LOCATION ALLIGATOR MS+AR KY LA MO TNEstablished Series
TAXONOMIC CLASS: Very-fine, smectitic, thermic Chromic Dystraquerts
TYPICAL PEDON: Alligator clay--cultivated. (Colors are for moist soil unless otherwise stated.)
Ap1--0 to 4 inches; dark grayish brown (10YR 4/2) clay; weak and moderate medium granular structure; firm; plastic, sticky; common fine and medium roots; cracks 1 to 2 inches wide; slightly acid; abrupt wavy boundary.
Ap2--4 to 7 inches; dark grayish brown (10YR 4/2) clay; massive in place, parts to moderate medium angular blocky structure; very firm, very sticky, very plastic; common fine roots in concentrated masses in cracks; pockets and old cracks that are 0.25 to 0.50 inches wide are filled with Ap soil material; common medium distinct yellowish brown (10YR 5/6) masses of iron accumulation; strongly acid; abrupt wavy boundary. (Combined thickness of A horizons is 4 to 10 inches)
Bg--7 to 19 inches; light brownish gray (10YR 6/2) clay; moderate fine and medium angular blocky structure; very firm, very sticky, very plastic; common fine roots; cracks 0.25 to 0.50 inches wide with material from Ap horizon in crack fillings; many medium and coarse prominent strong brown (7.5YR 5/6) masses of iron accumulation; few small black manganese concretions; very strongly acid; gradual wavy boundary.
Bssg1--19 to 29 inches; light brownish gray (10YR 6/2) clay; weak coarse wedge shaped aggregates that part to weak and moderate medium angular blocky structure; very firm, very plastic, very sticky; few fine roots; cracks 0.25 to 0.50 inches wide with some material from Ap horizon in crack fillings; common coarse slickensides that intersect; common medium and coarse prominent strong brown (7.5YR 5/6) masses of iron accumulation; very strongly acid; gradual wavy boundary.
Bssg2--29 to 52 inches; grayish brown (2.5Y 5/2) clay; weak coarse wedge-shaped aggregates that part to moderate fine and medium angular blocky structure; very firm, very sticky, very plastic; few fine roots; common coarse grooved slickensides that intersect; stress surfaces common on faces of peds; common fine faint light brownish gray (2.5Y 6/2) iron depletions, many medium distinct yellowish brown (10YR 5/4) and common medium distinct dark yellowish brown (10YR 4/4) masses of iron accumulation; strongly acid; gradual wavy boundary.
Bssycg--52 to 65 inches; grayish brown (2.5Y 5/2) clay; weak coarse wedge-shaped aggregates that part to moderate fine and medium angular blocky structure; very firm, very sticky, very plastic; few fine roots; common coarse grooved slickensides that intersect; stress surfaces common on faces of peds; few charcoal fragments; few fine prominent strong brown (7.5YR 4/6) and many medium distinct dark yellowish brown (10YR 4/4) masses of iron accumulation; common medium rounded iron and manganese concretions; common fine and medium gypsum crystals in veins; slightly alkaline; gradual wavy boundary. (Combined Bg and Bss horizons are more than 40 inches thick)
BCcg--65 to 76 inches; grayish brown (2.5Y 5/2) clay; weak coarse prismatic structure parting to weak medium subangular blocky; firm, very sticky, very plastic; few medium slickensides; many medium distinct yellowish brown (10YR 5/4) and few fine prominent strong brown (7.5YR 4/6) masses of iron accumulation; common medium rounded iron and manganese concretions; common fine gypsum crystals; slightly alkaline; gradual wavy boundary. (0 to 15 inches thick)
Cg--76 to 84 inches; grayish brown (2.5Y 5/2) clay loam; massive; firm, very sticky, very plastic; common medium distinct yellowish brown (10YR 5/6) and common medium prominent yellowish red (5YR 4/6) masses of iron accumulation; slightly alkaline.
TYPE LOCATION: LeFlore County, Mississippi; 7 miles west of Itta Bena, 1.7 mile north of U.S. Highway 82, 0.5 mile east of Sunflower County line, 14 paces north of field road, 10 paces east of curve in field road; SW1/4NE1/4 sec. 30, T. 19 N., R. 2 W.
RANGE IN CHARACTERISTICS: Solum thickness is 44 to more than 80 inches. These soils when dry have deep wide cracks. Intersecting slickensides are within a depth of 40 inches. The 10- to 40- inch particle-size control section averages 60 to 90 percent clay.
The A horizon has hue of 10YR, to 5Y, value of 4 or 5, and chroma of 2 or 3. Some pedons have hue of 10YR to 5Y, value of 2 or 3, and chroma of less than 2 in less than half of each pedon. Texture is clay, silty clay, or silty clay loam. Reaction is strongly acid or very strongly acid, except where limed.
The upper part of the B horizon has hue of 10YR to 5Y, value of 4 or 5 and chroma of 1, or value of 6 or 7, and chroma of 1 or 2; distinct or prominent masses of iron accumulation in shades of brown and yellow are few to many. Pressure faces on surfaces of peds and slickensides, if present are few to common in the lower part of this horizon. Texture is silty clay or clay. Reaction is strongly acid or very strongly acid.
The lower part of the B horizon has hue of 10YR to 5Y or is neutral, value of 4 to 7, and chroma of 0 to 2. Distinct or prominent masses of iron accumulation in shades of yellow, brown, and red are few to many. Texture is silty clay loam, silty clay, or clay. Fine to coarse, grooved intersecting slickensides are few to many. Pockets and veins of gypsum crystals and calcium carbonate concentrations, and dark iron and manganese concretions are few to common in most pedons. Reaction commonly is very strongly acid to moderately acid and ranges to moderately alkaline in the lower part.
The Cg horizon has hue of 10YR to 5Y, value of 4 to 7, and chroma of 1 or 2. Masses of iron accumulation in shades of brown or yellow are few to many. Texture is silty clay loam, clay loam, or loam. The C horizon ranges from neutral to moderately alkaline.
COMPETING SERIES: These include Ashford, Consul and Eutaw series in the same family. Ashford soils formed in clayey alluvium on Pleistocene terraces in the Western Coastal Plain, MLRA 133B. Ashford soils have a solum greater than 80 inches thick. Consul soils have a paralithic contact with alkaline shale bedrock at 40 to 60 inches. Eutaw soils developed on uplands of the Southern Coastal Plain and BlackLand Prairie and typically have a solum that is 16 to 30 inches thick.
GEOGRAPHIC SETTING: Alligator soils formed in clayey backswamp sediments of the Mississippi River flood plain and its tributaries. These soils are in broad backswamps, depressions, and interfluves on flood plains and low terraces. Slopes are mainly less than 1 percent but range to 5 percent on short escarpments bordering channels. The climate is warm and humid. The range of the mean annual temperature is 62 to 65 degrees F., and the mean annual precipitation is 48 to 60 inches.
GEOGRAPHICALLY ASSOCIATED SOILS: These include Dundee, Earle, Fausse, Forestdale, Sharkey, Tensas and Tunica series. All these soils are associated across the land forms of the Mississippi River flood plain. Earle, Dundee, and Tensas soils are better drained soils between backswamps and natural levees. Dundee soils formed in loamy alluvium and contains less than 35 percent clay. Fausse soils are ponded except during prolonged dry periods and do not dry out. Sharkey soils have higher pH in the subsoil. Tensas soils formed in clayey sediments containing less than 60 percent clay. Forestdale soils have 35 to 60 percent clay in the control section.
DRAINAGE AND PERMEABILITY: Poorly drained; very slow permeability; rate of runoff is very high on slopes of 1 percent or more, high on areas with slope less than 1 percent, and negligible in depressional areas. It is ponded in depressional areas for brief to very long duration. The frequency of flooding ranges from rare to common in low lying areas and along tributaries. Areas along the lower courses of tributary streams to the Mississippi River are subject to backwater flooding. Cracks ranging from 1 to 2.5 inches wide and extending to as much as 2 to 3 feet in depth, form in these soils during the summer and early fall months in normal years. This allows for very rapid infiltration of water; and as the clay is wetted, it swells, forcing the cracks to close. The soil is saturated in the surface layer and along cracks and slickenside faces in the subsoil from December through April during normal years.
USE AND VEGETATION: Most areas of Alligator soils are used for growing soybeans, rice, cotton, and wheat. Some are in bottomland hardwoods dominated by baldcypress, ash, tupelo gum, swamp maple, oaks, hickories, sweetgum, and cottonwood.
DISTRIBUTION AND EXTENT: Throughout the lower Mississippi River Delta in the states of Arkansas, Kentucky, Louisiana, Mississippi, Missouri, and Tennessee. The series is of large extent.
MLRA OFFICE RESPONSIBLE: Little Rock, Arkansas
SERIES ESTABLISHED: Quitman County, Mississippi; 1950.
REMARKS: This series is reclassified from very-fine, montmorillonitic, acid, thermic Vertic Haplaquepts as the result of a special study in April 1986 by NCSS representatives from Arkansas, Mississippi, Louisiana, the National Soil Survey Laboratory, and South National Technical Center. The classification was changed from Alfic to Chromic based on changes to the Keys to Taxonony, 8th Edition, 1998. The present type location pedon actually classifies in an Aeric subgroup by 1 inch (2.5Y 5/2 matrix at 29 inches deep), however additional study is needed to determine whether this is typical for Alligator soils.
Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - from the surface to a depth of 7 inches (Ap, Apd).
Cambic horizon - from a depth of about 7 inches to 65 inches (Bg, Bssg1, Bssg2, Bssycg).
Aquic conditions - episaturation in the A horizon and upper part of the B horizon.
Slickensides - from a depth of about 19 to 65 inches (intersecting).
ADDITIONAL DATA: National Soil Survey Laboratory Project No. 86T 31; Pedon No. 86T 55; Sample No. 86T734-7337; soil characterization data for one pedon are published in SS1R No. 13 p. 5. Characterization data for 2 pedons, Mississippi State Soil Genesis and Morphology Laboratory. Sample numbers 8816-1-7 and 8730-1-9.
All phases of the Alligator series are listed as hydric soils in the "Hydric Soils of the United States" (SCS Misc. Pub. No. 1491).
Drained phases (0-5 percent slopes) of the Alligator series that are protected from flooding and are not frequently flooded during the growing season are considered prime farmland.