POTASSIUM FIXATION AND RECCONSTITUTION OF MICACEOUS STRUCTURES IN SOILS

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Abstract
Clays from five selected soil series from the southern region of the United States were studied for their K fixation properties. The soils were very strongly to slightly acid in reaction. The CEC of the clay fractions of the soils ranged from 9.6 to 58.8 me/100 g. Kaolinite was a common clay mineral constituent of all the clays. The basal reflection intensities and the thermal peaks of kaolinite decreased in the order of Cecil > Varina ≈ Berks ≈ Iredell > Beaumont. All clays showed the high order mica reflection at 3.35 A, but not at 10 A, except in Berks clay. It is suggested that mica in Berks clay was less weathered than that in the other clays. The 14-A peak was present in all the clays, being highest in the Iredell clay. Montmorillonite was the dominant clay mineral in Beaumont and was probably also present in Iredell clay.All clays of the soils had the capacity to fix K. Potassium adsorption by the wedgezones in the interlayer surfaces of weathered mica was probably the controlling factor of K fixation in acid soils, such as Cecil, Varina, and Berks. Increased fixation of K by the clays from Cecil, Varina, and Iredell gradually increased the intensity of the 10-A peak in the X-ray diffractograms. Potassium fixation by Beaumont clay did not result in the appearance of the 10-A peak. The intensities of the 10-A diffraction of the Cecil and Varina clays were highly correlated with the amount of K added, but those of Iredell clay were not.There was no obvious disappearance of other X-ray reflections with the appearance of the 10-A peak in the X-ray diffractograms. The appearance of 10-A peaks supplemented existing 3.35-A basal reflection of mica in the clays. Potassium fixation had reconstituted the existing disordered mica in those clays. The clay mineral structure was of more importance than the CEC in determining K fixation properties of clays. Clays from five selected soil series from the southern region of the United States were studied for their K fixation properties. The soils were very strongly to slightly acid in reaction. The CEC of the clay fractions of the soils ranged from 9.6 to 58.8 me/100 g. Kaolinite was a common clay mineral constituent of all the clays. The basal reflection intensities and the thermal peaks of kaolinite decreased in the order of Cecil > Varina ≈ Berks ≈ Iredell > Beaumont. All clays showed the high order mica reflection at 3.35 A, but not at 10 A, except in Berks clay. It is suggested that mica in Berks clay was less weathered than that in the other clays. The 14-A peak was present in all the clays, being highest in the Iredell clay. Montmorillonite was the dominant clay mineral in Beaumont and was probably also present in Iredell clay. All clays of the soils had the capacity to fix K. Potassium adsorption by the wedgezones in the interlayer surfaces of weathered mica was probably the controlling factor of K fixation in acid soils, such as Cecil, Varina, and Berks. Increased fixation of K by the clays from Cecil, Varina, and Iredell gradually increased the intensity of the 10-A peak in the X-ray diffractograms. Potassium fixation by Beaumont clay did not result in the appearance of the 10-A peak. The intensities of the 10-A diffraction of the Cecil and Varina clays were highly correlated with the amount of K added, but those of Iredell clay were not. There was no obvious disappearance of other X-ray reflections with the appearance of the 10-A peak in the X-ray diffractograms. The appearance of 10-A peaks supplemented existing 3.35-A basal reflection of mica in the clays. Potassium fixation had reconstituted the existing disordered mica in those clays. The clay mineral structure was of more importance than the CEC in determining K fixation properties of clays. © Williams & Wilkins 1973. All Rights Reserved.

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