LOCATION ZAPATA TXEstablished Series
TAXONOMIC CLASS: Loamy, mixed, superactive, hyperthermic, shallow Petrocalcic Calciustepts
TYPICAL PEDON: Zapata loam in rangeland. (Colors are for dry soil unless otherwise stated.)
A1--0 to 3 cm (0 to 1 in); light brownish gray (10YR 6/2) loam, dark grayish brown (10YR 4/2) moist; massive; hard, friable; 5 percent angular petrocalcic and rounded chert fragments; strongly effervescent; moderately alkaline; abrupt smooth boundary. (3 to 5 cm [1 to 2 in])
A2--3 to 20 cm (1 to 8 in); grayish brown (10YR 5/2) loam, dark grayish brown (10YR 4/2) moist; moderate fine subangular blocky structure; hard, friable; many fine and very fine pores; 2 percent threads and films of calcium carbonate; 10 percent of angular petrocalcic fragments 5 to 15 cm (2 to 6 in) long and rounded chert gravel; violently effervescent; moderately alkaline; abrupt wavy boundary.(3 to 23 cm [1 to 9 in])
Bkkm1--20 to 28 cm (8 to 11 in); very pale brown (10YR 8/3) strongly cemented calcium carbonate; indurated, laminar cap contains thin brownish horizontal bands in the upper 3 cm (1 in); upper surface of the petrocalcic is smooth but etched and fractured; moderately alkaline; gradual wavy boundary. (3 to 10 cm [1 to 4 in])
Bkkm2--28 to 203 cm (11 to 80 in); very pale brown (10YR 8/2) weakly cemented calcium carbonate that is moderately cemented in the upper part; massive but has fractures and solution channels; moderately alkaline.
TYPE LOCATION: Starr County, Texas; from El Sauz, Texas, 8.5 miles north on Farm Road 649 to Farm Road 2686; 5.8 miles east on Farm Road 2686 to old county road; 0.4 mile north and northeast on old county road; 75 feet north in rangeland. Viboras, TX USGS topographic quadrangle. Latitude: 26 degrees, 41 minutes, 14.935 seconds N; Longitude: 98 degrees, 45 minutes, 22.605 seconds W; NAD 83.
RANGE IN CHARACTERISTICS:
Solum thickness ranges from 5 to 25 cm (2 to 10 in).
Coarse fragments consist of a few to 25 percent of angular caliche 3 to 20 cm (1 to 8 in) long and chert gravel.
A horizon
Hue: 10YR
Value: 4 to 6
Chroma: 2 or 3
Texture: loam, clay loam, fine sandy loam, or their gravelly counterparts
Calcium carbonate equivalent: 1 to 40 percent in the fraction less than 2 cm.
Effervescence: slight to violent with 10 percent HCL.
Bkkm1 horizon
Hue: 10YR
Value: 7 or 8
Chroma: 2 or 3
Petrocalcic is indurated to strongly cemented. Cementation becomes weaker in the lower part of the Bkkm1 horizon.
Bkkm2 horizon
Hue: 10YR
Value: 7 or 8
Chroma: 2 or 3
Petrocalcic is moderately or weakly cemented and becomes less cemented with depth.
COMPETING SERIES: There are no competing series in the same family. Similar soils are the
Cuevitas (TX),
Jimenez (TX),
Milkweed (AZ), Peidras (TX),
Quemado (TX), and
Randado (TX) series.
Cuevitas and Randado soils: are noncalcareous in the solum, in addition, Randado soils have an argillic horizon.
Jimenez,
Piedras, and Quemado soils: have loamy-skeletal particle-size control sections, in addition, Jimenez soils have mollic surfaces and Quemado soils have an argillic horizon
Milkweed soils: have a mesic soil temperature regime.
GEOGRAPHIC SETTING:
Parent material: calcareous loamy alluvium.
Landscape: inland dissected coastal plain.
Landform: ridges on interfluves.
Slope: 1 to 8 percent.
Mean annual air temperature: 21 to 23 degrees C (70 to 74 degrees F).
Mean annual precipitation: 457 to 610 mm (18 to 24 in).
Precipitation pattern: soil is driest during the months of June through August and December through February.
Frost-free period: 280 to 340.
Elevation: 91 to 168 m (300 to 550 ft).
Thornthwaite annual P-E indices: 20 to 28.
GEOGRAPHICALLY ASSOCIATED SOILS: These include the
Brennan,
Copita,
Cuevitas,
Delmita,
Jimenez,
Quemado, and
Randado series.
Brennan and Copita soils: have sola more than 51 cm (20 in) thick, do not have a petrocalcic horizon, and are on lower positions
Cuevitas, Delmita, and Randado soils: have noncalcareous, in addition Delmita and Randado soils have argillic horizons and are similar or slightly lower positions
Jimenez and Quemado soils: are gravelly and are on similar positions
DRAINAGE AND PERMEABILITY: Well drained. Permeability is moderate over a very slowly permeable petrocalcic horizon. Runoff is negligible on slopes less than 1 percent, low on slopes 1 to 5 percent, and medium on slopes 5 to 8 percent.
USE AND VEGETATION: Used mainly for wildlife habitat and livestock grazing. The principal grasses include a sparse cover of tanglehead, plains bristlegrass, twoflower trichloris, hooded windmillgrass and perennial threeawn. Common brushy plants are blackbrush, cenizo, guajillo, kidneywood, and ratany. The ecological site is Shallow Ridge 20-25 PZ (R083CY485TX).
DISTRIBUTION AND EXTENT: Central Rio Grande Plain,Texas; LRR I; MLRA 83C; the series is of moderate extent
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Temple, Texas
SERIES ESTABLISHED: Reconnaissance Soil Survey of South Texas; 1909.
REMARKS:
Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon: 0 to 20 cm (0 to 8 in) (A horizons).
Petrocalcic horizon: 20 to 203 cm (8 to 80 in) (Bkkm horizons).
ADDITIONAL DATA: none.
Taxonomic version: Keys to Soil Taxonomy, Tenth Edition, 2006.