LOCATION SMITHVILLE TXEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, thermic Pachic Argiustolls
TYPICAL PEDON: Smithville fine sandy loam - cropland. (Colors are for dry soil unless otherwise stated.)
Ap--0 to 6 inches; grayish brown (10YR 5/2) fine sandy loam, very dark grayish brown (10YR 3/2) moist; weak fine and medium granular structure; hard, very friable; few fine roots; many fine pores; slightly alkaline; clear smooth boundary. (4 to 20 inches thick)
A--6 to 16 inches; dark grayish brown (10YR 4/2) loam, very dark grayish brown (10YR 3/2) moist; moderate fine granular structure; hard, friable; many fine roots; many fine pores; few wormcasts; slightly alkaline; gradual smooth boundary. (8 to 20 inches thick)
Bt--16 to 30 inches; reddish brown (5YR 4/3) sandy clay loam, dark reddish brown (5YR 3/3) moist; moderate medium subangular blocky structure; very hard, firm; common wormcasts; patchy clay films; few small calcium carbonate concretions and fragments of shell; strongly effervescent; moderately alkaline; gradual smooth boundary. (thickness of Bt horizons range from 15 to 45 inches)
Btk--30 to 50 inches; reddish brown (5YR 5/4) sandy clay loam, reddish brown (5YR 4/4) moist; moderate fine subangular blocky structure; hard, friable; few wormcasts; patchy clay films; few calcium carbonate concretions and broken fragments of shell; few films and threads of calcium carbonate; strongly effervescent; moderately alkaline; clear smooth boundary. (10 to 30 inches thick)
BCk--50 to 62 inches; reddish yellow (5YR 6/6) fine sandy loam with a few thin faintly evident stratum of loam, yellowish red (5YR 5/6) moist; structureless; hard, very friable; few calcium carbonate concretions; few films and threads of calcium carbonate; strongly effervescent; moderately alkaline.
TYPE LOCATION: Bastrop County, Texas; 0.55 mile southeast on Texas Highways 71 and 95 from the intersection of Farm Road 153; 100 feet west in a cultivated field.
RANGE IN CHARACTERISTICS: Solum thickness over evident stratification is 40 to 60 inches. The mollic epipedon is 26 to 40 inches thick. Depth to visible secondary calcium carbonate is 15 to 36 inches. Mean annual soil temperature ranges from 68 to 72 degrees F.
The A horizon has hue of 7.5YR or 10YR, value of 3 to 5 and chroma of 2 or 3. Texture is loam, fine sandy loam, or sandy clay loam. Reaction is neutral or slightly alkaline.
The Bt horizon has hue of 5YR to 10YR, value of 3 to 5 and chroma of 2 to 4. Texture is sandy clay loam or loam. Clay content ranges from 18 to 32 percent. Reaction is neutral to moderately alkaline.
The Btk horizon has hue of 5YR or 7.5YR, value of 4 or 5 and chrome of 3 to 6. Texture is sandy clay loam, loam, or fine sandy loam. Visible secondary calcium carbonate in the form of films and threads, masses and concretions of calcium carbonate comprise 2 to 10 percent by volume in the Btk and C horizons.
The BCk horizon, where present, is brownish, yellowish, or reddish fine sandy loam or loam. In some pedons it is stratified and contains 0 to 15 percent by volume of siliceous and limestone pebbles.
COMPETING SERIES: These are the Altus (TX), Cuero (TX), Hackey (T NM), Texroy (TX), Tipton (OK), and Uvas (T NM) series. All these soils except for Cuero soils have mean annual soil temperatures less than 67 degrees F. In addition, Altus soils have grayish and brownish redoximorphic features in the lower argillic horizon. Cuero soils have a mollic epipedon less than 26 inches thick. Texroy soils are dry in the moisture control section for longer periods. Tipton soils have less than 20 percent medium and coarse sand in the argillic horizon.
GEOGRAPHIC SETTING: Smithville soils are on nearly level to gently undulating high bottomlands and low terraces along the Colorado River and other similar drainageways. Slopes are mostly less than 1 percent, but range up to 2 percent. The soil formed in calcareous, reddish, stratified loamy alluvium. Mean annual temperature ranges from 66 to 70 degrees F. and mean annual precipitation ranges from 35 to 42 inches. Frost free days range from 260 to 290 days and elevation ranges from 150 to 500 feet. Thornthwaite P-E indices range from 44 to 70.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Asa and Bosque soils. Asa and Bosque soils do not have argillic horizons and are calcareous throughout. They occur on similar surfaces.
DRAINAGE AND PERMEABILITY: Well drained. Permeability is moderate. Runoff is negligible on slopes less than 1 percent and very low on 1 to 3 percent slopes. Flooding by stream overflow for short periods may occur at intervals of once in 20 to 50 years unless protected by levees or dams.
USE AND VEGETATION: Mostly cultivated to crops of corn, grain sorghum, and cotton. Native vegetation includes switchgrass, indiangrass, little bluestem, and eastern gamagrass.
DISTRIBUTION AND EXTENT: Mainly along the Colorado River in Texas. The series is of minor extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Temple, Texas
ESTABLISHED SERIES: Bastrop County, Texas; 1973.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - 0 to 30 inches. (Ap and A horizons)
Argillic horizon - 16 to 50 inches. (Bt and Btk horizons)