LOCATION KNIPPA TXEstablished Series
TAXONOMIC CLASS: Fine, mixed, superactive, thermic Vertic Calciustolls
TYPICAL PEDON: Knippa clay - cropland. (Colors are for dry soil unless otherwise stated.)
Ap--0 to 8 inches; dark grayish brown (10YR 4/2) clay, very dark grayish brown (10YR 3/2) moist; weak fine subangular blocky structure; very hard, firm but crumbly; many fine roots; upper 1 inch is loose flattened granules; few fine strongly cemented calcium carbonate concretions to 1 mm; violently effervescent; moderately alkaline; abrupt smooth boundary. (3 to 10 inches thick)
A--8 to 18 inches; brown (7.5YR 4/2) clay, dark brown (7.5YR 3/2) moist; moderate fine and very fine angular blocky structure; extremely hard, very firm; many fine roots; few fine pores and old root channels; shiny pressure faces on peds; few strongly cemented calcium carbonate concretions to 3 mm; few worm casts; organic staining on few peds; violently effervescent; moderately alkaline; gradual wavy boundary. (6 to 22 inches thick)
Bw--18 to 28 inches; reddish brown (5YR 4/3) clay, dark reddish brown (5YR 3/3) moist; moderate fine and very fine angular blocky structure; extremely hard, very firm; few fine roots and old root channels; few fine pores; few worm casts; shiny pressure faces on peds; few strongly cemented calcium carbonate concretions to 3 mm; organic staining on few peds; violently effervescent; moderately alkaline; gradual wavy boundary. (8 to 28 inches thick)
Bk1--28 to 35 inches; brown (7.5YR 4/4) clay, dark brown (7.5YR 4/4) moist; moderate fine angular blocky structure; extremely hard, very firm; very few roots; few old root channels and fine pores; contains an estimated 5 percent by volume of strongly cemented calcium carbonate concretions; violently effervescent; moderately alkaline; gradual wavy boundary. (0 to 15 inches thick)
Bk2--35 to 48 inches; light brown (7.5YR 6/4) silty clay loam, brown (7.5YR 5/4) moist; weak fine subangular blocky structure; hard, friable; contains an estimated 30 percent by volume of cemented concretions and soft masses of calcium carbonate; violently effervescent; diffuse wavy boundary. (6 to 30 inches thick)
Bk3--48 to 62 inches; pink (7.5YR 7/4) silty clay loam, reddish yellow (7.5YR 6/6) moist; weak fine subangular blocky structure; hard, friable; contains an estimated 20 percent by volume of soft masses and cemented concretions of calcium carbonate; violently effervescent; moderately alkaline.
TYPE LOCATION: Uvalde County, Texas; 3.9 miles east of Knippa, Texas, on U.S. Highway 90, 0.1 mile north across railroad track in cultivated field.
RANGE IN CHARACTERISTICS: Solum thickness is more than 60 inches. Depth to the calcic horizon ranges from 24 to 40 inches. Total clay in the control section ranges from 35 to 55 percent, and carbonate clay ranges from 2 to 15 percent. These soils, when dry, have cracks 1/4 to 1 inch wide that extend from the surface or from the base of the Ap horizon to depths of about 36 inches. Coefficient of linear extensibility values range from 0.09 to 0.12. A few limestone fragments occur in the solum and gravel occurs at depths below 48 inches in some pedons. Reaction is mildly alkaline or moderately alkaline throughout.
The A horizons have hue 10YR to 5YR, with value of 3 to 5, and chroma of 2 to 3. The lower part of the A horizon is usually redder than the upper part. Texture of the A horizon is clay, or silty clay.
The Bw and Bk1 horizons have hue of 10YR to 5YR, with value of 4 or 5, and chroma of 2 or 6. Texture is clay or silty clay. Soft masses of calcium carbonate range from 0 to 10 percent by volume. Structure of the solum below the plow layer ranges from moderate to strong very fine and fine angular blocky.
The Bk2 and Bk3 horizons have hue 10YR to 5YR with value of 6 or 7, and chroma of 4 to 6. The soft masses and weakly to strongly cemented concretions of calcium carbonate range from about 15 to 40 percent by volume.
COMPETING SERIES: These include the Chatt and Rowena series and the similar Dant and Uvalde series. Chatt soils occur in areas of higher rainfall and are moist in the moisture control section for longer periods. Rowena soils occur in areas where the mean air temperature is less than 68 degrees F. Dant soils have loamy control sections and lack calcic horizons. Uvalde soils have fine-silty control sections.
GEOGRAPHIC SETTING: These soils occur on nearly level to gently sloping stream terraces of alluvial plains below limestone hills. The soil formed in calcareous alluvium. Slopes are mainly less than 1 percent by range up to about 3 percent. Mean annual precipitation ranges from 18 to 26 inches and mean annual air temperature ranges from 68 to 70 degrees F. Thornthwaite P-E indices ranges from 28 to 40. Frost free days range from 230 to 250 days and elevation ranges form 800 to 2,200 feet.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Castroville, Montell and the similar Uvalde soils. These soils occur on similar surfaces. Castroville soils have fine-silty control sections and carbonatic mineralogy. Montell soils are clayey throughout and have intersecting slickensides at depths of less than 40 inches.
DRAINAGE AND PERMEABILITY: Well drained and moderately slow permeability. The runoff is negligible on slopes of 0 to 1 percent and very low on slopes of 1 to 3 percent.
USE AND VEGETATION: The soil is used for rangeland and cropland, both dryland and irrigated. Under dryland operations, grain sorghums, small grains and introduced grasses are the principal crops. Under irrigation, grain sorghums, small grain and a variety of winter truck crops are grown. The present native grasses are red grama, threeawn, curlymesquite, bristlegrass, Hall's panicum, fall witchgrass and sideoats grama. Woody vegetation includes mesquite, whitebrush, Texas persimmon, twisted acacia, catclaw acacia, Texas colubrina, lotebush and bluewood condalia.
DISTRIBUTION AND EXTENT: Northern and Western Rio Grande Plain mlra's (83A and 83B) and Eastern Edwards Plateau mlra (81C) of Texas. The series is of moderate extent.
MLRA OFFICE RESPONSIBLE: Temple, Texas
SERIES ESTABLISHED: Uvalde County, Texas; 1966.
REMARKS:
Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon - 0 to 28 inches.
Calcic horizon - 28 to 62 inches.
SOIL INTERPRETATION RECORD: TX0435