LOCATION AUSTIN TXEstablished Series
TAXONOMIC CLASS: Fine-silty, carbonatic, thermic Udorthentic Haplustolls
TYPICAL PEDON: Austin silty clay--cropland. (Colors are for dry soil unless otherwise stated.)
Ap--0 to 6 inches; dark grayish brown (10YR 4/2) silty clay, very dark grayish brown (10YR 3/2) moist; weak fine granular and subangular blocky structure; hard, firm but crumbly, sticky, plastic; many fine roots; many fine and very fine pores; many wormcasts; few fine calcium carbonate concretions; calcareous, moderately alkaline; clear smooth boundary. (4 to 8 inches thick)
A--6 to 15 inches; dark brown (10YR 4/3) silty clay, dark brown (10YR 3/3) moist; moderate very fine subangular blocky and granular structure; hard, firm but crumbly, sticky, plastic; many fine roots; many fine and very fine pores; many wormcasts; common fine calcium carbonate concretions; calcareous, moderately alkaline; gradual smooth boundary. (4 to 12 inches thick)
Bw1--15 to 27 inches; brown (10YR 5/3) silty clay, dark brown (10YR 4/3) moist; moderate fine subangular blocky structure; hard, firm, crumbly, sticky, plastic; few fine roots; many fine pores; many light yellowish brown (2.5Y 6/4) wormcasts; common fine calcium carbonate concretions; few fine fragments of chalk; calcareous, moderately alkaline; clear smooth boundary. (10 to 20 inches thick)
Bw2--27 to 30 inches; brown (10YR 5/3) silty clay, dark brown (10YR 4/3) moist; moderate fine subangular blocky structure; hard, firm, sticky, plastic; few fine roots; common wormcasts; about 30 percent platy fragments of chalk less than 3 inches in the axis; calcareous, moderately alkaline; clear irregular boundary. (0 to 10 inches thick)
Cr--30 to 36 inches; white (10YR 8/2) and very pale brown (10YR 8/4) platy chalk that is less hard than 3, Mohs scale; few thin tongues of brown silty clay in crevices between chalk plates.
TYPE LOCATION: McLennan County, Texas; 0.4 mile northeast of the intersection of Robinson Road and Interstate 35, which is 2 miles northeast of Lorena, 150 feet southeast of Robinson Road and 200 feet south of a metal barn.
RANGE IN CHARACTERISTICS: The solum ranges from 20 to 40 inches thick. It is silty clay loam, silty clay, or clay, with clay contents of 35 to 55 percent. Silicate clay content ranges from 20 to 35 percent. Below the A horizon, the soil ranges from 40 to 70 percent calcium carbonate equivalent. Some pedons have few to common fragments of chalk on the surface and within the sola.
The A horizon is brown, dark grayish brown, grayish brown or very dark grayish brown with hue of 7.5YR, 10YR, or 2.5Y, moist value of 3.5 or less and chroma of 2 or 3. It is 8 to 20 inches thick.
The B horizon has colors in shades of brown or gray with hue of 7.5YR, 10YR or 2.5Y, value of 5 to 7, chroma of 2 to 4.
The substrata are platy chalk, interbedded chalk and marl, or soft limestone bedrock.
COMPETING SERIES: These are the Lott series in the same family and the Altoga, Bolar, Brackett, Denton, Krum, Lewisville, Nuvalde, Patrick, Somervell, Stephen, and Valera series. Altoga and Brackett soils lack mollic epipedons, and Brackett soils have sola less than 20 inches thick. Bolar soils have more than 15 percent coarser than very fine sand in the control section. Denton and Krum soils have cracks 0.4-inch wide at depths of 20 inches when dry. Lewisville soils have less than 40 percent calcium carbonate within depths of 40 inches and are not underlain by chalk. Lott soils have sola more than 40 inches deep and are underlain by marl. Nuvalde soils have more than 35 percent noncarbonate clay in the control section. Patrick soils are sandy in the lower part of the control section. Somervell soils contain more than 35 percent coarse fragments. Stephen soils lack B horizons and are less than 20 inches thick. Valera soils have petrocalcic horizons.
GEOGRAPHIC SETTING: Austin soils are on uplands. Slope gradients are mainly less than 5 percent but range from 0 to 8 percent. The soil formed in mainly chalk or interbedded marl and chalk and is mostly of the Austin Formation. In places, the soil formed in soft limestone. The climate is warm subhumid. Mean annual precipitation ranges from 30 to 45 inches, mean annual temperature from 63 degrees to 70 degrees F, and Thornthwaite P-E indices from 44 to 66.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Stephen series and the Eddy, Dalco, Fairlie, Houston Black, Howe, and Whitewright series. Eddy and Whitewright soils have sola less than 20 inches deep and in addition they have ochric epipedons. Dalco, Fairlie and Houston Black soils have intersecting slickensides. Howe soils have ochric epipedons. Eddy and Stephen soils occupy similar positions to Austin soils. Dalco, Fairlie and Houston Black soils occupy lower positions in the landscape. Howe and Whitewright soils occupy adjacent sideslopes.
DRAINAGE AND PERMEABILITY: Well drained; medium to rapid runoff; moderately slow permeability.
USE AND VEGETATION: Mainly cultivated. Principal crops are small grains, cotton, and grain sorghums. Some areas are used for native range. Original vegetation was mid and tall grasses such as little bluestem, indiangrass, and sideoats grama. Grasses now are mainly gramas and buffalograss.
DISTRIBUTION AND EXTENT: The Blackland Prairies of Texas. The series is extensive.
MLRA OFFICE RESPONSIBLE: Temple, Texas
SERIES ESTABLISHED: Travis County, Texas; 1904.
REMARKS: Classification was changed 11/89 from fine-silty, carbonatic, thermic Entic Haplustolls to fine-silty, carbonatic, thermic Udorthentic Haplustolls.
Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - 0 to 15 inches, the Ap and A horizons.
Cambic horizon - 15 to 30 inches, the Bw1 and Bw2 horizons.
Paralithic contact of platy chalk at a depth of 30 inches.
Calcium carbonate equivalent in the control section of more than 40 percent.