LOCATION SPIRO OKEstablished Series
TYPICAL PEDON: Spiro silt loam - rangeland.
(Colors are for moist soil unless otherwise stated.)
A1--0 to 10 inches; very dark grayish brown (10YR 3/2) silt loam, grayish brown (10YR 5/2) dry; weak fine granular structure; hard, friable; strongly acid; gradual smooth boundary. (6 to 14 inches thick)
A2--10 to 15 inches; dark brown (10YR 4/3) silt loam, brown (10YR 5/3) dry; weak fine granular structure; hard, friable; strongly acid; gradual smooth boundary. (2 to 8 inches thick)
Bt--15 to 27 inches; dark yellowish brown (10YR 4/4) silty clay loam, light yellowish brown (10YR 6/4) dry; few fine distinct yellowish red and strong brown mottles; weak fine subangular blocky structure; hard, firm; patchy clay films on faces of peds and in pores; very strongly acid; clear irregular boundary. (10 to 30 inches thick)
BC--27 to 34 inches; yellowish brown (10YR 5/4) very shaly silty clay loam; weak medium subangular blocky structure; hard, firm; fragments of shale comprise about 60 percent of the horizon; very strongly acid; abrupt irregular boundary. (0 to 10 inches thick)
Cr--34 to 40 inches; brownish yellow (10YR 6/6) weathered shale; strongly acid.
TYPE LOCATION : Sequoyah County, Oklahoma; about 1-1/2 miles southeast of Vian, Oklahoma, 1,400 feet south and 525 feet west of the northeast corner of sec. 35, T. 12 N., R. 22 E.
RANGE IN CHARACTERISTICS: The depth to bedrock and thickness of solum range from 20 to 40 inches.
The A horizon has hue of 7.5YR or 10YR, value of 2 to 4, and chroma of 2 or 3. Texture is silt loam, loam, or very fine sandy loam. Reaction ranges from slightly acid to strongly acid.
Some pedons have a BA horizon, and where present, the BA horizon is similar to the Bt horizon in color and texture, but the reaction is medium acid or strongly acid.
The Bt horizon has hue of 7.5YR or 10YR, value of 4 to 6, and chroma of 3 to 6. Texture is loam, silt loam, clay loam, or silty clay loam and the clay content averages between 18 and 35 percent. Reaction is medium acid to very strongly acid.
The BC horizon has color, texture, and reaction similar to the Bt horizon but contains shale fragments. Fragments of shale, siltstone, or sandstone less than 76mm in diameter comprise 10 to 80 percent of the volume.
The Cr horizon is interbedded shale, siltstone, and sandstone.
COMPETING SERIES: This is the Rexor series in the same family and the Armour, Barnsdall, Dexter, Dossman, and Hicks, series in similar families. Armour, Barnsdall, Dexter, Dossman, and Hicks soils have mixed mineralogy. In addition, Barnsdall, Dexter and Dossman soils have hue of 5YR or redder in the matrix of the argillic horizon; Hicks soils are underlain by phosphatic limestone below depths of 42 inches. Rexor soils lack bedrock within 60 inches of the soil surface.
GEOGRAPHIC SETTING: The Spiro soils are mainly on convex side slopes and ridges of uplands in the Arkansas Valley and Ridges and the Boston Mountains. Slopes are 1 to 8 percent but are dominantly less than 5 percent. These soils formed in material weathered from residuum interbedded shale, siltstone, and sandstone of Pennsylvanian age. The climate is humid. Mean average annual precipitation ranges from 38 to 46 inches; mean annual temperature ranges from 57 degrees to 65 degrees F; and Thornthwaite annual P-E indices range from 64 to 80.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Collinsville, Enders, Hector, Linker, Stigler, and Vian soils. Collinsville soils are on ridges in native grass areas and they have a mollic epipedon. Enders soils are on convex side slopes in higher elevations and they have a clayey control section. Hector soils are on similar positions to the Spiro series at higher elevations, and they are less than 20 inches thick over lithic sandstone. Linker soils are on convex foot slopes, side slopes, and ridges and they have a fine-loamy control section. Stigler soils are on similar areas to the Spiro series but have a thicker solum and have a clayey control section. Vian soils are on similar areas to the Spiro series but have a thicker solum.
DRAINAGE AND PERMEABILITY: Well drained; medium through rapid runoff; moderate permeability.
USE AND VEGETATION: Used primarily for range or tame pasture with small areas used for small grains, soybeans, and corn. Native vegetation is an open stand of hardwoods, primarily oaks, with an understory of big bluestem, little bluestem, indiangrass, and switchgrass.
DISTRIBUTION AND EXTENT: Arkansas Valley and Ridges and the Boston Mountains of Arkansas, Missouri, and Oklahoma. The series is limited in extent.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Temple, Texas
SERIES ESTABLISHED: Haskell County, Oklahoma; 1972.
ADDITIONAL DATA: Base saturation was determined by the field test kit. Base saturation of the B2t horizon is 47 percent and 38 percent in C horizon. Mineralogy was determined by the Lincoln Laboratory. Samples 71L254 and 71L255.