Potassium Status of Selected Paleudults in the Lower Coastal Plain
1976
Yuan, T. L. | Zelazny, L. W. | Ratanaprasatporn, A.
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.
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