LOCATION ZACK               TX
Established Series


The Zack series consists of soils that are moderately deep to thinly bedded loamy and clayey geologic materials. They are moderately well drained, very slowly permeable soils on dissected uplands. Slopes are dominantly 1 to 5 percent, but range from 1 to 25 percent.

TAXONOMIC CLASS: Fine, smectitic, thermic Udertic Paleustalfs

TYPICAL PEDON: Zack very fine sandy loam--pasture. (Colors are for dry soil unless otherwise stated.)

Ap--0 to 7 inches; dark brown (10YR 4/3) very fine sandy loam, dark brown (10YR 3/3) moist; weak medium subangular blocky structure; hard, very friable; common fine roots; few fine siliceous pebbles; strongly acid; abrupt smooth boundary. (4 to 10 inches thick)

Bt1--7 to 18 inches; mixed dark grayish brown (10YR 4/2) dark reddish brown (5YR 3/3) and dark red (2.5YR 3/6) clay; moderate medium angular blocky structure; very hard, very firm; common fine roots; few cracks 1/2 inch wide;few pressure faces;continuous clay films on surface of peds; few fine siliceous pebbles; slightly acid; clear wavy boundary.

Bt2--18 to 24 inches; dark brown (7.5YR 4/4) clay, dark brown (7.5YR 3/4) moist; moderate coarse angular blocky structure; very hard, very firm; common fine roots; few cracks 1/2 inch wide; few wedge-shaped peds; continuous clay films on surfaces of peds; few fine siliceous pebbles; neutral; clear smooth boundary. (combined Bt subhorizons are 12 to 24 inches thick)

2BCk--24 to 36 inches; mixed light yellowish brown (10YR 6/4) and very dark grayish brown (10YR 3/2) sandy clay loam; weak medium subangular blocky structure; slightly hard, firm; few fine roots; common concretions of calcium carbonate; moderately alkaline; abrupt irregular boundary. (0 to 20 inches thick)

2Ck--36 to 60 inches; thinly bedded light brownish gray (10YR 6/2), dark reddish brown (5YR 3/3), and light red (2.5YR 6/8) loam; massive; extremely hard, extremely firm; common calcium carbonate concretions; moderately alkaline.

TYPE LOCATION: Brazos County, Texas; from Texas Highway 6 bypass, 1.1 miles southeast on Farm Road 158 to Farm Road 1179, continue 2.0 miles southeast on Farm Road 158; 1.0 mile northeast on Copperfield Drive and Canturburg Drive; 2,000 feet south under post oak tree.

RANGE IN CHARACTERISTICS: Solum thickness ranges from 25 to 40 inches which is the depth to stratified loamy and/or clayey deltaic sediments. The boundary between the A and Bt horizons is abrupt, with some waviness evident. The COLE is greater than 0.09 in the argillic horizon and the soil has a potential linear extensibility of 6 cm or more in the upper meter. The soil cracks when dry and the cracks are 1/2 inch to 1-1/2 inches wide and extend to 20 inches or more. Colors with chroma of 2 or less are inherited from the parent material or they are relict redox features.

The A horizon has hue of 7.5YR or 10YR, value of 4 or 5, and chroma of 2 to 4. Redox concentrations in shades of brown range from none to few. Texture is fine sandy loam, very fine sandy loam, or their gravelly counterparts. It is hard or very hard and massive when dry. Siliceous pebbles make up 0 to 35 percent by volume. Reaction ranges from strongly acid to slightly acid.

The Bt or Btss horizon has matrix colors in shades of brown and red in hue of 2.5YR to 10YR, value of 4 or 5, and chroma of 3 to 6. Redox features in shades of brown, red, yellow, or gray range from few to many. Some pedons have a subhorizon with mixed colors or a matrix color with chroma of 2 in the lower part. The texture is mainly clay. Some pedons have clay loam texture in the lower part. Pressure faces and/or small slickensides range from few to common in some pedons. Siliceous pebbles range from few to common in most pedons. Calcium carbonate concretions range from none to few. Reaction ranges from moderately acid to neutral in the upper part and from neutral to moderately alkaline in the lower part.

The 2BC horizon has colors in shades of brown and gray with mottles in shades of brown, gray, or yellow. Texture is silty clay loam, clay loam, or sandy clay loam. Calcium carbonate concretions range from none to common. Threads and masses of salts range from none to few. Reaction ranges from neutral to moderately alkaline.

The 2Ck or 2C horizon has colors in shades mainly of gray or brown. The materials are weakly consolidated mudstones with texture of loam, clay loam or silty clay loam. It is stratified or thinly platy with rock like structure. Reaction ranges from neutral to moderately alkaline. The soil matrix ranges from noneffervescent to slightly effervescent. Exchangeable sodium ranges from 6 to 15 percent and electrical conductivity ranges from 1 to 5 mmhos/cm.

COMPETING SERIES: These are Axtell, Bremond, Crockett, Crosstell, Kurten, Tabor and Zulch in the same family. Silimar soils are Edge, Gredge, Payne and Singleton. Axtell, Bremond, Crockett, Crosstell, Gredge, Kurten, and Payne soils have sola greater than 60 inches thick. Edge soils have a solum 40 to 60 inches thick and do not classify in udertic subgroup. Crockett and Tabor soils do not significantly decrease in clay content within 40 inches of the surface. Singleton soils are moderately deep over a para-lithic contact of tuffaceous sandstone and do not exhibit udertic properties. Zulch soils have argillic horizons with chroma of 2 or less.

GEOGRAPHIC SETTING: Zack soils are on gently sloping to steep erosional uplands. Slopes are mainly 1 to 5 percent but range from 1 to 25 percent. The soil formed in dense alkaline clayey and loamy deltaic sediments of the Eocene Age mainly of the Yegua Formation. This formation is commonly covered with a thin layer of late Pliocene sediments. The mean annual temperature ranges from 66 to 69 degrees F. and mean annual precipitation ranges from 36 to 42 inches. Frost free days range from 260 to 290 days and elevation ranges from 250 to 550 feet. The Thornthwaite P-E indices range from 52 to 62.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the competing Gredge soils as well as the Axtell, Boonville, Kurten, Lufkin, and Zulch soils. The Axtell soils have sola more than 60 inches thick and are on nearby slightly lower terrace surfaces. Boonville and Zulch soils have argillic horizons with chroma of 2 or less and are on concave to plane slopes below the Zack soils. Gredge soils are on similar positions or slightly lower positions. Kurten soils classify in a vertic subgroup and and are on similar positions. Lufkin soils are on slightly lower positions and have grayish colors throughout.

DRAINAGE AND PERMEABILITY: Moderately well drained. Permeability is very slow. Runoff is medium on 1 to 3 percent slopes, high on 3 to 5 percent slopes, and very high on 5 to 25 percent slopes.

USE AND VEGETATION: Many areas have been cultivated in the past. Presently used mainly for range or pasture. Native vegetation is a prairie of mid and tall grasses with scattered post oak with some encroachment of mesquite and yaupon. Pastures of improved and common bermudagrass produce moderate yields.

DISTRIBUTION AND EXTENT: Mainly in east-central Texas. The series is of moderate extent.


SERIES ESTABLISHED: Grimes County, Texas, 1988. Series was proposed in adjoining Brazos County.

REMARKS: Classification change from Aquic Paleustalfs (2/91) is due to observations that the soil is not wet enough to meet requirements of the aquic subgroup. Low chroma colors, where present, are due primarily to weathering of gray colored parent materials or they are relict. The soils were formerly included in the Lufkin, Edge or Crockett series (Brazos County, 1958).

Diagnostic horizons and features recognized in this pedon are:

Ochric epipedon - 0 to 7 inches. (Ap horizon)

Argillic horizon - 7 to 24 inches. (Bt1 and Bt2 horizons)

Abrupt texture change - at 7 inches.

Udertic properties - cracks and high shrink-swell in 7- to 24-inch layers

C horizons of thinly bedded, weakly consolidated geologic materials.

ADDITIONAL DATA: TAMU Data from type location (S84TX-041-2).


National Cooperative Soil Survey