LOCATION OVAN TXEstablished Series
TAXONOMIC CLASS: Fine, smectitic, thermic Udic Haplusterts
TYPICAL PEDON: Ovan clay--cultivated. (Colors are for dry soil unless otherwise stated.)
Ap--0 to 6 inches; grayish brown (2.5Y 5/2) clay, very dark grayish brown (2.5Y 3/2) moist; moderate medium granular and moderate fine angular blocky structure; very hard, very firm, very sticky and plastic; common fine roots; few fine concretions of calcium carbonate; strongly effervescent; moderately alkaline; abrupt smooth boundary. (4 to 7 inches thick)
A--6 to 25 inches; grayish brown (2.5Y 5/2) clay, very dark grayish brown (2.5Y 3/2) moist; weak coarse angular blocky structure parting to medium blocky and subangular blocky; very hard, very firm, very sticky and plastic; common fine roots; few very fine pores; many shiny pressure faces; vertical cracks 1/2 inch wide extend through this horizon; strongly effervescent; moderately alkaline; clear wavy boundary. (6 to 32 inches thick)
Bss--25 to 66 inches; grayish brown (10YR 5/2) clay, very dark grayish brown (10YR 3/2) moist; few fine distinct dark reddish brown mottles; moderate medium and coarse angular blocky structure; very hard, very firm, very sticky and plastic; few fine roots; few very fine pores; few fine concretions of calcium carbonate; common grooved slickensides; strongly effervescent; moderately alkaline; diffuse wavy boundary. (7 to 40 inches thick)
Bkss--66 to 90 inches; grayish brown (2.5Y 5/2) clay, dark grayish brown (2.5Y 4/2) moist; few medium faint brown (10YR 4/3) mottles; moderate medium blocky structure; very hard, very firm, very sticky and plastic; few fine roots; few very fine pores; common grooved slickensides; few films, threads and fine concretions of calcium carbonate; few coarse slickensides; violently effervescent; moderately alkaline.
TYPE LOCATION: Denton County, Texas; from the intersection of Loop 288 and U.S. Highway 380 in Denton, about 16 miles east on U.S. Highway 380 to Navo, 0.8 mile south and 0.1 mile east on county road, 0.8 mile south on private road, and 300 feet southwest in rangeland. Site is 300 feet north of Doe Creek.
RANGE IN CHARACTERISTICS: The solum is more than 80 inches thick. In undisturbed areas there is gilgai microrelief with microknolls 4 to 8 inches above microdepressions. Cycles of knolls and depressions are repeated each 8 to 23 feet. Cracks 0.5 to 1 inch wide extend to a depth of more than 20 inches when the soil is dry. Intersecting slickensides begin at depths of 18 to 25 inches. The soil is moderately alkaline and calcareous clay or silty clay with 40 to 55 percent clay. Some pedons have thin grayish or brownish discontinuous clay or clay loam strata in the 10 to 40 inch control section.
The A horizon has colors in shades of brown hue of 10YR to 5Y, value of 3 to 5, and chroma of 2 or 3. Masses in shades of brown or olive range from none to common in the control section.
Colors of the B horizons are in hue of 10YR or 2.5Y, value of 3 to 6, and chroma of 2 to 4. Brownish masses range from few to common in most pedons.
The C horizon, when present, is clayey with or without loamy strata. It has gray, brown or olive colors.
COMPETING SERIES: These include Bleiblerville, Branyon, Burleson, Clarita, Dimebox, Fairlie, Heiden, Houston Black, Leson, Luling , Sanger, Slidell, Tamford and Watonga in the same family and the similar Kaufman, Tinn and Trinity series. Bleiblerville, Branyon, Burleson, Dimebox, Fairlie, Houston Black, Leson and Slidell soils have chroma of 1 throughout the upper 12 inches and are on uplands or terraces. Clarita and Tamford soils have hue 7.5YR or redder in the subsoil. Heiden, Luling and Sanger soils have a solum less than 80 inches thick. Watonga soils have a solum less than 60 inches thick. Kaufman and Tinn and Trinity soils have chroma of 1 in the upper 12 inches also Kaufman soils are noncalcareous.
GEOGRAPHIC SETTING: Ovan soils are on nearly level to gently sloping flood plains. Slopes are mainly less than 1 percent but some are as much as 2 percent. The soil formed in calcareous clayey alluvium. The climate is warm and subhumid. The annual precipitation ranges from 30 to 38 inches and the annual temperature ranges from 64 to 67 degrees F. Frost free days range from 220 to 255. The elevation ranges from 350 to 600 feet above sea level. The Thornthwaite P-E index ranges from 52 to 60.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Heiden, Houston Black, and the Ferris, Frio, Gowen, kaufman, Trinity and Whitesboro series. Ferris soils have color values of 3 or more within 10 inches of the soil surface. Frio soils do not have slickensides. Gowen and Whitesboro soils have fine loamy control sections. Kaufman and Trinity soils contain over 60 percent clay in the control section. Heiden, Houston Black, and Ferris soils are on uplands. Frio, Gowen, kaufman, Trinity, and Whitesboro soils are on similar flood plains positions.
DRAINAGE AND PERMEABILITY: Moderately well drained; slow runoff; very slow permeability. Flooding occurs one or more times each year for 2 to 7 days duration unless protected.
USE AND VEGETATION: Cleared areas are in pasture or planted to crops of cotton, corn, oats, or grain sorghum. Native vegetation is hardwood forests of elm, hackberry, pecan, oak, and ash.
DISTRIBUTION AND EXTENT: Mainly in Texas along tributaries draining Blackland Prairie soils. Moderately extensive with a total of about 30,000 acres.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Temple, Texas
SERIES ESTABLISHED: Denton County, Texas; 1975.
REMARKS: These soils were formerly included in the Trinity and Frio series.
Diagnostic horizons and features recognized in this pedon are:
Mollic- epipedon 0 to 66 inches in the A and Bss horizons
Cambic horizon - 66 to 90 inches in the Bkss horizon
Vertisol feature - Slickensides from 25 to 90 inches. High Shrink-swell properties and cracks that are 0.5 to 1 inch or more wide at a depth of 12 inches or more during dry periods.
SIR Number. TX0187