Interactions of pH-Dependent and Permanent Charges of Clays: III. Calcium and Rb Activities versus Soybean Root Uptake from Bentonite and Illite Suspensions1
- E. O. McLean,
- G. H. Snyder and
- R. E. Franklin2
Panther Creek bentonite and Fithian illite suspensions were reciprocally saturated with Ca and Rb. 45Ca and 86Rb were added as tracers for Ca and Rb, respectively. Increments of H-clay were added to aliquots of the Ca-Rb saturated clays to progressively decrease the base saturation of the clays. After equilibration, the activities of Ca and Rb were measured in the clay suspensions with the Orion divalent and the Beckman monovalent electrodes. Uptake of Ca and Rb by excised soybean roots was determined from the radioactivity of each tracer.
Decreased Ca saturation (increased Rb) shifted Ca ions from pH-dependent to permanent charges causing increased bonding and thus decreased Ca activities, fractions active, and root uptake. Except where specific ion bonding effects interfered, increased Rb saturation increased Rb activities and uptake—even though Rb fractions active were decreased, due to greater permanent charge bonding. With the same exception, additions of H-clays equilvalent to pH-dependent cation exchange capacity minimized Ca and Rb uptake as well as their activities and fractions active. Thus activity data generally correlated closely with uptake data, except where there were good reasons for this not to occur.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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