LOCATION ROBCO TXEstablished Series
TAXONOMIC CLASS: Loamy, siliceous, active, thermic Aquic arenic Paleustalfs
TYPICAL PEDON: Robco loamy fine sand--in pasture. (Colors are for dry soil unless otherwise stated.)
A--0 to 15 inches; brown (10YR 5/3) loamy fine sand, brown (10YR 4/3) moist; single grained; loose, very friable, nonsticky and nonplastic; many fine grass roots; slightly acid; clear smooth boundary. (4 to 16 inches thick)
E--15 to 28 inches; pale brown (10YR 6/3) loamy fine sand, brown (10YR 5/3) moist; single grained; loose, very friable, nonsticky and nonplastic; many fine grass roots; moderately acid; gradual wavy boundary. (4 to 36 inches thick)
Bt/E--28 to 33 inches; brownish yellow (10YR 6/6) sandy clay loam (Bt part), yellowish brown (10YR 5/6) moist; 40 percent of horizon is tongues of light gray (10YR 7/2) loamy fine sand (E part); moderate medium subangular blocky structure; slightly hard, friable, sticky and plastic; common fine roots, few fine pores, few patchy clay films; few fine distinct light gray (10YR 7/2) iron depletions; moderately acid; gradual wavy boundary. (0 to 7 inches thick)
Btg1--33 to 47 inches; light gray (10YR 7/2) sandy clay loam, moderate medium subangular blocky structure; hard, firm, sticky and plastic; few fine roots; few patchy clay films; few fine pores; common coarse red (2.5YR 4/6) and yellowish brown (10YR 5/6) masses of iron accumulation; strongly acid; gradual wavy boundary. (7 to 25 inches thick)
Btg2--47 to 65 inches; light gray (10YR 7/2) clay loam, light brownish gray (10YR 6/2) moist, weak medium subangular blocky structure; very hard, very firm, sticky and plastic; very fine roots; many medium prominent red (10R 4/6) masses of iron accumulation; strongly acid; gradual wavy boundary. (7 to 20 inches thick)
BCt--65 to 82 inches; red (2.5YR 4/6) sandy clay loam weak medium subangular blocky structure; some of red material is structureless; hard, friable, sticky and plastic; few patchy clay films; many medium prominent light gray (10YR 7/2) iron depletions; strongly acid.
TYPE LOCATION: Brazos County, Texas; from the intersection of state highway 21 and FM 2038 at Kurten, north 0.9 miles on FM 2038, west 0.3 miles on Kurten Cemetery Road, south 0.1 mile to cemetery entrance, then south 0.1 mile on private road along the east side of the cemetery. Site is 200 feet southwest of the southeast corner of cemetery in pasture.
RANGE IN CHARACTERISTICS: Thickness of the solum ranges from 60 to more than 80 inches. Average clay content of the upper 20 inches of the argillic horizon ranges from 25 to 35 percent.
The A horizon has hue of 7.5YR or 10YR, value of 4 to 7, and chroma of 3 or 4. Texture is loamy fine sand or fine sand. Thickness ranges from 20 to 40 inches. Reaction ranges from strongly acid to slightly acid.
The E horizon has hue of 10YR or 7.5YR, value of 5 to 7, and chroma of 2 to 4. Redoximorphic features in shades of gray or yellow range from none to common. Reaction is ranges from very strongly acid to moderately acid.
The Bt/E horizon, where present, is 60 to 90 percent by volume of B material. The Bt part has a matrix with hue of 10YR, value of 5 to 7, and chroma of 4 to 6. Texture is sandy clay loam, loam, or clay loam. The E material consists of tongues, interfingers, and pockets. The E part has a matrix with hue of 10YR, value of 6 to 8, and chroma of 1 to 4. Texture is loamy fine sand or fine sand. Redoximorphic features in shades of gray, yellow, and red range from few to a mottled matrix of these colors. Reaction ranges from very strongly acid to slightly acid.
The Bt1 horizon has hue of 7.5YR to 2.5Y, value of 4 to 7, and chroma of 2 to 6. Redoximorphic features in shades of gray, red, yellow, and brown range from few to many, or the matrix is mottled in shades of red, gray, and yellow. Texture is clay loam or sandy clay loam. Some pedons have sandy clay texture. Reaction ranges from very strongly acid to moderately acid.
The lower Bt horizon has hue of 7.5YR to 2.5Y, value of 4 to 7, and chroma of 1 to 8. Redoximorphic features is shades of red, yellow, brown, and gray range from few to many. In some pedons the soil is mottled in shades of red, gray and yellow. The texture is typically clay loam or clay. Reaction ranges from very strongly acid to slightly acid. Some pedons have interfingers of E material in the lower part.
The BCt horizon, where present, has colors with shades of red, gray, yellow or brown with few to many mottles. The texture is variable and ranges from sandy clay loam to clay. Reaction ranges from very strongly acid to neutral. Zones of gypsum accumulation, and other salts range from none to common.
COMPETING SERIES: These are Coving (TX) and Nimrod (TX) series. Similar soils are the Chazos, Demona, Nueces, Rader, Rehburg, Selden, and Tremona series. Coving soils are moderately acid to slightly alkaline throughout the argillic horizon, and are somewhat poorly drained. Nimrod soils do not have a Bt/E horizon, receive less effective precipitation and are have a typic/ustic moisture regime. Chazos soils are in the fine family, and have surface layers less than 20 inches thick. Demona and Tremona soils are in the fine family. Nueces soils are in the hyperthermic temperature regime. Rader soils do not have arenic surface layers. Rehburg soils are 20 to 40 inches thick over tuffaceous materials. Selden soils have surface layers less than 20 inches thick.
GEOGRAPHIC SETTING: Robco soils are on nearly level to moderately sloping uplands. They formed in loamy sediments on Pleistocene terrace deposits about 35 to 100 feet above present streams or local outwash colluvial plains. These soils are on low oval convex ridges, footslopes and concave sideslope positions or near the heads of drainageways. Slopes are mostly 0 to 5 percent but range from 0 to 8 percent. Mean annual temperature ranges from 65 to 68 degrees F., and mean annual precipitation ranges from 33 to 40 inches. Frost free days range from 240 to 275 days, and elevation ranges from 150 to 600 feet. Thornthwaite P-E indices range from 52 to 64. The soils are in an ustic moisture regime bordering udic.
GEOGRAPHICALLY ASSOCIATED SOILS: These are Arenosa, Chazos, Hearne, Jedd, Marquez, Padina, Rader, Rosanky, and Silstid series. Arenosa, Padina, and Silstid soils are mainly on broad smooth areas in higher better drained positions. Chazos soils do not have thick sandy surface layers and are on similar land forms. Hearne, Jedd, Rosanky, and Marquez soils are on higher ridges and side slopes and have a thinner sola. Rader soils are slightly lower in the landscape, and have fine sandy loam surface layers.
DRAINAGE AND PERMEABILITY: Moderately well drained. Permeability is slow. Runoff is low on slopes less than 1 percent, medium on 1 to 5 percent slopes, and high on 5 to 8 percent slopes. Water is perched above the argillic horizon during the cool season for short periods following heavy rains.
USE AND VEGETATION: These soils are used mainly for pasture and rangeland. Pastures are improved bermudagrass or native grasses. Tree species are mainly post oak and blackjack oak with an understory of yaupon, grasses, and other shrubs.
DISTRIBUTION AND EXTENT: Mainly in the Texas Claypan Area of east-central Texas. The series is of moderate extent.
MLRA OFFICE RESPONSIBLE: Temple, Texas
SERIES ESTABLISHED: Leon County, Texas, 1985.
REMARKS: This soil was formerly included within the Demona series. The original concept was a soil with a fine textured control section. Additional data has shown that the area mapped as Robco soils typically have a clay content of 30 to 35 percent. These soils have slow permeability. In 1988, it was changed to fine-loamy family.
Active cation exchange activity class. Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - 0 to 28 inches. (A and E horizons)
Arenic feature - 0 to 28 inches, loamy fine sand texture.
Argillic horizon - 28 to 82 inches (Bt/E, Btg1, and Btg2 and BCt horizons).
Aquic feature - iron depletions with low chroma due to wetness at 27 inches and below.
ADDITIONAL DATA: Base saturation by hach Kit was 50 percent at 50 inches below top of the argillic horizon at the type location, 91 percent at another location in Robertson County, and 77 percent from a pedon in Leon County, Texas. Results of mechanical analysis by the hydrometer method at the type location in Brazos County.
Also, NSSL data from pedon in Leon County Texas S82TX-289-26 (S82P3199- 3207).
Soil Interpretation Record No: TX0981