Soil Survey
Helping People Understand Soils
Soil TaxonomyNRCS
National Soil Survey Center
Soil Survey Standards
Soil Survey
Helping People Understand Soils
• Soil Taxonomy (ST) is the basic language of soil classification for your profession.
• You should become proficient in the parts of Soil Taxonomy that apply to the soils in your work area.
Why is this topic important?
Soil Survey
Helping People Understand Soils
Objectives
• You will be able to:– List 3 reasons we use Soil Taxonomy– List the 8 attributes of Soil Taxonomy– Describe the general concept for the categorical levels– Use the 2nd edition of ST and the Keys to Soil Taxonomy
(KST) properly to classify soils
Soil Survey
Helping People Understand Soils
Purpose of Soil Taxonomy
Provides a way to group soils that have similar properties and genesis
• Groupings made at various map scales- Soil maps of large areas use small map scales
(e.g., 1: 7.5 million) and the higher category taxa of order through subgroup
- Soil maps of small areas use large map scales (e.g., 1:12,000) and lower category taxa such as family and series
Soil Survey
Helping People Understand Soils
Purpose of Soil Taxonomy
Facilitates communication among soil scientists• Ustert• Aquiturbel• Loamy, mixed, superactive, frigid Lithic Argixeroll
Names of taxa are based on formative elements• The names of soil orders begin with a formative element
and end in the Latin root sol (e.g., Aridisols)• Underlying taxa also contain the formative element
(e.g., Vertic Natrigypsids)
Soil Survey
Helping People Understand Soils
Purpose of Soil Taxonomy
Transfer of Information and Technology• “A Basic System of Soil Classification for Making and
Interpreting Soil Surveys” (USDA, AH-436)• Estimated soil property data from sampling a few
locations• Estimated productivity (crop yields, tree growth, etc.)• Estimated soil performance (suitability for houses,
need for irrigation, need for lime and fertilizer, etc.)
Soil Survey
Helping People Understand Soils
8 Fundamental Attributes of Soil Taxonomy
(2nd ed. Chapter 2)
1.) Definitions are operational
Soil Survey
Helping People Understand Soils
8 Fundamental Attributes of Soil Taxonomy
2.) Multicategoric System
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Helping People Understand Soils
8 Fundamental Attributes of Soil Taxonomy
3.) Taxa represent real bodies of soil
Soil Survey
Helping People Understand Soils
8 Fundamental Attributes of Soil Taxonomy
4.) Differentia are observable/inferable properties
Soil Survey
Helping People Understand Soils
8 Fundamental Attributes of Soil Taxonomy
5.) Soil Taxonomy is (relatively) easy to modify as new knowledge & experience is gained
Soil Survey
Helping People Understand Soils
8 Fundamental Attributes of Soil Taxonomy
6.) Native & cultivated pedons classified the same
Soil Survey
Helping People Understand Soils
8 Fundamental Attributes of Soil Taxonomy
7.) All soils in the landscape can be accommodated
Soil Survey
Helping People Understand Soils
8 Fundamental Attributes of Soil Taxonomy
8.) All soils known in the world are included
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Helping People Understand Soils
Concepts by Category (Level)
Orders (12)
Differentiated by properties resulting from major soil-forming processes
Soil Survey
Helping People Understand Soils
Concepts by Category (Level)
Suborders (70)
Differentiated by important properties, such as soil climate, exerting major controls on the current set of soil-forming processes
Soil Survey
Helping People Understand Soils
Concepts by Category (Level)
Great Groups (344)
Presence of key horizons, or other properties exerting subordinate controls
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Helping People Understand Soils
Concepts by Category (Level)
Subgroups (2,664)
Represent:
1) Overlapping of processes recognized in other taxa (intergrades)
2) Processes or conditions not recognized in other taxa (extragrades)
3) Others (Typic)
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Helping People Understand Soils
Concepts by Category (Level)
Families (~11,252)
- Groups soils in a subgroup that have similar physical and chemical properties that affect their response to management and manipulation for use
Soil Survey
Helping People Understand Soils
Concepts by Category (Level)
Series (~23,500)
- Properties are many of the same ones used as differentia at higher levels, whether used as the formative elements in the names of taxa
- Used to differentiate natural bodies of soils within a family
- Phases of series are not a category of ST
Soil Survey
Helping People Understand Soils
Using the Keys Correctly
Know what to Classify (Ch. 1, KST) • Top (boundary between soil and air, shallow
water, live plants, or undecomposed plant material)
• Bottom (200 cm, lithic contact, 25 cm into paralithic materials)
• There are rules for buried soils
Soil Survey
Helping People Understand Soils
Using the Keys Correctly
– Definitions of the diagnostic horizons and required characteristics for mineral and organic soils are in Ch. 3 of KST
– You need to be familiar with these for the soils in your area
Soil Survey
Helping People Understand Soils
Using the Keys Correctly– 2nd edition of ST has more in-depth
discussions than KST on the diagnostic horizons and required characteristics
– Realize that each new edition of KST updates and supersedes the older version of the text or keys in ST
Soil Survey
Helping People Understand Soils
Using the Keys Correctly
With a key, you must start at the beginning and systematically work your way down comparing your soil to the criteria• Don’t make a habit of jumping into the
middle
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Helping People Understand Soils
Using the Keys CorrectlyChapter 17 (KST) has the information
needed for family level differentiae• Separate sections for mineral and organic
soils• 9 family classes, but there are different
rules for when they are used• There are varying rules for identifying
control sections• Each is arranged as a key
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Helping People Understand Soils
Using the Keys CorrectlyAppendix
• Gives a brief description of the physical, chemical, and mineralogical laboratory determinations as used in ST – Remember: We use “operational definitions”– Full details are in the Lab Methods Manual
Rounding• Pay attention to decimal points in criteria
and use conventional rules for rounding
Soil Survey
Helping People Understand Soils
Summary– Soil taxonomy helps us organize our
knowledge, communicate about soils, and transfer experience
– Soil taxonomy adheres to 8 fundamental attributes
– It is a 6-category hierarchical system with general concepts for each level
– Definitions of criteria are operational
Soil Survey
Helping People Understand Soils
Summary
– The 2nd edition of Soil Taxonomy (1999) has in-depth discussion of many aspects of the system not present in Keys to Soil Taxonomy but
– Each new edition of the Keys to Soil Taxonomy updates and supersedes the older version of the text or keys in ST