1. Field Indicators of Hydric Soils in the United States

2. Version 7.0 and errata and all info on hydric soils can be downloaded from the NTCHS website at

3. Field Indicators
Field indicators are soil morphological features used to identify hydric soils
The features result from soil genesis in the presence of “anaerobic conditions”
They are used for on-site verification

4. Development of Field Indicators
Continuous process
On-going since mid-80’s
Inter-agency
Including universities, private sector, federal, state, and local agencies
Multi-disciplinary
Soil scientists, hydrologists, botonists

5. Hydromorphic Processes
Reduction, translocation, and precipitation of iron and manganese
Accumulation and differential translocation of organic matter
Reduction of sulfur

6. Hydric Soil Indicators
Indicators are not intended to replace or relieve the requirements contained in the Hydric Soil Definition
Indicators are used to identify the hydric soil component of wetlands; however, there are some hydric soils that lack one of the currently listed indicators

7. Biogeochemical Processes Used as Indicators

8. Iron
Many indicators are based on iron reduction, transformation, and differential accumulation.

9. Carbon
Many indicators are based on carbon accumulation and differential decomposition

10. Carbon and Iron
Some indicators are based on carbon accumulation and differential decomposition and iron reduction, translocation, and differential accumulation.

11. Carbon and/or Iron
One indicator is based on carbon accumulation and differential decomposition and/or iron reduction, translocation, and differential accumulation:
S6 Stripped Matrix.

12. Carbon and Iron/Manganese
One indicator is based on carbon accumulation and differential decomposition and iron/manganese reduction, translocation, and differential accumulation:
F16 High Plains Depression

13. Iron/Manganese
One indicator is based on iron/manganese reduction, transformation, and differential accumulation:
F12 Iron-Manganese Masses

14. Sulfur
One indicator is based on sulfur reduction:
A4 Hydrogen Sulfide

15. Algae
One indicator is based on precipitation of calcium carbonate by algae:
F10 Marl

16. Chroma 2 or less Not all indicators require a chroma 2 or less
F8 Redox Depressions
F19 Piedmont Flood Plain Soils
F20 Anomalous Bright Loamy Soils

17. Field Indicators of Hydric Soils in the United States
Refinement of the 1987 indicators
Low chroma colors, mottles
Gleyed colors
“High” organic matter content
Organic streaking
Histosol, histic epipedon
Sulfidic material
Address problem soils and situations

18. Important Concepts and Terminology

19. Proof positive If it meets a Field Indicator it is a hydric soil
If it does not meet a Field Indicator it may still be a hydric soil if it meets the definition of a hydric soil

20. Regional Listed by Land Resource Region Addresses “Problem” soils
Mollisols and vertisols
Sandy soils
Flooded and ponded soils
Red parent material

21. Control Sections or Zones
Layers with:
High value, low chroma or;
Redoximorphic features or;
Organic matter accumulations
At at depth
Of a certain thickness

22. Field Indicators Glossary
An * indicates a definition in the glossary that is different from other references such as Soil Taxonomy, Soil Survey Manual, National Soils Handbook, and Field Book for Describing and Sampling Soils.

23. Important Definition Depleted matrix Gleyed matrix
Organic soil material (muck, mucky peat, and peat)
Mucky mineral

24. Depleted Matrix Value Chroma Redox concentrations ≥5 1 Not required ≥6≤2
4 or 5 2
Required 4

25. Moist Color All color requirements are for moist color.
Features are usually more readily identifiable in moist state; they may be hard to see or missing if the soil is too wet, or too dry.

26. Depleted Matrix
The range in colors for the depleted matrix is value 4 or more and chroma 1 or 2; however, colors of value 4 and chroma 1 or 2 and value 5 and chroma 2 must have redox concentrations.

27. A, E, and Calcic Horizons
A, E, and calcic horizons are excluded from the concept of a depleted matrix unless common or many, distinct or prominent redox concentrations as soft masses or pore linings are present.

28. Depleted Matrices

29. Gleyed Matrix All colors found on the gleyed pages with value ≥ 4.
The range of colors for the gleyed matrix is value 4 or more on either of the two color charts.

30. Gleyed Matrix

31. Reduced Matrix
Soils that have high value and low chroma in situ but color changes when exposed to air
Reduced iron is present
Iron is oxidized upon exposure

32. Organic Soil Material Color of organic soil material may be important
Muck – sapric material
Mucky peat – hemic material
Peat – fibric material

33. Mucky Modified Textures
Mucky modified mineral soil has 0% clay and between 5 and 12% organic carbon, 60% clay and between 12% and 18% organic carbon, or intermediate amounts of clay and intermediate amounts of organic carbon.

34. Three Major Divisions All soils Sandy soils Loamy soils
Use regardless of texture
Mostly organic based indicators
Sandy soils
Loamy soils
Use sandy indicators in sandy layers, and loamy indicators in loamy layers

35. Indicators Format Alpha numeric symbol Short name
Applicable Land Resource Region
Description of the indicator
User notes

36. Example

37. Rules for Field Indicator Use
A chroma of 2 or less means that the chroma cannot be higher than 2
Except for F8, F12, F19, F20, and F21 all mineral Field Indicators must have less then 15 cm (6 in) of a chroma > 2 above the indicator.

38. Soil Surface
The soil surface for Field Indicators A1, A2, A3, S2, and S3 begins at the actual surface.
In LRRs W, X and Y for all other Field Indicators measurements begin at the mineral soil surface.
For all other LRRs all other Field Indicators the measurements should start at the muck or mineral surface.

39. Combining Indicators
It is permissible to combine certain hydric soil indicators if all requirements of the indicators are met except thickness
The most restrictive requirements for thickness of layers in any indicators used must be met

40. Minimum Thickness Requirements for Commonly Combined Indicators
S5 – Sandy Redox 4 in. (10 cm) thick starting within 6 in. (15 cm) of the soil surface
S7 – Dark Surface 4 in. (10 cm) thick starting within 6 in. (15 cm) of the soil surface
F1 – Loamy Mucky Mineral 4 in. (10 cm) thick starting within 6 in. (15 cm) of the soil surface
F3 – Depleted Matrix 6 in. (15 cm) thick starting within 10 in. (25 cm) of the soil surface
F6 – Redox Dark Surface 4 in. (10 cm) thick entirely within the upper 12 in. (30 cm)
F7 – Depleted Dark Surface 4 in. (10 cm) thick entirely within the upper 12 in. (30 cm)

41. Example of a Soil That is Hydric Based on a Combination of Indicators
3-6 inches meets F6 Redox Dark Surface, but thickness requirement is 4 inches
6 to 10 inches meets F3 Depleted Matrix requirements, but thickness requirement is 6 inches
Add the 3-6 inch and 6 to 10 inch layer thicknesses together to get 7 inches which is thicker than the most restrictive requirement of 6 inches

42. Example of a Soil That is Hydric Based on a Combination of Indicators
0 to 3 inches meets F6 Redox Dark Surface, but thickness requirement is 4 inches
3 to 6 inches meets S5 Sandy Redox, but thickness requirement is also 4 inches
Combine the thickness of the 2 layers to get 6 inches

43. Key to Soils that Lack Field Indicators
Dig a hole to 6 in.
Do organic soil materials or mucky modified layers exist?
Does chroma ≤ 2 exist?
Are there any distinct or prominent redox concentrations as soft masses or pore linings?
Is there a hydrogen sulfide odor?
Do stripped zones in a sandy layer exist?
Are you in red parent material, a depression, on a floodplain, or within 200 m of an estuarine marsh and 1 m of mean high water?
If answer is no to all questions, the soil will not meet an indicator.

44. Summary
Field Indicators are soil morphological features used to identify hydric soils
It is important to understand some of the terminology, concepts, and rules in order to use the Field Indicators of Hydric Soils in the United States