LOCATION NEPESTA CO

Established Series
Rev. AJC/LAN
01/2014

NEPESTA SERIES

The Nepesta series consists of very deep, well drained soils that formed in alluvium derived from mixed sedimentary materials. Nepesta soils are on paleoterraces and interfluves. The surface horizons formed in clayey alluvium from sediment-rich irrigation water and the subsoil and substratum formed in eolian deposits and silty alluvium derived from mixed sedimentary sources. Slopes range from 0 to 5 percent. The mean annual temperature is about 11 degrees C (52 degrees F.) and the mean annual precipitation is about 305 millimeters (12 inches).

TAXONOMIC CLASS: Fine-silty, mixed, superactive, mesic Calcidic Argiustolls

TYPICAL PEDON: Nepesta clay loam, on a southeast facing, linear, 0.5 percent slope in a cultivated field at an elevation of 1,271 meters (4,168 feet). (Colors are for dry soil unless otherwise noted.)

Ap--0 to 38 centimeters (0 to 15 inches); brown (10YR 4/3) clay loam, dark brown (10YR 3/3) moist; moderate fine granular structure; moderately hard, friable, slightly sticky and moderately plastic; many very fine and fine roots throughout; slightly effervescent, 2 percent calcium carbonate equivalent; slightly alkaline (pH 7.6); clear smooth boundary. (25 to 49 centimeters thick)

Bt--38 to 66 centimeters (15 to 26 inches); yellowish brown (10YR 5/4) silty clay loam, dark yellowish brown (10YR 4/4) moist; moderate fine subangular blocky structure; moderately hard, friable, slightly sticky and moderately plastic; 5 percent faint clay films on ped faces; slightly effervescent, 3 percent calcium carbonate equivalent; slightly alkaline (pH 7.4); gradual wavy boundary. (13 to 38 centimeters thick)

Btk--66 to 91 centimeters (26 to 36 inches); pale brown (10YR 6/3) silt loam, yellowish brown (10YR 5/4) moist; moderate fine prismatic structure; moderately hard, friable, slightly sticky and moderately plastic; 5 percent faint clay films on faces of peds; 10 percent medium distinct irregular carbonate masses in matrix; violently effervescent, 19 percent calcium carbonate equivalent; moderately alkaline (pH 8.0); gradual wavy boundary. (18 to 38 centimeters thick)

Bk--91 to 200 centimeters (36 to 79 inches); light yellowish brown (10YR 6/4) silt loam, yellowish brown (10YR 5/4) moist; weak medium subangular blocky structure; moderately hard, friable, slightly sticky and moderately plastic; 3 percent fine faint irregular carbonate masses in matrix; violently effervescent, 7 percent calcium carbonate equivalent; moderately alkaline (pH 8.0).

TYPE LOCATION: Otero County, Colorado; approximately 2.4 kilometers (1.5 miles) northwest of Cheraw, Colorado; about 350 meters (1,150 feet) east and 366 meters (1,200 feet) north of the southwest corner Sec. 24, T. 22 S., R. 55 W.; Cheraw, Colorado USGS topographic quadrangle; UTM zone 13 629432 E, 4219916 N; latitude 38 degrees, 7 minutes, 4.1 seconds N. and longitude 103 degrees, 31 minutes, 24.5 seconds W., NAD 83.

RANGE IN CHARACTERISTICS:
Soil moisture: moist in some part March through May and intermittently moist June through October. It is driest December through February.
Moisture regime: aridic bordering on ustic
Mean annual soil temperature: 9 to 12 degrees C. (49 to 54 degrees F.)
Depth to secondary calcium carbonate: 38 to 76 centimeters (15 to 30 inches)
Depth to the base of the argillic horizon: 56 to 102 centimeters (22 to 40 inches)
Depth to calcic horizon: 38 to 89 centimeters (15 to 35 inches)

Ap horizons have increases of clay and organic matter content due to prolonged irrigation, cultivation, and fertilization. Phosphorous content is not high enough for an anthropic epipedon. The alluvium from irrigation enriched sediments results in a truncated horizon with the original argillic horizons below often having lower clay content than the surface horizon.

Particle size control section:
Clay content: 18 to 35 percent
Silt content: 50 to 65 percent
Sand content: 5 to 25 percent, with less than 15 percent fine and coarser sand

Ap horizon:
Hue: 10YR
Value: 4 or 5 dry, 2 or 3 moist
Chroma: 1 to 3
Texture: clay loam, silty clay loam
Clay content: 27 to 35 percent
Calcium carbonate equivalent: 1 to 5 percent
Reaction: slightly alkaline or moderately alkaline

Bt horizon:
Hue: 7.5YR or 10YR
Value: 5 or 6 dry, 4 or 5 moist
Chroma: 2 to 6
Texture: clay loam, silty clay loam
Clay content: 27 to 35 percent
Sand content: 5 to 25 percent, with less than 15 percent fine or coarser sand
Calcium carbonate equivalent: 1 to 5 percent
Reaction: slightly alkaline or moderately alkaline.

Btk horizon:
Hue: 7.5YR or 10YR
Value: 5 to 8 dry, 4 to 6 moist
Chroma: 3 to 6
Texture: clay loam, silty clay loam, silt loam
Clay content: 20 to 35 percent
Sand content: 5 to 25 percent, with less than 15 percent fine or coarser sand
Rock fragment content: 0 to 5 percent Calcium carbonate equivalent: 15 to 25 percent
Electrical conductivity: 0 to 2 dS/m
Reaction: moderately alkaline or strongly alkaline

Bk horizon:
Hue: 7.5YR or 10YR
Value: 5 to 8 dry, 4 to 6 moist
Chroma: 3 to 6
Texture: silt loam, loam
Clay content: 18 to 27 percent
Rock fragment content: 0 to 5 percent
Calcium carbonate equivalent: 5 to 30 percent
Electrical conductivity: 0 to 4 dS/m
Reaction: moderately alkaline or strongly alkaline

COMPETING SERIES: This is the Oslo series.
Oslo soils: have argillic horizons that extend to depths of 100 centimeters (40 inches) or more.

GEOGRAPHIC SETTING:
Parent material: clayey alluvium derived from sediment-rich irrigation water over eolian deposits and silty alluvium derived from mixed sedimentary sources
Landform: paleoterraces and interfluves
Slopes: 0 to 5 percent or more

Elevation: 1,158 to 1,585 meters (3,800 to 5,000 feet)
Average annual temperature is 10 to 12 degrees C. (50 to 54 degrees F.)
Average annual precipitation: 254 to 356 millimeters (10 to 14 inches)
Precipitation pattern:
Peak period: May through August
Driest period: December through February
Frost free period: 130 to 170 days

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Numa, Rocky Ford, and Wapiti soils. Numa soils average more than 25 percent sand in the particle size control section and occur on stream terraces. Rocky Ford soils lack an argillic horizon and occur on paleoterraces. Wapiti soils have a fine-silty particle size control section and are on interfluves.

DRAINAGE AND SATURATED HYDRAULIC CONDUCTIVITY:
Drainage: well drained
Saturated hydraulic conductivity: moderately high or high

USE AND VEGETATION: Used primarily as irrigated cropland.
Principal irrigated crops are alfalfa, small grains, corn, sorghum, truck crops, and melons. Native vegetation is mainly blue grama, galleta, and western wheatgrass. ESD R069XY006CO: Loamy Plains.

DISTRIBUTION AND EXTENT: Arkansas River Valley, Colorado, LRR G, MLRA 69 and 67B. The series is of moderate extent.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Denver, Colorado

SERIES ESTABLISHED: Prowers County, Colorado, 1963. Name is coined from a town site in the area.

REMARKS:
Diagnostic horizons and features in this pedon are:
Series control section: The zone from 0 to 150 centimeters (0 to 59 inches)
Particle size control section: The zone from 38 to 89 centimeters (15 to 35 inches)
Mollic epipedon: 0 to 38 centimeters (0 to 15 inches). (Ap horizon)
Argillic horizon: 38 to 91 centimeters (15 to 35 inches). (Bt and Btk horizons)
Calcic horizon: 66 to 91 centimeters (26 to 35 inches). (Btk horizon)

The assignment of the cation-exchange activity class is inferred from lab data from similar soils in the surrounding area.

5/2013 The previous classification of Ustic Haplargids is changed to the taxonomic class, fine-silty, mixed, superactive, mesic Calcidic Argiustolls based on an update field project in the upper Arkansas River Valley. This also moves the type location from Prowers County to Otero County, Colorado.

Modified format by LRM and JCR in 10/2005 to include metric conversion and change permeability to saturated hydraulic conductivity.

Taxonomic Version: Eleventh Edition, 2010

National Cooperative Soil Survey
U.S.A.