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Soil Science Society of America Journal Abstract -

Single Empirical Relationship for Potassium Exchange Equilibria in Various Soils1


This article in SSSAJ

  1. Vol. 51 No. 4, p. 918-920
    Received: July 7, 1986

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  1. Joseph E. Dufey and
  2. Jean M. Marot2



The exchange behavior of K ions was studied in a collection of 40 soil samples from southern Belgium. These soils are characterized by wide differences of mineralogical composition, cation exchange capacity (CEC), and base saturation percentage. The prevailing basic cations on the exchange complexes are Ca, Mg, and K; Na is negligible. The Gapon formalism (i.e., exchangeable K ratio, EKR, vs. K adsorption ratio, KAR) is used to describe the relationship between the K concentrations in the surface and solution (water extract at 1:3 soil/H2O ratio) phases. When EKR is expressed (as it is usual) as [K]i/([Ca]i + [Mg]i)-[ ]i refers to surface concentrations, molckg−1—the dispersion of the experimental points around the line EKR vs. KAR is very high. However if EKR is expressed as [K]i/(CEC − [K]i), a fair linear relationship with low statistical dispersion is observed. This relationship shows that the exchange equilibria of K in our soils cannot be simply regarded as a K vs. (Ca + Mg) exchange reaction. This is likely related to the fact that in most samples the sum of exchangeable bases was lower than the CEC. Such a single relationship, though difficult to explain, may be especially useful for modeling purpose.

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