne National Laboratory and field studies across regions like the Great Lakes informed successive editions and updates.

Criticisms and Revisions

Scholars and practitioners from organizations such as Harvard University, Yale University, and international partners at the Commonwealth Scientific and Industrial Research Organisation have critiqued aspects of the taxonomy for complexity, regional bias, and limitations in representing urban soils found in cities like New York City and Los Angeles. Revisions have been driven by technological advances in remote sensing from programs at the National Aeronautics and Space Administration and by modeling work at the National Center for Atmospheric Research. Ongoing dialogues occur within forums hosted by the Soil Science Society of America and international meetings including the World Soil Congress to refine criteria, integrate pedotransfer functions, and enhance applicability to global challenges such as soil degradation addressed by the United Nations Convention to Combat Desertification.

Category:Soil science