LOCATION RILLA LA+AREstablished Series
The Rilla series consists of very deep, well drained, moderately permeable soils that formed in reddish silty and loamy alluvium. These soils are on nearly level to gently sloping natural levees along the Red River and the present and abandoned channels of the Arkansas River. Slopes range from 0 to 5 percent.
TAXONOMIC CLASS: Fine-silty, mixed, active, thermic Typic Hapludalfs
TYPICAL PEDON: Rilla silt loam - cultivated field. (Colors are for moist soil unless otherwise stated.)
Ap--0 to 5 inches; brown (10YR 4/3), pale brown (10YR 6/3) dry, silt loam; massive; slightly hard, friable; slightly acid; abrupt smooth boundary. (4 to 6 inches thick)
E--5 to 8 inches; brown (10YR 5/3), very pale brown (10YR 7/3) dry, silt loam; many fine faint brown mottles; weak fine subangular blocky structure; slightly hard, friable; slightly acid; abrupt wavy boundary. (0 to 10 inches thick)
Bt1--8 to 14 inches; reddish brown (5YR 5/4) silty clay loam; moderate medium and coarse subangular blocky structure; hard, firm; many faint light brown (7.5YR 6/4) silt coatings on faces of peds; few faint clay films on faces of peds; very strongly acid; gradual smooth boundary. (4 to 10 inches thick)
Bt2--14 to 21 inches; reddish brown (5YR 4/4) silty clay loam; moderate medium and coarse subangular blocky structure; hard, firm; many faint light brown (7.5YR 6/4) silt coatings on faces of peds; few faint clay films on faces of peds; few fine black concretions; very strongly acid; gradual smooth boundary. (5 to 14 inches thick)
Bt3--21 to 35 inches; reddish brown (5YR 4/4) silty clay loam; few medium distinct yellowish red (5YR 5/8) mottles and common thin pale brown (10YR 6/3) silt pockets and streaks; weak and moderate coarse subangular blocky structure; hard, firm; common faint clay films on faces of peds; few fine black concretions; very strongly acid; clear smooth boundary. (10 to 20 inches thick)
BC--35 to 49 inches; reddish brown (5YR 4/4) loam; common pale brown (10YR 6/3) silt pockets and many silt streaks; massive; hard, firm; few fine pores; few thin patchy clay films; few fine black and brown concretions; very strongly acid; clear smooth boundary. (0 to 15 inches thick)
2C1--49 to 63 inches; brown (7.5YR 4/4) silty clay loam; light brownish gray (10YR 6/2) silt pockets up to 1/2 inch thick and many silt streaks in a reticulate pattern; massive; hard, firm; few black stains; few fine brown and black concretions; moderately acid; clear smooth boundary.
2C2--63 to 69 inches; brown (7.5YR 4/4) loam; light brownish gray (10YR 6/2) silt pockets and streaks; massive; hard, firm; few black streaks; neutral.
TYPE LOCATION: Ouachita Parish, Louisiana; 1.0 mile south of junction Louisiana Highway 15 and Louisiana Highway 841; west on farm road across Youngs Bayou; south .67 mile to a point 174 feet west of west bank of bayou; 800 feet west and 2,280 feet south of northeast corner, sec. 27, T. 17 N., R. 4 E.
RANGE IN CHARACTERISTICS: The solum thickness ranges from 40 to 60 inches.
The A and E horizons have hue of 10YR or 7.5YR, chroma of 4 or 5, and value of 2 or 3. Texture is very fine sandy loam, loam, or silt loam. Reaction ranges from very strongly acid through neutral. The effective cation exchange capacity typically ranges from 10 to 30 percent or more saturated with exchangeable hydrogen.
The Bt horizon has hue of 7.5YR or 5YR, value of 4 or 5, and chroma of 3 through 6, or hue of 5YR, value of 3, and chroma of 3 or 4. Texture is silt loam, loam, silty clay loam, or clay loam. Silt coatings are on major structural surfaces. Reaction ranges from extremely acid through strongly acid.
The BC horizon has hue of 5YR, value of 4 or 5, and chroma of 4 or 6. Texture is loam, silt loam, silty clay loam, or clay loam. Reaction ranges from very strongly acid to slightly acid.
The C horizon has hue of 7.5YR or 5YR, value of 4 or 5, and chroma of 3 through 6. Texture is very fine sandy loam, loam, or silty clay loam with thin strata of these textures in some pedons. Reaction ranges from very strongly acid through moderately alkaline.
COMPETING SERIES: These include Dubbs, Gallion, Memphis, and Siwell of the same family and Dexter and Hebert in similar families. All of these soils lack silt coatings in the major part of the Bt horizon. In addition, Dexter soils have lower base saturation. Dubbs soils have colors of 10YR and 7.5YR in the Bt horizon. Gallion soils are medium acid to moderately alkaline in the B horizon. Hebert soils have gray ped coatings dominant in the Bt horizon. Memphis soils have less than about 10 percent total sand throughout and Bt horizons that are 7.5YR or yellower. Siwell soils have clayey 2Bt horizons.
GEOGRAPHIC SETTING: Rilla soils occur mainly on level to gently sloping natural levees of the Red River and along present and abandoned channels of the Arkansas River. They have formed in silty alluvium of mixed mineralogy. The climate is warm and humid. Average annual rainfall ranges from about 45 to 55 inches. Mean annual temperature ranges from about 60 to 70 degrees F. Annual Thornthwaite P-E index is 68 to 74.
GEOGRAPHICALLY ASSOCIATED SOILS: These include Hebert soils of the competing series and Mer Rouge, Perry, and Portland soils. Mer Rouge soils have a mollic epipedon. Perry and Portland soils have fine textured control sections.
DRAINAGE AND PERMEABILITY: Well drained; slow or medium runoff; moderate permeability. An apparent seasonal high water table is at depths of 4 to 6 feet, December through April.
USE AND VEGETATION: Most areas are cleared and used for cotton, soybeans, corn, or pasture.
DISTRIBUTION AND EXTENT: Northeast Louisiana and Arkansas. The series is of moderate extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Temple, Texas
SERIES ESTABLISHED: Quachita Parish, Louisiana; 1970.
REMARKS: Rilla soils formerly have been included in the Gallion series. Diagnostic horizons and features recognized in this pedon are:
Ochric Epipedon......................0 to 8 inches (A, E)
Argillic Horizon.............8 to 35 inches (Bt1,Bt2,Bt3)
Active CE activity class added in 2002.