LOCATION ONARGA IL+INEstablished Series
TAXONOMIC CLASS: Coarse-loamy, mixed, superactive, mesic Typic Argiudolls
TYPICAL PEDON: Onarga sandy loam on a 1 percent north-facing convex slope in a cultivated field at an elevation of about 495 feet above mean sea level. (Colors are for moist soil unless otherwise stated.)
Ap--0 to 10 inches; very dark grayish brown (10YR 3/2) sandy loam, dark grayish brown (10YR 4/2) dry; weak fine subangular blocky structure parting to weak fine granular; friable; common very fine roots throughout; many faint very dark gray (10YR 3/1) organic coatings on faces of peds; slightly acid; abrupt smooth boundary.
A--10 to 18 inches; very dark grayish brown (10YR 3/2) sandy loam, dark grayish brown (10YR 4/2) dry; weak fine subangular blocky structure parting to weak fine granular; friable; common very fine roots throughout; many faint very dark gray (10YR 3/1) organic coatings on faces of peds; slightly acid; abrupt smooth boundary. (Combined thickness of the A horizons is 10 to 20 inches)
Bt1--18 to 25 inches; brown (10YR 4/3) sandy loam; moderate medium subangular blocky structure; friable; common very fine roots throughout; many distinct very dark grayish brown (10YR 3/2) and common distinct dark brown (10YR 3/3) organo-clay films on faces of peds; moderately acid; clear smooth boundary.
Bt2--25 to 33 inches; dark yellowish brown (10YR 4/4) sandy loam; weak medium prismatic structure parting to moderate medium subangular blocky; friable; few very fine roots throughout; common distinct dark brown (10YR 3/3) organo-clay films on faces of peds; moderately acid; clear smooth boundary. (Combined thickness of the Bt horizons is 10 to 25 inches)
BC--33 to 36 inches; dark yellowish brown (10YR 4/6) loamy sand; weak medium prismatic structure parting to weak medium subangular blocky; very friable; few very fine roots throughout; moderately acid; gradual smooth boundary. (0 to 15 inches thick)
C1--36 to 63 inches; dark yellowish brown (10YR 4/6) sand; single grain; loose; moderately acid; gradual smooth boundary.
C2--63 to 80 inches; 50 percent dark yellowish brown (10YR 4/4) and 50 percent brown (7.5YR 4/4) stratified loamy sand and sand; single grain; loose; 2 percent fine gravel; slightly acid.
TYPE LOCATION: Mason County, Illinois; about 1 mile south of Forest City; 2,530 feet south and 2,350 feet east of the northwest corner of section 18, T. 22 N., R. 6 W.; USGS Forrest City, Illinois topographic quadrangle; lat. 40 degrees 21 minutes 17 seconds N. and long. 89 degrees 49 minutes 11 seconds W.; NAD 27.
RANGE IN CHARACTERISTICS: The depth to the base of the argillic horizon ranges from 25 to 40 inches. Thickness of the mollic epipedon ranges from 10 to 20 inches. The particle-size control section averages about 12 to 18 percent clay. The series control section averages between 45 to 75 percent total sand. The sand size is dominantly medium sand and finer in all layers of the series control section.
The Ap or A horizon has hue of 10YR or 7.5YR; value of 2 or 3, value of 3 to 5 dry; and chroma of 1 to 3. It is sandy loam or fine sandy loam. Reaction ranges from strongly acid to slightly alkaline depending upon liming practices.
Some pedons have an AB or BA horizon.
The Bt horizon has hue of 10YR or 7.5YR, value of 4 or 5, and chroma of 3 to 6. Some pedons have redoximorphic features with chroma that range to 8. The Bt horizon typically is loam or sandy loam. Individual subhorizons are fine sandy loam, sandy clay loam, or clay loam. The Bt horizon commonly is slightly acid or moderately acid, but ranges from very strongly acid to neutral.
The BC horizon has hue of 10YR or 7.5YR, value of 4 to 6, and chroma of 3 to 6. Some pedons have redoximorphic features with chroma that range to 8. It typically is sandy loam or loamy sand and includes textures of fine sandy loam and loamy fine sand. Reaction ranges from strongly acid to neutral.
The C or 2C horizon has hue of 10YR or 7.5YR, value and chroma of 4 to 6. It typically is stratified. Textures of individual strata include loamy fine sand, fine sand, fine sandy loam, loamy sand, sand, sandy loam, loam, and silt loam. The content of very fine sand plus fine sand is greater than the content of coarse sand plus very coarse sand. This horizon is moderately acid to neutral. Rock fragment content is less than 2 percent.
COMPETING SERIES: These are the
Malardi and
Rasset series in the same family and the
Billett,
Coyne,
Dickinson,
Flagler,
Hesch,
Jasper and
Norborne series.
Malardi soils have free carbonates within 18 inches of the surface and contain more than 2 percent coarse fragments in the lower part of the series control section.
Rasset soils have, in the lower part of the series control section, more coarser sand and very coarse sand than fine sand and very fine sand.
Billett soils have a mollic surface less than 10 inches.
Coyne soils have the upper boundary of the argillic horizon below a depth of 40 inches. (The Coyne series has not been updated for cation exchange activity class.)
Dickinson and Flagler soils do not have argillic horizons.
Hesch soils have a lithic contact within a depth of 40 inches. (The Hesch series has not been updated for cation exchange activity class.)
Jasper soils are fine-loamy.
Norborne soils have mollic epipedons greater than 24 inches thick. (The Norborne series has not been updated for cation exchange activity class.)
GEOGRAPHIC SETTING: Onarga soils formed in 30 to 50 inches of eolian or water sorted loamy material and the underlying stratified outwash. They are on summits, shoulders and backslopes on stream terraces, outwash plains, beach ridges and lake plains. Slope gradients range from 0 to 10 percent. Mean annual air temperature ranges from 48 to 55 degrees F., mean annual precipitation ranges from 32 to 40 inches, frost free days ranges from 160 to 190 days, and elevation ranges from 350 to 700 feet above sea level.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Ade, Jasper, La Hogue, Ridgeville, and Selma soils. The Ade and Jasper soils are on similar landforms as Onarga soils. Ade soils have argillic horizons that consist of lamellae or bands. Jasper soils average more than 18 percent clay in the particle-size control section. The somewhat poorly drained La Hogue soils and the poorly drained Selma soils have more clay in the particle-size control section and are on slightly lower positions in the landscape. The somewhat poorly drained Ridgeville soils form a drainage sequence with the Onarga soils and are on adjoining lower elevations.
DRAINAGE AND PERMEABILITY: Well drained. The potential for surface runoff ranges from negligible to medium. Permeability is moderate or moderately rapid in the upper part of the series control section and rapid in the lower part. A rarely flooded phase is recognized.
USE AND VEGETATION: Most areas are cultivated. Corn and soybeans are the principal crops. Native vegetation is prairie grasses.
DISTRIBUTION AND EXTENT: Illinois and southern Indiana. The soils are of moderate extent.
MLRA OFFICE RESPONSIBLE: Indianapolis, Indiana
SERIES ESTABLISHED: Vermilion County, Illinois, 1931.
REMARKS: The type location was moved in May, 2000. Lab data for the previous typical pedon did not support placement in the coarse-loamy textural family. The percent clay in the particle-size control section has been expanded from 12 to 18 percent.
Diagnostic horizons and features recognized in this pedon are:
mollic epipedon -zone from the surface to a depth of 18 inches (Ap and A horizons);
argillic horizon -zone from approximately 18 to 33 inches (Bt1 and Bt2 horizons).
Additional Data: Site of typical pedon 85IL-125-046 from Mason County Illinois, University of Illinois Soil Characterization Lab.