LOCATION PLACEDO                 TX+LA

Established Series
WLM-CDB-RM
09/2015

PLACEDO SERIES

The Placedo series consists of very deep, very poorly drained, very slowly permeable, ponded soils that have formed in saline, alkaline, clayey alluvium near sea level. These nearly level soils occur on flood plains. Slope ranges from 0 to 1 percent. Mean annual precipitation is about 1016 mm (40 in), and mean annual air temperature is about 21 degrees C (70 degrees F).

TAXONOMIC CLASS: Fine, smectitic, nonacid, hyperthermic Typic Fluvaquents

TYPICAL PEDON: Placedo silty clay--rangeland. (Colors are for moist soil unless otherwise stated.)

Ag1--0 to 20 cm (0 to 8 in); dark gray (10YR 4/1) silty clay, gray (10YR 5/1) dry; weak medium angular blocky structure; firm; very sticky and plastic; many fine roots; few fine pores; strongly saline; slightly alkaline; gradual smooth boundary. (10 to 53 cm [4 to 21 in] thick)

Ag2--20 to 64 cm (8 to 25 in); dark gray (10YR 4/1) clay, gray (10YR 5/1) dry; weak medium angular blocky structure; very firm, extremely sticky and plastic; common fine roots; few fine roots; strongly saline; slightly alkaline; gradual smooth boundary. (30 to 61 cm [12 to 24 in] thick)

Ag3--64 to 91 cm (25 to 36 in); dark gray (10YR 4/1) clay, gray (10YR 6/1) dry; weak coarse angular blocky structure; very firm, very sticky and plastic; few fine roots; few fine pores; few fine faint olive brown (2.5Y 4/3) masses of oxidized iron; strongly saline; slightly alkaline; clear smooth boundary. (25 to 51 cm [10 to 20 in] thick)

Cg1--91 to 127 cm (36 to 50 in); dark gray (10YR 4/1) clay loam, gray (10YR 6/1) dry; massive; very hard, firm, sticky and plastic; few fine roots; few fine pores; few thin strata of fine sandy loam; strongly saline; slightly alkaline; clear smooth boundary. (Combined thickness of the Cg horizons is 81 to 164 cm [32 to 65 in] thick)

Cg2--127 to 203 cm (50 to 80 in); gray (10YR 5/1) loam, gray (10YR 6/1) dry; massive; slightly hard, friable; few thin strata of fine sandy loam and clay; strongly saline; slightly alkaline.

TYPE LOCATION: Calhoun County, Texas; 3.6 miles southwest of intersection of Highways U. S. 87 and State 238 in Port Lavaca; 100 ft west of State Highway 238 and between two channels of Big Chocolate Bayou. Port Lavaca West USGS quadrangle; Latitude: 28 degrees 34 minutes, 36.83 N; Longitude: 96 degrees, 38 minutes, 56.03 seconds W; WGS84.

RANGE IN CHARACTERISTICS:
Soil Moisture: An aquic soil moisture regime.
Mean annual soil temperature: 21.7 to 22 degrees C (71 to 72 degrees F)
Clayey and loamy alluvium: more than 203 cm (80 in) thick.

Reaction throughout: slightly or moderately alkaline
Effervescence throughout: none to strong

Particle-size control section (weighted average)
Clay content: 35 to 50 percent.
Electrical Conductivity (mmhos/cm): 16 to 40

Ag1 Horizon:
Hue: 10YR to N
Value: 4 or 5
Chroma: 1
Texture: clay, silty clay, clay loam, or silty clay loam (some pedons have a mucky peat Oe horizon 3 to 8 cm (1 to 3 in) thick that is above the Ag1 horizon)
Secondary Carbonates: amount- none or few; kind- nodules or concretions

Ag2 and Ag3 Horizons:
Hue: 10YR to 5GY
Value: 4 to 7
Chroma: 1 to 7
Texture: clay, silty clay, or silty clay loam
Redox concentrations: amount-none to common, shades-yellow or brown
Secondary Carbonates: amount- none or few; kind- nodules or concretions

Cg (2C where present) Horizon:
Hue: 10YR to 5GY
Value: 4 to 7
Chroma: 1 to 7
Texture: loam to clay with strata of sandier texture
Secondary Carbonates: none or few; kind- nodules or concretions

COMPETING SERIES: There are no competing series in the same family. Similar soils are the Aransas, Austwell, Barrada, Harris, Ijam, Surfside, Swan, Tracosa and Veston series.
Aransas soils: vertic properties.
Austwell soils: cambic horizon; water table is below 61 cm (24 in) for extended periods.
Barrada soils: a salic horizon.
Harris, Surfside, and Swan soils: mollic colored epipedon.
Ijam soils: vertic properties; forming in dredge material
Trascosa soils: do not have stratification; are subject to daily tidal flooding.
Veston soils: are in a fine-silty family.

GEOGRAPHIC SETTING:
Parent material: clayey over loam Holocene age alluvium derived from igneous, metamorphic, and sedimentary rock
Landscape: delta plains or low coastal plains
Landform: flood plains
Slope: 0 to 1 percent
Mean annual precipitation: 940 to 1092 mm (37 to 43 in)
Precipitation Pattern: Precipitation is fairly uniform throughout the year with slight peaks in the spring and fall months.
Thornthwaite P-E Index: 40 to 64
Mean annual air temperature: 20.6 to 21.7 degrees C (69 to 71 degrees F)
Frost-free period: 275 to 300 days
Elevation: near sea level to 3 m (0 to 10 ft)

GEOGRAPHICALLY ASSOCIATED SOILS: These include the competing Aransas, Follet, Ijam, Swan, Tracosa and Veston series.
Aransas, Ijam, and Veston: are on a slightly higher landform. Follet, Tracosa, and Swan soils: on a similar landform.

DRAINAGE AND PERMEABILITY: Very poorly drained; runoff is negligible or the soil is ponded; very slow permeability. A water table fluctuates from above the soil surface to about 30 cm (12 in) below the surface in normal years. Following rains the soils are flooded by fresh water. Tides frequently flood the soils with sea water.

USE AND VEGETATION: Used for rangeland and wildlife. Native vegetation includes marshhay cordgrass, smooth cordgrass, gulf cordgrass, bushy sea-oxeye, seashore saltgrass, spiny aster, shoregrass, sedges, and rushes.

DISTRIBUTION AND EXTENT: Flood plains of rivers and small streams near sea level in the central part of the gulf coast of Texas. LRR-T; MLRA- 150B (Gulf Coast Saline Prairies); moderate extent.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Temple, Texas

SERIES ESTABLISHED: Calhoun County, Texas; 1972.

REMARKS: Diagnostic horizons and features recognized in this pedon are:

Ochric epipedon: 0 to 91 cm (0 to 36 in)

N-value of less than 0.7

Irregular distribution of organic carbon

Aquic conditions throughout.

ADDITIONAL DATA: Sampled for SDHPT from Jackson County, TX (THD84TX-239-002).

Taxonomic Version: Keys to Soil Taxonomy, Twelfth Edition, 2014

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National Cooperative Soil Survey
U.S.A.