LOCATION KNOBTOP MO
Established Series
Rev. RLT-LJG
12/2021
KNOBTOP SERIES
The Knobtop series consists of moderately deep, moderately well drained soils formed in loess and the underlying residuum from igneous rock. These soils are on uplands and have slopes of 2 to 15 percent. Mean annual temperature is 55 degrees F, and mean annual precipitation is 43 inches.
TAXONOMIC CLASS: Fine-silty, mixed, active, mesic Aquic Hapludults
TYPICAL PEDON: Knobtop silt loam - on a 3 percent south-facing slope in mixed hardwoods. (Colors are for moist soil unless otherwise stated.)
Oi--0 to 1 inches; slightly decomposed layer of leaves, twigs, roots and other organic materials.
A--1 to 3 inches; dark grayish brown (10YR 4/2) silt loam; light brownish gray (10YR 6/2) dry; weak fine granular structure; very friable; common fine and medium roots; very strongly acid; abrupt smooth boundary. (1 to 5 inches thick)
E--3 to 8 inches; brown (10YR 5/3) silt loam; weak thin and medium platy structure; very friable; common medium roots; very strongly acid; abrupt smooth boundary. (0 to 8 inches thick)
Bt1--8 to 14 inches; brown (7.5YR 5/4) silt loam; weak medium subangular blocky structure; friable; common medium roots; few faint clay films on faces of peds; very strongly acid; clear smooth boundary.
Bt2--14 to 22 inches; brown (7.5YR 4/4) silty clay loam; weak fine and medium subangular blocky structure; firm; common medium roots; common faint clay films on faces of peds; very strongly acid; clear smooth boundary.
Bt3--22 to 27 inches; brown (7.5YR 4/4) silty clay loam; common fine and medium prominent grayish brown (10YR 5/2) and distinct brown (10YR 5/3) iron depletions; weak medium subangular blocky structure; firm; common medium roots; common faint clay films on faces of peds; very strongly acid; clear smooth boundary.
Bt4--27 to 31 inches; grayish brown (10YR 5/2) silty clay loam; common medium prominent brown (7.5YR 4/4) and strong brown (7.5YR 5/8) mottles; weak thick platy structure parting to weak subangular blocky; firm; few fine roots; common distinct clay films and flows on vertical faces of peds and along old root channels; extremely acid; clear smooth boundary. (Combined thickness of the Bt horizons is 14 to 30 inches.)
2BC--31 to 37 inches; light brownish gray (2.5Y 6/2) silt loam; common medium prominent yellowish red (5YR 4/6) and brown (7.5YR 4/4) masses of iron accumulation; weak thick platy structure parting to weak medium subangular blocky; firm; few fine roots, 1 to 2 cm thick mat of partially decayed fine and medium roots along the lower boundary and hard rock contact; 14 percent gravel, 1 percent cobble; extremely acid; abrupt irregular boundary. (3 to 9 inches thick)
R--37 inches; hard igneous felsite.
TYPE LOCATION: Iron County, Missouri; about 2.5 miles west and 3 miles north of Banner; 2300 feet north and 925 feet east of the southwest corner of sec. 24, T. 35 N., R. 1 E. Latitude 37 degrees, 43 minutes, 35.5 seconds N., longitude 90 degrees, 53 minutes, 23.1 seconds W., NAD83.
RANGE IN CHARACTERISTICS: Depth to bedrock ranges from 20 to 40 inches. Rock fragment content is 0 to 25 percent for the A, E and Bt horizons and 5 to 65 percent for the 2BC horizon. Some pedons are stony on the surface.
The A horizon has value of 3 or 4 and chroma of 2 or 3. It is very strongly acid or strongly acid, and ranges up to neutral where limed.
The E horizon has hue of 10YR or 7.5YR, value of 4 or 5, and chroma of 2 to 6. It is very strongly acid or strongly acid. Some pedons have a BA or BE horizon.
The Bt horizon has hue of 7.5YR or 10YR, value or 4 or 5, and chroma of 2 to 6 with the lower part mottled. It is silt loam or silty clay loam or clay loam and strongly acid to extremely acid.
The 2Bt or 2BC horizon has hue of 5YR to 2.5Y, value of 4 to 6, and chroma is commonly 2 but ranges from 2 to 6. If the matrix has chroma of 3 to 6, it has mottles with chroma of 2. If the matrix has chroma of 2, brighter mottles are present. It is silt loam, loam, silty clay loam, gravelly silt loam , gravelly silty clay loam, cobbly clay loam or the cobbly or very cobbly analogues of silt loam. Reaction is extremely acid or very strongly acid.
COMPETING SERIES: These are the (T)
Crosiadore, (T)
Cumberstone,
Deputy,
Marquand,
Mattapex, and
Sharptown series. Crosiadore, Cumberstone, Marquand, Mattapex, and Sharptown soils are very deep to a lithic or paralithic contact. Deputy soils are deep a lithic contact.
GEOGRAPHIC SETTING: Knobtop soils are on ridgetops of mountainous areas. A silty overburden, presumably loess, has weathered to grade into a weakly expressed discontinuity of residuum from acid felsitic or similar igneous rock. Slopes range from 2 to 15 percent. Mean annual temperature ranges from 55 to 57 degrees F, and mean annual precipitation ranges from 40 to 44 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the
Delassus,
Irondale, and
Loughboro series. Delassus soils have fragipans and are at lower elevations. Irondale soils have more than 35 percent coarse fragments in the upper argillic horizon and commonly are on steeper slopes surrounding the Knobtop soils. Loughboro soils are poorly drained and are on nearly level areas at the foot of the mountains.
DRAINAGE AND PERMEABILITY: Moderately well drained. Runoff is low to medium. Permeability is moderately slow. The saturated hydraulic conductivity is moderately high.
USE AND VEGETATION: Most areas remain in mixed hardwood forest because of inaccessibility. A few acres are cleared for pasture and hay.
DISTRIBUTION AND EXTENT: The St. Francois Mountains area (MLRA 116C) of southeast Missouri. The series is of small extent.
SOIL SURVEY REGIONAL OFFICE (SSRO) RESPONSIBLE: INDIANAPOLIS, INDIANA
SERIES ESTABLISHED: St. Francois County, Missouri, 1979.
REMARKS: Diagnostic horizons and features recognized in this series are: ochric epipedon - the zone from the surface to a depth of 8 inches (Oi, A and E horizons); argillic horizon - the zone from approximately 8 inches to 31 inches (Bt1, Bt2, Bt3 and Bt4 horizons); Lithic contact - 37 inches; udic moisture regime.
National Cooperative Soil Survey
U.S.A.