LOCATION CHARCO TXEstablished Series
TAXONOMIC CLASS: Fine, smectitic, hyperthermic Torrertic Paleustolls
TYPICAL PEDON: Charco loam--rangeland. (Colors are for dry soils unless otherwise stated.)
A--0 to 9 inches; dark gray (10YR 4/1) loam, very dark gray (10YR 3/1) moist; moderate fine and medium subangular blocky structure; hard, friable; common very fine and fine roots; few fine tubular pores; nonsaline; slightly acid; clear smooth boundary. (6 to 20 inches thick)
Bt--9 to 18 inches, very dark gray (10YR 3/1) clay, black (10YR 2/1) moist; moderate fine and medium angular blocky structure; extremely hard; very firm; common very fine roots mainly along faces of peds; few fine tubular pores; common faint clay films on faces of peds; few distinct stress surfaces on faces of peds; nonsaline; neutral, gradual wavy boundary. (0 to 22 inches thick)
Btk--18 to 25 inches; dark gray (10YR 4/1) clay loam, very dark gray (10YR 3/1) moist; moderate fine and medium angular blocky structure; very hard, firm; common very fine roots mainly along faces of peds; few fine tubular pores; few faint clay films on faces of peds; very slightly saline; few fine rounded weakly cemented nodules of calcium carbonate; 12 percent calcium carbonate equivalent violently effervescent; moderately alkaline; gradual wavy boundary. (6 to 20 inches thick)
Btyz1--25 to 34 inches; grayish brown (10YR 5/2) clay loam, dark grayish brown (10YR 4/2) moist; weak fine and medium subangular blocky structure; very hard, firm; few very fine roots; few faint clay films on faces of peds; few fine threads and soft masses of calcium carbonate; few fine and medium irregular soft masses and clusters of crystals of gypsum and other salts; 11 percent calcium carbonate equivalent; slightly saline; violently effervescent; moderately alkaline; gradual wavy boundary. (0 to 12 inches thick)
Btyz2--34 to 39 inches; grayish brown (10YR 5/2) loam, dark grayish brown (10YR 4/2) moist; weak fine and medium subangular blocky structure; hard, firm; few very fine roots; few faint clay films on faces of peds; few fine irregular threads and soft masses of calcium carbonate; 8 percent calcium carbonate equivalent; common fine to medium irregular soft masses and clusters of crystals of gypsum and other salts; common distinct coats of gypsum crystals on faces of peds; slightly saline; violently effervescent; moderately alkaline, abrupt wavy boundary. (0 to 18 inches thick)
Byz1--39 to 50 inches; very pale brown (10YR 7/3) clay loam; pale brown (10YR 6/3) moist, common fine and medium distinct yellowish brown (10YR 5/6) mottles; few fine distinct grayish brown (10YR 5/2) vertical streaks; weak fine and medium subangular blocky structure; hard, firm; about 25 percent by volume of fine to coarse irregular soft masses and clusters of crystals of gypsum and other salts; about 8 percent calcium carbonate equivalent; slightly saline; strongly effervescent; moderately alkaline; diffuse wavy boundary. (0 to 30 inches thick)
Byz2--50 to 64 inches; very pale brown (10YR 7/3) clay loam; pale brown (10YR 6/3) moist; common fine and medium distinct yellowish brown (10YR 5/6)mottles, few fine distinct grayish brown (10YR 5/2) vertical streaks in upper part; weak fine and medium subangular blocky structure: hard, firm; few white (5Y 8/2) soft shale fragments that slake in water; few fine and medium rounded weakly cemented yellow nodules; about 25 percent by volume of fine to coarse irregular soft masses and clusters of crystals of gypsum and other salts; about 7 percent calcium carbonate equivalent; moderately saline; strongly effervescent; moderately alkaline.
TYPE LOCATION: La Salle County, Texas. From Cotulla, 5.8 miles east on Texas Highway 97, 1.6 mile southeast on small ranch road, 150 feet northeast in rangeland.
RANGE IN CHARACTERISTICS: Solum thickness ranges from 40 to more than 60 inches. Electrical conductivities of the saturation extract ranges from about 0.2 to 2 millimhos in the A horizon; 1.0 to 4.0 millimhos in the upper Bt horizon; 4.0 to 12.0 in the lower Bt and C horizons. COLE of the control section ranges from .07 to .09.
The A and Bt horizons are dark gray, very dark gray, gray or dark grayish brown in hue of 10YR, values of 3 and 4, and chroma of 1 and 2. The Bt horizons are also grayish brown, brown, or pale brown in hue of 10YR, values of 5 and 6, and chroma of 1 to 3. The A horizon is loam, clay loam, or sandy clay loam. Reaction is slightly acid or neutral. The boundary between the A and Bt horizons is abrupt or clear with a clay increase of 20 to 30 percent in the upper Bt horizon. The Bt horizons are clay or clay loam.
The Btyz horizons are dark gray, gray, dark grayish brown, grayish brown, brown, and pale brown in hue of 10YR; values of 5 through 6 and chroma of 1 through 3. They are loam, clay loam or sandy clay loam and clay content decreases with depth. Reaction is mildly alkaline to moderately alkaline.
The Byz horizon is pale brown, very pale brown, or light yellowish brown in hue of 10YR; It is value of 6 to 8 and chroma of 3 and 4. Clay loam,clay, or clay loam intermingled with soft shale fragments that slake in water. It contains common to many accumulations of calcium carbonate, calcium sulfate and other salts.
The C horizon where present is similar to the Byz but has higher color values. It has few to common streaks with colors of the Bt horizons. Reaction is mildly alkaline or moderately alkaline.
COMPETING SERIES: There are no series in the same family. Similar soils include Amphion, Barbarosa, Chacon, Divot, Hanis, Pullman, Sproul, and Tordia. Amphion and Hanis soils have mollic epipedons more than 20 inches thick and mixed mineralogy. Barbarosa, Pullman, and Sproul soils have soil temperatures less than 72 degrees F. Chacon soils lack an absolute clay increase of 20 percent within 3 inches of the upper boundary of the argillic horizon. Divot and Tordia soils lack argillic horizons.
GEOGRAPHIC SETTING: Charco soils are on nearly level uplands. These soils occupy the microlows in complex soil areas. Slopes range from 0 to 2 percent but are mostly less than 0.5 percent. The soil formed in calcareous loamy materials. Mean annual precipitation ranges from 20 to 25 inches and mean annual air temperature ranges from 70 to 73 degrees F., Frost free days range from 275 to 300 days and elevation ranges from 400 to 600 feet. Thornthwaite P-E index ranges from 25 to 34.
GEOGRAPHICALLY ASSOCIATED SOILS: These include the competing Altita, Amphion, Chacon, Divot, and Hanis soils and the Cotulla and Moglia soils. Altita soils occur as micro-highs in a complex with Charco soil that occur in micro-depressions. Amphion, Chacon, Cotulla, and Hanis soils occur on similar landscapes to Charco soils. Cotulla soils have more than 35 percent clay throughout. Divot soils have more than 15 percent calcium carbonate equivalent and occur on bottomlands derived from sediments from areas of limestone. Moglia soils occur on slightly higher landscapes and have less clayey subsoils.
DRAINAGE AND PERMEABILITY: Well drained; slow to medium runoff; moderately slow permeability.
USE AND VEGETATION: Mainly used as native rangeland and wildlife habitat. The grasses are mainly red grama, curlymesquite, pink pappusgrass, threeawn, bristlegrass, Hall panicum, and lovegrass tridens. Woody plants include mesquite, guayacan, blackbrush, whitebrush, pricklypear, tasajillo, allthorn, lotebush, condalia and leatherstem.
DISTRIBUTION AND EXTENT: In north-central part of Rio Grande Plain of Texas. The series is of minor extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Temple, Texas
SERIES ESTABLISHED: La Salle County, Texas, 1988.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon: 0 to 25 inches
Argillic horizon: 9 to 39 inches
Abrupt texture change: At 9 inches
Gypsic horizon - 39 to 64 inches.