LOCATION MCALLEN TXEstablished Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, hyperthermic Aridic Calciustepts
TYPICAL PEDON: McAllen fine sandy loam--cropland. (Colors are for dry soil unless otherwise stated.)
Ap--0 to 6 inches; light brownish gray (10YR 6/2) fine sandy loam, dark grayish brown (10YR 4/2) moist; weak fine granular structure; soft, very friable; few snail shell fragments; strongly effervescent, moderately alkaline; clear smooth boundary. (4 to 8 inches thick)
A--6 to 14 inches; light brownish gray (10YR 6/2) fine sandy loam, dark grayish brown (10YR 4/2) moist; weak subangular blocky structure; soft, very friable; many fine pores and root channels; few snail shell fragments; strongly effervescent, moderately alkaline; gradual smooth boundary. (6 to 12 inches thick)
Bw--14 to 37 inches; pale brown (10YR 6/3) sandy clay loam, brown (10YR 5/3) moist; weak subangular blocky structure; slightly hard, friable; many fine pores and root channels; few films and threads of calcium carbonate in the upper part, increasing in the lower part; few snail shell fragments; strongly effervescent, moderately alkaline; diffuse smooth boundary. (10 to 30 inches thick)
BCk--37 to 72 inches; very pale brown (10YR 7/3) sandy clay loam, pale brown (10YR 6/3) moist; massive; slightly hard, friable; many fine pores; few snail shell fragments; about 15 percent masses and concretions of calcium carbonate; violently effervescent; moderately alkaline.
TYPE LOCATION: Hidalgo County, Texas; about 3.3 miles south of McCook, Texas; on Farm Road 2058; 100 feet west of road in cultivated field.
RANGE IN CHARACTERISTICS: Solum thickness is 24 to 48 inches. Secondary lime in the form of films and threads occurs at depths of 15 to 25 inches. Electrical conductivity is 1 to 4 dS/m in the 10- to 40-inch control section and increases with depth.
The A horizon has hue of 7.5YR or 10YR, value of 5 to 7, and chroma of 2 or 3. Texture is fine sandy loam or sandy clay loam.
The Bw horizon has hue of 7.5YR or 10YR, value of 5 or 6, and chroma of 2 to 4. Texture is fine sandy loam, sandy clay loam, or clay loam with a clay content of 18 to 31 percent. Amount of visible segregated calcium carbonate ranges from a few films and threads to a few masses in the lower part of the horizon.
The BCk horizon has hue of 7.5YR or 10YR, value of 6 to 8, and chroma of 2 or 3. Texture is sandy clay loam or clay loam. Calcium carbonate equivalent ranges from about 15 to 35 percent and is relatively constant or increases with depth. Visible forms are films and threads, masses, or strongly cemented nodules.
COMPETING SERIES: These include the Aguilares and Moglia series. A similar soil is the Copita series. Aguilares soils have higher amounts of salts in the lower subsoil. Moglia soils have SAR of greater than 15 within 25 inches of the soil surface. In addition, Moglia soils have a lithologic discontinuity. Copita soils have a paralithic contact with sandstone at depths of less than 40 inches, and have active cation exchange activity class.
GEOGRAPHIC SETTING: McAllen soils are on nearly level to gently sloping uplands or old terraces. Slope gradients are less than 5 percent. The soil formed in moderately fine-textured calcareous sediments many feet thick of alluvial or eolian origin. Average annual precipitation ranges from 17 to 24 inches, mean annual temperature is about 74 degrees F., and Thornthwaite annual P-E indices range from 21 to 30.
GEOGRAPHICALLY ASSOCIATED SOILS: These include the competing Copita and Hidalgo series and the Brennan, Delmita, and Pharr series. These soils have Bt horizons and occur on similar surfaces. Pharr soils have mollic epipedons.
DRAINAGE AND PERMEABILITY: Well drained; slow medium runoff; moderate permeability. When irrigated, water may accumulate at depths of 4 to 8 feet below the surface.
USE AND VEGETATION: Use is primarily rangeland although several thousand acres are dry farmed and a few hundred acres are irrigated. The main crops are cotton and grain sorghum on dryland. Irrigated crops are cotton, grain sorghum, and some citrus. Native grasses are two- and four-flower trichloris, Alovegrass tridens, Arizona cottontop, and plains bristlegrass. Woody species include Texas ebony, mesquite, spiny hackberry, lotebush, blackbrush, cenizo, Coyotillo, lime pricklyash, and pricklypear.
DISTRIBUTION AND EXTENT: Southern Rio Grande Plain of Texas, possibly in Mexico. Series is extensive.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Temple, Texas
SERIES ESTABLISHED: Starr County, Texas; 1972.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon: 0 to 14 inches. (A horizons)
Calcic horizon: 37 or 72 inches. (BCk horizon)