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Deeply Weathered Soils in the Texas Coastal Plain¹

ABSTRACT

Four seasonally saturated soils along a toposequence were analyzed to improve aquic moisture regime identification and soil classifications. The four soils are deeply developed and ranged from an Aquic Paleudalf to a Natric Vermaqualf (proposed great group). Sola thicknesses ranged from 4 to 7 m with argillic horizons extending to the base of each solum. Plinthite was identified in two soils, but not in concentrations large enough to affect classifications. Organic carbon contents were low across the landscape and reached maximum concentrations of 1 to 2% in the A horizons of the four soils. Soil pHs ranged from 5.0 to 7.6 and generally increased from upper to lower topographic positions with base saturations following a similar trend. Exchangeable Na percentages increased from upper to lower topographic positions from < 5 to 17%. Kaolinite was the dominant clay mineral in the two soils at the upper topographic positions. The kaolinite was highly crystalline and may be inherited from the parent materials as kaolinite concentrations increased with depth. Smectite was the predominant clay mineral in the upper sola of the two lowland soils with kaolinite concentrations increasing with depth. Upland soils had well-developed clay maxima at depths between 2 and 3 m. Clay illuviation has resulted in nearly complete infilling of the maxtrix of horizons containing maximum clay contents, and clay films as thick as 6 mm were observed in some interpedal voids. Soils in the lower topographic positions had massive, structureless A2 and A&B horizons. Crayfish krotovinas occupied > 75% (by volume) of some of these horizons and imparted unique morphological properties to the layers. It is proposed that the presence of numerous krotovinas be recognized in the great group and subgroup soil classifications of these Aqualfs.

¹ Contribution from the Soil and Crop Sciences Department, Texas A&M University. Paper no. 17564 of the Texas Agric. Exp. Stn., College Station.

² Former Research Assistant and Professor of Soil and Crop Sciences Department, Texas A&M University, College Station, TX 77843, respectively. Senior Author is presently Assistant Professor, Soil Science Dep., North Carolina State University, Raleigh, NC 27607.

Received for publication August 31, 1981. Accepted for publication September 24, 1982.