LOCATION TOBOSA TX
Established Series
Rev. OLB-RM
08/2017
TOBOSA SERIES
The Tobosa series consists of very deep, well drained, very slowly permeable soils formed in calcareous clayey alluvium derived from limestone. These nearly level to very gently sloping soils occur on dissected plateaus. Slopes range from 0 to 3 percent. Mean annual precipitation is about 558 mm (22 in) and the mean annual air temperature is about 18 degrees C (64 degrees F).
TAXONOMIC CLASS: Fine, smectitic, thermic Aridic Haplusterts
TYPICAL PEDON: Tobosa clay--cropland. At center of microflat. (Colors are for dry soil unless otherwise stated.)
Ap--0 to 30 cm (0 to 12 in); dark grayish brown (10YR 4/2) clay, very dark grayish brown (10YR 3/2) moist; moderate very fine and fine subangular blocky structure; very hard, very firm, sticky and plastic; common fine roots; few siliceous gravel; slightly effervescent; moderately alkaline; clear smooth boundary.
A--30 to 41 cm (12 to 16 in); dark grayish brown (10YR 4/2) clay, very dark grayish brown (10YR 3/2) moist; strong medium angular blocky structure that form wedge-shaped aggregates with long axis tilted 5 to 30 degrees from the horizontal; extremely hard, very firm, sticky and plastic; few fine roots; few siliceous gravel; strongly effervescent; moderately alkaline; gradual wavy boundary. (Combined thickness of the A horizon is 30 to 54 cm [12 to 21 in])
Bss1--41 to 112 cm (16 to 44 in); dark grayish brown (10YR 4/2) clay, very dark grayish brown (10YR 3/2) moist; strong medium and coarse angular blocky structure that forms wedge-shaped aggregates with long axis tilted 5 to 30 degrees from the horizontal; extremely hard, very firm, very sticky and very plastic; few fine roots; few fine pores; common distinct slickensides; few siliceous gravel; strongly effervescent; moderately alkaline; diffuse wavy boundary.
Bss2--112 to 152 cm (44 to 60 in); brown (10YR 5/3) clay, brown (10YR 4/3) moist; moderate medium angular blocky structure that forms wedge-shaped aggregates with their long axis tilted 5 to 30 degrees from the horizontal; very hard, very firm, very sticky and very plastic; few fine roots; common vertical streaks of darker soil from above; common grooved slickensides; few siliceous gravel; few soft masses of calcium carbonate in lower 25 cm (10 in); violently effervescent; moderately alkaline; gradual wavy boundary. (Combined thickness of the Bss horizon is 96 to 155 cm [38 to 61 in])
BCk--152 to 203 cm (60 to 80 in); pink (7.5YR 7/4) clay, light brown (7.5YR 6/4) moist; weak medium and coarse angular blocky structure; extremely hard, very firm, very sticky and plastic; 15 percent soft masses of calcium carbonate; violently effervescent; moderately alkaline.
TYPE LOCATION: Tom Green County, Texas; From San Angelo, approximately 10 miles northeast to intersection of U.S. Highway 67 and Farm Road 1692, 6.2 miles in a northeasterly direction along Farm Road 1692, 100 ft south in field.
USGS topographic quadrangle: Miles, TX;
Latitude: 31 degrees, 36 minutes, 35 seconds N;
Longitude: 100 degrees, 14 minutes, 54 seconds W;
Datum: WGS 84.
RANGE IN CHARACTERISTICS:
Soil Moisture: Aridic-ustic moisture regime
Depth to bedrock: typically greater than 203 cm (80 in), but some pedons are underlain by marl, shale, or limestone below 102 cm (40 in)
Depth to slickensides: 36 to 76 cm (14 to 30 in)
Linear extensibility: greater than 6.0 cm in the top 100 cm (40 in)
Cracks: 8 to 25 mm (0.3 to 1 in) wide that extend from the surface to a depth of 51 to 152 cm (20 to 60 in)
Microrelief: microdepressions occupy 5 to 25 percent of the pedon and are repeated horizontally every 4 to 8 m (12 to 24 ft).
Depth to calcic horizon: below 152 cm (60 in)
Carbonate clay content: 1 to 12 percent
Particle-size control section (weighted average):
Total Clay content: 40 to 60 percent
Silicate clay content: 35 to 55 percent
A horizon
Hue: 7.5YR or 10YR
Value: 3 to 5, 2 to 4 moist
Chroma: 2 to 4 dry or moist
Texture: clay or silty clay
Total Clay content: 40 to 60 percent
Rock fragments: 0 to 10 percent total; 0 to 10 percent gravel, 0 to 2 percent cobbles, and 0 to 2 percent stones; nonflat, rounded, indurated limestone or quartz
Calcium carbonate equivalent: 0 to 10 percent
Electrical conductivity (decisiemens per meter): 0 to 2
Sodium Adsorption Ratio: 0 to 10
Reaction: slightly alkaline or moderately alkaline
Bss horizon
Hue: 7.5YR or 10YR
Value: 4 to 6, 3 to 5 moist
Chroma: 2 to 4 dry or moist
Texture: clay or silty clay
Total Clay content: 40 to 60 percent
Rock fragments: 0 to 10 percent total; 0 to 10 percent gravel, 0 to 2 percent cobbles, and 0 to 2 percent stones; nonflat, rounded, indurated limestone or quartz
Calcium carbonate equivalent: 2 to 30 percent
Electrical conductivity (decisiemens per meter): 0 to 2
Sodium Adsorption Ratio: 0 to 15
Reaction: slightly alkaline or moderately alkaline
BCk horizon
Hue: 5YR to 10YR
Value: 5 to 8, 4 to 6 moist
Chroma: 2 to 6 dry or moist
Texture: clay or silty clay
Total Clay content: 40 to 60 percent
Rock fragments: 0 to 12 percent total; 0 to 10 percent gravel, 0 to 2 percent cobbles, and 0 to 2 percent stones; nonflat, rounded, indurated limestone or quartz
Calcium carbonate equivalent: 2 to 45 percent
Electrical conductivity (decisiemens per meter): 0 to 2
Sodium Adsorption Ratio: 0 to 15
Reaction: moderately alkaline
COMPETING SERIES: There are no competing series in the same family. Similar soils are the
Anhalt,
Campwood,
Depalt,
Irion, and
Lipan series.
Anhalt: have a very-fine particle-size control section and is moderately deep to fractured moderately cemented limestone bedrock
Campwood,
Depalt,
Irion, and
Lipan: are moist for longer periods and have cracks that are open for less than 210 cumulative days per year
GEOGRAPHIC SETTING:
Parent Material: calcareous clayey alluvium derived from limestone
Landscape: dissected plateaus
Landform: slightly concave areas and swales on ridges
Slope: mainly 0 to 1 percent, but ranges up to 3 percent
Mean annual precipitation: 457 to 610 mm (18 to 24 in)
Thornthwaite P.E. indices: 22 to 34
Mean annual air temperature: 16 to 20 degrees C (61 to 68 degrees F)
Frost-free period: 210 to 240 days
Elevation: 528 to 853 m (1732 to 2800 ft).
GEOGRAPHICALLY ASSOCIATED SOILS: These are the
Angelo,
Lipan,
Mereta, and
Rioconcho series.
Angelo soils: have a fine-silty particle-size control section, have a calcic horizon, and occur on slightly higher positions.
Lipan soils: have chroma of less than 1.5 in the upper 30 cm (12 in) and occur in depressions.
Mereta soils: are shallow to a petrocalcic horizon and occur on higher positions
Rioconcho soils: lack wedge shaped peds and slickensides and occur on lower flood plains
DRAINAGE AND PERMEABILITY:
Drainage class: Well.
Permeability class: Very slow.
Runoff: high on less than 1 percent slopes and very high on 1 to 3 percent slopes.
Water enters the soil rapidly when dry and cracked and very slowly when moist.
USE AND VEGETATION: The major uses are cropland and rangeland. Small grains, sorghums, and cotton are the main crops. Native vegetation is tobosa, buffalograss, curlymesquite, mesquite, and cacti.
DISTRIBUTION AND EXTENT: The Edwards Plateau of Texas; LRR I - Southwest Plateaus and Plains Range and Cotton Region; MLRA 81A - Edwards Plateau, Western Part. The series is extensive.
SOIL SURVEY REGIONAL OFFICE (SSRO) RESPONSIBLE: Temple, Texas
SERIES ESTABLISHED: Crockett County, Texas; 1930.
REMARKS: Classification change from Typic Chromusterts to Aridic Haplusterts based on Amendment 16, SOIL TAXONOMY (2/94).
Edited 12/2013 (RFG-THW): Changed to tabular format and included metric values. Updated the competing series, geographic setting, and associated soils sections.
Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon: 0 to 112 cm (0 to 44 in) (Ap, A, and Bss1 horizons)
Vertic feature: Slickensides and wedge-shaped aggregates - 41 to 152 cm (16 to 60 in) (Bss horizons)
Cambic horizon: 41 to 152 cm (16 to 60 in) (Bss horizons)
Calcic horizon: 152 to 203 cm (60 to 80 in) (BCk horizon)
Aridic feature: have cracks in normal years that are 5 mm or more wide, through a thickness of 25 cm or more within 50 cm (10 or more within 20 in) of the mineral soil surface, for 210 or more cumulative days per year.
ADDITIONAL DATA: TAMU Laboratory data No. S84TX-105-003 from Crockett County.
Taxanomic Version: Keys to Soil Taxonomy, Twelfth Edition, 2014
National Cooperative Soil Survey
U.S.A.