LOCATION ROLFE IA+MNEstablished Series
TAXONOMIC CLASS: Fine, smectitic, mesic Typic Argialbolls
TYPICAL PEDON: Rolfe silt loam, in a depression, in a hayfield. (Colors are for moist soil unless otherwise stated.)
A--0 to 10 inches; black (10YR 2/1) silt loam, dark gray (10YR 4/1) dry; weak fine granular structure; friable; common prominent discontinuous strong brown (7.5YR 5/6) iron oxide coats in root channels; slightly acid; clear smooth boundary. (7 to 10 inches thick)
Eg1--10 to 13 inches; dark gray (10YR 4/1) silt loam, gray (10YR 6/1) dry; moderate thin platy structure; friable; common medium prominent yellowish brown (10YR 5/6) iron concentrations; moderately acid; clear smooth boundary.
Eg2--13 to 21 inches; gray (10YR 5/1) silt loam, light gray (10YR 7/1) dry; moderate thick platy structure; friable; few prominent patchy very dark gray (5Y 3/1) organic coats on faces of peds; few fine distinct yellowish brown (10YR 5/4) iron concentrations; moderately acid; abrupt smooth boundary. (Combined thickness of the E horizon is 4 to 14 inches.)
Btg1--21 to 27 inches; very dark gray (5Y 3/1) silty clay, dark gray (5Y 4/1) dry; strong fine and medium angular blocky structure; firm; thin discontinuous silt coats on faces of peds; few fine prominent brown (7.5YR 5/4) iron concentrations; moderately acid; gradual smooth boundary.
Btg2--27 to 32 inches; dark gray (5Y 4/1) silty clay; strong fine prismatic structure parting to fine angular blocky; firm; thin continuous very dark gray (5Y 3/1) clay films on faces of peds; common fine prominent dark yellowish brown (10YR 4/6) iron concentrations; slightly acid; gradual smooth boundary.
Btg3--32 to 40 inches; olive gray (5Y 4/2) silty clay; strong fine prismatic structure; friable; thin discontinuous very dark gray (5Y 3/1) clay films on faces of peds; few fine dark slightly hard accumulations (oxides); common medium prominent light olive brown (2.5Y 5/4) iron concentrations; neutral; gradual smooth boundary.
Btg4--40 to 55 inches; olive gray (5Y 5/2) silty clay; moderate medium prismatic structure; firm; thin patchy very dark gray (5Y 3/1) clay films on faces of peds; few fine slightly hard dark accumulations (oxides); common medium prominent yellowish brown (10YR 5/6) iron concentrations; neutral; clear smooth boundary. (Combined thickness of the Btg horizon is 25 to 38 inches.)
2BCg--55 to 71 inches; light olive gray (5Y 6/2) clay loam; weak medium prismatic structure; friable; few distinct patchy black (10YR 2/1) clay films in root channels; few fine slightly hard dark accumulations (oxides); about 2 percent gravel; many fine and medium prominent yellowish brown (10YR 5/4) iron concentrations; neutral; clear smooth boundary. (0 to 20 inches thick)
2Cg--71 to 80 inches; light brownish gray (2.5Y 6/2) loam; massive: friable; few fine slightly hard dark accumulations (oxides); about 2 percent gravel; common fine and medium prominent yellowish brown (10YR 5/6) iron concentrations; slightly effervescent; slightly alkaline.
TYPE LOCATION: Humboldt County, Iowa; about 5 miles west of Humboldt; located about 500 feet south and 620 feet east of the northwest corner of section 6, T. 91 N., R. 29 W., USGS Unique topographic quadrangle; lat. 42 degrees 43 minutes 52 seconds N. and long. 94 degrees 19 minutes 26 seconds W., NAD 83.
RANGE IN CHARACTERISTICS: The depth to carbonates ranges from 42 to 80 inches. The mollic epipedon is 10 to 24 inches thick and commonly is interrupted by an albic horizon. The top of the argillic horizon starts at depths of 24 inches or less. The depth to the underlying glacial drift is 24 to 60 inches. The underlying glacial drift has 18 to 35 percent clay and 30 to 45 percent sand.
The A or Ap horizon has hue of 10YR, value of 2 or 3 and chroma of 1 or 2. It is silt loam, loam or silty clay loam. Reaction is strongly acid to neutral.
The E horizon has hue of 10YR or 2.5Y, value of 3 to 6 and chroma of 1 or 2. Redoximorphic concentrations occur somewhere within this horizon. It is silt loam or loam. Reaction is strongly acid to slightly acid.
The Btg horizon has hue of 5Y, 2.5Y or less commonly 10YR, value of 3 to 6 (3 being mostly in the upper part) and chroma of 1 or 2. It is clay, silty clay or clay loam with 35 to 45 percent clay. Reaction is moderately acid to neutral. The clay increase is more than 20 percent compared to the E horizon.
The 2Btg horizon has hue of 5Y or 2.5Y, value of 4 or 5 and chroma of 1 or 2. It is loam or clay loam with 25 to 35 percent clay. It has 1 to 5 percent rock fragments. The reaction is slightly acid or neutral.
The 2BCg horizon has colors and textures similar to the 2Cg horizon. It has 1 to 5 percent rock fragments. It is neutral or slightly alkaline.
The 2Cg horizon has hue of 5Y or 2.5Y, value of 4 to 6 and chroma of 1 through 3. It has 1 to 5 percent rock fragments and 18 to 35 percent clay. Reaction is slightly alkaline or moderately alkaline.
COMPETING SERIES: These Chauncey, Concord, Plankinton, Sperry, Willowcreek (T) and Willowfork series. Chauncey and Willowfork soils have argillic horizons that start at depths of more than 24 inches. Concord and Sperry soils have silty substratums with less than 20 percent sand. Plankinton soils have a mollic epipedon greater than 24 inches thick. Willowcreek (T) soils are not currently in the OSED file.
GEOGRAPHIC SETTING: Rolfe soils are in shallow potholes and other depressions on the relatively undissected, gently undulating till plain thought to be Wisconsinan in age. They are mainly in the uplands, but in a few places are on stream terraces or glacial outwash areas. The soils have formed in local loamy alluvium and glacial drift. Slope gradients typically are less than 1 percent. Mean annual air temperature ranges from 45 to 50 degrees F. Mean annual precipitation from 28 to 32 inches. Frost-free period ranges from 145 to 170 days. Elevation ranges from 800 to 1,500 feet above mean sea level.
GEOGRAPHICALLY ASSOCIATED SOILS: These are mainly the Canisteo, Cordova, Clarion, Glencoe, Nicollet, Okoboji, Wacousta, and Webster soils. Canisteo and Webster soils are on concave slopes above the Rolfe soils. Cordova soils are on broad flat areas above Rolfe soils. Clarion and Nicollet soils are better drained and are on convex or plane slopes above the Rolfe soils. Glencoe, Okoboji, and Wacousta soils are on similar landscapes as the Rolfe soils.
DRAINAGE AND PERMEABILITY: Very poorly drained. This soil has an apparent seasonal high water table at a depth of +1 to 1 foot from November to July in most years. Surface runoff is very low or ponded. Permeability is slow.
USE AND VEGETATION: Mostly under cultivation where adequately drained. Corn, soybeans, small grain, and legume hay are the major crops. The native vegetation is wet prairie and marsh grasses and sedges.
DISTRIBUTION AND EXTENT: North-central Iowa and southern Minnesota. The series is small in extent.
MLRA OFFICE RESPONSIBLE: St. Paul, Minnesota
SERIES ESTABLISHED: Polk County, Iowa, 1958.
REMARKS: There is some question as to whether Rolfe soils in some areas do not have an abrupt clay increase in the argillic horizon, but at the present time it is believed best to classify them as Typic Argialbolls.
The type location was moved to this site from a site in Clay County to better portray the series concept and its geographic location.
Diagnostic horizons and features recognized in this pedon are: Mollic epipedon - the zone from the surface to a depth of 10 inches and 21 to 27 inches (Ap and Btg1 horizons); Albic horizon - the zone from a depth of 10 to 21 inches (Eg horizons); Argillic horizon - the zone from a depth of 21 to 55 inches (Btg1, Btg2, Btg3, and Btg4 horizons); Aquic moisture regime. Abrupt textural change at about 21 inches.