LOCATION CORWITH IA+MNEstablished Series
TAXONOMIC CLASS: Coarse-silty, mixed, superactive, mesic Aquic Hapludolls
TYPICAL PEDON: Corwith loam--on a 2 percent convex slope in a cultivated field. (All colors are for moist soil unless otherwise stated.)
Ap--0 to 9 inches; black (10YR 2/1) loam with some very dark brown (10YR 2/2) peds, very dark gray (10YR 3/1) dry; some mixing of very dark grayish brown (10YR 3/2); weak fine and very fine granular structure; friable; few fine roots; slight effervescence; moderately alkaline; abrupt smooth boundary.
A--9 to 14 inches; very dark grayish brown (10YR 3/2) loam, dark gray (10YR 4/1) dry; very dark gray (10YR 3/1) coatings on faces of peds; weak fine subangular blocky structure parting to weak fine and very fine granular; friable; few fine roots; brown (10YR 4/3) and dark yellowish brown (10YR 4/4) worm castings; strong effervescence; moderately alkaline; gradual smooth boundary. (Combined thickness of the A horizon is 8 to 18 inches.)
BA--14 to 18 inches; very dark grayish brown (10YR 3/2) silt loam, dark grayish brown (10YR 4/2) in lower part; very dark gray (10YR 3/1) coatings on faces of peds; weak very fine subangular blocky structure parting to weak fine and medium granular; friable; few fine roots; brown (10YR 4/3) and dark yellowish brown (10YR 4/4) worm castings; strong effervescence; moderately alkaline; gradual smooth boundary. (0 to 6 inches thick)
Bw1--18 to 24 inches; yellowish brown (10YR 5/4) and dark grayish brown (10YR 4/2) silt loam; weak medium subangular blocky structure parting to weak fine and very fine subangular blocky; friable; very dark grayish brown (10YR 3/2) worm castings; strong effervescence; moderately alkaline; gradual smooth boundary.
Bw2--24 to 31 inches; mottled yellowish brown (10YR 5/6 and 5/4), dark grayish brown (10YR 4/2), and brown (10YR 4/3) silt loam high in sand; common fine distinct pale brown (10YR 6/3) mottles; weak medium subangular blocky structure; friable; few fine tubular pores; few fine strong brown (7.5YR 5/6) oxide concretions; strong effervescence; moderately alkaline; gradual wavy boundary. (Combined thickness of the Bw horizons is 10 to 20 inches.)
C--31 to 60 inches; mottled light brownish gray (2.5Y 6/2), pale brown (10YR 6/3), and light yellowish brown (2.5Y 6/4) silt loam; few fine distinct brown (7.5YR 4/4) and strong brown (7.5YR 5/6) and common medium distinct yellowish brown (10YR 5/8) mottles; massive; friable; few fine tubular pores; few fine and medium dark reddish brown (5YR 3/4) concretions (oxides); few fine light gray (10YR 7/2) calcium carbonate accumulations in thread-like streaks; strong effeverscence; moderately alkaline.
TYPE LOCATION: Kossuth County, Iowa; 5 miles east and 3 miles north of West Bend; 2,440 feet north and 315 feet east of the southwest corner of sec. 25, T. 95 N., R. 30 W.
RANGE IN CHARACTERISTICS: The thickness of the solum is 24 to 44 inches. Free carbonates are throughout the solum. The solum is mildly or moderately alkaline. The mollic epipedon is 10 to 20 inches thick. About 50 to 80 percent of the sand in the control section is very fine sand.
The A horizon is neutral or has hue of 10YR, value of 2 or 3, and chroma of 0 to 2. It is loam or silt loam that has a high content of sand. An AB horizon is in some pedons.
The BA horizon typically has hue of 10YR or 2.5Y, value of 3 or 4, and chroma of 2, but value of 2 or 3 with chroma of 1 are in some pedons. It is loam or silt loam that has a high content of very fine sand.
The Bw horizon typically has hue of 10YR or 2.5Y, value of 4 or 5, and chroma of 2 to 6. The BC horizonis in some pedons and has hue of 10YR to 5Y, value of 4 or 5, and chroma of 2 to 6. The Bw and BC horizons usually are loam or silt loam, but in a few pedons they are very fine sandy loam. The Bw and BC horizons lack stones and pebbles. Black, strong brown, dark brown, or dark reddish brown oxide concretions are few or common. In some pedons, calcium carbonate nodules are present.
The C horizon has hue of 10YR to 5Y, value of 4 to 6, and chroma of 2 to 8. The C horizon usually is silt loam or very fine sandy loam but ranges to include loamy fine or medium sand. In some pedons, strata of silty clay loam are present. Glacial till is at a depth of 60 to 100 inches or more in most pedons but ranges to as shallow as 50 inches.
COMPETING SERIES: There are no other series in the same family. Closely competing series are the Crippin, Fostoria, Grogan, Kingston, Nicollet and Yahara series. Crippin, Fostoria, and Nicollet soils are fine-loamy. In addition, the Fostoria and Nicollet soils lack free carbonates within the solum. Grogan soils are well or moderately well drained and are leached of carbonates to a depth of 20 inches or more. Kingston soils are fine-silty and lack free carbonates in the solum. Yahara soils are coarse-loamy and are leached of carbonates to a depth of 24 inches or more.
GEOGRAPHIC SETTING: Typically, Corwith soils are on slightly convex slopes with gradients of 1 to 3 percent. The soils formed in medium- textured sediments that mantle the Early Wisconsin till plains. Mean annual temperature ranges from 45 to 49 degrees F, and mean annual precipitation ranges from 26 to 29 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Crippin, Fostoria, Kingston and Nicollet and the Canisteo soils. Canisteo soils are poorly drained and are lower in the landscape. The competing soils are on similar landscape positions.
DRAINAGE AND PERMEABILITY: Corwith soils are somewhat poorly drained. Runoff is slow. Permeability is moderate.
USE AND VEGETATION: Most areas of Corwith soils are cultivated. Corn and soybeans are the principal crops. The native vegetation was tall prairie grasses.
DISTRIBUTION AND EXTENT: Corwith soils are not extensive. They are in north-central Iowa and south-central Minnesota.
MLRA OFFICE RESPONSIBLE: St. Paul, Minnesota
SERIES ESTABLISHED: Kossuth County, Iowa, 1980.
ADDITIONAL DATA: Particle-size data including sand fraction are available at the soil survey laboratory, Iowa State University, Ames, Iowa.