Plinthite: Plinthic soil over the "brick" layer (aquitard)
A plinthic soil contains a significant amount of plinthite. Plinthite (Gr. plinthos, brick) is an iron-rich, humus-poor mixture of clay with quartz and other highly weathered minerals. It commonly occurs as reddish redox concentrations in a layer that has a polygonal (irregular), platy (lenticular), or reticulate (blocky) pattern. Plinthite irreversibly hardens upon exposure to repeated wetting and drying, especially if exposed to heat from the sun. Other morphologically similar iron-rich materials that do not progressively harden upon repeated wetting and drying are not considered plinthite. The horizon in which plinthite occurs commonly has 2.5 percent (by mass) or more citrate dithionite extractable iron in the fine-earth fraction and a ratio between acid oxalate extractable Fe and citrate-dithionite extractable Fe of less than 0.10.
In soil science, the "C" horizon is the soil layer consisting more or less of weathered parent rock or deposited material that is little affected by pedogenesis (soil formation). If an overlying horizon contains a significant amount of clay, over time, the clay may be transported into and along vertical cracks or along channels within macropores creating clay coats or clay flows.
The dark red zone in the lower part of this profile is an example of the aquitard layer below a well developed plinthic B horizon of a coastal plain soil. This layer seasonally perches water facilitating plinthite formation. The horizon exhibits very weak very coarse blocky structure with very thick clay coating on internal seams or cracks. Clay coating is common in the very deep layers (3-4 meters or more below the soil surface) where pedogenesis is thought to be minimal or not present. The red area has a sandy loam to sandy clay loam texture, whereas the gray area has texture of clay loam or clay.
The gray tubes or channels throughout the aquitard layer are thought to be formed by biological activity at a time when the sediments were being deposited. In the current environment, they commonly contain coarse roots within elongated macropores. The macropores may be completed filled with soil material or they be open (areas that once contained live roots, but are currently void of roots due to decomposition), allowing for the transmission of air and water within the channel.
Because of the dark red color and dense characteristics, these layers are referred to by the local soil scientists as the "brick" layer.
For more information about a plinthic horizon, visit;
www.researchgate.net/publication/242649722_Rationale_for_...
or;
www.sciencedirect.com/science/article/pii/S00167061220043...
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-...
Plinthite: Plinthic soil over the "brick" layer (aquitard)
A plinthic soil contains a significant amount of plinthite. Plinthite (Gr. plinthos, brick) is an iron-rich, humus-poor mixture of clay with quartz and other highly weathered minerals. It commonly occurs as reddish redox concentrations in a layer that has a polygonal (irregular), platy (lenticular), or reticulate (blocky) pattern. Plinthite irreversibly hardens upon exposure to repeated wetting and drying, especially if exposed to heat from the sun. Other morphologically similar iron-rich materials that do not progressively harden upon repeated wetting and drying are not considered plinthite. The horizon in which plinthite occurs commonly has 2.5 percent (by mass) or more citrate dithionite extractable iron in the fine-earth fraction and a ratio between acid oxalate extractable Fe and citrate-dithionite extractable Fe of less than 0.10.
In soil science, the "C" horizon is the soil layer consisting more or less of weathered parent rock or deposited material that is little affected by pedogenesis (soil formation). If an overlying horizon contains a significant amount of clay, over time, the clay may be transported into and along vertical cracks or along channels within macropores creating clay coats or clay flows.
The dark red zone in the lower part of this profile is an example of the aquitard layer below a well developed plinthic B horizon of a coastal plain soil. This layer seasonally perches water facilitating plinthite formation. The horizon exhibits very weak very coarse blocky structure with very thick clay coating on internal seams or cracks. Clay coating is common in the very deep layers (3-4 meters or more below the soil surface) where pedogenesis is thought to be minimal or not present. The red area has a sandy loam to sandy clay loam texture, whereas the gray area has texture of clay loam or clay.
The gray tubes or channels throughout the aquitard layer are thought to be formed by biological activity at a time when the sediments were being deposited. In the current environment, they commonly contain coarse roots within elongated macropores. The macropores may be completed filled with soil material or they be open (areas that once contained live roots, but are currently void of roots due to decomposition), allowing for the transmission of air and water within the channel.
Because of the dark red color and dense characteristics, these layers are referred to by the local soil scientists as the "brick" layer.
For more information about a plinthic horizon, visit;
www.researchgate.net/publication/242649722_Rationale_for_...
or;
www.sciencedirect.com/science/article/pii/S00167061220043...
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-...