LOCATION ACUNA TXEstablished Series
TAXONOMIC CLASS: Fine-silty, carbonatic, hyperthermic Aridic Calciustolls
TYPICAL PEDON: Acuna silty clay--rangeland.
(Colors are for dry soil unless otherwise stated.)
A1--0 to 18 inches; dark grayish brown (10YR 4/2) silty clay, very dark grayish brown (10YR 3/2) moist; the upper 2 inches is grayish brown (10YR 5/2); moderate medium subangular blocky
structure parting to moderate medium granular; slightly hard, friable; common fine and medium roots; common fine pores; few fine threads and films of calcium carbonate; few fine calcium carbonate concretions less than 2 mm across; calcareous; moderately
alkaline; clear wavy boundary. (10 to 20 inches thick)
B21--18 to 30 inches; brown (7.5YR 5/4) clay, dark brown
(7.5YR 4/4) moist; moderate medium subangular blocky structure parting to moderate medium granular; hard, friable; few fine
roots; common very fine pores; few films and threads of calcium carbonate; few thin discontinuous clay films on vertical ped surfaces; calcareous; moderately alkaline; abrupt wavy boundary.
(6 to 28 inches thick)
B22ca--30 to 38 inches; pink (7.5R 7/4) silty clay, brown
(7.5YR 5/4) moist; weak fine subangular blocky structure; slightly hard; friable; many very fine pores; 15 percent by volume of
threads, films, and concretions 2 mm to 2 cm across of calcium carbonate; calcareous; moderately alkaline; clear wavy boundary.
(8 to 28 inches thick)
B23ca--38 to 60 inches; pink (7.5YR 8/4) silty clay, reddish yellow (7.5YR 7/6) moist; weak fine subangular blocky structure; slightly hard, friable; common very fine pores; 8 percent by
volume of threads, films and soft masses of 2 mm to 2 cm across of calcium carbonate, calcareous; moderately alkaline; gradual wavy boundary. (10 to 25 inches thick)
B24ca--60 to 72 inches; reddish yellow (7.5YR 6/6) silty
clay, strong brown (7.5YR 5/6) moist; weak fine subangular blocky structure; slightly hard, friable; about 5 percent by volume of
soft masses and concretions 2 mm to 2 cm across of calcium
carbonate; calcareous; moderately alkaline. (9 to 20 inches
thick)
TYPE LOCATION: Val Verde County, Texas; from the intersection of
U. S. Highway 90 and U. S. Highway 277 in Del Rio; 3.3 miles east
on U. S. Highway 90 to Ranch Road 2523; 8.3 miles generally
northeast on Ranch Road 2523 to ranch entrance; 0.3 mile west on private road; 75 feet north in range.
RANGE IN CHARACTERISTICS: Solum thickness ranges from 40 to more than 60 inches. The depth to distinct accumulations of calcium carbonate is about 16 to 40 inches with 5 to 30 percent visible secondary forms. Total calcium carbonate content in the 10 to 40 inch control section is about 40 to 55 percent. Depth to
limestone or gravel ranges from 6 to 20 feet. Limestone fragments
of pebble size range from 0 to 15 percent. COLE ranges from 0.03
to 0.05. Total clay of the 10 to 40 inch control section ranges
from 35 to 50 percent and silicate clay ranges from 20 to 35
percent.
The A horizon is very dark grayish brown, dark grayish brown,
grayish brown, dark brown, or brown in hue 10YR, chromas of 2
through 3 and values of 3 through 5. Moist values and chromas are less than 3.5. Texture of the A horizon is silty clay loam, silty clay or clay.
The B21t horizon is brown, light brown, or pale brown in hues of
10YR and 7.5Y, chromas of 3 through 4, and values of 5 through 6.
It is silty clay loam, silty clay, or clay. Structure ranges from weak to moderate subangular blocky.
The B2ca horizons are brown, light brown, pale brown, very pale brown, light yellowish brown, or pink in hues of 10YR and 7.5YR, chromas of 3 through 4 and values of 5 through 8. It is silty
clay loam, silty clay, or clay. Some pedons have Cca horizons
below 40 inches with colors the same as the B2ca horizons.
COMPETING SERIES: There are no soils in the same family. Similar soils are the
Angelo,
Castroville,
Dant,
Elindio,
Knippa,
Lewisville,
Nuvalde, and
Uvalde series. All of these soils have
less than 40 percent calcium carbonate equivalent in the 10 to 40 inch control section. Angelo and Knippa soils crack when dry and have mean annual soil temperatures less than 72 degrees F. Castroville, Lewisville, and Nuvalde soils are most in the control section for longer periods of time. Dant soils lack a calcic
horizon within a depth of 40 inches and have a fine-loamy control section.
GEOGRAPHIC SETTING: Acuna soils are on nearly level to gently sloping filled valleys and ancient stream terraces. Slope
gradients range from 0 to 3 percent but are mainly less than 1 percent. The soil formed in alluvium high in calcium carbonate
from limestone areas. The climate is semiarid. Mean annual precipitation ranges from 16 to 21 inches and mean annual air temperature ranges from 69 degrees to 73 degrees F. The
Thornthwaite P-E indices are 25 to 34.
GEOGRAPHICALLY ASSOCIATED SOILS: These include the
Darl,
Langtry,
Mavco,
Olmos,
Valverde,
Zapata, and
Zorra series. Darl, Olmos,
and Zapata soils have a petrocalcic horizon within 20 inches of
the surface. Langtry and Zorra soils are shallow to limestone. Mavco and Valverde soils have ochric epipedons and in addition, Valverde soils have bedrock at depths of 40 to 60 inches.
DRAINAGE AND PERMEABILITY: Well drained; slow to medium runoff; moderate permeability.
USE AND VEGETATION: Used mainly as rangeland. In good and
excellent range condition it is dominated by sideoats grama, slim tridens, plains bristlegrass, and silver bluestem. As
retrogression occurs red grama, perennial threeawn, fall
witchgrass, and Hall's panicum increase along with woody shrubs.
As deterioration continues a large percent of the plants consists
of woody shrubs such as mesquite, whitebrush, agarita, yuccas, and cacti with an understory of red grama, hairy tridens, and
perennial treeawn. Some areas are irrigated and seeded to
improved forage grasses. Oats are grown for forage in some areas.
DISTRIBUTION AND EXTENT: The northwestern Rio Grande Plain and southern Edwards Plateau of Texas and probably Mexico. The series
is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Temple, Texas
SERIES ESTABLISHED: Val Verde County, Texas; 1979.
REMARKS: The Acuna series would have been classified in the
Calcisol great soil group. It was formerly included with the
Elindio series.
ADDITIONAL DATA: Acuna soil samples: Texas Highway Department
Lab Nos. E78640039, E78640040, E78640041.