LOCATION THORP IL+IA
Established Series
Rev. JBF-JCD-RJB
06/2015
THORP SERIES
The Thorp series consists of very deep, poorly drained soils formed in loess or other silty material and in the underlying loamy stratified outwash or sandy loam till. They are on broad low summits or in depressions on outwash plains, stream terraces, or till plains. Slope ranges from 0 to 2 percent. Mean annual air temperature is about 10 degrees C (50 degrees F), and mean annual precipitation is about 914 mm (36 inches).
TAXONOMIC CLASS: Fine-silty, mixed, superactive, mesic Argiaquic Argialbolls
TYPICAL PEDON: Thorp silt loam - in a nearly level cultivated field at an elevation of about 195 meters (640 feet) above mean sea level. (Colors are for moist soil unless otherwise stated.)
Ap--0 to 18 cm (0 to 7 inches); black (10YR 2/1) silt loam, dark gray (10YR 4/1) dry; moderate very fine granular structure; friable; neutral; abrupt smooth boundary.
A--18 to 36 cm (7 to 14 inches); very dark gray (10YR 3/1) silt loam, gray (10YR 5/1) dry; moderate fine granular structure; friable; slightly acid; abrupt smooth boundary. [Combined thickness of the Ap and A horizon is 25 to 36 cm (10 to 14 inches).]
Eg--36 to 48 cm (14 to 19 inches); dark gray (10YR 4/1) silt loam, gray (10YR 6/1) dry; weak fine granular structure; friable; few fine prominent yellowish brown (10YR 5/6) masses of oxidized iron in the matrix; moderately acid; clear smooth boundary. [10 to 25 cm (4 to 10 inches) thick]
Btg1--48 to 53 cm (19 to 21 inches); dark gray (10YR 4/1) and dark grayish brown (2.5Y 4/2) silty clay loam; weak fine prismatic structure parting to moderate fine subangular blocky; firm; many distinct very dark gray (10YR 3/1) organo-clay films on faces of peds; few fine prominent yellowish brown (10YR 5/6) masses of oxidized iron in the matrix; moderately acid; clear smooth boundary.
Btg2--53 to 84 cm (21 to 33 inches); gray (5Y 5/1) and olive gray (5Y 4/2) silty clay loam; moderate medium prismatic structure parting to moderate fine and medium subangular blocky; firm; many prominent very dark gray (10YR 3/1) organo-clay films on faces of peds; many fine prominent yellowish brown (10YR 5/6) masses of oxidized iron in the matrix; moderately acid; clear smooth boundary.
Btg3--84 to 109 cm (33 to 43 inches); grayish brown (2.5Y 5/2) silty clay loam; weak fine prismatic structure parting to moderate fine angular and subangular blocky; firm; many distinct very dark gray (10YR 3/1) organo-clay films and dark gray (N 4/) clay films on faces of peds; common fine prominent yellowish brown (10YR 5/6) and distinct light yellowish brown (2.5Y 6/4) masses of oxidized iron in the matrix; slightly acid; clear smooth boundary. [Combined thickness of the Btg horizons is 28 to 89 cm (11 to 35 inches).]
2Btg4--109 to 127 cm (43 to 50 inches); grayish brown (10YR 5/2) and yellowish brown (10YR 5/6) sandy clay loam; weak coarse subangular blocky structure; friable; few distinct dark grayish brown (2.5Y 4/2) clay films on faces of peds; neutral; clear smooth boundary. [10 to 30 cm (4 to 12 inches) thick]
2Cg--127 to 165 cm (50 to 65 inches); mixed grayish brown (10YR 5/2) and yellowish brown (10YR 5/8) sandy loam with thin strata of sand; massive; friable in sandy loam; loose in sand; strongly effervescent; moderately alkaline.
TYPE LOCATION: La Salle County, Illinois; about 14.5 kilometers (9 miles) east of Baker; 302 m (990 feet) north and 683 m (2,240 feet) west of the southeast corner, sec. 27, T. 36 N., R. 5 E.; USGS Sheridan topographic quadrangle; lat. 41 degrees 33 minutes 42 seconds N., and long. 88 degrees 38 minutes 49 seconds W., NAD 27; UTM Zone 16, 0362665 easting and 4602414 northing, NAD 83.
RANGE IN CHARACTERISTICS: The depth to the base of the argillic horizon ranges from 102 to 165 cm (40 to 65 inches). The depth to horizons with more than 10 percent sand ranges from 76 to 137 cm (30 to 54 inches). The mollic epipedon is 25 to 36 cm (10 to 14 inches) in thickness. The common clay mineral in the upper silty layers is smectite and in the lower loamy layers is illite. The particle-size control section averages between 27 and 35 percent clay and less than 10 percent fine sand or coarser. Carbonates are not present above 102 cm (40 inches).
The Ap or A horizon has hue of 10YR, value of 2 or 3, and chroma of 1 to 3. It is silt loam. Clay content ranges from 20 to 27 percent. Reaction is strongly acid to slightly alkaline depending upon liming practices.
The Eg horizon has hue of 10YR or 2.5Y, value of 4 to 6, and chroma of 1 or 2. It is silt loam. Clay content ranges from 18 to 25 percent. Reaction is strongly acid to neutral.
The Btg horizon has hue of 10YR, 2.5Y, or 5Y; value of 4 to 6; and chroma of 1 or 2. Redoximorphic features commonly have chroma of 1 to 8. The Btg horizon typically is silty clay loam, but some pedons are silt loam in some subhorizons. Clay content ranges from 22 to 35 percent. Reaction is strongly acid to neutral.
The 2Btg or 2BCg horizon has hue of 10YR, 2.5Y, 5Y, or is neutral; value of 4 to 6; and chroma of 0 to 8. Typically it is sandy clay loam, loam, clay loam, silt loam, or sandy loam. Many pedons contain strata of silty clay loam, loamy sand, or sand. Average clay content ranges from 18 to 30 percent, and average sand content ranges from 10 to 55 percent. Volume of rock fragments is less than 10 percent. Reaction is moderately acid to slightly alkaline.
The 2Cg horizon has hue of 10YR, 2.5Y, 5Y, or is neutral; value of 4 to 6; and chroma of 0 to 8. It typically is stratified; textures include sandy loam, sandy clay loam, clay loam, loam, silt loam, and silty clay loam. Some pedons contain thin strata of sand or loamy sand. Clay content ranges from 5 to 30 percent, and sand content ranges from 15 to 75 percent. Volume of rock fragments is less than 15 percent. Reaction is slightly acid to moderately alkaline.
COMPETING SERIES: These are the
Corley,
Ebbert,
Edgington,
Knight,
Marissa,
Normal,
Speed, and
Vesser series. Corley, Ebbert, Edgington, Normal, Speed, and Vesser soils average less than 10 percent sand in the lower part of the series control section. Knight soils do not have horizons with more than 10 percent sand within a depth of 137 cm (54 inches). Marissa soils average less than 15 percent sand in the lower part of the series control section and have mean annual soil temperature of more than 12 degrees C (54 degrees F).
GEOGRAPHIC SETTING: Thorp soils are on broad low summits and in depressions on outwash plains, stream terraces, or till plains. Slopes range from 0 to 2 percent. Thorp soils formed in 76 to 137 cm (30 to 54 inches) of loess or other silty material and in the underlying loamy stratified outwash or sandy loam till. Mean annual air temperature ranges from 7 to 12 degrees C (45 to 54 degrees F), mean annual precipitation ranges from 762 to 1067 mm (30 to 42 inches), frost-free days range from 140 to 180 days, and elevation ranges from 155 to 396 m (510 to 1300 feet) above sea level.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the
Bowes,
Brenton,
Elburn,
Flanagan,
Millbrook,
Plano,
Proctor, and
Waupecan soils. All of these soils are on slightly higher elevations and are better drained.
DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY: Poorly drained. Where drained, the apparent seasonal high water table is 15 cm (0.5 foot) above the surface to 30 cm (1.0 foot) below the surface at some time between January and May in most years. In undrained conditions, the apparent seasonal high water table is 15 cm (0.5 foot) above the surface to 15 cm (0.5 foot) below the surface at some time between November and June in most years. The potential for surface runoff is negligible. Saturated hydraulic conductivity is moderately high (0.42 to 1.41 micrometers per second) in the solum and high (14.11 to 42.33 micrometers per second) in the underlying material. Permeability is moderately slow in the solum and moderately rapid in the underlying material.
USE AND VEGETATION: Most areas are cropped. Corn and soybeans are the principal crops. Some areas are used for growing small grain or meadow. Native vegetation is marsh grasses and sedges. See Additional Data section for native vegetative cover in Iowa.
DISTRIBUTION AND EXTENT: Northern and central Illinois and in Iowa. The extent is moderate in MLRAs 95B, 104, 105, 108, 110, and 115.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Indianapolis, Indiana
SERIES ESTABLISHED: Stark County, Illinois, 1932.
REMARKS: A flooded phase and Thorp Variant are presently recognized. These soils will be evaluated during MLRA updating to determine if new series are needed.
Diagnostic horizons and features recognized in this pedon are: mollic epipedon - the zone from the surface to a depth of 36 cm (14 inches) (Ap and A horizons); albic horizon - the zone from 36 to 48 cm (14 to 19 inches) (Eg horizon); argillic horizon - the zone from 48 to 127 cm (19 to 50 inches) (Btg1, Btg2, Btg3, and 2Btg4 horizons); aquic conditions - chroma of 1 or 2 and masses of iron accumulation in all horizons below the mollic epipedon.
ADDITIONAL DATA: University of Illinois sample numbers 21238-21248; data from another pedon in the same map unit and near the typical pedon.
In Iowa, the native vegetative cover is a herbaceous wetland community commonly inhabited with Rice Cutgrasses, Softstem Bulrushes, Needle Spikerushes, Broadfruit Burreeds, Pickerel Weeds, Broadleaf Cattails, Water Smartweeds, American Water Lilies, Yellow Pond Lilies, American Lotuses, Small Pondweeds, Sago Pondweeds, and Arrowheads. Source: Iowa State Office, Natural Resources Conservation Service, Des Moines, IA.
National Cooperative Soil Survey
U.S.A.