Redoximorphic Features (RMFs): Contemporary
Note the accumulation of iron (red color) and areas of reduction (gray color). Redoximorphic features (RMFs) consist of color patterns in a soil that are caused by loss (depletion) or gain (concentration) of pigment compared to the matrix color, formed by oxidation/reduction of iron and/or manganese coupled with their removal, translocation, or accrual.
Redox depletions are localized zones of decreased pigmentation due to a loss of iron or manganese, with or without clay loss. The pigment loss produces a color grayer, lighter, or less red than that of the adjacent matrix (fig. 3-27). The pigment loss reveals the underlying mineral color. Redox depletions have a hue that is yellower, greener, or bluer than that of the adjacent matrix and/or a higher value and/or a lower chroma. Redox depletions include, but are not limited to, what were previously called “low chroma mottles” (chroma < 2), which are key indicators of seasonal or periodic soil saturation. Redox depletions occur in the following forms:
Iron depletions.—Localized zones that have lost iron and/or manganese pigment due to oxidation or reduction reactions under anaerobic conditions but that have a clay content similar to that of the adjacent matrix.
Clay depletions.—Localized zones that have lost iron, manganese, and clay. These features are commonly referred to as silt coatings or skeletans. Silt coatings may form by eluvial processes rather than from oxidation and reduction. Soil features of inferred eluvial origin (for example, albic materials, silt coatings, and skeletans) are not considered or described as a redox depletion.
Reduced matrix.—A soil horizon, layer, or zone that is reduced in respect to iron. It has an in situ matrix chroma < 2 and/or a hue of 5GY, 5G, or 5BG that reflects the presence of Fe(II). The color of a soil sample becomes visibly redder or brighter (oxidizes) when exposed to air. The color change typically occurs within 30 minutes. A 0.2% solution of alpha,alpha-dipyridyl dissolved in 1N ammonium acetate (NH4OAc) pH 7 can verify the presence of Fe+2 in the field (Childs, 1981).
www.flickr.com/photos/jakelley/40158035731/in/album-72157...
Although the red redox concentrations have sharp boundaries, they could not be separated as discrete bodies and did not exhibit stronger rupture resistance nor a brittle manner of failure.
For more information about describing and sampling soils, visit:
www.nrcs.usda.gov/resources/guides-and-instructions/field...
or Chapter 3 of the Soil Survey manual:
www.nrcs.usda.gov/sites/default/files/2022-09/The-Soil-Su...
For additional information on "How to Use the Field Book for Describing and Sampling Soils" (video reference), visit:
www.youtube.com/watch?v=e_hQaXV7MpM
For additional information about soil classification using USDA-NRCS Soil Taxonomy, visit:
www.nrcs.usda.gov/resources/guides-and-instructions/keys-...
or;
www.nrcs.usda.gov/resources/guides-and-instructions/soil-...
For more information about Hydric Soils and their Field Indicators, visit:
www.nrcs.usda.gov/resources/guides-and-instructions/field...
Redoximorphic Features (RMFs): Contemporary
Note the accumulation of iron (red color) and areas of reduction (gray color). Redoximorphic features (RMFs) consist of color patterns in a soil that are caused by loss (depletion) or gain (concentration) of pigment compared to the matrix color, formed by oxidation/reduction of iron and/or manganese coupled with their removal, translocation, or accrual.
Redox depletions are localized zones of decreased pigmentation due to a loss of iron or manganese, with or without clay loss. The pigment loss produces a color grayer, lighter, or less red than that of the adjacent matrix (fig. 3-27). The pigment loss reveals the underlying mineral color. Redox depletions have a hue that is yellower, greener, or bluer than that of the adjacent matrix and/or a higher value and/or a lower chroma. Redox depletions include, but are not limited to, what were previously called “low chroma mottles” (chroma < 2), which are key indicators of seasonal or periodic soil saturation. Redox depletions occur in the following forms:
Iron depletions.—Localized zones that have lost iron and/or manganese pigment due to oxidation or reduction reactions under anaerobic conditions but that have a clay content similar to that of the adjacent matrix.
Clay depletions.—Localized zones that have lost iron, manganese, and clay. These features are commonly referred to as silt coatings or skeletans. Silt coatings may form by eluvial processes rather than from oxidation and reduction. Soil features of inferred eluvial origin (for example, albic materials, silt coatings, and skeletans) are not considered or described as a redox depletion.
Reduced matrix.—A soil horizon, layer, or zone that is reduced in respect to iron. It has an in situ matrix chroma < 2 and/or a hue of 5GY, 5G, or 5BG that reflects the presence of Fe(II). The color of a soil sample becomes visibly redder or brighter (oxidizes) when exposed to air. The color change typically occurs within 30 minutes. A 0.2% solution of alpha,alpha-dipyridyl dissolved in 1N ammonium acetate (NH4OAc) pH 7 can verify the presence of Fe+2 in the field (Childs, 1981).
www.flickr.com/photos/jakelley/40158035731/in/album-72157...
Although the red redox concentrations have sharp boundaries, they could not be separated as discrete bodies and did not exhibit stronger rupture resistance nor a brittle manner of failure.
For more information about describing and sampling soils, visit:
www.nrcs.usda.gov/resources/guides-and-instructions/field...
or Chapter 3 of the Soil Survey manual:
www.nrcs.usda.gov/sites/default/files/2022-09/The-Soil-Su...
For additional information on "How to Use the Field Book for Describing and Sampling Soils" (video reference), visit:
www.youtube.com/watch?v=e_hQaXV7MpM
For additional information about soil classification using USDA-NRCS Soil Taxonomy, visit:
www.nrcs.usda.gov/resources/guides-and-instructions/keys-...
or;
www.nrcs.usda.gov/resources/guides-and-instructions/soil-...
For more information about Hydric Soils and their Field Indicators, visit:
www.nrcs.usda.gov/resources/guides-and-instructions/field...