Effect of Plant Weathering of Soil Clays on Plant Availability of Native and Added Potassium and on Clay Mineral Structure

Abstract

AbstractPlants were grown for 4 weeks in suspensions of Brookston and Clermont soil clays for the purpose of removing K. At weekly intervals, samples of the plant‐weathered clays were removed for determination of K uptake by soybean plants (Glycine max) and for X‐ray analysis. Labeled K was added and equilibrated with the clay samples. Specific activity of 42K adsorbed by cation‐exchange resin confined in cellulose tubing was lower than that added to the clay and decreased relatively more with time of weathering. This indicated that K was released from the clays diluting the 42K added, but that fixation of 42K (and 39K) added eventually became relatively greater than K released.Plant uptake of K during the weekly 1‐hour uptake periods was determined from 42K uptake and specific activity of 42K adsorbed by the resin at weekly intervals. Amounts of K uptake initially decreased with time or did so ultimately as more K was removed from the clays. X‐ray diffractograms revealed that plant weathering altered the basal spacings of the clays. Weathering effects noted were partial degradation of illite and apparent reduction in amount of kaolinite in both soil clays, and reduction in amount of vermiculite in the Clermont.