LOCATION OLMITO TXEstablished Series
TAXONOMIC CLASS: Fine, smectitic, hyperthermic Vertic Calciustolls
TYPICAL PEDON: Olmito silty clay--cultivated. (Colors are for dry soil unless otherwise stated.)
Ap--0 to 7 inches; dark gray (10YR 4/1) silty clay, very dark gray (10YR 3/1) moist; moderate medium granular structure; hard, friable; many roots and wormcasts; calcareous; moderately alkaline; abrupt smooth boundary. (5 to 9 inches thick)
A--7 to 16 inches; dark gray (10YR 4/1) silty clay, very dark gray (10YR 3/1) moist; moderate very fine subangular blocky structure; very hard, firm but crumbly; few fine pores; few snail shell fragments; common wormcasts; calcareous; moderately alkaline; clear smooth boundary. (6 to 11 inches thick)
Ak--16 to 23 inches; grayish brown (10YR 5/2) silty clay, very dark grayish brown (10YR 3/2) moist; moderate fine and medium subangular blocky structure; very hard, firm but crumbly; few fine pores; shiny pressure faces; few fine weakly cemented calcium carbonate concretions; calcareous; moderately alkaline; diffuse wavy boundary. (5 to 11 inches thick)
Bk--23 to 34 inches; dark brown (10YR 4/3) silty clay, dark brown (10YR 3/3) moist; moderate fine and medium subangular blocky structure; moderate fine angular blocky structure in lower 3 or 4 inches; very hard, firm but crumbly; few fine pores; shiny pressure faces; few fine weakly cemented calcium carbonate concretions; calcareous; moderately alkaline; gradual smooth boundary. (5 to 19 inches thick)
Ck1--34 to 48 inches; very pale brown (10YR 7/3) silty clay, brown (10YR 5/3) moist with common fine distinct brownish yellow mottles; massive; very hard, firm; common fine pores; contains 8 percent by volume of hard concretions and soft masses of calcium carbonate; calcareous; moderately alkaline; diffuse smooth boundary. (4 to 12 inches thick)
Ck2--48 to 63 inches; very pale brown (10YR 7/3) silty clay, brown (10YR 5/3) moist with few fine distinct brownish yellow mottles; massive; hard, firm; few thin strata of silt loam; few Fe-Mn concretions; few soft masses of calcium carbonate; calcareous; moderately alkaline.
TYPE LOCATION: Cameron County, Texas; 0.5 mile west of the intersection of Farm Road 2893 and Farm Road 1575 in Laureles; 1,200 feet north and 200 feet west into cultivated field.
RANGE IN CHARACTERISTICS: Solum thickness ranges from 30 to 50 inches. Depth to contrasting strata of silt loam or very fine sandy loam ranges from 40 to 80 inches. These soils, when dry, have cracks from 0.4 to 1.0 inch wide and 12 inches or more long that extend to depths of 24 to 40 inches. COLE ranges from 0.07 to 0.15 throughout the solum. The mollic epipedon ranges from 20 to 32 inches in thickness. The 10- to 40-inch control section is silty clay or silty clay loam with a clay content of 35 to 55 percent and a sand content of 2 to 12 percent. Soil salinity increases with depth and ranges from 1 to 4 mmhos/cm in the upper 1 foot, 1 to 6 mmhos/cm between 1 and 3 feet and 3 to 10 mmhos/cm below.
The A horizon is dark gray (10YR 4/1), dark grayish brown (10YR 4/2), grayish brown (10YR 5/2), or dark brown (7.5YR 4/2; 10YR 4/3).
The B horizon is dark brown (10YR 4/3; 7.5YR 4/2), brown (10YR 5/3; 7.5YR 5/2), gray (10YR 5/1), or grayish brown (10YR 5/2). The B horizon is silty clay or silty clay loam. It has weak to moderate subangular blocky and angular blocky structure.
The C horizon is pale brown (10YR 6/3), very pale brown (10YR 7/3), light brown (7.5YR 6/4), or light brownish gray (10YR 6/2). It is a silty clay or silty clay loam. Visible secondary calcium carbonate in the C horizons is 5 to 20 percent in the form of soft masses and concretions. Depth to a calcic horizon is 24 to 40 inches.
COMPETING SERIES: There are no series in the same family. Similar soils include Cameron, Dant, Harlingen, Knippa, Krum, Laredo, and Raymondville series. Cameron soils have contrasting clayey over loamy 10- to 40-inch control sections. Dant soils have mollic epipedons less than 20 inches thick. Harlingen soils contain intersecting slickensides within 40 inches and have moist values of more than 3.5. Knippa and Krum soils have mean annual soil temperatures less than 72 degrees F. Laredo soils have less than 35 percent clay in the 10- to 40-inch control section. Raymondville soils have mollic epipedons that average less than 20 inches in thickness and they contain more than 12 percent sand in the 10- to 40-inch control section.
GEOGRAPHIC SETTING: Olmito soils are on low river terraces above overflow. Surfaces are plane to weakly concave with gradients mainly less than 1 percent. The soil formed in stratified calcareous loamy and clayey sediments many feet thick. The climate is dry subhumid to semiarid. The mean annual precipitation ranges from 25 to 30 inches, and the mean annual temperature ranges from 74 to 76 degrees F. Thornthwaite P-E indices range from 22 to about 34.
GEOGRAPHICALLY ASSOCIATED SOILS: These include the similar Cameron, Harlingen, and Laredo series. These soils occur on similar surfaces.
DRAINAGE AND PERMEABILITY: Moderately well drained; slow runoff; slow permeability.
USE AND VEGETATION: Mostly cultivated and irrigated. Crops grown are cotton, grain sorghum, sugarcane, and a wide variety of cool season vegetables. Native vegetation is midgrasses with thorny shrubs.
DISTRIBUTION AND EXTENT: Principally on old flood plains and deltas in the lower reaches of the Rio Grande and its major tributaries in southern Texas and probably in Mexico. The soil is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Temple, Texas
SERIES ESTABLISHED: Cameron County, Texas; 1970.
REMARKS: Characterization data by ARS-SCS available.