LOCATION OKOBOJI                 IA+MN

Established Series
Rev. RIT-TCJ-TWN
02/2014

OKOBOJI SERIES

The Okoboji series consists of very deep, very poorly drained soils formed in alluvium or lacustrine sediments. These soils are in closed depressions on till plains and moraines. Slope ranges from 0 to 1 percent. Mean annual air temperature is about 8 degrees C. Mean annual precipitation is about 740 millimeters.

TAXONOMIC CLASS: Fine, smectitic, mesic Cumulic Vertic Endoaquolls

TYPICAL PEDON: Okoboji silty clay loam, in a depression, in a cultivated field, at an elevation of about 341 meters above sea level. (All colors are for moist soil unless otherwise stated.)

Ap--0 to 15 centimeters; black (N 2/0) silty clay loam, black (10YR 2/1) dry; weak fine granular and very fine subangular blocky structure; friable; slightly alkaline; abrupt smooth boundary.

A1--15 to 41 centimeters; black (N 2/0) silty clay loam, black (10YR 2/1) dry; weak fine granular and very fine subangular blocky structure; friable; slightly alkaline; gradual smooth boundary.

A2--41 to 66 centimeters; black (10YR 2/1) silty clay loam, very dark gray (10YR 3/1) dry; weak fine granular and very fine subangular blocky structure; friable; few very fine prominent olive (5Y 4/3) redoximorphic concentrations; slightly alkaline; gradual smooth boundary.

A3--66 to 81 centimeters; black (10YR 2/1) silty clay loam, very dark gray (10YR 3/1) dry; weak very fine subangular blocky structure; firm; very few fine prominent olive (5Y 4/3) redoximorphic concentrations; few medium prominent olive gray (5Y 5/2) redoximorphic depletions; slightly alkaline; gradual smooth boundary. (Combined thickness of the A horizon is 60 to 90 centimeters.)

Bg1--81 to 91 centimeters; very dark gray (N 3/0) silty clay loam; weak very fine prismatic structure parting to weak very fine subangular blocky; firm; few fine prominent black (10YR 2/1) iron-manganese concretions; common fine distinct olive gray (5Y 5/2) redoximorphic depletions; slightly alkaline; clear smooth boundary.

Bg2--91 to 122 centimeters; dark gray (5Y 4/1) and olive gray (5Y 5/2) silty clay loam; weak fine prismatic structure parting to weak very fine subangular blocky; firm; common medium prominent black (10YR 2/1) iron-manganese concretions; few dark krotovinas; slightly effervescent; slightly alkaline; gradual smooth boundary.

Bg3--122 to 142 centimeters; dark gray (5Y 4/1) and olive gray (5Y 5/2) silty clay loam; weak medium prismatic structure parting to weak medium subangular blocky; friable; few very fine prominent black (10YR 2/1) iron-manganese concretions; few dark krotovinas; common coarse prominent olive brown (2.5Y 4/4) redoximorphic concentrations; slightly effervescent; slightly alkaline; clear smooth boundary. (Combined thickness of the Bg horizon is 0 to 75 centimeters.)

BCg--142 to 178 centimeters; dark gray (5Y 4/1) silty clay loam; weak medium prismatic structure parting to weak medium subangular blocky; friable; few very fine prominent black (10YR 2/1) iron-manganese concretions; few medium prominent olive brown (2.5Y 4/4) redoximorphic concentrations; strongly effervescent; moderately alkaline; clear smooth boundary. (0 to 41 centimeters thick)

Cg--178 to 200 centimeters; olive gray (5Y 5/2) silt loam; massive; friable; few fine and medium prominent black (10YR 2/1) iron-manganese concretions; thin strata of loam and sandy loam at 191 centimeters; many medium distinct light olive brown (2.5Y 5/4) redoximorphic concentrations; strongly effervescent; moderately alkaline.

TYPE LOCATION: Major Land Resource Area (MLRA) 103-Central Iowa and Minnesota Till Prairies, Webster County, Iowa subset; about 6 miles south of Fort Dodge; located about 220 feet east and 1,310 feet south of the northwest corner of section 26, T. 88 N., R. 29 W.; USGS Fort Dodge South topographic quadrangle; lat. 42 degrees 24 minutes 33 seconds N. and long. 94 degrees 12 minutes 11 seconds W., NAD 83.

RANGE IN CHARACTERISTICS:
Thickness of mollic epipedon--60 to 150 centimeters
Depth to carbonates--50 to 150 centimeters
Clay content of the particle-size control section (weighted average)--35 to 40 percent
Sand content of the particle-size control section (weighted average)--10 to 20 percent, fine sand and coarser

Ap and A horizon:
Hue--10YR to 5Y or is neutral
Value--2
Chroma--0 or 1
Texture--silty clay loam, mucky silty clay loam, silty clay, silt loam, or mucky silt loam
Clay content--20 to 42 percent
Sand content--less than 15 percent
Reaction--slightly acid to slightly alkaline

Bg horizon (when present):
Hue--2.5Y, 5Y, or is neutral
Value--3 to 6
Chroma--0 to 2
Texture--silty clay loam or silty clay
Clay content--30 to 45 percent
Sand content--5 to 20 percent
Reaction--neutral or slightly alkaline

Some pedons have a Bkg horizon with secondary carbonate accumulation

BCg horizon (when present):
Hue--2.5Y, 5Y, or is neutral
Value--4 to 6
Chroma--0 to 2
Texture--silty clay loam
Clay content--27 to 40 percent
Sand content--5 to 20 percent
Reaction--slightly alkaline or moderately alkaline

Cg horizon:
Hue--2.5Y, 5Y, or is neutral
Value--4 to 6
Chroma--0 to 2
Texture--silty clay loam or silt loam
Clay content--20 to 40 percent
Sand content--10 to 60 percent
Rock fragment content--0 percent
Reaction--slightly alkaline or moderately alkaline
Moist bulk density--1.4 to 1.5 g/cc

Some pedons have stratified material in the lower part of the Cg horizon with textures of silt loam, very fine sandy loam or clay loam

2Cg horizon (when present), below a depth of 150 centimeters:
Hue--2.5Y, 5Y, or is neutral
Value--4 to 6
Chroma--0 to 2
Texture--loam, clay loam, or sandy loam
Clay content--12 to 30 percent
Sand content--30 to 65 percent
Rock fragment content--1 to 8 percent
Reaction--slightly alkaline or moderately alkaline
Moist bulk density--1.4 to 1.6 g/cc

Some pedons have a 2Cg horizon with a texture of clay loam and a moist bulk density range of 1.6 to 1.9 g/cc (firm till)

COMPETING SERIES: These are the Chehalem, Clamo, Derrynane, Peotone, Rantoul, Shiloh, Southbrook, Wabash, Zoe, and Zook series.
Chehalem--have matrix chroma of 2 to 4 in the lower two thirds of the series control section and have a frequently saturated zone at a depth of 0.4 meter during the wettest periods of years when precipitation is within one standard deviation of the 30 year mean of annual precipitation
Clamo--have carbonates within depths of 35 to 75 centimeters, are in areas with a mean annual precipitation range of 485 to 1,170 millimeters and a mean annual air temperature range of 4 to 11 degrees C
Derrynane--have a sand content of more than 30 percent in the lower one fourth of the series control section and have 2 to 8 percent rock fragments in the lower third of the series control section
Peotone--have a mollic epipedon 60 to 90 centimeters thick and have a sand content that averages less than 10 percent in the particle-size control section
Rantoul--have a mollic epipedon 60 to 90 centimeters thick, have carbonates within a depth of 150 centimeters, and have a clay content that averages 45 to 60 percent in the particle-size control section
Southbrook--have a sand content of more than 70 percent in the lower third of the series control section
Shiloh--have a mollic epipedon 60 to 90 centimeters thick and have a sand content that averages less than 10 percent in the particle-size control section
Wabash--have a clay content that averages 45 to 60 percent in the particle-size control section
Zoe--have carbonates within a depth of 60 centimeters and do not have a cambic horizon
Zook--do not have carbonates within a depth of 150 centimeters

GEOGRAPHIC SETTING:
Parent material--alluvium or lacustrine sediments
Landform--closed depressions on till plains and moraines
Slope--0 to 1 percent
Elevation--300 to 400 meters above sea level
Mean annual air temperature--6 to 10 degrees C
Mean annual precipitation--585 to 890 millimeters
Frost-free period--155 to 200 days

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Canisteo, Harps, Klossner, Wacousta, and Webster soils.
Canisteo, Harps, and Webster--are at slightly higher landscape positions on rims of depressions and on flats and have a clay content that averages less than 35 percent in the particle-size control section
Klossner--are on landscape positions similar to that of the Okoboji soils and have 40 to 127 centimeters of sapric material over loamy deposits
Wacousta--are on landscape positions similar to that of the Okoboji soils and have a mollic epipedon less than 50 centimeters thick

DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY:
Drainage--very poorly drained--in undrained conditions, a frequently saturated zone occurs at the surface to a depth of 0.3 meters during the wettest periods of years when precipitation is within one standard deviation of the 30 year mean of annual precipitation
Saturated hydraulic conductivity--0.10 to 10.00 micrometers per second, 0.01 to 0.10 micrometers per second in the underlying materials in the firm till phase
Ponding--frequently ponded for long duration

USE AND VEGETATION:
Where drained, these areas are cultivated. The principal crops are corn, soybeans, and small grain. Reed canarygrass commonly dominates partially drained pasture. The native vegetation is herbaceous marsh species tolerant of excessive wetness such as, cattails, bulrushes, giant burreed, giant reed grass and hydrophytic sedges.

DISTRIBUTION AND EXTENT:
Physiographic Division--Interior Plains
Physiographic Province--Central Lowland
Physiographic section--Western lake section
MLRA--Central Iowa and Minnesota Till Prairie (103)
LRR M; north-central Iowa and south-central Minnesota
Extent--large

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: St. Paul, Minnesota

SERIES ESTABLISHED: Polk County, Iowa, 1958.

REMARKS:
Particle-size control section--the zone from a depth of 25 to 100 centimeters;
series control section--the zone from the surface to a depth of 150 centimeters.

Diagnostic horizons and features recognized in this pedon include:
mollic epipedon--the zone from the surface to a depth of 91 centimeters (Ap, A1, A2, A3 and Bg1 horizons);
cambic horizon--the zone from a depth of 81 to 142 centimeters (Bg1, Bg2, and Bg3 horizons);
aquic moisture regime.

Vertic subgroup based on linear extensibility greater than 6.0 centimeters between the surface and a depth of 100 centimeters.

Taxonomy version--Keys to Soil Taxonomy, tenth edition, 2006.

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National Cooperative Soil Survey
U.S.A.