Reticulately mottled zone with plinthite
A soil in which a reticulately mottled zone with plinthite (darkest red colors) is below a depth of about 2 feet (60 centimeters). Figure 3-24 (p. 170). Soil Survey Manual (issued March 2017), USDA Handbook No. 18.
For more information about the major principles and practices needed for making and using soil surveys and for assembling and using related soils data and a copy of the Soil Survey Manual, visit:
www.nrcs.usda.gov/resources/guides-and-instructions/soil-...
Plinthite consists of reddish, iron-enriched bodies that have a low content of organic matter. In contrast to most other masses, plinthite bodies are coherent enough to be separated readily from the surrounding soil.
Plinthite commonly occurs within and above reticulately mottled horizons (fig. 3-24). It has higher penetration resistance than adjacent brown or gray bodies or than red bodies that do not harden. Soil layers that contain plinthite rarely become dry in their natural setting. Plinthite bodies are commonly about 5 to 20 mm across their smallest dimension. They are firm or very firm when moist, hard or very hard when air dry, and moderately cemented on repetitive wetting and drying, especially when exposed to sunlight (e.g., in road banks and gully walls).
Upon repeated wet-dry cycles, plinthite may irreversibly harden and convert to indurated ironstone. Plinthite bodies commonly occur as discrete nodules or plates. The plates are oriented horizontally. The nodules occur above, and the plates within, the upper part of the reticulately mottled horizon. The plates generally have a uniformly reddish color and have sharp boundaries with the surrounding brown or gray material. The part of the iron-rich body that is not plinthite normally stains the fingers if rubbed while wet, but the plinthite center does not. Plinthite has a harsh, dry feel when rubbed, even if wet. Horizons containing plinthite are more difficult to penetrate with an auger than adjacent horizons at the same water state and with the same clay content. Plinthite generally becomes less cemented after prolonged submergence in water. An air-dried sample can be dispersed by normal procedures for particle-size distribution.
Ironstone is an iron-oxide concentration that is at least weakly cemented. Ironstone nodules commonly occur in layers above plinthite. They are thought to be plinthite that has cemented irreversibly because of repeated wet-dry cycles. Commonly, the center of iron-rich bodies cement upon repeated wetting and drying while the periphery does not.
For more information about describing and sampling soils, visit:
www.nrcs.usda.gov/resources/guides-and-instructions/field...
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-...
Reticulately mottled zone with plinthite
A soil in which a reticulately mottled zone with plinthite (darkest red colors) is below a depth of about 2 feet (60 centimeters). Figure 3-24 (p. 170). Soil Survey Manual (issued March 2017), USDA Handbook No. 18.
For more information about the major principles and practices needed for making and using soil surveys and for assembling and using related soils data and a copy of the Soil Survey Manual, visit:
www.nrcs.usda.gov/resources/guides-and-instructions/soil-...
Plinthite consists of reddish, iron-enriched bodies that have a low content of organic matter. In contrast to most other masses, plinthite bodies are coherent enough to be separated readily from the surrounding soil.
Plinthite commonly occurs within and above reticulately mottled horizons (fig. 3-24). It has higher penetration resistance than adjacent brown or gray bodies or than red bodies that do not harden. Soil layers that contain plinthite rarely become dry in their natural setting. Plinthite bodies are commonly about 5 to 20 mm across their smallest dimension. They are firm or very firm when moist, hard or very hard when air dry, and moderately cemented on repetitive wetting and drying, especially when exposed to sunlight (e.g., in road banks and gully walls).
Upon repeated wet-dry cycles, plinthite may irreversibly harden and convert to indurated ironstone. Plinthite bodies commonly occur as discrete nodules or plates. The plates are oriented horizontally. The nodules occur above, and the plates within, the upper part of the reticulately mottled horizon. The plates generally have a uniformly reddish color and have sharp boundaries with the surrounding brown or gray material. The part of the iron-rich body that is not plinthite normally stains the fingers if rubbed while wet, but the plinthite center does not. Plinthite has a harsh, dry feel when rubbed, even if wet. Horizons containing plinthite are more difficult to penetrate with an auger than adjacent horizons at the same water state and with the same clay content. Plinthite generally becomes less cemented after prolonged submergence in water. An air-dried sample can be dispersed by normal procedures for particle-size distribution.
Ironstone is an iron-oxide concentration that is at least weakly cemented. Ironstone nodules commonly occur in layers above plinthite. They are thought to be plinthite that has cemented irreversibly because of repeated wet-dry cycles. Commonly, the center of iron-rich bodies cement upon repeated wetting and drying while the periphery does not.
For more information about describing and sampling soils, visit:
www.nrcs.usda.gov/resources/guides-and-instructions/field...
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-...