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This article in SSSAJ

  1. Vol. 33 No. 1, p. 105-109
    Received: May 13, 1968
    Accepted: July 22, 1968

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Potassium Supplying Power of Iowa Soils at Their “Minimal” Levels of Exchangeable Potassium1

  1. M. A. Tabatabai and
  2. J. J. Hanway2



The plant removal of native K from seven surface soils and seven subsoils from Iowa was studied at their “minimal” levels of exchangeable K. The “minimal” levels of exchangeable K were directly related to the percentages of <2 μ clay present in the surface soil samples. Plant uptake of nonexchangeable K was a linear function of time of cropping for all the soils and was highly correlated with the “minimal” level of exchangeable K. In the 758-day cropping period, an average of about 24 times as much K was removed by the plants as was present as exchangeable K in the soils at their “minimal” exchangeable K levels. Long-term K supplying powers of the soils used were highly correlated with their “minimal” levels of exchangeable K.

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