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Calcic Horizon Distribution and Soil Classification in Selected Soils of the Texas Coast Prairie¹

ABSTRACT

In the nearly level southeastern Texas Coast Prairie, extensive areas of Udolls with calcic horizons are intimately associated with noncalcareous Aqualfs. Transect and grid studies of 1- to 2-ha plots and other field studies in the area indicate that soils with calcic horizons are confined to microtopographic highs. Aqualfs occupy irregular microdepressions only 0.5 m lower than microhighs. This soil pattern is found on coastal plain geomorphic surfaces of both the Beaumont and Montgomery Pleistocene geological formations, especially on distributary elements of deltaic origin.

Variation in depth to the calcic horizon in Mollisols ranges from 18 to 115 cm and results in complex soil patterns of Aeric Calciaquolls and Aquic Haplustolls in microhighs. Multitaxa map units are necessary to accurately map the soils in these landscapes. Local relief differential of <1 m within the study area is the key landform indicator of soil differences. A new category for Soil Taxonomy, Calciaquic Hapludolls, is proposed to accommodate soils currently placed as Haplustolls that have udic moisture regimes despite calcic horizons within 1.5 m of the soil surface.

¹ Joint contribution from USDA-SCS and the Soil and Crop Sciences Department, Texas Agric. Exp. Stn., State Project no. H-6222. Presented before Div. S-5, Soil Science Society of America, Ft. Collins, Colo., 7 Aug. 1979. Texas Agric. Exp. Stn. Paper no. TA-18063.

² Soil Scientist with USDA-SCS, Tyler, Tex., and Professor, Texas Agric. Exp. Stn., Texas A&M University Systems, College Station. Mr. Sobecki was formerly a Graduate Research Assistant in the Soil and Crop Sciences Department.

Received for publication November 13, 1981. Accepted for publication July 3, 1982.