LOCATION IRAAN TXEstablished Series
TAXONOMIC CLASS: Fine-silty, mixed, superactive, thermic Cumulic Haplustolls
TYPICAL PEDON: Iraan silty clay loam, on a smooth valley floor - in rangeland. (Colors are dry soil unless other stated.)
A1--0 to 7 inches; dark grayish brown (10YR 4/2) silty clay loam, very dark grayish brown (10YR 3/2) moist; weak fine and medium granular and subangular blocky structure; hard, friable; common wormcasts, many fine roots, few fine rounded limestone gravel; slightly effervescent; moderately alkaline; gradual smooth boundary. (4 to 24 inches thick)
A2--7 to 28 inches; dark grayish brown (10YR 4/2) silty clay loam, very dark grayish brown (10YR 3/2) moist; moderate fine and medium subangular blocky structure; hard, firm; few wormcasts, common pores, few rounded limestone gravel less than 1/8 inch in diameter; few films and threads of calcium carbonate; strongly effervescent; moderately alkaline; clear smooth boundary. (8 to 32 inches thick)
Bw1--28 to 43 inches; brown (10YR 5/3) silty clay loam, brown (10YR 4/3) moist; moderate medium subangular blocky structure; hard, firm; few rounded gravel less than 1/8 inch in diameter; few films and threads of calcium carbonate; strongly effervescent; moderately alkaline; diffuse wavy boundary. (8 to 40 inches)
Bw2--43 to 60 inches; brown (10YR 5/3) silty clay loam, brown (10YR 4/3) moist; weak medium subangular blocky structure; hard, firm; common rounded gravel less than 1/8 inch in diameter; few films and threads of calcium carbonate; strongly effervescent; moderately alkaline.
TYPE LOCATION: Pecos County, Texas; from the intersection of U.S. Highway 285 and U.S. Highway 290 in Fort Stockton, 11.3 miles southeast on U.S. Highway 285, then 3.1 miles south on county road, then 1.4 miles west on ranch road, and 50 feet north in pasture. (Latitude: 30 degrees, 42 minutes, 54 seconds North: Longitude: 102 degrees, 41 minutes, 06 seconds West.)
RANGE IN CHARACTERISTICS: Solum thickness is 60 to more than 80 inches. The mollic epipedon is 20 to 40 inches thick. Clay content of the 10- to 40- inch control section ranges from 30 to 45 percent and non-carbonate clay ranges from 27 to 35 percent. Calcium carbonate equivalent is about 5 to 30 percent with 0 to 5 percent in visible secondary forms. Limestone fragments range from 0 to 15 percent.
The A horizon has hue of 10YR or 7.5YR, value of 3 to 5, and chroma of 2 or 3. Texture is silt loam, silty clay loam, or clay loam.
The Bw horizons have hue of 7.5YR or 10YR, value of 4 to 6, and chroma of 2 to 4. Texture is clay loam, silty clay loam, or silty clay.
The C or Ck horizons, where present, are loam, clay loam, silty clay loam, or silty clay. Some pedons have gravelly or cobbly strata below 40 inches. Buried horizons occur in some pedons.
COMPETING SERIES: These are the Bergstrom (TX), Bigetty (NM), Elandco (TX), and Port (OK) series. Similar soils are the Bippus, Frio, Gageby, Rioconcho, Spur, and Toyah series. Bergstrom, Elandco, Frio, and Port soils are moist for longer periods. In addition, Frio soils have a fine control section and Bergstrom and Elandco soils do not have secondary carbonates within a depth of 20 inches. Bigetty soils occur at elevations above 3100 feet. Bippus, Gageby, Spur, and Toyah soils have fine-loamy control sections and, in addition, Spur and Toyah soils have mollic epipedons less than 20 inches thick. Rioconcho soils have a fine control section and have vertic properties.
GEOGRAPHIC SETTING: Iraan soils are on nearly level flood plains and in valleys that drain from soils that formed in limestone. Slope gradients are 0 to 2 percent. Mean annual precipitation ranges from 12 to 20 inches, and mean annual temperature ranges from 60 to 70 degrees F. Frost-free days range from 210 to 240 and elevation ranges from 1,500 to 3,100 feet. Thornthwaite P-E indices range from 20 to 33.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Dalby, Dev, Ector, Hodgins, Reagan, Sanderson, Toyah and Upton series. Dalby soils have more than 40 percent clay in the control section and have slickensides. They are in similar positions. Dev and Sanderson soils have loamy-skeletal control sections. Dev soils are in similar positions and Sanderson soils are on higher fans and footslopes. Ector soils are shallow over limestone bedrock and are on mountains and ridges. Hodgins and Reagan soils have ochric epipedons and are on broader alluvial flats. Upton soils are shallow over indurated caliche and are on fans and footslopes in higher positions.
DRAINAGE AND PERMEABILITY: Well drained. Permeability is moderately slow. Runoff is negligible on slopes less than 1 percent and very low on 1 to 2 percent slopes.
USE AND VEGETATION: Most areas are in native rangeland. A few areas are in irrigated cropland. Crops are mainly cotton, grain sorghum, small grain, alfalfa and vegetables. The native vegetation is sideoats grama, tobosa grass, plains bristlegrass, blue grama and vine-mesquite. Woody species include mesquite, black walnut, hackberry and western soapberry.
DISTRIBUTION AND EXTENT: Mainly in the Western part of the Edwards Plateau Land Resource area. MLRA 81A. The series is of moderate extent.
MLRA OFFICE RESPONSIBLE: Temple, Texas
SERIES ESTABLISHED: Pecos County, Texas; 1977.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - 0 to 28 inches. (A1 and A2 horizons)
Cambic horizon - 28 to 60 inches. (Bw horizons)
Cumulic feature - has a mollic epipedon greater than 20 inches thick; an irregular decrease in organic-carbon content with depth, and greater than 0.3 percent organic-carbon within 50 inches of the surface.
ADDITIONAL DATA:
TAXONOMIC VERSION: Keys to Soil Taxonomy, Tenth Edition, 2006