LOCATION RATHBUN IAEstablished Series
TAXONOMIC CLASS: Fine, smectitic, mesic Vertic Epiaqualfs
TYPICAL PEDON: Rathbun silt loam - pasture, with a 3 percent convex north-facing slope. (Colors are for moist soil unless otherwise stated.)
A--0 to 4 inches; very dark gray (10YR 3/1) silt loam (21 percent clay), light gray (10YR 6/1) dry; moderate thin and very thin platy structure; friable; thin patchy light gray (10YR 7/1) dry silt coatings on faces of peds; few fine brown (7.5YR 4/4) accumulations (oxides); medium acid; abrupt smooth boundary. (2 to 5 inches thick)
E1--4 to 7 inches; brown (10YR 5/3) silt loam (21 percent clay), pale brown (10YR 6/3) dry; moderate thin platy structure; friable; few dark grayish brown (10YR 4/2) mottles; thin discontinuous light gray (10YR 7/2) dry silt coatings on faces of peds; few fine dark reddish brown (5YR 3/2) accumulations (oxides); very strongly acid; clear smooth boundary.
E2--7 to 13 inches; yellowish brown (10YR 5/4) silt loam (26 percent clay), pale brown (10YR 6/3) dry; weak coarse platy structure parting to weak medium and fine subangular blocky; friable; thin discontinuous light gray (10YR 7/2) dry silt coatings on faces of peds; few fine dark reddish brown (5YR 3/2) accumulations (oxides); very strongly acid; clear smooth boundary. (Combined thickness of the E horizons is 0 to 12 inches.)
BE--13 to 17 inches; yellowish brown (10YR 5/4) silty clay (37 percent clay); brown (10YR 5/3) coatings on peds; strong fine and very fine angular and subangular blocky structure; firm; thin nearly continuous light gray (10YR 7/1) dry silt coatings on faces of peds; few fine dark reddish brown (5YR 3/2) accumulations (oxides); very strongly acid; abrupt smooth boundary. (0 to 6 inches thick)
Bt1--17 to 25 inches; dark grayish brown (10YR 4/2) silty clay (52 percent clay); few fine faint dark yellowish brown (10YR 4/4) mottles; moderate very fine subangular blocky structure; very firm; few fine dark brown (7.5YR 3/2) oxides; common distinct clay films; very strongly acid; clear smooth boundary.
Bt2--25 to 31 inches; dark grayish brown (10YR 4/2) silty clay (47 percent clay); common fine faint dark yellowish brown (10YR 4/4) mottles; weak fine subangular blocky structure; very firm; common distinct clay films; few fine dark brown (7.5YR 3/2) accumulations (oxides); very strongly acid; clear smooth boundary.
Bt3--31 to 36 inches; mottled grayish brown (2.5Y 5/2) and yellowish brown (10YR 5/4) silty clay (43 percent clay); few fine faint dark brown (7.5YR 4/4) mottles; weak medium prismatic structure parting to weak fine and medium subangular blocky; firm; common distinct clay films; common fine dark brown (7.5YR 3/2) accumulations (oxides); strongly acid; gradual smooth boundary.
Bt4--36 to 44 inches; mottled grayish brown (2.5Y 5/2) and strong brown (7.5YR 5/6) silty clay loam (38 percent clay); weak medium prismatic structure parting to weak medium subangular blocky; firm; few faint dark grayish brown (10YR 4/2) clay films; common fine dark brown (7.5YR 3/2) accumulations (oxides); strongly acid; gradual smooth boundary.
Bt5--44 to 54 inches; mottled light brownish gray (2.5Y 6/2) and strong brown (7.5YR 5/6) silty clay loam (34 percent clay); weak medium prismatic structure; firm; few thin patchy clay films on vertical prism faces; common fine dark brown (7.5YR 3/2) accumulations (oxides); few black (5YR 2/1) concretions (iron and manganese oxides) and stains on prism faces; slightly acid; gradual smooth boundary. (Combined thickness of the Bt horizons is 30 to 50 inches.)
BC--54 to 63 inches; light brownish gray (2.5Y 6/2) silty clay loam (31 percent clay); many fine and medium prominent strong brown (7.5YR 5/6) mottles; weak medium prismatic structure parting to weak medium subangular blocky; friable; common fine dark brown (7.5YR 3/2) and few medium yellowish red (5YR 4/6) accumulations (oxides); few clay flows in root channels; thin discontinuous light gray (10YR 7/1) dry silt coats on faces of prisms; slightly acid.
TYPE LOCATION: Wayne County, Iowa; about 12 miles south of Corydon; 680 feet south and 540 feet west of the center, sec. 19, T. 67 N., R. 21 W.
RANGE IN CHARACTERISTICS: Solum thickness typically exceeds 5 feet. Carbonates are absent even below the solum. The solum typically is strongly or very strongly acid in the most acid part.
The Ap horizon has hue of 10YR, value of 4 or 5, and chroma of 1 through 3. It is silt loam or silty clay loam. The A horizon ranges from very dark gray (10YR 3/1) to dark gray (10YR 4/1) or dark grayish brown (10YR 4/2).
The E horizon has hue of 10YR, value of 5, and chroma of 2 through 4. It is incorporated in the Ap horizon in some eroded areas.
The silt coats are oriented horizontally in the lower part of the BE horizon. The BE horizon typically has hue of 10YR, value of 5, and chroma of 3 or 4.
The upper part of the Bt horizon typically is dark grayish brown (10YR 4/2), but hue ranges to 2.5Y. Below depths of about 30 inches hue is 2.5Y or 5Y, value is 5 or 6, and chroma is 2 or in some pedons 3. Mottles have hue of 7.5YR to 2.5Y, value of 5 or 6, and chroma of 2 to 6. They commonly are present within depths of 20 inches and become more distinct and more numerous with depth. Colors of the lower part of the Bt horizon appear to be relict and related to a deoxidized and leached weathering zone. The clay maximum typically is about 16 to 20 inches below the surface on stable slopes and has a range in clay content from 48 to 56 percent. Depth to clay maximum decreases with increasing gradient on convex slopes.
COMPETING SERIES: These are the Bluford, Calwoods, Hurst, Keomah, Kernan, and Sabina series in the same family and the Clinton, Kniffin, Pershing, and Weller series. Bluford, Keomah, and Sabina soils have Bt horizon with a clay maximum of less than 48 percent. Calwoods soils have a thinner solum and have red mottles. Hurst soils have a thinner solum and lack a decrease in clay content from the lower B horizon to the C horizon. Kernan soils have lower clay maximum in the Bt horizon and have a less acid solum. Clinton soils have higher chroma in the B horizon. Kniffin and Pershing soils have a thicker and/or darker colored A horizon and usually have 1 chroma clay coatings in the upper part of the B horizon. Also, Pershing soils have a clay maximum from 42 to 48 percent clay. Weller soils lack 2 chroma in the upper part of the B horizon.
GEOGRAPHIC SETTING: Rathbun soils typically are on convex ridge crests and side-valley slopes adjoining the nearly level, stable upland divides in the loess-covered Kansas and Nebraskan till plain. Some are on high benches. Slope gradients range from 2 to about 9 percent. These soils formed partly in oxidized and leached and partly in deoxidized and leached loess (Wisconsinan) low in sand content (5 percent). On upland areas the Rathbun soils are underlain by a paleosol. Mean annual temperature ranges from 50 to 54 degrees F, and mean annual precipitation ranges from 32 to 34 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Beckwith, Keswick, Lindley, and Marion soils. Rathbun soils are on the gently to moderately sloping, ribbed interfluves that slope away from the stable Beckwith and Marion flats. Beckwith and Marion soils have an abrupt textural change between the A and B horizons. Rathbun soils are upslope and generally at slightly higher elevations than the Keswick and Lindley soils. Keswick soils have redder hue, Lindley soils are less clayey, and both contain more sand in the solum. Rathbun soils are the forested member of the biosequence that includes the Kniffin as the intergrade and the Seymour as the prairie member.
DRAINAGE AND PERMEABILITY: Somewhat poorly drained; medium runoff; very slow permeability.
USE AND VEGETATION: Mainly hay and pasture but some cropped to corn and oats and some areas are left in woodland. Native vegetation was deciduous trees.
DISTRIBUTION AND EXTENT: Southern Iowa and possibly northern Missouri. The series is of moderate extent and is important to agriculture in the area of its occurrence.
MLRA OFFICE RESPONSIBLE: St. Paul, Minnesota
SERIES ESTABLISHED: Appanoose County, Iowa, 1970.
Classification only was updated 3/94 for final correlations in Iowa. Changes include proposals made in Amendment 17 of Soil Taxonomy. Competing series and other updates will me made later. Diagnostic horizons and features recognized in this pedon are: ochric epipedon - the zone from the surface to a depth of 13 inches (A and E horizons); argillic horizon - the zone from approximately 13 inches to 54 inches (BE, Bt1, Bt2, Bt3, Bt4, and Bt5 horizons); an aquic soil moisture regime.
ADDITIONAL DATA: This site was sampled (Sample No. S-69-Iowa-93-2) for characterization by the Lincoln Soil Survey Laboratory, 11/69.