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Potassium Status of Selected Paleudults in the Lower Coastal Plain¹

ABSTRACT

An attempt was made to explain the lack of crop response to K fertilization for corn (Zea mays L.), soybean (Glycine max L.), and small grain in some Ultisols in the Lower Coastal Plain. Profile samples of a Rhodic Paleudult (Red Bay fsl), a Plinthic Paleudult (Dothan fsl), and Psammentic Paleudult (Eustis lfs) were analyzed for exchangeable K, nonexchangeable K which could be released, and total soil K. Although the first two forms of K were relatively low, a K reserve of about 1,500–2,800 kg/ha was found in each 15-cm thickness of soil sampled throughout these soil profiles. Potassium may be released from this reserve as indicated by the hot 1N HNO₃ extraction which produced an amount of K equivalent to 96 kg or better/ha for each 15-cm soil depth. Chemical studies showed that this K was not associated with noncrystalline hydrous oxides, silicates, or phosphates. No K-bearing minerals were evident in X-ray diffractograms of clay fractions except after removal of noncrystalline material, but peaks for K-feldspars were observed in silt fractions. Sodium pyrosulfate fusion method suggested that slightly < 50% of the K reserve occurred in the K-feldspar form and most of the rest was probably in micaceous mineral forms.

¹ Florida Agric. Exp. Stn. Journal Series no. 4848.

² Professor (Chemist), Associate Professor (Soil Physical Chemist and Mineralogist), and former graduate student, respectively, Soil Science Dep., IFAS, Univ. of Florida, Gainesville, FL 32611.

Received for publication August 14, 1975. Accepted for publication November 6, 1975.