LOCATION HOBSON MOEstablished Series
TAXONOMIC CLASS: Fine-loamy, siliceous, active, mesic Oxyaquic Fragiudalfs
TYPICAL PEDON: Hobson loam - on a convex slope of 4 percent under brushy pasture at an elevation of 1,340 feet. (Colors are for moist soil unless otherwise stated.)
A--0 to 2 inches; very dark grayish brown (10YR 3/2) and dark grayish brown (10YR 4/2) loam, grayish brown (10YR 5/2) and light brownish gray (10YR 6/2) dry; moderate very fine granular structure; very friable; common fine and few medium and coarse roots; very strongly acid; clear smooth boundary. (1 to 8 inches thick)
E--2 to 6 inches; yellowish brown (10YR 5/4) loam; weak very fine granular structure; very friable; few fine medium and coarse roots; very strongly acid; clear smooth boundary. (3 to 6 inches thick)
BE--6 to 10 inches; yellowish brown (10YR 5/4) loam; weak very fine subangular structure; friable; few fine common medium and few coarse roots; few fine prominent strong brown (7.5YR 5/8) masses of iron accumulation; very strongly acid; clear smooth boundary. (0 to 6 inches thick)
Bt--10 to 21 inches; strong brown (7.5YR 4/6) clay loam; moderate very fine and fine subangular blocky structure; firm; common fine and medium and few coarse roots; few faint clay films on faces of peds; 5 percent chert gravel; very strongly acid; clear smooth boundary.
2Btx1--21 to 26 inches; mottled yellowish brown (10YR 5/4), brown (7.5YR 5/2), and strong brown (7.5YR 5/6) gravelly clay loam; weak thin platy structure; firm; about 65 percent brittle; few prominate clay flows in cracks; 25 percent chert gravel; very strongly acid; gradual smooth boundary.
2Btx2--26 to 40 inches; mottled yellowish brown (10YR 5/4), strong brown (7.5YR 5/6), and brown (7.5YR 5/2) very gravelly sandy clay loam; massive; firm; about 65 percent brittle; few prominent clay flows in cracks; 55 percent chert gravel and a few sandstone fragments 15 to 24 inches in diameter; very strongly acid; abrupt smooth boundary.
3Bt--40 to 60 inches; red (2.5YR 4/6) gravelly clay; moderate fine angular blocky structure; very firm; common faint clay films on faces of peds; 20 percent chert gravel and a few sandstone fragments; very strongly acid.
TYPE LOCATION: Webster County, Missouri; about 2.5 miles south of Elkland; 1,780 feet north and 1,715 feet west of the southeast corner, sec. 17, T. 31 N., R. 19 W.; USGS Elkland, Missouri quadrangle, lat. 37 degrees 24 minutes 19 seconds N. and long. 93 degrees 2 minutes 33 seconds W.
RANGE IN CHARACTERISTICS: Depth to the fragipan ranges from 18 to 27 inches and at some sites the fragipan is underlain by weathered sandstone. Reaction is very strongly acid to moderately acid throughout, but is higher in the upper horizons where limed.
The Ap or A horizon has hue of 10YR, value of 3 to 5, and chroma of 2 or 3. The E horizon has hue of 10YR or 7.5YR, value of 4 to 6, and chroma of 3 or 4. Texture is loam, silt loam, or fine sandy loam. Rock fragments are 0 to 10 percent.
The BE horizon has hue of 10YR or 7.5YR, value of 3 to 5, and chroma of 4 to 6. Texture is loam, sandy clay loam, silt loam, or clay loam.
The Bt horizon has hue of 10YR to 5YR; value of 3 to 5; and chroma of 4 to 6. It is sandy clay loam, loam, silty clay loam, silt loam, or clay loam. Rock fragments are 0 to 10 percent.
The 2Ex and 2Btx horizons have hue of 10YR to 2.5YR, value of 3 to 6, and chroma of 1 to 6. Texture is fine sandy loam, loam, silt loam, silty clay loam, clay loam, or sandy clay loam or their gravelly to extremely gravelly analogues. Rock fragments are 0 to 70 percent.
The 3Bt horizon is multicolored. It is sandy clay loam, clay loam, clay, or their gravelly, cobbly, very gravelly, or very cobbly analogues. Rock fragments are 0 to 50 percent.
Some pedons have a 2C horizon that is similar in color and texture to the 3Bt horizon.
COMPETING SERIES: These are the Hoberg and Viraton series. Hoberg soils have a surface horizon that meets the requirements for mollisols except for thickness or base saturation. Viraton soils have less than 20 percent sand in the series control section and do not have the sandstone coarse fragments common to the Hobson series.
GEOGRAPHIC SETTING: The Hobson soils typically are on gently sloping ridgetops and upper side slopes. Some areas are on structural benchs. Slopes are dominantly 3 to 6 percent with extreme ranges of 2 to 14 percent. They formed in residuum from mixed sandstone and cherty limestone or cherty dolomite. There is sometimes a thin silty mantle of loess, ranging in maximum thickness to about 10 inches. Mean annual temperature ranges from 53 to 57 degrees F, and mean annual precipitation ranges from 42 to 48 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Clarksville, Coulstone, Lebanon, Nixa, and Plato soils. Clarksville, Coulstone, and Nixa soils contain more than 35 percent rock fragments in the particle-size control section. Lebanon and Plato soils average more than 35 percent clay in the particle-size control section. Clarksville and Coulstone soils commonly are on steeper slopes. Lebanon and Nixa soils are on similar landscapes. Plato soils are at higher elevations and more gentle slopes.
DRAINAGE AND PERMEABILITY: Moderately well drained. Runoff is high to very high. Permeability is moderate above the fragipan and slow in the fragipan. The saturated hydraulic conductivity is low.
USE AND VEGETATION: Mostly cleared and used for hay and pasture. Some areas are cropped to corn and small grains. The remainder is in mixed hardwoods. Native vegetation consists of mixed hardwoods.
DISTRIBUTION AND EXTENT: The Ozarks of Missouri (MLRAs 116A and 116B). They are of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Morgantown, West Virginia
SERIES ESTABLISHED: Dent County, Missouri, 1977.
REMARKS: The series type location is moved to Webster County because the fragipan and underlying residuum is more typical in chert fragment content and texture. Diagnostic horizons and features recognized in this series are:
ochric epipedon - the zone from the surface of the soil to a depth of 10 inches (A, E and BE horizons);
argillic horizon - the zone from approximately 10 inches to 60 inches or more (Bt, 2Btx1, 2Btx2 and 3Bt horizons).
fragipan - the depth from approximately 21 to 40 inches (2Btx1 and 2Btx2 horizons).