LOCATION URSA ILEstablished Series
TAXONOMIC CLASS: Fine, smectitic, mesic Chromic Vertic Hapludalfs
TYPICAL PEDON: Ursa loam - on a southwest-facing slope of 13 percent in a cultivated field. (Colors are for moist soil unless otherwise stated.)
Ap--0 to 7 inches; mixed dark grayish brown (10YR 4/2) and yellowish brown (10YR 5/4) loam, light brownish gray (10YR 6/2) and light yellowish brown (10YR 6/4) dry; moderate medium granular structure; friable; common fine roots; about 2 percent fine gravel; medium acid; abrupt smooth boundary. (4 to 10 inches thick)
Bt1--7 to 14 inches; yellowish brown (10YR 5/4) loam; weak fine subangular blocky structure; friable; few fine roots; few faint dark yellowish brown (10YR 4/4) clay films on faces of peds; few fine concretions (iron and manganese oxides); about 2 percent fine gravel; strongly acid; clear smooth boundary.
Bt2--14 to 21 inches; yellowish brown (10YR 5/6) clay loam; moderate fine subangular blocky structure; firm; few fine roots; common distinct dark yellowish brown (10YR 4/4) clay films on faces of peds; few fine concretions (iron and manganese oxides); about 5 percent fine gravel; strongly acid; clear smooth boundary.
Bt3--21 to 31 inches; yellowish brown (10YR 5/6) clay loam; strong medium subangular blocky structure; firm; few fine roots; many distinct dark brown (7.5YR 4/4) clay films on faces of peds; few fine concretions (iron and manganese oxides); about 5 percent fine gravel; strongly acid; clear smooth boundary.
Bt4--31 to 46 inches; yellowish brown (10YR 5/6) clay loam; few fine distinct grayish brown (10YR 5/2) mottles; strong medium subangular blocky structure; firm; few fine roots; few distinct dark brown (7.5YR 4/4) clay films on faces of peds; few fine concretions (iron and manganese oxides); about 5 percent fine gravel; medium acid; clear smooth boundary.
Bt5--46 to 52 inches; yellowish brown (10YR 5/6) clay loam; few fine distinct grayish brown (10YR 5/2) and brownish yellow (10YR 6/8) mottles; moderate medium subangular blocky structure; firm; few fine roots; few distinct dark brown (7.5YR 4/4) clay films on faces of peds; few fine concretions (iron and manganese oxides); about 5 percent fine gravel; neutral; clear smooth boundary. (Combined thickness of the Bt horizons is 30 to 50 inches.)
BC--52 to 60 inches; yellowish brown (10YR 5/6) clay loam; common medium prominent light brownish gray (2.5Y 6/2) mottles; weak coarse subangular blocky structure; firm; few fine roots; few fine concretions (iron and manganese oxides); about 5 percent fine gravel; neutral. (0 to 20 inches thick)
TYPE LOCATION: Brown County, Illinois; about 7.5 miles west and 7 miles north of Mt. Sterling; l000 feet east and 740 feet north of the southwest corner of oversized sec. 6, T. 1 N., R. 4 W.
RANGE IN CHARACTERISTICS: The solum is 50 to more than 60 inches in thickness. The dominant clay mineral in the upper part of the control section is montmorillonite, and in the lower part of the control section and substratum it is illite. The control section averages between 35 and 45 percent clay, 15 and 35 percent sand, and 2 and 10 percent gravel.
The Ap or A horizon has hue of 10YR or 7.5YR, value of 4 or 5, and chroma of 2 through 4. Some pedons have lighter colored silt coats or darker colored organic coats on the faces of peds. The Ap or A horizon typically is silt loam or loam, but eroded pedons include silty clay loam, clay loam, or clay. They are very strongly acid to medium acid except pedons that have been limed are slightly acid or neutral.
Uneroded pedons typically have E horizons and BE or Bt horizons formed in loess or pedisediment above the till.
The Bt or 2Bt horizon that formed in till typically has hue of 7.5YR or 10YR, value of 4 through 6, and chroma of 3 through 8. The lower part of some pedons have hue of 2.5Y or 5Y, and chroma of 1 through 8 (see remarks). The Bt or 2Bt horizon is mottled with a wide range of colors that are believed to be inherited from the paleosol that formed in the till. Clay films on faces of peds in the upper part of the horizon have hue of 10YR or 7.5YR, value of 4 or 5, and chroma of 3 or 4. In the lower part, some pedons have chroma of 1 or 2 on the faces of peds. In addition, some pedons have coats of silt or very fine sand on the faces of peds in one or more subhorizons. The Bt or 2Bt horizon is clay loam, clay, silty clay, silty clay loam, or loam. It is very strongly acid or strongly acid in the upper part and becomes less acid with increasing depth in most pedons. It is strongly acid to neutral in the lower part.
The BC or 2BC horizon typically has hue of 10YR or 7.5YR and less commonly 2.5Y or 5Y, value of 4 through 6, and chroma of 1 through 6. Most pedons contain mottles. The BC or 2BC horizon is clay loam, clay, silty clay, or loam. It is medium acid to mildly alkaline.
Some pedons contain a C or 2C horizon that has color and texture in the same range as stated for the BC or 2BC horizon. Other pedons contain buried horizons of the paleosol beneath the modern solum. The C or 2C horizon is neutral to moderately alkaline and contains free carbonates in some pedons, but commonly not within a depth of 60 inches.
COMPETING SERIES: These are the Ainsworth, Brevator, Clinton, Hatton, Haymarket, Lunt, and Welda series. Ainsworth and Lunt soils contain more than 35 percent sand in the lower part of the control section. Brevator soils have hues redder than 7.5YR in the upper part of the control section. Clinton soils contain less than 10 percent sand and have no gravel in the control section. Hatton soils have a 2Bx horizon. Haymarket and Welda soils are dominated by 5YR and 7.5YR hue in the Bt horizon. In addition, Haymarket soils contain rock fragments of diabase and basalt and Welda soils contain less than 15 percent sand and have no gravel in the control section.
GEOGRAPHIC SETTING: Ursa soils are on convex slopes along drainageways in dissected uplands. They formed in till that contains a strongly developed Sangamon paleosol. Many pedons have a mantle of loess or silty pedisediment that is 20 inches or less in thickness. Slopes commonly are 10 to 20 percent but range from 5 to 50 percent. The mean annual temperature rannges from 54 to 57 degrees F, and the mean annual precipitation ranges from 35 to 45 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Alford, Atlas, Blair, Clinton, Elco, Fishhook, Hickory, Hosmer, and Rozetta soils. Atlas soils are on similar or slightly higher parts of the landscape or nearby in the upper ends of incised drainageways. Elco and Fishhook soils are up slope and in many places adjacent to Ursa soils. Alford, Clinton, Hosmer, and Rozetta soils formed in loess on the upper parts of slopes or on ridge crests above Ursa soils. They do not contain gravel and contain less than 10 percent sand throughout their sola. Blair soils formed in loamy water-worked sediments above the till and are up slope from Ursa soils. They are dominated by grayer colors on the exteriors of peds. Hickory soils contain less clay in the control section and are down slope from Ursa soils. They formed in till that did not have a paleosol formed in it.
DRAINAGE AND PERMEABILITY: Well drained (see remarks). Runoff is rapid. Permeability is slow.
USE AND VEGETATION: Many areas of Ursa soils are used for growing forage crops used for hay or pasture. Some of the more gentle slopes are used to grow cultivated crops. Corn is the principal crop on these areas. Steeper areas are used for growing hardwood trees. Native vegetation was hardwood trees.
DISTRIBUTION AND EXTENT: Western and southwestern Illinois. They are of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Indianapolis, Indiana
SERIES ESTABLISHED: Adams County, Illinois, 1974.
REMARKS: Classification was adjusted to agree with ST Issue #17 on 25 Aug 94 by CLG. The concept of the Ursa series is soils formed in till with a modern solum superimposed upon a brown mottled paleosol. Many of the properties are believed to have been inherited from the paleosol. It is difficult to differentiate the properties of the lower part of the modern solum from those of the paleosol in many pedons. Some pedons contain grayer colors in the lower part of the solum but they are believed to be unrelated to modern soil drainage. The evidence used to assign these soils as well drained is the brownish colored clay films on the faces of peds. It is believed that they do not contain a water table for 30 consecutive days. These soils are very moist about one-twelfth to one-fourth of the time and are periodically wet. Water seeps from the loess up slope and runs onto these soils at the interface of materials at the surface of the till.
Diagnostic horizons and features recognized in this pedon are: ochric epipedon - the zone from the surface to a depth of approximately 7 inches (Ap horizon); argillic horizon - the zone from approximately 7 to 52 inches (Bt1, Bt2, Bt3, Bt4, and Bt5 horizons); udic soil moisture regime.