LOCATION ZAVCO TX

Established Series
Rev. CLG-WJG-JDN
11/2010

ZAVCO SERIES

The Zavco series consists of very deep, well drained soils that formed in calcareous loamy residuum from interbedded sandstone and siltstone of the Yegua Formation. These nearly level to gently sloping soils occur on summits, backslopes, and footslopes of interfluves. Slopes range from 0 to 5 percent. Mean annual temperature is about 22.2 degrees C (72 degrees F) and mean annual precipitation is about 610 mm (24 in).

TAXONOMIC CLASS: Fine, mixed, active, hyperthermic Aridic Argiustolls

TYPICAL PEDON: Zavco sandy clay loam in rangeland; elevation is 211 meters (692 feet). (Colors are for dry soil unless otherwise stated.)

A--0 to 28 cm (0 to 11 in); dark brown (7.5YR 3/2) sandy clay loam, very dark brown (7.5YR 2/2) moist; moderate fine and medium subangular blocky structure; hard, friable; many fine roots; fine pores; upper one inch is slightly lighter in color; neutral; clear smooth boundary. (15 to 41 cm [6 to 16 in] thick)

AB--28 to 41 cm (11 to 16 in); dark reddish brown (5YR 3/2) sandy clay loam, dark reddish brown (5YR 2/2) moist; moderate medium subangular and blocky parting to moderate fine angular blocky structure; very hard, firm; many fine roots; fine pores; few dark stains on surfaces of peds; neutral; gradual smooth boundary. (10 to 28 cm [4 to 11 in] thick)

Bt--41 to 91 cm (16 to 36 in); reddish brown (5YR 4/4) sandy clay, dark reddish brown (5YR 3/4) moist; moderate fine and medium angular blocky structure; very hard, very firm; few fine roots; fine pores; thin patchy clay films on peds; few dark stains on surfaces of peds; few krotovina; few threads of calcium carbonate on vertical ped faces; moderately alkaline; gradual wavy boundary. (15 to 74 cm [6 to 29 in] thick)

BCk1--91 to 142 cm (36 to 56 in); yellowish red (5YR 5/6) clay loam, yellowish red (5YR 4/6) moist; weak fine and medium subangular blocky structure; hard, firm; few fine roots and pores; about 5 percent by volume of soft masses and few strongly cemented concretions of calcium carbonate in upper part increasing to about 10 percent in lower part; few fine yellowish brown and reddish brown fragments of sandstone; few dark stains and old channels partially filled with darker material; calcareous; moderately alkaline; clear wavy boundary. (10 to 76 cm [4 to 30 in] thick)

BCk2--142 to 183 cm (56 to 72 in); light brown (7.5YR 6/4) sandy clay loam, brown (7.5YR 5/4) moist; many fine and medium distinct gray (10YR 6/1), strong brown (7.5YR 5/6), and yellowish red (5YR 5/6) mottles; weak fine and medium subangular blocky structure; hard, friable; few soft masses and cemented concretions of calcium carbonate; calcareous; moderately alkaline.

TYPE LOCATION: Zavala County, Texas; 9.0 miles west of LaPryor on U.S. Highway 57, 1.6 miles south on Chaparrosa Ranch headquarters road, then northwest and west 2.1 miles on small ranch road, 100 feet south of road in rangeland. Chacon Creek NE USGS topographic quadrangle; Latitude: 28 degrees, 54 minutes, 47.05 seconds N; Longitude: 100 degrees, 1 minute, 36.18 seconds W. (NAD 83).

RANGE IN CHARACTERISTICS:

Soil Moisture: A typic-ustic moisture regime. The soil moisture control section is dry in some or all parts for more than 90 days but less than 180 cumulative days in normal years. June through August and December through February are the driest months. These soils are intermittently moist in September through November and March through May.
Mean annual soil temperature: 22.2 to 23.9 degrees C (72 to 75 degrees F)
Depth to argillic: 18 to 55 cm (7 to 22 in)
Depth to secondary forms of calcium carbonate: 25 to 71 cm (10 to 28 in)
Particle size control section (weighted average): clay content: 38 to 55 percent

A and AB horizon

Hue: 10YR, 7.5YR, and 5YR
Value: 3 and 4
Chroma: 2 and 4
Texture: sandy clay loam or clay loam
Reaction: slightly acid through mildly alkaline

Bt horizon

Hue: 7.5YR and 5YR
Value: 3 to 5
Chroma: 3 through 6
Texture: sandy clay loam or Clay upper 50 cm (20 in) of the Bt horizon ranges from 35 to 45 percent.
Reaction: neutral through moderately alkaline

BCk horizons

Hue: 10YR, 7.5YR, and 5YR
Value: 4 to 7
Chroma: 3 to 6
Texture: sandy clay loam or clay loam
Concentrations: 2 to 30 percent secondary concretions or soft bodies of calcium carbonate.
Reaction: mildly alkaline through moderately alkaline
Salinity: 0 to 8 m/ds

COMPETING SERIES: There are no competing series. Similar soils are Amphion, Campbellton, Clareville, Elmendorf, Hindes, Marcelinas, Musquiz, and Ramadero series.
Amphion soils: have a mollic epipedon more than 51 cm (20 in) thick.
Campbellton soils: are moist in the moisture control sections for longer periods.
Clareville soils: have a mollic epipedon more than 51 cm (20 in) thick and have COLE values greater than 0.07
Elmendorf soils: have COLE values greater than 0.07
Hindes soils: have more than 35 percent coarse fragments in their control sections
Marcelinas soils: have COLE values greater than 0.07
Musquiz soils: have mean annual soil temperatures less than 22 degrees C (72 degrees F)
Ramadero soils: have a mollic epipedon more than 51 cm (20 in) thick and have less than 35 percent clay in their control sections.

GEOGRAPHIC SETTING:
Parent Material: calcareous residuum from sandstone and siltstone
Landscape: inland dissected coastal plain
Landform: summits, backslopes, and footslopes of interfluves
Slope: 0 to 5 percent
Mean annual air temperature: 20 to 22 degrees C (69 to 72 degrees F)
Mean annual precipitation: 533 to 660 mm (21 to 26 in)
Frost-free period: 240 to 290 days
Elevation: 137 to 274 m (450 to 900 ft)
Thornthwaite annual P-E indices: 26 to 36

GEOGRAPHICALLY ASSOCIATED SOILS: These are Caid, Chacon, Duval, Hindes, Ramadero, Tonio and Webb series.
Caid soils: occur on similar surfaces, are calcareous throughout, and are in a fine-loamy particle-size class
Chacon soils: occur on similar surfaces, are calcareous throughout, have montmorillonitic mineralogy and have a COLE exceeding 0.07
Duval soils: occur on similar surfaces, lack mollic epipedons, and are in a fine-loamy particle-size class
Hindes soils: occur on ridges at higher elevations
Ramadero soils: occur in slightly depressed areas at lower elevationsTonio soils: occur on similar surfaces, are calcareous throughout, lack
mollic epipedons, and are in a fine-loamy particle-size class
Webb soils: occur on similar surfaces and lack mollic epipedons

DRAINAGE AND PERMEABILITY: Well drained. Permeability is moderately slow. Runoff is slow to medium.

USE AND VEGETATION: The major use is wildlife habitat. A few acres are cultivated and the principal crops are grain sorghum, small grain, and introduced perennial grasses. Grasses which make up about 70 percent of the plant community under climax conditions are fourflower trichloris, twoflower trichloris, pinhole bluestem, plains bristlegrass, buffalograss, and pink pappusgrass. About 5 percent forbs such as bundleflower and orange zexmenia, and about 5 percent shrubs such as guajillo and guayacan also occur. With retrogression, plants such as pink pappusgrass and buffalograss increase initially. With continued retrogression, increasers and invaders such as curlymesquite, threeawn, Hall's panicum, red grama, mesquite, whitebrush, blackbrush, twisted acacia and Texas persimmon dominate the plant community. The ecological site is Clay Loam, PE 26-36 (R083CY446TX).

DISTRIBUTION AND EXTENT: Northern and Central Rio Grande Plain of Texas. LRR I; MLRA 83A, 83C. The series is of moderate extent.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Temple, Texas

SERIES ESTABLISHED: Uvalde County, Texas; 1970.

REMARKS: Coined from Zavala County

Diagnostic horizons and features recognized in this pedon are:

Mollic epipedon: 0 to 41 cm (0 to 16 in).

Argillic horizon: 41 to 91 cm (16 to 36 in).

Paralithic materials: occurs below a depth of 152 cm (60 in). The soft or weakly cemented sandstone or shale bedrock slakes or crushes to sandy clay loam or clay loam.

ADDITIONAL DATA: Particle size analysis, sieve analysis, sodium absorption ratio, electrical conductivity, pH were all performed at the local project office for 3 pedons from McMullen County.

TAXONOMIC VERSION: Keys to Soil Taxonomy, Eleventh Edition, 2010

National Cooperative Soil Survey
U.S.A.