Paralithic contact
Paralithic (lithic-like) contact is a contact between soil and paralithic materials (defined below) where the paralithic materials have no cracks or the spacing of cracks that roots can enter is 10 cm or more.
Paralithic materials are relatively unaltered materials that have an extremely weakly cemented to moderately cemented rupture resistance class. Cementation, bulk density, and the organization are such that roots cannot enter, except in cracks. Paralithic materials have, at their upper boundary, a paralithic contact if they have no cracks or if the spacing of cracks that roots can enter is 10 cm or more. Commonly, these materials are partially weathered bedrock or weakly consolidated bedrock, such as sandstone, siltstone, or shale. Fragments of paralithic materials 2.0 mm or more in diameter are referred to as pararock fragments.
The photo is from the Polkton soil series. Polkton soils are moderately deep, moderately well drained, and very slowly permeable, occurring on uplands of the Triassic Basins in the Southern Piedmont. They formed in residuum weathered from Triassic siltstone, mudstone, shale, and sandstone. Slope ranges from 2 to 25 percent.
TAXONOMIC CLASS: Fine, mixed, active, thermic Oxyaquic Vertic Hapludalfs
Polkton soil series:
soilseries.sc.egov.usda.gov/OSD_Docs/P/POLKTON.html
Blocky structure. In this type of soil structure, the structural units are blocklike or polyhedral. They are bounded by flat or slightly rounded surfaces that are casts of the faces of surrounding peds. Typically, blocky structural units are nearly equidimensional but may grade to prisms or plates.
The structure is described as angular blocky if the faces intersect at relatively sharp angles; as subangular blocky if the faces are a mixture of rounded and plane faces and the corners are mostly rounded.
Blocky structures are common in subsoil but also occur in surface soils that have a high clay content. The strongest blocky structure is formed as a result of swelling and shrinking of the clay minerals which produce cracks. Sometimes the surface of dried-up sloughs and ponds shows characteristic cracking and peeling due to clays.
Clayey soils have 35 (more than 30 percent in Vertisols) to less than 60 percent (by weight) clay in the particle-size control section.
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:
Paralithic contact
Paralithic (lithic-like) contact is a contact between soil and paralithic materials (defined below) where the paralithic materials have no cracks or the spacing of cracks that roots can enter is 10 cm or more.
Paralithic materials are relatively unaltered materials that have an extremely weakly cemented to moderately cemented rupture resistance class. Cementation, bulk density, and the organization are such that roots cannot enter, except in cracks. Paralithic materials have, at their upper boundary, a paralithic contact if they have no cracks or if the spacing of cracks that roots can enter is 10 cm or more. Commonly, these materials are partially weathered bedrock or weakly consolidated bedrock, such as sandstone, siltstone, or shale. Fragments of paralithic materials 2.0 mm or more in diameter are referred to as pararock fragments.
The photo is from the Polkton soil series. Polkton soils are moderately deep, moderately well drained, and very slowly permeable, occurring on uplands of the Triassic Basins in the Southern Piedmont. They formed in residuum weathered from Triassic siltstone, mudstone, shale, and sandstone. Slope ranges from 2 to 25 percent.
TAXONOMIC CLASS: Fine, mixed, active, thermic Oxyaquic Vertic Hapludalfs
Polkton soil series:
soilseries.sc.egov.usda.gov/OSD_Docs/P/POLKTON.html
Blocky structure. In this type of soil structure, the structural units are blocklike or polyhedral. They are bounded by flat or slightly rounded surfaces that are casts of the faces of surrounding peds. Typically, blocky structural units are nearly equidimensional but may grade to prisms or plates.
The structure is described as angular blocky if the faces intersect at relatively sharp angles; as subangular blocky if the faces are a mixture of rounded and plane faces and the corners are mostly rounded.
Blocky structures are common in subsoil but also occur in surface soils that have a high clay content. The strongest blocky structure is formed as a result of swelling and shrinking of the clay minerals which produce cracks. Sometimes the surface of dried-up sloughs and ponds shows characteristic cracking and peeling due to clays.
Clayey soils have 35 (more than 30 percent in Vertisols) to less than 60 percent (by weight) clay in the particle-size control section.
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: