LOCATION STRAHAN IAEstablished Series
TAXONOMIC CLASS: Fine-silty, mixed, superactive, nonacid, mesic Typic Udorthents
TYPICAL PEDON: Strahan silt loam - on a convex slope of 10 percent - cultivated. (Colors are for moist conditions unless otherwise stated.)
Ap--0 to 7 inches; mixed brown (10YR 4/3) and very dark grayish
brown (10YR 3/2) silt loam; pale brown (10YR 6/3) and dark grayish brown (10YR 4/2) dry; moderate fine subangular blocky structure; friable; neutral; clear smooth boundary. (4 to 10 inches thick)
C1--7 to 18 inches; mottled brown (10YR 4/3), grayish brown (10YR 5/2) and yellowish brown (10YR 5/6) silt loam; massive; very friable; neutral; gradual smooth boundary. (6 to 14 inches thick)
C2--18 to 39 inches; grayish brown (10YR 5/2) silt loam; common medium and coarse faint yellowish brown (10YR 5/6-5/8) mottles; massive; very friable; neutral; gradual smooth boundary. (15 to 30 inches thick)
C3--39 to 60 inches; mottled grayish brown (10YR 5/2) and yellowish brown (10YR 5/6) silt loam; massive; very friable; few nodules high in iron (pipestems), few dark stains, and few soft calcium carbonate accumulations; slight effervescence; mildly alkaline.
TYPE LOCATION: Mills County, Iowa; about 7 miles southeast of Malvern; 522 feet east and 1,528 feet south of the northwest corner of sec. 18, T. 71 N., R. 42 W.
RANGE IN CHARACTERISTICS: The solum thickness is less than 10 inches and corresponds to the thickness of the Ap or A1 horizon. The depth to free carbonates ranges from 30 to 60 inches. Depth to carbonates typically decreases with increasing gradient on convex slopes.
The Ap horizon is dark grayish brown (10YR 4/2) or brown (10YR 4/3). Colors of very dark grayish brown (10YR 3/2) make up as much as 30 percent of this horizon in some pedons.
The C horizon has hue of 10YR to 5Y, value of 4 to 6, and chroma of 2 to 8. Clay content ranges from 18 to 25 percent. The C horizon is neutral or mildly alkaline in the upper part and mildly alkaline or moderately alkaline in the lower part.
COMPETING SERIES: No other series is in this family. The Dow and Ida soils are similar but are calcareous throughout.
GEOGRAPHIC SETTING: Strahan soils are on upland side slopes and low interfluves with slope gradients of 5 to 14 percent. These soils formed in thick loess. The mean annual temperature ranges from 49 to 56 degrees F., and mean annual precipitation ranges from about 26 to 32 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Dow and Ida soils and the Marshall and Monona soils. The Marshall and Monona soils have B horizons and mollic epipedons. Typically the Strahan soils occur as horizontal bands within areas of the associated soils.
DRAINAGE AND PERMEABILITY: Well drained. Permeability is moderate. Surface runoff is medium to rapid.
USE AND VEGETATION: They are used for cultivated crops. Corn and soybeans are the principal crops. Native vegetation was prairie grasses.
DISTRIBUTION AND EXTENT: Southwestern Iowa and possibly northern Missouri. The series is of minor extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Indianapolis, Indiana
SERIES ESTABLISHED: Mills County, Iowa, 1979.
REMARKS: The Strahan soils have been mainly included with Ida and Dow soils in previous mapping. The matrix colors and mottles in the C horizon are inherited and unrelated to present drainage conditions; thus, they are not considered in the classification of this soil.