LOCATION ASSUMPTION IL
Established Series
Rev. JCD-SLE
10/2018
ASSUMPTION SERIES
The Assumption series consists of very deep, moderately well drained soils on till plains. These soils formed in loess and the underlying till that contains a strongly developed paleosol. Some pedons have a layer of silty or loamy mixed loess and drift between the loess and the underlying till. Slope ranges from 0 to 18 percent. The mean annual temperature is about 10 degrees C (50 degrees F), and the mean annual precipitation is about 940 mm (37 inches).
TAXONOMIC CLASS: Fine-silty, mixed, superactive, mesic Aquic Argiudolls
TYPICAL PEDON: Assumption silt loam on a west-facing, convex, 4 percent slope in a cultivated field at an elevation of 220 meters (720 feet) above mean sea level. (Colors are for moist soil unless otherwise stated.)
Ap--0 to 15 cm (0 to 6 inches); very dark grayish brown (10YR 3/2) silt loam, grayish brown (10YR 5/2) dry; weak medium granular structure; friable; many fine roots throughout; neutral; abrupt smooth boundary.
A--15 to 33 cm (6 to 13 inches); very dark grayish brown (10YR 3/2) silt loam, grayish brown (10YR 5/2) dry; moderate medium granular structure; friable; many fine roots throughout; slightly acid; clear smooth boundary. [combined thickness of A horizon is 25 to 49 cm (10 to 19 inches).]
AB--33 to 41 cm (13 to 16 inches); very dark grayish brown (10YR 3/2) and brown (10YR 4/3) silt loam, grayish brown (10YR 5/2) and brown (10YR 5/3) dry; weak medium subangular blocky structure; friable; many fine roots throughout; neutral; clear wavy boundary. [0 to 15 cm (0 to 6 inches) thick]
Bt1--41 to 66 cm (16 to 26 inches); brown (10YR 4/3) silty clay loam; weak medium prismatic structure parting to moderate fine subangular blocky; firm; common fine roots between peds; many distinct brown (10YR 5/3) clay films on faces of peds; slightly acid; clear wavy boundary.
Bt2--66 to 89 cm (26 to 35 inches); brown (10YR 5/3) silty clay loam; weak medium prismatic structure parting to moderate medium subangular blocky; firm; common fine roots between peds; many distinct brown (10YR 4/3) clay films on faces of peds; many medium distinct brownish yellow (10YR 6/6) masses of oxidized iron and common faint grayish brown (2.5Y 5/2) iron depletions in the matrix; slightly acid; abrupt wavy boundary. [Combined thickness of the Bt horizon is 35 to 76 cm (14 to 30 inches).]
2Bt3--89 to 130 cm (35 to 51 inches); yellowish brown (10YR 5/4) clay loam; weak medium subangular blocky structure; firm; common fine roots between peds; common distinct dark yellowish brown (10YR 4/4) clay films on faces of peds; many coarse prominent yellowish brown (10YR 5/8) masses of oxidized iron and common medium prominent light olive gray (5Y 6/2) iron depletions in the matrix; slightly acid; clear wavy boundary.
2Bt4--130 to 152 cm (51 to 60 inches); brown (10YR 5/3) silty clay loam; weak medium prismatic structure parting to moderate medium subangular blocky; firm; common fine roots between peds; many distinct brown (10YR 4/3) clay films on faces of peds; many medium distinct brownish yellow (10YR 6/6) masses of oxidized iron in the matrix; slightly acid; clear wavy boundary. [Combined thickness of the 2Bt horizon is 51 to 100 cm (20 to 39 inches).]
2C--152 to 203 cm (60 to 80 inches); brown (10YR 5/3) clay loam; massive; firm; common coarse faint brown (7.5YR 4/4) masses of oxidized iron and common coarse faint grayish brown (2.5Y 5/2) iron depletions in the matrix; slightly effervescent; slightly alkaline.
TYPE LOCATION: Henry County, Illinois; about 3 miles south and 1/4 mile west of Andover, 100 feet north and 300 feet east of the southwest corner of sec. 29, T. 15 N., R. 2 E. USGS Andover quadrangle; lat. 41 degrees 15 minutes 01 seconds N., and long. 90 degrees 17 minutes 58 seconds W.; UTM Zone 15, 726271 easting and 4570058 northing, NAD 83; lat. 41.2502778 degrees and long. -90.2994444 degrees, WGS84.
RANGE IN CHARACTERISTICS:
Depth to base of argillic horizon: 122 to 178 cm (48 to 70 inches) or more
Thickness of the mollic epipedon: 25 to 49 cm (10 to 19 inches)
Thickness of the loess mantle: 51 to 102 cm (20 to 40 inches)
Clay content in the particle-size control section (weighted average): 27 to 35 percent
Depth to carbonates: greater than 102 cm (40 inches)
Special features: a layer of silty or loamy mixed loess and drift material of variable thickness is present in some pedons between the loess and till which contains a strongly developed paleosol within a depth of 152 cm (60 inches)
Redox depletions with chroma 2 or less: not present in the 15 cm (6 inches) immediately below the mollic epipedon.
Ap or A horizon:
Hue: 10YR
Value: 2 or 3
Chroma: 1 to 3
Texture: typically silt loam, but severely eroded pedons include silty clay loam.
Reaction: moderately acid to neutral
An AB horizon is present in some pedons.
Bt or Btg horizon:
Hue: 10YR or 2.5Y
Value: 4 or 5
Chroma: 3 to 6 in the upper part and 2 to 6 in the lower part
Texture: typically silty clay loam in the finest part, and some pedons contain one or more silt loam subhorizons.
Consistence: typically friable or firm
Reaction: strongly acid to neutral
2Bt or 2Btg horizon:
Hue: 7.5YR, 10YR, 2.5Y or 5Y
Value: 3 to 6
Chroma: 1 to 6
Texture: clay loam, silty clay loam, loam, clay or silty clay
Clay content: 30 to 45 percent
Sand content: 15 to 35 percent
Rock fragment content: 0 to 10 percent
Consistence: firm or very firm
Reaction: strongly acid to neutral
Other features: This horizon typically contains more clay than the Bt horizon and always a higher content of sand, and commonly has redoximorphic features in some part. In some pedons the redoximorphic features have a redder hue or chroma as high as 8 or both redder hue and higher chroma.
2C or 2Cg horizon:
Hue: 7.5YR, 10YR, 2.5Y or 5Y
Value: 3 to 6
Chroma: 1 to 6
Texture: clay loam, silty clay loam, loam, clay or silty clay
Clay content: 30 to 45 percent
Sand content: 15 to 35 percent
Rock fragment content: 0 to 10 percent
Reaction: slightly acid to moderately alkaline
COMPETING SERIES: These are the
Arrowsmith,
Bearpen,
Brenton,
Edwardsville,
Elburn,
Grundelein,
Hacreek,
Harco,
Higginsville,
Keller,
Lafayette,
Lawndale,
Lisbon,
Lismod,
Loran,
Mundelein,
Muscatune,
Nira,
Raub,
Rooks,
Rowley, and
Shannondale series. Arrowsmith, Brenton, Edwardsville, Elburn, and Nira soils contain less than 30 percent clay in the lower part of the series control section. Bearpen and Rowley soils average less than 27 percent clay in the particle control section. Grundelein and Lafayette soils contain more than 10 percent rock fragments in the lower part of the series control section. Hacreek, Higginsville and Muscatune soils contain less than 15 percent sand in the lower part of the series control section. Harco, Lisbon, Lismod, Mundelein, and Rooks soils contain carbonates at depths less than 102 cm (40 inches). Keller soils contain redox depletions with chroma 2 or less immediately below the mollic epipedon. Lawndale soils contain more than 35 percent sand in the lower part of the series control section. Loran soils have paralithic contact within a depth of 152 cm (60 inches). Raub soils have a densic contact within a depth of 178 cm (70 inches). Shannondale soils have a mean annual temperature greater than 12.2 degrees C (54 degrees F).
GEOGRAPHIC SETTING: Assumption soils are on head slopes, side slopes and interfluves on nearly level to moderately steep ground moraines on till plains of Illinois age. Slope ranges from 0 to 18 percent. These soils formed in 51 to 102 cm (20 to 40 inches) of loess and in the underlying till that contains a strongly developed paleosol. Some pedons contain a layer of silty or loamy mixed loess and drift material of variable thickness between the loess and the underlying till. The mean annual temperature ranges from 7.8 to 12.2 degrees C (46 to 54 degrees F), mean annual precipitation ranges from 864 to 1016 mm (34 to 40 inches), and frost free period is 150 to 185 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the
Atlas,
Coatsburg,
Keller,
Osco, and
Velma soils. The somewhat poorly drained Atlas soils and poorly drained Coatsburg soils are on similar landform positions as Assumption soils or are down slope. Atlas and Coatsburg soils have a thinner surface mantle of loess or other silty material. In addition, Atlas soils do not have a mollic epipedon. The somewhat poorly drained Keller soils are on similar parts of the landform nearby and have redox depletions or 2 chroma matrix colors immediately below the mollic epipedon. The well drained Osco soils are on nearby interfluves and slopes above Assumption soils and formed in loess. The well drained Velma soils formed in Illinois till and are down slope from Assumption soils that have a paleosol.
DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY: Moderately well drained. Saturated hydraulic conductivity is moderately high to high (4.23 to 14.11 micrometers per second) in the loess, moderately high (1.41 to 4.23 micrometers per second) in the silty or loamy mixed loess and drift, and moderately low to moderately high (0.42 to 4.23 micrometers per second) in the till that contains a strongly developed paleosol. Permeability is moderate in the loess, moderately slow in the mixed loess and drift, and slow or very slow in the till that contains a strongly developed paleosol. The perched seasonal high water table is 61 to 107 cm (2 to 3.5 feet) below the surface from February to April. Seep spots on side slopes are common as the result of perched water above the paleosol.
USE AND VEGETATION: Almost all areas of Assumption soils are cultivated. Corn, soybeans, small grain, and meadow are the principal crops. Native vegetation is prairie grass.
DISTRIBUTION AND EXTENT: Central, western, and northern Illinois. LRR K and M, MLRAs 95B, 108B, 114B, and 115C. The series is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Indianapolis, Indiana
SERIES ESTABLISHED: Christian County, Illinois, 1946.
REMARKS: The 2Btg or 2Bt horizon of Assumption soils is the lower part of the solum superimposed upon a Sangamon paleosol in the Illinoisan till. Many of the properties of those horizons are believed to have been inherited from the paleosol. It is difficult to differentiate the properties of the lower part of the modern solum from those of the paleosol in many pedons. The variability of the properties is related to the degree of geologic truncation of the paleosol before it was buried by loess, and to the extent of modern soil development into the old materials. Some pedons have a dark colored layer at the top of the paleosol that was the surface layer of the paleosol, and is now part of the 2Bt or 3Bt horizon of the modern soil. In pedons that do not have the mixed loess and drift layer, the Peoria loess lies directly on the paleosol. The paleosolic Bt horizon typically is gray, but ranges to brown in some pedons. Calcium and other bases have been replenished in the paleosol in some pedons after burial by loess by seepage from the mantling material up slope.
Diagnostic horizons and features recognized in this pedon are:
mollic epipedon -- from a depth of 0 to 41 cm (0 to 16 inches) [Ap, A, and AB horizons]
argillic horizon -- from a depth of 41 to 152 cm (16 to 60 inches) [Bt1, Bt2, 2Bt3, and 2Bt4 horizons]
lithologic discontinuity at 89 cm (35 inches)
The slope range was expanded to include Assumption on A slopes. The A slope units were correlated as part of an MLRA project in Ogle County, Illinois.
The taxonomic classification was changed from fine-silty, mixed, superactive, mesic Oxyaquic Argiudolls to fine-silty, mixed, superactive, mesic Aquic Argiudolls. The change was based on data review and field investigations as part of an MLRA project.
Taxonomy version -- Keys to Soil Taxonomy, twelfth edition, 2014.
ADDITIONAL DATA: The typical pedon is 1997IL073900.
National Cooperative Soil Survey
U.S.A.