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Field and Laboratory Studies of the Lufkin Soil, a Planosol¹

ABSTRACT

The Lufkin soil is an extreme type of clay pan Planosol found in a warm-temperature humid climate and is developed in moderately clayey sediments of deltaic and marine origin. It occupies mainly, smooth erosional upland with gradients dominantly less than 2%. The solum is composed of a relatively thin A₁ horizon with an erratically developed thin, vesicular A₂ resting abruptly on a dense subsoil of clay loam to clay texture.

Analyses were made on four profiles for particle size distribution, pH, organic matter, cation-exchange capacities, exchangeable cations, surface area, and mineral composition.

The < 2_µ fraction in the B₂₁ horizons was found to range from 35 to 48%. The largest amount of fine clay (< 0.2_µ) occurred in the B₂₁ horizons. Montmorillonite dominated the clay raction in all profiles investigated. Relatively large amounts of exchangeable sodium and magnesium are reported for the lower portions of each soil profile.

It is believed that eluviation of the fine clay from the A horizons with subsequent accumulation in the B horizon (illuviation) and clay formation in combination with the relatively large amounts of exchangeable sodium and possibly magnesium, plus a swelling type clay, are responsible for development of the clay pan, but which was the more important is not known.

¹ Contribution from the Texas Agr. Exp. Sta., and the Soil Conservation Service, U.S.D.A. Presented before Div. V, Soil Science Society of America, Cincinnati, Ohio, Nov. 14, 1956.

² Associate Professor of Soil Mineralogy, and Soil Correlator for Texas, respectively. The authors wish to acknowledge Mr. Irving Mowery for his assistance in collecting the soil samples.

Received for publication November 7, 1956. Accepted for publication January 31, 1957.