Masters Theses

Date of Award

3-1981

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

David A. Lietzke

Committee Members

Frank F. Bell, Jeffrey Wolt

Abstract

Relations of the upland fragipan soils of Weakley county to parent material and topography are not well known. Information on variability within upland soil series in Weakley county, expecially Loring, is lacking. This study attempts to provide some information on these relationships. Thirty-two transects were conducted and four representative pedons sampled in Weakley county. Transects provided field data. Laboratory analyses were made to determine soil texture, particle size ratios, CEC, base saturation, and pH, along with mineralogical characterization. Data gathered indicated that loess thinned eastward in the county from 465 cm to 165 cm. Two separate loess layers—Peoria and Roxana— were identified, each occupying one half the total loess. The two loess layers were separated on the basis of morphology, particle size, and mineralogy. Fragipan thickness was related to parent material thickness and prevailing slope gradients, with thicker fragipans on more gentle slopes. Fragipans became harder with thinning loess, regardless of soil series. Fragipans were considered genetic soil horizons whose hardness was enhanced by past weathering zones near the fragipan upper boundary. Soil series varied according to landform with Loring soils occurring on narrow ridgetops and convex sideslopes and Grenada soils on broad, level ridgetops and concave sideslopes. The Grenada soil was more highly weathered than the Loring as revealed by chloritized vermiculite in the clay fraction and low pH values in the Grenada. Regardless of series, soils were more weathered eastward in the county due to the thinning loess becoming effectively older. This increased soil weathering in the east was revealed by lower CEC, base saturation, and salt pH, along with an increase in quartz relative to feldspar content compared to values for soils in the west. West Weakley county soils were formed entirely in Peoria loess while those in the east were formed in the entire loess column. The Loring series encompasses wide variation within the county, developing a harder fragipan and more highly weathered profile in the east and a more variable B horizon color and clay content in west Weakley county. Sufficient difference between the Loring of the west and of the east was found to define a thin loess phase of the Loring series occurring in loess less than 220 cm deep. Actual creation of a new phase will depend on discovering the range of the Loring variants outside of Weakley county.

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