LOCATION ATCO TXEstablished Series
TAXONOMIC CLASS: Coarse-loamy, carbonatic, hyperthermic Typic Haplustepts
TYPICAL PEDON: Atco loam - rangeland. (Colors are for dry soil unless otherwise stated.)
A--0 to 9 inches; light brownish gray (10YR 6/2) loam, dark grayish brown (10YR 4/2) moist; weak fine subangular blocky structure; slightly hard, very friable; many fine roots, fine pores and old root channels; few worm casts; few snail shell fragments; upper 1 inch is slightly compact; thin 1/6 to 1/4 inch surface crust that is slightly lighter in color and slightly more sandy; violently effervescent; moderately alkaline; clear smooth boundary. (6 to 16 inches thick)
Bk1--9 to 15 inches; pale brown (10YR 6/3) loam, dark brown (10YR 4/3) moist; weak fine subangular blocky structure; slightly hard, friable; many fine roots; many fine pores and old root channels; few worm casts; common fine threads of segregated calcium carbonate; few snail shell fragments; violently effervescent; moderately alkaline; gradual smooth boundary. (6 to 18 inches thick)
Bk2--15 to 29 inches; very pale brown (10YR 7/3) sandy clay loam, brown (10YR 5/3) moist; weak fine subangular blocky structure; slightly hard, friable; many fine roots; many fine pores and old root channels; few worm casts; common fine threads and few soft segregated calcium carbonate masses; violently effervescent; moderately alkaline; gradual wavy boundary. (10 to 14 inches thick)
Bk3--29 to 48 inches; very pale brown (10YR 7/4) sandy clay loam, yellowish brown (10YR 5/4) moist; weak fine and medium subangular blocky structure; slightly hard, friable; few roots; few worm casts; few snail shell fragments; few threads of segregated calcium carbonate; violently effervescent; moderately alkaline; gradual wavy boundary. (15 to 25 inches thick)
C--48 to 72 inches; very pale brown (10YR 7/4) loam, light yellowish brown (10YR 6/4) moist; massive; hard, friable and somewhat compact; violently effervescent; moderately alkaline.
TYPE LOCATION: Uvalde County, Texas; From the intersection of U.S. Highways 83 and 90 in Uvalde. 11.8 miles north (45 degrees) east of courthouse on U. S. Highway 90; 2.6 miles north from Knippa on Farm Market Road 1049; 0.7 mile west on county road; 150 feet north in rangeland.
RANGE IN CHARACTERISTICS: The solum thickness ranges from 40 to 60 inches. Coarse fragments in the solum, consisting of rounded limestone and siliceous pebbles, range from 1.0 percent to about 5 percent by volume. The 10 to 40 inch control section has a total clay content ranging from 18 to 30 percent with the silicate clay about 10 to 18 percent. Calcium carbonate ranges from 40 to 50 percent of the Bk and C horizons.
The A horizon has hue of 10YR, value of 5 or 6, and chroma of 2 or 3. Texture is loam, fine sandy loam, sandy clay loam or clay loam. The Bk horizon has hue of 10YR, value of 5 to 7, and chroma of 3 or 4.
The C horizon has hue of 10YR, value of 6 to 8 and chroma of 3 or 4. In some pedons gravel occurs below 72 inches.
COMPETING SERIES: There are no soils in the same family. Similar soils include Altoga, Brackett, Copita, Hext, Karnes, McAllen, Sabenyo, and Sanderson series. Altoga, Brackett, Hext, Karnes, and Sanderson soils have soils temperature less than 72 degrees F. In addition, Altoga soils contain more than 35 percent clay in the 10 to 40 inch control section; Brackett soils have sola less than 20 inches thick over chalk or Marl; Hext soils as well as Copita and McAllen soils have mixed mineralogy; and Sanderson soils are dry for longer periods in the moisture control section and have loamy-skeletal control section. Copita soils have a paralithic contact with sandstone at depths of less than 40 inches. Sabenyo soils have 15 to 35 percent cemented calcium carbonate concretions in the control section.
GEOGRAPHIC SETTING: The Atco soils occur on nearly level stream terraces and piedmont fans. Slopes are dominantly less than 3 percent and range from 0 to 5 percent. The soil formed in loamy alluvium derived from soils formed from soft limestone, chalk, and marl. The climate is dry subhumid to semiarid. Mean annual precipitation ranges from 29 to 30 inches. Mean annual air temperature ranges from 70 to 73 degrees F. Frost free days ranges from 235 to 255. Elevation ranges from 650 to 1500 feet above sea level. Thorthwaite annual P-E index ranges from 31 to 44.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Orif and the similar Sabenyo soils and the Castroville, Knippa and Uvalde soils. Knippa Castroville, and Uvalde soils have mollic epipedons and more than 18 percent silicate clay in the control section. They occur at slightly higher elevations. Sabenyo soils occur along beveled edges of older and higher land surfaces than those in which Atco soils developed. The Orif soils are skeletal and occur in lower positions on floodplains.
DRAINAGE AND PERMEABILITY: Well drained. Runoff is negligible on 0 to 1 percent slopes, very low on 1 to 3 percent slopes, and low on 3 to 5 percent slopes. Permeability is moderate.
USE AND VEGETATION: The soil is used mostly for rangeland. Some areas are used for growing cotton, corn, grain sorghums, and small grain in the eastern part of its occurrence. Smaller areas are irrigated to these same crops plus some winter vegetables. The principal native grasses are red grama, threeawn, hooded windmillgrass, bristlegrass, pink pappusgrass, lovegrass, tridens, sideoats grama, Hall's panicum, and grassbur. Woody plants include mesquite, Texas colubrina, lotebush, guajillo, bluewood condalia, whitebrush, spiny hackberry, and prickelypear cactus.
DISTRIBUTION AND EXTENT: Northern Rio Grande Plain of Texas. The series is of moderate extent with an estimated 50,000 acres.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Temple, Texas
SERIES ESTABLISHED: Uvalde County, Texas; 1970.
DIAGNOSTIC HORIZONS AND FEATURES:
Ochric epipedon - 0 to 9 inches. (A horizon)
Calcic horizon - 9 to 48 inches. (Bk horizons)