LOCATION RIO GRANDE TXEstablished Series
TAXONOMIC CLASS: Coarse-silty, mixed, superactive, calcareous, hyperthermic Aridic Ustifluvents
TYPICAL PEDON: Rio Grande silt loam, on nearly level less than 1 percent slope in cropland; elevation is 49 m (160 ft). (Colors are for dry soil unless otherwise stated.)
Ap--0 to 18 cm (0 to 7 in); light brownish gray (10YR 6/2) silt loam, dark grayish brown (10YR 4/2) moist; weak fine subangular blocky; slightly hard, friable, slightly sticky and slightly plastic; few roots; few flakes of mica; strongly effervescent; moderately alkaline; abrupt smooth boundary. (13 to 25 cm [5 to 10 in] thick)
C1--18 to 41 cm (7 to 16 in); light brownish gray (10YR 6/2) silt loam, with few strata less than 12 mm (1/2 in)thick of silty clay loam, dark grayish brown (10YR 4/2) moist; massive; bedding planes are evident; slightly hard, friable, slightly sticky and slightly plastic; few flakes of mica; few fragments of snail shell; few dark yellowish brown and strong brown organic stains along bedding planes; few roots, few fine pores and wormcasts; violently effervescent; moderately alkaline; clear smooth boundary. (20 to 31 cm [8 to 12 in] thick)
C2--41 to 203 cm (16 to 63 in); pale brown (10YR 6/3) silt loam, brown (10YR 4/3) moist, with thin strata and lenses of very fine sandy loam and silty clay loam; massive; has many bedding planes; slightly hard, very friable, slightly sticky and slightly plastic; few flakes of mica; few roots; few root channels, and bedding planes have brownish organic stains; violently effervescent; moderately alkaline.
TYPE LOCATION: Starr County, Texas; from the intersection of U.S. Highway 83 and Farm Road 2360 in La Grulla, Texas; 1.1 miles south on Farm Road 2360 to Main Street; 0.75 mile west on Main Street to El Salado Road; 0.80 mile south on El Salado Road, 400 feet in cropland. La Grulla, Texas USGS topographic quadrangle. Latitude: 26 degrees, 15 minutes, 24.196 seconds, W; Longitude: 98 degrees, 38 minutes, 28.915 seconds, N; NAD 83.
RANGE IN CHARACTERISTICS:
Soil Moisture: An ustic soil moisture regime bordering on aridic. The soil moisture control section remains moist in some or all parts for less than 90 consecutive days in normal years. The soil is driest during the months of June through August and December through February. These soils are intermittently moist in September through November and March through May.
Mean annual soil temperature: 22 to 24 degrees C (72 to 76 degrees F).
Particle-size control section (weighted average)
Clay content: 4 to 20 percent
Coarse Fragments: 0 to 2 percent
CEC/clay ratio: 0.40 to 0.60
A horizon
Hue: 10YR
Value: 5 to 7
Chroma: 2 or 3
Texture: very fine sandy loam, silt loam, loam, or loamy very fine sand
Clay content: 4 to 18 percent
Coarse fragments: 0 to 2 percent
Base saturation: 85 to 100 percent
Calcium carbonate equivalent: 1 to 20 percent
EC (dS/m): 0 to 4
SAR: 0 to 1
Effervescence: very slightly to strongly
Reaction: moderately alkaline
C horizon
Hue: 10YR
Value: 4 to 7
Chroma: 2 to 4
Texture: loamy fine sand to silty clay loam. Few to common strata is evident in the majority of pedons. These strata are 2.5 to 7.6 cm (1 to 3 in) thick.
Clay content: 4 to 20 percent. Individual strata may contain clay content as high as 35 percent but the average of the particle control section is less than 18 percent.
Coarse fragments: 0 to 2 percent
Base saturation: 100 percent
Calcium carbonate equivalent: 1 to 20 percent
Identifiable secondary carbonate: 0 to 2 percent fine threads and films
EC (dS/m): 0.5 to 4
SAR: 0 to 2
Effervescence: strong or violent
Reaction: moderately alkaline
COMPETING SERIES: There are no competing series in the same family. Similar soils are the
Camargo (TX),
Craft (NE),
Lagloria (TX),
Sparham (NM), and
Zalla (TX) series.
Camargo soils: are in the fine-silty family
Craft soils: are in a mesic soil temperature regime
Lagloria soils: do not have evidence of stratification
Sparham soils: are in a fine family and have a mesic soil temperature regime
Zalla soils: are in the sandy family
GEOGRAPHIC SETTING:
Parent material: calcareous silty alluvium
Landform: flood plain steps
Slope: 0 to 3 percent
Mean annual air temperature: 21 to 23 degrees C (70 to 74 degrees F).
Mean annual precipitation: 432 to 686 mm (17 to 27 in)
Precipitation pattern: moist spring and fall months and dry summer and winter months
Frost-free period: 280 to 360 days
Elevation: 15 to 427 m (50 to 1,400 ft)
Thornthwaite annual P-E indices: 24 to 35
GEOGRAPHICALLY ASSOCIATED SOILS: These are the
Camargo,
Grulla,
Matamoros, and
Zalla series.
Camargo soils: are in a fine-silty family and are on similar positions.
Matamoros soils: are in a fine family, have vertic properties, and are on similar positions
Grulla soils: are in a fine family, have vertic properties, and redox features due to wetness. In addition, Grulla soils are in abandoned riverbeds (Resecas) separated from present streams by terrace sediments.
Zalla soils: are in a sandy family and are in lower positions
DRAINAGE AND PERMEABILITY: Well drained. Permeability is moderately rapid. Runoff is negligible on slopes less than 1 percent and very low on 1 to 3 percent slopes.
USE AND VEGETATION: Mostly irrigated cropland of cotton, grain sorghum, and a wide variety of cool season vegetables. Native vegetation consists of four-flower trichloris, saccaton, cottontop, and plains bristlegrass. Woody plants consist of hackberry, Rio Grande ash, and mesquite trees. In the low parts of the flood plain the soils produce high yields of giant reedgrass. The ecological site is Loamy Bottomland, 20-35 PZ (R083DY505TX).
DISTRIBUTION AND EXTENT: Lower Rio Grande Plain, Texas; LRR I; MLRA 83D; the series is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Temple, Texas
SERIES ESTABLISHED: Starr County, Texas, 1966.
REMARKS: Classification change from Typic Ustifluvents to Aridic Ustifluvents based on geographic distribution of the series, rainfall patterns, and vegetative production and composition. The soil has an ustic soil moisture regime that borders an aridic moisture regime.
Diagnostic horizons and features recognized in this pedon are:
Particle size control section: 25 to 102 cm (10 to 40 in) (parts of the C1 and C2 horizons)
Ochric epipedon: 0 to 18 cm (0 to 7 in) (A horizon)
ADDITIONAL DATA: NSSL data number 84TX061001 from Cameron County, Texas. The assignment of the cation-exchange activity class is inferred from lab data from surrounding surveys.
TAXONOMIC VERSION: Keys to Soil Taxonomy, Tenth Edition, 2006