LOCATION ROBCO                   TX

Established Series
Rev. CLN-RMR-JAW-RM
02/2018

ROBCO SERIES

The Robco series consists of very deep, moderately well drained, slowly permeable soils that formed in loamy sediments. These nearly level to moderately sloping soils are on uplands. Slopes range from 0 to 8 percent. Mean annual precipitation is about 978 mm (38.5 in) and the mean annual air temperature is about 19.2 degrees C (66.6 degrees F).

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 38 cm (0 to 15 in); 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. (10 to 41 cm [4 to 16 in] thick)

E--38 to 71 cm (15 to 28 in); 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. (10 to 91 cm [4 to 36 in] thick)

Bt/E--71 to 84 cm (28 to 33 in); 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 18 cm [0 to 7 in] thick)

Btg1--84 to 119 cm (33 to 47 in); 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. (18 to 64 [7 to 25 in] thick)

Btg2--119 to 165 cm (47 to 65 in); 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. (18 to 51 cm [7 to 20 in] thick)

BCt--165 to 208 cm (65 to 82 in); 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 ft southwest of the southeast corner of cemetery in pasture.

USGS topographic quadrangle: Kurten, Texas;
Latitude: 30 degrees 47 minutes 19.5 seconds North;
Longitude: 96 degrees 16 minutes 51.3 seconds West;
Datum: WGS84.

RANGE IN CHARACTERISTICS:
Solum depth: 152 to 203 cm (60 to 80 in)
Soil Moisture: An ustic soil moisture regime. The soil moisture control section is dry in some or all parts for more than 90 days but less than 150 cumulative days in normal years.
Depth to redox concentrations: 0 to 132 cm (0 to 52 in)
Depth to redox depletions: 13 to 74 cm (5 to 52 in)
Depth to episaturation: 69 to 86 cm (27 to 34 in)
Depth to reduced matrix: 69 to 86 cm (27 to 34 in)

Particle-size control section (weighted average)
Clay content: 25 to 35 percent of the upper 51 cm (20 in) of the argillic horizon

A horizon:
Hue: 7.5YR or 10YR
Value: 4 to 7
Chroma: 1 to 4
Texture: loamy fine sand, fine sand or fine sandy loam
Thickness: 51 to 102 cm (20 to 40 in)
Rock fragments: amount- 0 to 11 percent; size- 2 to 75 mm; kind- quartzite
Reaction: strongly acid to slightly acid

E horizon:
Hue: 10YR or 7.5YR
Value: 4 to 7
Chroma: 2 to 6
Texture: loamy fine sand, or fine sandy loam
Redoximorphic features in shades of gray or yellow range from none to common
Rock fragments: amount- 0 to 11 percent; size- 2 to 75 mm; kind- quartzite
Reaction: very strongly acid to moderately acid

Bt/E horizon (where present):
Bt part
Hue: 10YR
Value: 5 to 7
Chroma: 4 to 6
Texture: sandy clay loam, loam, or clay loam
Rock fragments: amount- 0 to 11 percent; size- 2 to 75 mm; kind- quartzite
Special features: 60 to 90 percent by volume of B material

E part
Hue: 10YR
Value: 6 to 8
Chroma: 1 to 4
Texture: 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
Rock fragments: amount- 0 to 11 percent; size- 2 to 75 mm; kind- quartzite
Reaction: very strongly acid to slightly acid
Location: material consists of tongues, interfingers, and pockets

Btg horizon (upper):
Hue: 2.5YR to 2.5Y
Value: 4 to 7
Chroma: 1 to 8
Texture: clay loam sandy clay, sandy clay loam, or sandy loam
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
Rock fragments: amount- 0 to 1 percent; size- 2 to 75 mm; kind- quartzite
Reaction: very strongly acid to moderately acid

Btg horizon (lower)
Hue: 2.5YR to 2.5Y
Value: 4 to 7
Chroma: 1 to 8
Texture: clay loam or clay
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.
Rock fragments: amount- 0 to 1 percent; size- 2 to 75 mm; kind- quartzite
Reaction: very strongly acid to slightly acid
Some pedons have interfingers of E material in the lower part

BCt horizon (where present):
Hue: 2.5YR to 2.5Y
Value: 4 to 8
Chroma: 1 to 8
Texture: sandy clay loam, clay loam, or clay
Redoximorphic features has colors with shades of red, gray, yellow or brown with few to many mottles.
Rock fragments: amount- 0 to 1 percent; size- 2 to 75 mm; kind- quartzite
Reaction: very strongly acid to neutral
Gypsum: 0 to 5 percent
Salts: 0 to 5 percent

COMPETING SERIES: This is Nimrod (TX) series. Similar soils are the Coving, Chazos, Demona, Nueces, Rader, Rehburg, Selden, Tanglewood (TX-T), and Tremona series.
Nimrod soils: do not have a Bt/E horizon, receive less effective precipitation and are have a typic/ustic moisture regime.
Coving soils: are moderately acid to slightly alkaline throughout the argillic horizon, and are somewhat poorly drained.
Chazos soils: are in the fine family, and have surface layers less than 51 cm (20 in) thick.
Demona, Tanglewood, 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 51 to 102 cm (20 to 40 in) thick over tuffaceous materials.
Selden soils: have surface layers less than 51 cm (20 in) thick.

GEOGRAPHIC SETTING:
Parent material: loamy sediments on Pleistocene terrace deposits about 10.7 to 30.5 m (35 to 100 ft) above present streams or local outwash colluvial plains
Landscape: low oval convex ridges, footslopes and concave sideslope positions or near the heads of drainageways
Slope: 0 to 8 percent, but are mostly 0 to 5 percent
Mean annual precipitation: 891 to 1153 mm (35 to 45.4 in)
Mean annual air temperature: 17.8 to 20.3 degrees C (64 to 68.5 degrees F)
Frost-free period: 240 to 280 days
Elevation: 46 to 183 m (150 to 600 ft)
Thornthwaite P-E Index: 52 to 64

GEOGRAPHICALLY ASSOCIATED SOILS: These are Arenosa, Chazos, Hearne, Jedd, Marquez, Padina, Rader, Rosanky, Silstid, and Tanglewood (T-TX) 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.
Tanglewood soils: occur on similar positions but are formed in loamy and clayey residuum derived primarily from claystone and shale of Eocene Age.

DRAINAGE AND PERMEABILITY:
Drainage class: Moderately well.
Permeability class: slow.
Runoff: low on slopes less than 1 percent, medium on 1 to 5 percent slopes, and high on 5 to 8 percent slopes.
Wetness: 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 Texas Claypan Area (MLRA 87A) of east-central Texas. The series is of large extent.

SOIL SURVEY REGIONAL OFFICE (SSRO) 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.

Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon: 0 to 71 cm (0 to 28 in) (A and E horizons)
Albic horizon: 38 to 71 cm (15 to 28 in)
Arenic feature: 0 to 71 cm (0 to 28 in), loamy fine sand texture.
Argillic horizon: 71 to 208 cm (28 to 82 in) (Bt/E, Btg1, and Btg2 and BCt horizons)
Reduced matrix: 84 to 165 cm (33 to 65 in) (Btg1 and Btg2 horizons)
Redoximorphic concentrations: 84 to 165 cm (33 to 65 in) (Btg1 and Btg2 horizons)
Redoximorphic depletions with chroma of 2 or less: 38 to 71 cm (15 to 28 in). (E horizons)
Episaturation: The zone of saturation at 69 to 119 cm (27 to 65 in) (Btg1, and Btg2 horizons)

ADDITIONAL DATA: Base saturation by hach Kit was 50 percent at 127 cm (50 in) 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

Taxonomic Version: Keys to Soil Taxonomy, Twelfth Edition, 2014.

---

National Cooperative Soil Survey
U.S.A.