LOCATION SEYMOUR IA+MO WIEstablished Series
TAXONOMIC CLASS: Fine, smectitic, mesic Aquertic Argiudolls
TYPICAL PEDON: Seymour silt loam with a convex, north-facing slope of 2 percent - cultivated. (Colors are for moist soil unless otherwise stated.)
Ap--0 to 7 inches; very dark gray (10YR 3/1) silt loam (23 percent clay), gray (10YR 5/1) dry; very weak thick platy structure parting to weak fine subangular blocky and fine granular; friable; many fine roots; very few very fine dark brown (10YR 3/3) soft (oxides) accumulations; slightly acid; abrupt smooth boundary.
A1--7 to 11 inches; very dark gray (10YR 3/1) and some very dark grayish brown (10YR 3/2) silt loam (25 percent clay), gray (10YR 5/1) dry; weak very fine subangular blocky and weak fine granular structure; friable; many fine roots; few krotovinas; common very fine dark brown (10YR 3/3) and black (10YR 2/1) concretions (oxides); medium acid; clear smooth boundary.
A2--11 to 15 inches; very dark gray (10YR 3/1) and 20 percent very dark grayish brown (10YR 3/2) silty clay loam (28 percent clay), grayish brown (10YR 5/2) dry; moderate very fine subangular blocky structure; friable; many fine roots; few worm casts or mixing of dark grayish brown (10YR 4/2); few krotovinas; few thin silt coats on peds; few very fine soft dark brown (10YR 3/3) and black (10YR 2/1) accumulations (oxides); medium acid; clear smooth boundary. (Combined thickness of the A horizons is 10 to 18 inches.)
BA--15 to 19 inches; dark grayish brown (2.5Y 4/2) silty clay loam (35 percent clay), light brownish gray (10YR 6/2) dry; few fine faint olive brown (2.5Y 5/4) mottles; moderate very fine subangular blocky structure; firm; common fine roots; fine dark brown (10YR 3/3) and black (10YR 2/1) accumulations (oxides); medium acid; clear smooth boundary. (0 to 6 inches thick)
Bt1--19 to 23 inches; dark grayish brown (10YR 4/2) silty clay (47 percent clay); faces of peds dark gray (10YR 4/1); common fine faint dark yellowish brown (10YR 4/4) mottles on faces and many fine distinct yellowish brown (10YR 5/4) mottles in interiors of peds; strong very fine subangular blocky structure; very firm; few fine roots; few faint clay films; krotovina filled with very dark gray (10YR 3/1) silty clay loam; common very fine soft dark brown (10YR 3/3) and black (10YR 2/1) accumulations (oxides); medium acid; clear smooth boundary.
Bt2--23 to 28 inches; dark grayish brown (10YR 4/2) silty clay (51 percent clay); few fine faint brown (10YR 4/3) mottles on faces of peds; many fine distinct yellowish brown (10YR 5/4-5/6) mottles in interiors of peds; strong very fine angular and subangular blocky structure; very firm; few fine roots; some large oblique pressure faces; few distinct very dark gray (10YR 3/1) clay films; few fine tubular pores; common fine black (10YR 2/1) concretions (oxides); slightly acid; clear smooth boundary.
Bt3--28 to 36 inches; dark gray (10YR 4/1), dark grayish brown (10YR 4/2), and grayish brown (2.5Y 5/2) silty clay (46 percent clay); faces of peds are dark gray (10YR 4/1); common fine distinct yellowish brown (10YR 5/4) mottles; weak medium prismatic structure parting to moderate fine and medium subangular blocky; firm; some oblique pressure faces; few faint clay films; very few silt coats; slightly acid; clear irregular boundary.
Bt4--36 to 54 inches; olive gray (5Y 5/2) and some dark gray (2.5Y 4/1) silty clay loam (38 percent clay); common medium and fine prominent yellowish brown (10YR 5/6) mottles; moderate medium prismatic structure parting to moderate medium subangular blocky; firm; some oblique pressure faces; very thin discontinuous clay films on prism faces and in a few pores; common fine black (10YR 2/1) concretions (oxides); a few 1/2 inch diameter clay balls in lower part; neutral; gradual smooth boundary. (Combined thickness of the Bt horizons is 16 to 40 inches.)
BC--54 to 64 inches; olive gray (5Y 5/2) and some dark gray (2.5Y 4/1) silty clay loam (32 percent clay); few fine distinct yellowish brown (10YR 5/6) and strong brown (7.5YR 5/6) mottles; very weak coarse prismatic structure parting to very weak coarse angular blocky; friable; few dark gray (10YR 4/1) clay coats in pores; common 1/2 inch clay balls; neutral.
TYPE LOCATION: Wayne County, Iowa; about 2 miles south of Promise City; 342 feet west and 497 feet south of the center, sec. 3, T. 68 N., R. 20 W.
RANGE IN CHARACTERISTICS: Thickness of the solum commonly is 60 inches or more, and usually the loess lacks carbonates throughout. On uplands, these soils are underlain by paleosols at depths of 4 to 8 feet. On benches, the Seymour soils are underlain below 4 feet by alluvium of early Wisconsin or pre-Wisconsin Age. Content of fine sand and coarser is less than 3 percent.
The A or Ap horizon typically is very dark gray (10YR 3/1), but the color ranges from black (10YR 2/1) to very dark gray grayish brown (10YR 3/2). It is silt loam or silty clay loam. Clay content of the A horizon increases as gradient increases on convex slopes. On the less sloping parts of the landscape where these soils intergrade to Edina soils, they have in the A2 horizon thin discontinuous grainy coats, which are not discernible when the soil is moist.
The matrix of the upper part of the Bt horizon is 10YR or 2.5Y in hue with value of 4 or 5 and chroma of 2. The Bt horizon has a subhorizon with a clay content of 50 to 55 percent. Depth to clay maximum decreases as gradient increases on convex slopes. Clay films are common on both horizontal and vertical faces of peds in the Bt horizon. The matrix of the lower part of the Bt horizon has hue of 10YR to 5Y, value of 4 to 6, and chroma of 1 or 2.
The BC horizon and the C horizon, where present, have hue of 2.5Y or 5Y, value of 5 or 6, and chroma of 2. The upper part of the C horizon commonly is silty clay loam.
COMPETING SERIES: These are the Adair, Arispe, Chase, Flanagan, Greenton, Grundy, Herrick, Ipava, Lagonda, Lamoni, Macksburg, Mahaska, Malvern, Martin, Mayberry, Pawnee, Rutland, Shorewood, and Wymore series in the same family and the Clarinda, Edina, Kilwinning, and Kniffin series. Adair and Lamoni soils contain more sand and pebbles, and Adair soils have redder hues. Arispe, Flanagan, Grundy, Herrick, Ipava, Macksburg, and Mahaska soils are lower in clay in the finest part of the B horizon. Chase soils have thicker mollic epipedons. Greenton soils have higher chroma colors in the argillic horizon and more clay in the 2BC and 2C horizons. Lagonda, Mayberry, and Pawnee soils have more sand in the solum. Malvern soils have redder hue in much of the solum. Martin soils formed in residuum of clayey shale and have a mollic epipedon 24 to 36 inches thick. Rutland soils have 2B and 2C horizons of lacustrine sediments or glacial till that are clay or silty clay textures. Shorewood soils have a thinner solum. Wymore soils have a thinner solum, are less acid, and have a drier climate. Clarinda soils have lower chroma and fewer mottles in the upper part of the B horizon and contain more sand. Edina soils have an albic horizon, an abrupt change in texture from the A to the B horizon, and dark coatings with chroma of 1 in the upper part of the B horizon. Kilwinning soils lack a mollic epipedon. Kniffin soils lack a mollic epipedon and have an E horizon.
GEOGRAPHIC SETTING: Most of the Seymour soils are on convex ridgetops and on side slopes surrounding the nearly level stable upland divides in the loess-covered Kansan and Nebraskan till plains. Some are on benches and are underlain at depths greater than 4 feet by alluvium of Wisconsin or pre-Wisconsin Age. Slope gradients range from 2 to 9 percent. Seymour soils formed in loess containing less than 5 percent sand. Mean annual temperature ranges from about 50 to 58 degrees F, and mean annual precipitation ranges from about 32 to 38 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Adair, Clarinda, Edina, Kniffin, and Lagonda series and the Rathbun series. The Seymour soils are in a drainage sequence with the Edina soils. Seymour soils are on the gently sloping to moderately sloping convex interfluves that slope away from Edina soils on stable flats. In uplands, Seymour soils are upslope and generally at slightly higher elevations than Adair, Clarinda, and Lagonda soils which are on steeper, more strongly dissected topography. Seymour, Kniffin, and Rathbun soils are a biosequence of which the Seymour soils are the prairie member, the Kniffin soils the transitional member, and the Rathbun soils the forested member. These soils are on similar landscape positions.
DRAINAGE AND PERMEABILITY: Somewhat poorly drained. Runoff is medium. Permeability is very slow.
USE AND VEGETATION: Corn, oats, and hay and pasture are the major uses. Native vegetation was tall prairie grasses.
DISTRIBUTION AND EXTENT: Southern Iowa and northern Missouri. The series is extensive, and individual areas are large in size.
MLRA OFFICE RESPONSIBLE: St. Paul, Minnesota
SERIES ESTABLISHED: Wayne County, Iowa, 1942.
REMARKS: Classification only was updated for final correlations in Iowa. Changes include proposals made in Amendment 17 to Soil Taxonomy. Competing series and other updates will be made later. Diagnostic horizons and features recognized in this pedon are: mollic epipedon - the zone from the surface of the soil to a depth of 15 inches (Ap, A1, and A2 horizons); argillic horizon - the zone from a depth of 15 to 54 inches (Bt1, Bt2, Bt3, and Bt4 horizon).