LOCATION OKAW IL+IA KY MO
Established Series
Rev. RJH-JWS-DJF-RJB
06/2015
OKAW SERIES
The Okaw series consists of very deep, poorly drained, very slowly permeable soils on lacustrine terraces and lake plains; mainly along major tributaries of the Mississippi River. They formed in the dominantly clayey lacustrine sediments and have a thin mantle of loess or other silty material. Slope ranges from 0 to 2 percent. Mean annual temperature is about 55 degrees F., and mean annual precipitation is about 40 inches.
TAXONOMIC CLASS: Fine, smectitic, mesic Chromic Vertic Albaqualfs
TYPICAL PEDON: Okaw silt loam - with a slope of 1 percent on a lacustrine terrace in a cultivated field at an elevation of about 390 feet above mean sea level. (Colors are for moist soil unless otherwise stated.)
Ap--0 to 7 inches; dark grayish brown (10YR 4/2) silt loam, light brownish gray (10YR 6/2) dry; moderate very fine and fine granular structure; friable; common very fine roots; few very fine constricted tubular pores; few fine and medium rounded black (N 2.5/0) iron-manganese nodules with sharp boundaries; slightly acid; abrupt smooth boundary. (5 to 9 inches thick)
Eg1--7 to 11 inches; light brownish gray (10YR 6/2) silt loam, very pale brown (10YR 8/2) dry; moderate thin platy structure parting to weak fine granular; friable; few very fine roots; many very fine and fine continuous tubular pores; common fine distinct dark yellowish brown (10YR 4/4) masses of iron accumulation in the matrix; common fine and medium rounded black (N 2.5/0) iron-manganese nodules with sharp boundaries; strongly acid; clear smooth boundary.
Eg2--11 to 15 inches; light brownish gray (10YR 6/2) silt loam, very pale brown (10YR 8/2) dry; weak thin platy structure parting to weak fine granular; friable; few very fine roots; many very fine and fine pores; common fine prominent yellowish brown (10YR 5/8) masses of iron accumulation in the matrix; many fine and medium rounded black (N 2.5/0) iron-manganese nodules with sharp boundaries; very strongly acid; abrupt wavy boundary. (Combined thickness of the Eg horizon is 5 to 11 inches.)
2Btg--15 to 31 inches; grayish brown (10YR 5/2) silty clay; weak fine prismatic structure parting to weak fine angular blocky; very firm; few very fine roots; common faint grayish brown (10YR 5/2) clay films on faces of peds; few fine and medium prominent yellowish brown (10YR 5/6) masses of iron accumulation in the matrix; common fine and medium rounded black (5YR 2.5/1) iron-manganese nodules with sharp boundaries; light brownish gray (10YR 6/2) silt loam material in krotovinas and along cracks; very strongly acid; clear smooth boundary. (15 to 25 inches thick)
2Bg--31 to 41 inches; olive gray (5Y 5/2) silty clay; weak medium prismatic structure parting to weak medium and coarse angular and subangular blocky; very firm; few very fine roots along ped faces; few prominent very dark brown (10YR 2/2) iron-manganese stains on faces of peds; few fine and medium prominent yellowish brown (10YR 5/6) masses of iron accumulation in the matrix; common fine and medium rounded black (5YR 2.5/1) iron-manganese nodules with clear strong brown (7.5YR 4/6) boundaries; light brownish gray (10YR 6/2) silt loam material along cracks; very strongly acid; gradual smooth boundary. (8 to 15 inches thick)
2BCg--41 to 54 inches; olive gray (5Y 5/2) silty clay; weak coarse prismatic structure; very firm; few prominent very dark brown (10YR 2/2) iron-manganese stains on faces of peds; common medium prominent yellowish brown (10YR 5/6) masses of iron accumulation in the matrix; few fine and medium rounded black (5YR 2.5/1) iron-manganese nodules with clear strong brown (7.5YR 4/6) boundaries; strongly acid; gradual smooth boundary. (7 to 15 inches thick)
2Cg1--54 to 63 inches; olive gray (5Y 5/2) silty clay; massive; firm; common prominent very dark brown (10YR 2/2) iron-manganese stains on faces along some cleavage planes; many medium and coarse irregular black (10YR 2/1) masses of iron-manganese accumulation with diffuse strong brown (7.5YR 4/6) boundaries; neutral; clear smooth boundary.
2Cg2--63 to 73 inches; olive gray (5Y 5/2) clay; massive; very firm; few prominent shiny slickensides and common distinct olive gray (5Y 4/2) pressure faces along vertical cleavage planes; common fine and medium irregular dark reddish brown (5YR 3/4) masses of iron-manganese accumulation with clear boundaries and few medium irregular black (10YR 2/1) iron-manganese nodules with diffuse strong brown (7.5YR 4/6) boundaries; slightly alkaline; gradual smooth boundary.
2Cg3--73 to 80 inches; light olive gray (5Y 6/2) silty clay loam; massive; firm; few distinct shiny slickensides and few faint olive gray (5Y 5/2) pressure faces along cleavage planes; common medium and coarse prominent yellowish brown (10YR 5/6) masses of iron accumulation in the matrix; many medium and coarse irregular black (10YR 2/1) masses of iron-manganese accumulation with clear strong brown (7.5YR 4/6) boundaries; slightly alkaline.
TYPE LOCATION: Jackson County, Illinois; about 1.25 miles northwest of Vergennes; approximately 1,944 feet west and 105 feet north of the southeast corner of sec. 8, T. 7 S., R. 2 W.; USGS Vergennes, IL. topographic quadrangle; lat. 37 degrees 55 minutes 26 seconds N. and long. 89 degrees 20 minutes 48 seconds W.
RANGE IN CHARACTERISTICS: Depth to the base of soil development is 40 to 75 inches. Depth to the clayey lacustrine sediments is 10 to 20 inches. The particle-size control section averages 40 to 60 percent clay and less than 15 percent sand. Sand content of the A and E horizons is less than 10 percent and includes iron-manganese nodules and concretions.
The upper part of the series control section (Ap and Eg) has properties as follows: The Ap horizon has value of 4 or 5 (5 to 7 dry) and chroma of 1 or 2. Some pedons have value of 3 (6 or more dry). Pedons in uncultivated areas have an A horizon 3 to 5 inches thick with ranges in color and texture similar to those for the Ap horizon. Texture is silt loam. Clay content is 15 to 27 percent. Reaction is very strongly acid to moderately acid except pedons that have been limed range to neutral.
The Eg horizon has value of 4 to 7 and chroma of 1 or 2. Texture is silt loam or, less commonly, silty clay loam. Clay content is 12 to 30 percent. Reaction is very strongly acid or strongly acid, except pedons that have been limed range to slightly acid.
Some pedons have a B/E horizon less than 3 inches in thickness that is mostly Bt material with clay depletions on faces of peds.
The second part of the series control section (2Btg and 2Bg) has hue of 10YR, 2.5Y, 5Y, or is neutral; value of 4 to 6; and chroma of 0 to 2. Redoximorphic concentrations commonly have colors with hue redder than 10YR. The 2Btg and 2Bg horizons typically are silty clay or clay. Some pedons have thin subhorizons that are silty clay loam. Some pedons have slickensides or pressure faces on the exteriors of peds. Reaction is very strongly acid or strongly acid, and some pedons have subhorizons that are extremely acid.
The third part of the series control section (2BCg) has hue of 10YR, 2.5Y, 5Y, or is neutral; value of 4 to 6; chroma of 0 to 2. Redoximorphic concentrations commonly have colors with hue redder than 10YR. The 2BCg horizon is silty clay loam, silty clay, or clay. Clay content is 35 to 60 percent and sand content is less than 15 percent. Reaction typically is very strongly acid to moderately acid, but ranges to neutral in some pedons.
The lower part of the series control section (2Cg) has colors for the matrix and redoximorphic concentrations in the same range as stated for the 2BCg horizon. The 2Cg horizon is silty clay loam, silty clay, or clay. It typically is stratified. Clay content is 35 to 55 percent and sand content is less than 15 percent. Reaction is very strongly acid to moderately alkaline. Some pedons contain carbonates.
COMPETING SERIES: These are the
Beckwith,
Floraville, and
Mariosa series. Beckwith soils contain less clay in the lower part of the B horizon and in the C horizon and have higher B/C clay ratios and are in areas that have a mean annual soil temperature less than 56 degrees F. Floraville soils contain less clay in the upper part of the B horizon. Mariosa soils have fragic characteristics in the lower part of the B horizon.
GEOGRAPHIC SETTING: Okaw soils are on nearly level areas of lacustrine terraces and lake plains; mainly along major tributaries of the Mississippi River. Some areas are subject to rare or common flooding for brief periods from March to June. Slopes typically are 0 to 1 percent but range from 0 to 2 percent. Okaw soils formed in the dominantly clayey lacustrine sediments and have a mantle of loess or other silty material between 10 and 20 inches in thickness. The lacustrine sediments in and underlying the Okaw series are weathered to depths of 10 or 12 feet. Below 80 inches the stratified lacustrine sediments have coarse structure and widely-spaced cleavage planes, clay films on faces of structural units and in channels, segregation of iron-manganese oxides, accumulation of secondary carbonates, and the presence of dark strata. Mean annual temperature is 54 to 57 degrees F., mean annual precipitation is 36 to 44 inches, frost-free period is 180 to 210 days, and elevation is 340 to 450 feet above mean sea level.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the
Bartelso,
Colp,
Geff,
Hurst,
Lakaskia,
Ridgway,
Wabash, and
Wagner soils. The somewhat poorly drained Bartelso soils and the poorly drained Lakaskia soils have mollic epipedons and typically have a slightly thicker silty mantle. The moderately well drained Colp soils and the somewhat poorly drained Hurst soils are on more sloping parts of the landform and they form a hydrosequence with the poorly drained Okaw soils. The somewhat poorly drained Geff soils and the well drained Ridgway soils contain less clay and more sand in the control section and are on high flood plains and stream terraces nearby. Wabash soils have a mollic epipedon greater than 36 inches in thickness and are in old oxbows and drainageways. The poorly drained Wagner soils are in slightly depressional areas adjacent to the Okaw soils. The dark Lakaskia soils and the moderately dark Wagner soils form a biosequence with the light-colored Okaw soils.
DRAINAGE AND PERMEABILITY: Poorly drained and very slow permeability. The potential for surface water runoff is low to negligible. In drained areas, depth to an intermittent perched high water table is 0.5 foot above the surface to 1.0 foot below from November to May in most years.
USE AND VEGETATION: Most areas are cropped. Corn, soybeans, and wheat are the principal crops. Some areas are pastured or wooded. Native vegetation is mixed hardwood forest. See Additional Data section for native vegetative cover in Iowa.
DISTRIBUTION AND EXTENT: Southern Illinois, Missouri, Iowa, and northwest Kentucky; extent is moderate, and mainly in MLRA(s) 113, 114B, and 115.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Indianapolis, Indiana
SERIES ESTABLISHED: Washington County, Illinois, 1927.
REMARKS: The typical pedon was originally published in the Soil Survey of Jackson County, Illinois (1979) and 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 15 inches (Ap, Eg1, and Eg2 horizons). Albic horizon - from a depth of 7 to 15 inches (Eg1 and Eg2 horizons).
Albaqualf feature - abrupt textural change from the Eg2 horizon to the 2Btg horizon.
Argillic horizon - from a depth of approximately 15 to 31 inches (2Btg horizon).
Aquic conditions - periodic saturation and reduction indicated by redoximorphic features throughout the soil.
ADDITIONAL DATA: Data for a pedon in Williamson County, Illinois is on file in the Illinois state office. It was sampled on August 14, 1968 and is identified by lab. numbers 21145 to 21152.
In Iowa, the native vegetative cover is a mixed herbaceous and woody community commonly inhabited with Green Ashes, American Elms, Common Hackberries, Eastern Cottonwoods, American Sycamores, Silky Dogwoods, Black Willows, Wild Black Currants, Riverbank Grapes, Grays Sedges, Hop Sedges, Virginia Wildryes, Stiff Bedstraws, White Avens, Wood Nettles, False Nettles, Canadian Clearweeds, and Common Bonesets. Source: Iowa State Office, Natural Resources Conservation Service, Des Moines, IA.
National Cooperative Soil Survey
U.S.A.