LOCATION PIASA ILEstablished Series
TAXONOMIC CLASS: Fine, smectitic, mesic Mollic Natraqualfs
TYPICAL PEDON: Piasa silt loam - on a nearly level interfluve in a cultivated field at an elevation of about 630 feet above mean sea level. (Colors are for moist soil unless otherwise stated.)
Ap--0 to 8 inches; very dark gray (10YR 3/1) silt loam, gray (10YR 5/1) dry; weak fine granular structure; friable; common very fine roots; few fine continuous tubular pores; few fine and medium rounded black (5YR 2.5/1) iron manganese nodules with sharp boundaries; neutral; abrupt smooth boundary. (6 to 9 inches thick)
Eg--8 to 12 inches; dark gray (10YR 4/1) silt loam, gray (10YR 6/1) dry; moderate thin and medium platy structure; friable; few very fine roots; few fine pores filled with black (10YR 2/1) soil material; light gray (10YR 7/1), dry, clay depletions on faces of peds; common fine and medium rounded black (5YR 2.5/1) iron manganese nodules with sharp boundaries; slightly alkaline; abrupt wavy boundary. (3 to 8 inches thick)
Btng--12 to 16 inches; dark grayish brown (2.5Y 4/2) silty clay loam; weak very coarse columnar structure parting to moderate fine angular blocky; firm; few very fine roots; few fine tubular pores; common distinct gray (10YR 6/1), dry, clay depletions on the slightly rounded caps of the columns and on the faces of the columns; common prominent black (10YR 2/1) organic coatings lining root channels and filling pores; many distinct dark gray (10YR 4/1) clay films on faces of peds; common fine prominent dark yellowish brown (10YR 4/4) masses of iron accumulation in the matrix; few fine rounded strong brown (7.5YR 4/6) masses of iron-manganese accumulation; slightly alkaline; clear smooth boundary.
Btkng1--16 to 20 inches; dark grayish brown (2.5Y 4/2) silty clay; weak very coarse prismatic structure parting to moderate medium and coarse angular blocky; firm, sticky; few very fine roots; few fine tubular pores; few prominent black (10YR 2/1) organic coatings lining root channels and filling pores; common distinct dark gray (10YR 4/1) clay films on faces of peds; few fine faint very dark grayish brown (2.5Y 3/2) and few fine prominent dark yellowish brown (10YR 4/4) masses of iron accumulation in the matrix; few fine rounded strong brown (7.5YR 4/6) masses of iron-manganese accumulation, few fine and medium irregular black (10YR 2/1) iron-manganese nodules with sharp boundaries, and few medium rounded white (10YR 8/1) carbonate concretions; slightly effervescent; slightly alkaline; clear smooth boundary.
Btkng2--20 to 26 inches; dark grayish brown (2.5Y 4/2) silty clay; weak very coarse prismatic structure parting to moderate medium and coarse angular blocky; firm, sticky; few very fine roots; few fine tubular pores; few prominent black (10YR 2/1) organic coatings lining root channels and filling pores; common distinct dark gray (10YR 4/1) clay films on faces of peds; common fine distinct olive brown (2.5Y 4/4) masses of iron accumulation in the matrix; few fine rounded strong brown (7.5YR 5/6) masses of iron-manganese accumulation, few fine and medium irregular black (10YR 2/1) iron-manganese nodules with sharp boundaries, and common medium and coarse rounded white (10YR 8/1) carbonate concretions; slightly effervescent; moderately alkaline; clear smooth boundary.
Btkng3--26 to 33 inches; dark grayish brown (2.5Y 4/2) silty clay loam; weak very coarse prismatic structure parting to weak and moderate medium angular blocky; firm, slightly sticky; few very fine roots; common distinct dark gray (10YR 4/1) clay films on faces of peds; common medium prominent yellowish brown (10YR 5/6) and few fine prominent strong brown (7.5YR 5/8) masses of iron accumulation in the matrix; common fine and medium irregular black (10YR 2/1) iron-manganese nodules with clear strong brown (7.5YR 5/6) boundaries and common medium and coarse rounded white (10YR 8/1) carbonate concretions; slightly effervescent; moderately alkaline; clear smooth boundary.
Btkng4--33 to 37 inches; dark grayish brown (2.5Y 4/2) silty clay loam; weak very coarse prismatic structure parting to weak coarse angular blocky; friable; few very fine roots; few distinct dark gray (10YR 4/1) clay films on faces of peds; many medium and coarse prominent yellowish brown (10YR 5/8) masses of iron accumulation in the matrix; few fine and medium irregular black (10YR 2/1) iron-manganese nodules with clear strong brown (7.5YR 5/6) boundaries and few medium rounded white (10YR 8/1) carbonate concretions; slightly effervescent; slightly alkaline; clear smooth boundary. (Combined thickness of the Btg horizons is 21 to 33 inches.)
BCg--37 to 48 inches; grayish brown (2.5Y 5/2) silt loam; weak coarse angular blocky structure; friable; few very fine roots; few faint gray (10YR 5/1) clay films on vertical faces of peds; many coarse prominent yellowish brown (10YR 5/6) masses of iron accumulation in the matrix; common fine and medium irregular strong brown (7.5YR 5/6) masses of iron-manganese accumulation and few fine irregular black (10YR 2/1) iron-manganese nodules with sharp boundaries; slightly alkaline; clear smooth boundary. (6 to 14 inches thick)
2Btgb1--48 to 62 inches; gray (10YR 5/1) silt loam; moderate fine and medium prismatic structure parting to weak medium angular blocky; friable; few fine vesicular pores; few prominent very dark gray (10YR 3/1) organic coatings lining root channels and filling pores and many distinct dark gray (10YR 4/1) clay films on faces of peds; many coarse prominent yellowish brown (10YR 5/8) and reddish brown (5YR 4/4) masses of iron accumulation in the matrix; few medium and coarse irregular black (10YR 2/1) iron-manganese nodules with diffuse strong brown (7.5YR 5/6) boundaries; about 10 to 15 percent sand and 1 percent pebbles; slightly alkaline; gradual smooth boundary.
2Btgb2--62 to 80 inches; grayish brown (10YR 5/2) clay loam; moderate medium prismatic structure parting to weak medium angular blocky; firm; few fine vesicular pores; few prominent very dark gray (10YR 3/1) organic coatings lining root channels and filling pores and common distinct dark gray (10YR 4/1) clay films on faces of peds; many medium and coarse prominent yellowish brown (10YR 5/8) masses of iron accumulation in the matrix; few fine and medium irregular strong brown (7.5YR 5/6) masses of iron-manganese accumulation; about 5 percent pebbles; neutral.
TYPE LOCATION: Montgomery County, Illinois; about 3 miles north of Hillsboro; approximately 277 feet west and 85 feet south of the northeast corner of sec. 26, T. 9 N., R. 4 W.; USGS Hillsboro, IL. topographic quadrangle; lat. 39 degrees 12 minutes 8 seconds N. and long. 89 degrees 29 minutes 37 seconds W.
RANGE IN CHARACTERISTICS: Depth to the base of the natric horizon is 30 to 50 inches. Loess thickness ranges from 40 to 72 inches. Exchangeable sodium ranges from 15 percent to more than 35 percent in the natric horizon. Depth to carbonates and their abundance is variable and they are not everywhere present. The particle-size control section averages 35 to 43 percent clay and averages less than 10 percent sand.
The upper part of the series control section (A or Ap, and Eg) has properties as follows: The A or Ap horizon has value of 2 or 3 (4 or 5 dry) and chroma of 1 or 2. Texture is silt loam. Clay content is 18 to 27 percent and sand content is less than 15 percent and includes iron-manganese nodules and concretions. Reaction typically is slightly acid or neutral, but ranges from moderately acid to slightly alkaline.
The Eg horizon has value of 4 or 5 (6 or 7 dry) and chroma of 1 or 2. It typically has platy structure, but in some pedons it is granular or subangular blocky. Texture is silt loam. Clay content is 18 to 27 percent and sand content is less than 15 percent and includes iron-manganese nodules and concretions. Reaction is moderately acid to slightly alkaline.
The second part of the control section (Btg) has hue of 10YR, 2.5Y, or 5Y; value of 4 to 6; and chroma of 1 or 2. Redoximorphic masses of iron accumulation in the matrix have hue of 7.5YR, 10YR, or 2.5Y; value of 3 to 6; and chroma of 2 to 8. It commonly has columnar or prismatic structure that parts to angular or subangular blocky. The Btg horizon is silty clay loam or silty clay. Clay content averages 35 to 43 percent and sand content is less than 10 percent. Reaction is slightly acid to strongly alkaline in the upper part and slightly alkaline to strongly alkaline in the lower part.
The third part of the control section (BCg) has the same range of colors as stated for the Btg horizon. Texture is silty clay loam or silt loam. Clay content averages 20 to 35 percent and sand content is less than 15 percent. Reaction is slightly alkaline to strongly alkaline.
The lower part of the control section (Cg or 2Cg, where present, and 2Ab and/or 2Bb, where present) has hue of 10YR, 2.5Y, 5Y, or is neutral; value of 3 to 6; and chroma of 0 to 2. Texture is silt loam, loam, silty clay loam, or clay loam. Clay content averages 20 to 35 percent and sand content averages 10 to 40 percent. Reaction is neutral to moderately alkaline.
Some pedons have a Cg horizon that is underlain by buried horizons of older soils, and other pedons do not have a Cg horizon; where the modern soil is welded to a strongly developed paleosol contained in the Illinoian till.
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING: Piasa soils are on broad, nearly level interfluves on the Illinoian till plain. Slope ranges from 0 to 2 percent. These soils contain a concentration of exchangeable sodium. These soils formed in 40 to 72 inches of loess. The material beneath the loess is Illinois till or the silty pedisediment that lies above the till and contains a component of sand. The loess is late Wisconsinan Peoria Loess and the underlying silty material is early Wisconsinan Roxana Silt. The soils are underlain at depths of about 4 to 7 feet by Illinoian till that commonly contains a strongly developed paleosol. Mean annual temperature 54 to 57 degrees F., mean annual precipitation 36 to 40 inches, frost-free period is 180 to 200 days, and elevation is 400 to 700 feet above mean sea level.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Cisne, Cowden, Darmstadt, Ebbert, Herrick, Huey, Oconee, Tamalco, and Virden soils. The associated soils, except for Darmstadt, Huey, and Tamalco soils, do not have a natric horizon. The poorly drained Cisne and Huey soils formed in generally thinner loess and have a 2B horizon. The somewhat poorly drained Darmstadt soils are on convex summits and are in small drainageways. The poorly drained Ebbert soils have a mollic epipedon and are in depressions. The somewhat poorly drained Herrick and Oconee soils are on slightly higher landform positions. The moderately well drained Tamalco soils are typically deeper to the natric horizon and are on convex summits and drainageways nearby. The poorly drained Virden soils have a mollic epipedon and are on broad interfluves nearby. Piasa soils are adjacent to and in a complex intermingled pattern with Cowden and Herrick soils.
DRAINAGE AND PERMEABILITY: Poorly drained, slow or ponded runoff, very slow permeability. In drained areas, depth to an intermittent perched high water table is from 0.5 foot above the surface to 1 foot below the surface from November to May in most years.
USE AND VEGETATION: Most areas are cropped. Alfalfa, corn, soybeans, and wheat are the principal crops. Native vegetation is prairie grasses.
DISTRIBUTION AND EXTENT: South-central Illinois; extent is moderate, and mainly in MLRA(s) 108, 113, and 114.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Indianapolis, Indiana
SERIES ESTABLISHED: Jersey County, Illinois, 1957.
REMARKS: The Piasa series was previously classified as fine, montmorillonitic, mesic Typic Natralbolls and later as fine, montmorillonitic, mesic Mollic Natraqualfs.
The typical pedon was resampled and described to 80 inches for this revision.
Diagnostic horizons and features in this pedon include:
Ochric epipedon - from the surface of the soil to a depth of 12 inches (Ap and Eg horizons). Albic horizon - from a depth of 8 to 12 inches (Eg horizon). Natric horizon - from a depth of approximately 12 to 37 inches (Btng, Btkng1, Btkng2, Btkng3, and Btkng4 horizons). Aquic conditions - periodic saturation and reduction indicated by redoximorphic features throughout the soil.
ADDITIONAL DATA: Data for the typical pedon is published in the Soil Survey of Montgomery County, Illinois, 1969.