LOCATION VALCO TXEstablished Series
TAXONOMIC CLASS: Loamy, mixed, superactive, hyperthermic, shallow Petrocalcic Calciustolls
TYPICAL PEDON: Valco clay loam--rangeland. (Colors are for dry soil unless otherwise stated.)
A1--0 to 7 inches; grayish brown (10YR 5/2) clay loam, very dark grayish brown (10YR 3/2) moist; weak fine and medium subangular blocky and fine granular structure; hard, friable; many fine roots and root channels; few wormcasts and termite tunnels; few threads of calcium carbonate, few calcium carbonate concretions to 3 mm diameter; few small angular limestone fragments to 1 inch diameter, 1/4 inch light gray (10YR 7/2) surface crust; slightly effervescent; moderately alkaline; clear smooth boundary. (4 to 14 inches thick)
A2--7 to 15 inches; brown (10YR 5/3) clay loam, dark brown (10YR 3/3) moist; weak fine and medium subangular blocky structure; hard, friable; many fine roots; few fine pores and root channels; few threads of calcium carbonate, few calcium carbonate concretions to 5 mm diameter; few angular limestone fragments; up to 2 inches across; slightly effervescent; moderately alkaline; clear smooth boundary. (4 to 11 inches thick)
Ak--15 to 17 inches; brown (10YR 5/3) very gravelly clay loam, dark brown (10YR 3/3) moist; weak fine subangular blocky structure; hard, friable; contains an estimated 60 percent by volume of strongly cemented caliche fragments 1/2 inch to 2 inches in diameter; slightly effervescent; moderately alkaline; abrupt smooth boundary. (0 to 8 inches thick)
Bkm--17 to 19 inches; very pale brown (10YR 7/3) to white (10YR 8/2) strongly cemented caliche that is weakly laminar in upper part; contains a few solution cavities more than 20 inches apart that are partially filled with soil material like that of the horizon above, strongly effervescent; abrupt smooth boundary. (1 to 9 inches thick)
BCk--19 to 60 inches., very pale brown (10YR 7/3) to white (10YR 8/2) weakly cemented caliche of loam texture. Contains a few rounded limestone pebbles; strongly effervescent; moderately alkaline.
TYPE LOCATION: Uvalde County, Texas; 6.5 miles south of courthouse in Uvalde on U.S. Highway 83; 850 feet east from a metal gate along a ranch road; 140 feet south in rangeland.
RANGE IN CHARACTERISTICS: Solum thickness above the petrocalcic horizon ranges from 8 to 20 inches. Weighted average coarse fragments in the solum range from a few to about 30 percent by volume and increase with depth.
The A horizon has colors of 7.5YR or 10YR value of 3 to 5 and chroma of 2 to 3. Moist values are less than 3.5. Texture is fine sandy loam, loam or clay loam or their gravelly or very gravelly counterparts. Clay content ranges from about 12 to 35 percent.
The upper part of the Bkm horizon is laminar in most pedons.
The BCk horizon is weakly cemented caliche or pinkish limy earth of fine sandy loam, loam, sandy clay loam or clay loam texture.
COMPETING SERIES: There are no other series in the same family. Similar series include Cho, Darl, Espy, Kimbrough, Mereta, Olmos, and Queeny series. Cho, Espy, Kimbrough, Mereta, and Queeny soils have average soil temperatures of less than 72 degrees F. In addition, Cho soils have carbonatic mineralogy and Mereta soils have clayey control sections. Darl soils lack mollic epipedons. Olmos soils have loamy-skeletal control sections.
GEOGRAPHIC SETTING: Valco soils are on nearly level to moderately sloping outwash plains similar to the Goliad and Oakville formations and old stream terraces. Slopes are 0 to 8 percent. The soil formed in loamy calcareous sediments. The climate is hot and dry subhumid to semiarid. Average annual precipitation is 20 to 36 inches; annual P-E indices are 25 to about 40; and mean annual temperature is about 70 to 73 degrees F. Frost free days range from 260 to 295. Elevation ranges from 150 to 1200 feet.
GEOGRAPHICALLY ASSOCIATED SOILS: In addition to the competing Darl and Olmos series, these are Caid, Elindio, Tonio, and Uvalde series. Darl soils occur on surfaces similar to Valco soils. Olmos soils occur on slightly higher elevations. Caid, Elindio, Tonio, and Uvalde soils are very deep and occur on slightly lower elevations.
DRAINAGE AND PERMEABILITY: Well drained; slow to medium runoff; moderate permeability above the Bkm horizon which has slow permeability.
USE AND VEGETATION: Mostly rangeland. Some small areas are cultivated with small grain, grain sorghum, and introduced perennial grasses as primary crops. In climax conditions, dominant grasses include pink pappusgrass, pinhole bluestem, plains bristlegrass, sideoats grama, plains lovegrass, Arizona cottontop, and slim tridens. Shrubs make up about 5 percent of the plant community and perennial forbs make up about 5 percent. With retrogression, plants such as red grama, threeawn, Hall's panicum, Texas bristlegrass, and fall witchgrass increase or invade. Brush plants such as mesquite, guajilo, cenizo, condalia, blackbrush, Texas persimmon, guayacan, agarito and pricklypear also increase and invade. Gray coldenia is a common forb. The woody vegetation is sparse in most places.
DISTRIBUTION AND EXTENT: Northern Rio Grande Plain of Texas. The series is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Temple, Texas
SERIES ESTABLISHED: Uvalde County, Texas; 1970.
REMARKS:
Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - 0 to 17 inches.
Petrocalcic horizon - 17 to 19 inches.