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Exchangeable Potassium Levels in Vermiculite and K-Depleted Micas, and Implications Relative to Potassium Levels in Soils¹

ABSTRACT

Fe- and Mg-rich micas were depleted of K in the laboratory by the action of sodium tetraphenylboron, and the products were examined by X-ray diffraction. A natural vermiculite was included in this study. Exchangeable K was determined in relation to total K where possible.

Nearly constant levels of exchangeable K were maintained by the vermiculite and weathered trioctahedral micas over the range of K concentrations at which fixation occurred. The materials functioned as K fixers below approximately 3% K₂O but little fixation could be induced at moderate temperatures and K concentrations above 3% K₂O. Total K below 3% K₂O was not related to exchangeable K. Above 3% K₂O, exchangeable K increased rapidly with K additions. Interstratified layer silicates were produced by K removal from the natural micas, and were also formed by additions of K to vermiculite. At natural levels of total K in the micas (7 to 10% K₂O), 10Å. material was present; considerable 14Å. material was produced as removal of K approached completion.

Dilution of the fixing mineral with montmorillonite resulted in exchangeable K levels which were very similar to those in the fixing mineral alone. Numerous workers have noted that certain soils seem to exhibit characteristic exchangeable K levels which are not altered appreciably by additions or removals of K. These data tend to substantiate such observations and seem to explain the characteristic K exchange levels within such soils.

¹ Contribution from the Department of Agronomy, Mississippi Agr. Exp. Sta., Paper No. 741. Presented before Div. II, Soil Science Society America, Aug. 5, 1958, Lafayette, Ind.

² Assistant Agronomist.

Received for publication August 8, 1958. Accepted for publication October 3, 1958.