Illustrated Guide to Soil Taxonomy

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The “Illustrated Guide to Soil Taxonomy” is presented in four parts, each covering a specific aspect of the USDA’s soil classification system (Soil Taxonomy). It is a PDF document designed for use on a PC, tablet, or smart phone. Each part contains many internal links, and bookmarks are provided for the major items in each part.

Part 1—How to Use This Version of the Keys

This part has five main sections:

  • An overall summary of each part of the guide.
  • A brief discussion of the general steps to follow when classifying a soil.
  • A list of a few things to know about classifying soils. This information needs to be understood and followed when using these keys.
  • A discussion of soil moisture and temperature regimes. This section includes generalized maps of the continental United States that can be used to estimate the correct class based on location in the country.
  • A brief list of important sources of information along with a list of abbreviations and acronyms. The sources can be used to find more indepth definitions or explanations of the terms and concepts presented in any of the parts.


Part 2—Horizon Nomenclature Used for Describing Soil Profiles

This section provides a brief description of the master horizon designations, letter suffixes, number prefixes and suffixes, special symbols, and conventions for using standard horizon nomenclature to describe soil profiles. In addition to background information and basic conventions for using the nomenclature, tables are provided listing the master horizon symbols (table 1) and the subordinate suffix symbols (tables 2A and 2B) and a general description of each.

Part 3—Diagnostic Horizons and Characteristics

This part has two major sections. In the first section, the eight diagnostic surface horizons (“epipedons”) are presented. In the second section, 49 diagnostic horizons and characteristics are presented. A diagnostic horizon constitutes a continuous horizon in the soil profile. Diagnostic characteristics are features found within some horizons (e.g., plinthite or slickensides) but that do not form a continuous layer in the soil profile. This part discusses only those needed to classify a soil to the great group level (for more, see the current edition of the “Keys to Soil Taxonomy”). It also includes information on each of the soil moisture and soil temperature regimes. For each diagnostic horizon or feature presented, the following is provided:

  • Heading. A brief descriptive phrase is given for the item.
  • Concept and background information. A brief narrative describes the concept and basic information of the item.
  • Generalized characteristics. The criteria given in the “Keys to Soil Taxonomy,” 12th edition, are presented in a somewhat simplified and illustrated version. Information has been reworded, and, in a few cases, the critera have been reorganized. Some of the more complex details have been omitted. Generally, a note (italicized text that follows) alerts the reader if there are exceptions to the presented information or if additional information is available in the full version of the keys.
  • Common horizon nomenclature. The master horizon and/or subordinate symbols that are commonly used in soil descriptions to indicate a particular diagnostic horizon or characteristic are identified.
  • Photos (for most of the diagnostic horizons and characteristics)


Part 4—Keys to the Orders, Suborders, and Great Groups

This part is an illustrated and somewhat simplified version of the keys to the orders, suborders, and great groups. Narrative descriptions are provided for each category.


Janis Boettinger
Joe Chiaretti
Craig Ditzler
John Galbraith
Kim Kerschen
Cam Loerch
Paul McDaniel
Shawn McVey
Curtis Monger
Phillip Owens
Mickey Ransom
Kenneth Scheffe
Joey Shaw
Mark Stolt
David Weindorf