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Effect of Potassium and Calcium Activities in Clay Suspensions and Solutions on Plant Uptake¹

ABSTRACT

The clay membrane electrode was used to evaluate average activities of K and Ca in clay suspensions and in solutions throughout an 11-day growth period. Uptake of K and Ca by soybeans, barley, and buckwheat was compared in bentonite and Putnam clay suspensions and in solutions with the same cationic activities. The media were changed frequently to maintain relatively constant K and Ca activities. The other essential elements were supplied by periodically placing the plants in solutions containing Mg, N, P, S, and Fe.

In soybeans and barley, both yield and percentage of K were higher in clays than in solutions of equal or even higher activities, but were not significantly different between clays. At the levels tested, K uptake was more closely related to total amount present than to activity. Thus, there was no evidence that bonding of exchangeable K regulated uptake.

On the other hand, it was shown that bonding of Ca by clays may have regulated uptake. All plants removed as much or more Ca from solution as from suspension of equal activity. In soybeans, uptake of Ca was proportional to the Ca activity in the medium, while in barley and buckwheat, Ca uptake of this element was greater from solution than from clays, even when the Ca activities in both media were equal. The order of Ca accumulated was buckwheat > soybeans > barley. Some evidence was noted for contact interaction between root and clay colloids in both K and Ca uptake.

¹ Contribution from the Department of Agronomy, The Ohio State University and Ohio Agr. Exp. Sta., Journal Article No. 109-58. Part of a dissertation submitted by the senior author in partial fulfillment of the requirements for the Ph.D. degree at The Ohio State University and presented before Div. II, Soil Science Society of America, Lafayette, Ind., Aug. 8, 1958.

² Assistant Professor of Agronomy, University of Vermont and Vermont Agr. Exp. Sta., formerly graduate assistant, Ohio State University; and Professor of Agronomy, Ohio State University and Ohio Agr. Exp. Sta., respectively.

Received for publication November 25, 1958. Accepted for publication December 10, 1958.