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Clay Mineralogical Relationships in Florida Haplaquods¹

ABSTRACT

The clay mineralogy of 59 Alfic and Ultic Haplaquod pedons was studied with respect to distributional relationships involving horizons, chemical parameters, and geomorphic surfaces. Relative estimates of clay-sized minerals were based on x-ray diffraction (XRD) peak height ratios after calibration with standards and normalization. Mineralogical differences based on horizon, base status, or elevational groupings were tested statistically. Quartz dominated the clay fractions of upper, sandier horizons for all pedons. Kaolinite, smectite, and gibbsite were usually more abundant in deeper, finer textured horizons. Hydroxy-interlayered minerals, relative to other phyllosilicates, were significantly concentrated (p <0.0001) in Bh horizons. Kaolinite tended to be more abundant than other phyllosilicates in A and E horizons. Alfic subgroup pedons usually contained less kaolinite and more smectite than ultic pedons. Most pedons on older (>30 m) geomorphic surfaces: (i) were virtually depleted of bases, (ii) contained little or no smectite, and (iii) were dominated by kaolinite in lower horizons. Soils on younger (>30 m) surfaces contained significantly (p = 0.0054) more smectite than older surfaces on the average, and differences were even greater when only ultic subgroups were considered. The mineralogical-chemical-geomorphic relationships collectively support the concept that smectite stability decreases with the loss of bases which has occurred most thoroughly on the oldest surfaces.

¹ Florida Agric. Exp. Stn. Journal Series no. 7291. This research was partially supported by State Legislative appropriations (administered by the Dep. of Agriculture and Consumer Services) and supplemental funds contributed by participating counties in support of the Florida Cooperative Soil Survey.

² Assistant Professor of Soil Genesis and Mineralogy and Professor of Soil Science, respectively, Soil Science Dep., Univ. of Florida, Gainesville, FL 32611.

Received for publication May 9, 1986.