LOCATION SOMONAUK ILEstablished Series
TAXONOMIC CLASS: Fine-silty, mixed, superactive, mesic Oxyaquic Hapludalfs
TYPICAL PEDON: Somonauk silt loam - on an east-facing convex slope of 1 percent in a cultivated field at an elevation of about 251 meters (822 feet) above mean sea level. (Colors are for moist soil unless otherwise stated.)
Ap--0 to 10 cm (0 to 4 inches); 85 percent dark grayish brown (10YR 4/2) and 15 percent dark brown (10YR 3/3) silt loam, grayish brown (10YR 5/2) dry; weak fine and medium granular structure; friable; common very fine and fine roots; neutral; gradual wavy boundary. [8 to 20 cm (3 to 8 inches) thick]
E--10 to 23 cm (4 to 9 inches); 80 percent dark grayish brown (10YR 4/2) and 20 percent brown (10YR 4/3) silt loam, light brownish gray (10YR 6/2) dry; weak medium and thick platy structure; friable; common very fine and fine roots; neutral; clear smooth boundary. [0 to 20 cm (0 to 8 inches) thick]
Bt1--23 to 36 cm (9 to 14 inches); brown (10YR 4/3) silty clay loam; moderate fine and medium subangular blocky structure; friable; common fine roots; many distinct dark brown (10YR 3/3) clay films on faces of peds and on surfaces along pores; few distinct light brownish gray (10YR 6/2) (dry) silt coatings on faces of peds; common fine rounded black (10YR 2/1) iron-manganese nodules throughout; moderately acid; gradual wavy boundary.
Bt2--36 to 53 cm (14 to 21 inches); dark yellowish brown (10YR 4/4) silty clay loam; moderate medium prismatic structure parting to moderate medium subangular blocky; friable; common very fine and fine roots; common distinct brown (10YR 4/3) clay films on faces of peds and on surfaces along pores; few distinct light gray (10YR 7/2) (dry) silt coatings on faces of peds; common medium rounded black (10YR 2/1) iron-manganese nodules throughout; moderately acid; gradual wavy boundary.
Bt3--53 to 74 cm (21 to 29 inches); dark yellowish brown (10YR 4/4) silty clay loam; moderate medium and coarse prismatic structure; friable; common fine roots; common distinct brown (10YR 4/3) clay films on faces of peds and on surfaces along pores; few distinct light gray (10YR 7/2) (dry) silt coatings on faces of peds; common medium rounded black (10YR 2/1) iron-manganese nodules throughout; few fine distinct grayish brown (10YR 5/2) iron depletions in the matrix; moderately acid; gradual wavy boundary.
Bt4--74 to 86 cm (29 to 34 inches); yellowish brown (10YR 5/4) silty clay loam; moderate fine and medium subangular blocky structure; friable; common very fine and fine roots; common distinct brown (10YR 4/3) clay films on faces of peds and in pores; few distinct light gray (10YR 7/2) (dry) silt coatings on faces of peds; common fine rounded black (10YR 2/1) iron-manganese nodules throughout; few fine distinct grayish brown (10YR 5/2) iron depletions in the matrix; moderately acid; gradual wavy boundary. [Combined thickness of the Bt horizon ranges from 25 to 76 cm (10 to 30 inches).]
2Bt5--86 to 99 cm (34 to 39 inches); yellowish brown (10YR 5/4) silty clay loam, with a 13 percent sand content; moderate medium angular blocky structure; friable; few distinct dark yellowish brown (10YR 4/4) clay films on faces of peds and in pores; few distinct light gray (10YR 7/2) (dry) silt coatings on faces of peds; common fine rounded black (10YR 2/1) iron-manganese nodules throughout; few fine distinct grayish brown (10YR 5/2) iron depletions in the matrix; 1 percent gravel; moderately acid; gradual wavy boundary.
2Bt6--99 to 124 cm (39 to 49 inches); yellowish brown (10YR 5/4) loam; moderate medium and coarse angular blocky structure; friable; few distinct dark yellowish brown (10YR 4/4) clay films on faces of peds and on surfaces along pores; few fine rounded black (10YR 2/1) iron-manganese nodules throughout; common fine prominent yellowish brown (10YR 5/8) masses of oxidized iron in the matrix; 6 percent gravel; moderately acid; gradual wavy boundary.
2Bt7--124 to 140 cm (49 to 55 inches); brown (7.5YR 4/3) loam; weak medium and coarse angular blocky structure; friable; common distinct dark yellowish brown (10YR 4/4) clay films on faces of peds and on surfaces along pores; few fine rounded black (10YR 2/1) iron-manganese nodules throughout; common fine prominent yellowish brown (10YR 5/8) masses of oxidized iron in the matrix; 8 percent gravel; slightly acid; clear smooth boundary.
2Bt8--140 to 155 cm (55 to 61 inches); brown (7.5YR 4/3) sandy loam; weak medium angular blocky structure; friable; common distinct dark brown (10YR 3/3) clay films on faces of peds and on surfaces along pores; 10 percent gravel; slightly acid; clear smooth boundary.
2Bt9--155 to 178 cm (61 to 70 inches); 60 percent dark yellowish brown (10YR 4/4) and 40 percent brown (7.5YR 4/3) sandy loam; weak medium subangular blocky structure; friable; few distinct dark brown (10YR 3/3) clay films on faces of peds and on surfaces along pores; 8 percent gravel; neutral; gradual wavy boundary. [Combined thickness of 2Bt horizon ranges from 25 to 102 cm (10 to 40 inches).]
2C--178 to 203 cm (70 to 80 inches); 70 percent dark yellowish brown (10YR 4/4) and 30 percent yellowish brown (10YR 5/4) stratified gravelly sandy loam and sand; massive; very friable; 15 percent gravel; strongly effervescent; moderately alkaline.
TYPE LOCATION: DeKalb County, Illinois; about 3.2 kilometers (2 miles) west of Sycamore; 213 meters (700 feet) south and 732 meters (2,400 feet) west of the northeast corner of sec. 25, T. 41 N., R. 4 E.; USGS Genoa topographic quadrangle; lat. 42 degrees 00 minutes 26 seconds N. and long. 88 degrees 43 minutes 24 seconds W., NAD 27; UTM Zone 16T, 357276 easting, 4652019 northing, NAD 83.
RANGE IN CHARACTERISTICS: The depth to the base of the argillic horizon ranges from 76 to 178 cm (30 to 70 inches). The depth to horizons with more than 10 percent sand ranges from 51 to 102 cm (20 to 40 inches). Carbonates are below a depth of 102 cm (40 inches). The particle-size control section averages between 22 and 35 percent clay and less than 10 percent fine sand or coarser.
The Ap or A horizon has hue of 10YR, value of 3 to 5 (greater than 5.5 dry), and chroma of 2 or 3. It is silt loam. Reaction ranges from strongly acid to neutral.
The E horizon has hue of 10YR, value of 4 to 6, and chroma of 2 or 3. is silt loam. Reaction ranges from strongly acid to neutral.
The Bt horizon has hue of 7.5YR or 10YR, value of 4 to 6, and chroma of 3 to 6. It is silty clay loam or silt loam. Reaction ranges from strongly acid to neutral.
The 2Bt horizon has hue of 7.5YR or 10YR, value of 4 to 6, and chroma of 3 to 6. Redoximorphic features have chroma of 2 to 8. Texture is silty clay loam, clay loam, loam, sandy loam, sandy clay loam, or silt loam. Clay content ranges from 15 to 32 percent, and sand content ranges from 15 to 65 percent. Individual subhorizons range from 10 to 35 percent clay and 10 to 75 percent sand. Volume of rock fragments is less than 10 percent. Reaction ranges from strongly acid to slightly alkaline.
Some pedons have 2BC horizon which ranges in hues, chromas, values and textures as the 2Bt horizon.
The 2C horizon has hue of 10YR or 7.5YR, value of 4 to 6, and chroma of 3 to 6. Redoximorphic features have chroma of 2 to 8. Texture is commonly stratified sandy loam, loam, silt loam or their gravelly analogues with thin strata of other textures. Clay content ranges from 5 to 20 percent, and sand content ranges from 30 to 75 percent. Individual subhorizons range from 75 to 95 percent sand. Volume of rock fragments is less than 20 percent. Reaction ranges from slightly acid to moderately alkaline.
COMPETING SERIES: These are the Baraboo, Birkbeck, Cadiz, Campton, Elco, Eleroy, Homen, Inton, Iona, Libre, Mayville, Minnith, Morningsun, Redbud , Rocheport , Rockfield, Uniontown, Winfield, and Zurich soils. Baraboo, Eleroy and Rocheport soils have a lithic or paralithic contact within a depth of 152 cm (60 inches).Birkbeck, Campton, Homen, Inton, Iona, Redbud, and Winfield soils do not have horizons with more than 15 percent sand within a depth of 102 cm (40 inches). Cadiz and Elco soils contain more than 20 percent clay in the lower part of the series control section. Libre soils contain a densic contact in the middle part of the series control section. Mayville and Zurich soils contain carbonates above 102 cm (40 inches). Minnith and Uniontown soils have a mean annual air temperature range of over 12 degrees C (54 degrees F). Morningsun and Rockfield soils have a well graded sand fraction in the lower one-half of the series control section.
GEOGRAPHIC SETTING: Somonauk soils are on Wisconsinan age outwash plains, and stream terraces. These soils are on terrace risers and terrace treads. Slope gradients range from 0 to 5 percent. These soils formed in 51 to 102 cm (20 to 40 inches) of loess or other silty material and in loamy stratified outwash. Mean annual temperature ranges from 8 to 12 degrees C (46 to 53 degrees F). Mean annual precipitation ranges from 760 to 1,140 mm (30 to 45 inches). Frost-free period ranges from 140 to 180 days. Elevation ranges from 207 to 311 meters (680 feet to 1,020 feet) above sea level.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Barony soils and the competing Mayville soils and the Drummer, Elburn, Millbrook, and Otter soils. The moderaterly well drained Barony soils have a dark colored surface layer and are on similar landforms nearby. Mayville soils are on nearby landforms on till uplands. The somewhat poorly drained Elburn and Millbrook soils are on lower lying areas. The poorly drained Drummer and Otter soils are in depressions and on floodplain positions respectively.
DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY: Moderately well drained. An intermittent apparent water table is at a depth of 61 to 107 cm (2.0 to 3.5 feet) at some time between February and April in most years. The potential for surface runoff is negligible to low. Saturated hydraulic conductivity is moderately high or high (4.23 to 14.11 micrometers per second) in the upper part of the solum and moderately high or high (4.23 to 42.33 micrometers per second) in the lower part of the solum and in the substratum. Permeability is moderate in the upper part of the solum and moderate or moderately rapid in the lower part of the solum and in the substratum.
USE AND VEGETATION: Somonauk soils are used mainly for cultivated crops such as corn, soybeans, small grain; some areas are used for pasture and woodland. Native vegetation is mixed hardwood forest.
DISTRIBUTION AND EXTENT: Illinois. The extent is small in MLRAs 95B, 108A, and 110.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Indianapolis, Indiana
SERIES ESTABLISHED: DeKalb County, Illinois, 1998. The name Somonauk is from the town of Somonauk in southeastern DeKalb County.
REMARKS: This soil was formerly mapped as Camden in DeKalb County. Through MLRA update activities these soils were found to be moderately well drained instead of well drained and fit an oxyaquic subgroup rather than a typic subgroup.
Diagnostic horizons and features recognized in this pedon are: ochric epipedon - the zone from the surface of the soil to a depth of 23 cm (9 inches) (Ap and E horizon); argillic horizon - the zone from approximately 23 to 178 cm (9 to 70 inches) (Bt1, Bt2, Bt3, Bt4, 2Bt5, 2Bt6, 2Bt7, 2Bt8 and 2Bt9 horizons); udic moisture regime.