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This article in SSSAJ

  1. Vol. 35 No. 5, p. 718-721
    Received: Jan 26, 1971
    Accepted: Apr 1, 1971

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Interpretation of Curves Describing Soil Potassium Exchange1

  1. S. J. Smith,
  2. M. Liu,
  3. L. J. Clark and
  4. A. D. Scott2



Curves describing the release of K from soil samples in NaTPB solutions depict a linear relationship between the amount of K replaced and the logarithm of the extraction period. Such curves are quite different from the diffusion-controlled curves observed with mica particles and have yet to be explained. Reports of a similar relationship being observed with soil organic N release that also obeyed a second-order reaction led to an unsuccessful application of second-order kinetics to the release of K from 16 soils. On the other hand, linear K-releases versus log t curves were obtained by combining K-release curves for mica particles of different size and by placing mixtures of mica particles in the same NaTPB solution. Therefore, a soil was fractionated, and the K-release curves for the individual size-fractions were determined. The curves for the soil fractions were nonlinear and more like mica curves, whereas various combinations of these curves yielded linear K-release versus log t relationships like those observed with soils. Thus, the curves for soil K-release merely represent the combined effects of various particle sizes in the soil and not a distinctive mode of release.

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