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This article in SSSAJ

  1. Vol. 29 No. 6, p. 699-702
     
    Received: Oct 12, 1964
    Accepted: Aug 24, 1965


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doi:10.2136/sssaj1965.03615995002900060030x

Release of Potassium from Soil Fractions During Cropping1

  1. E. C. Doll,
  2. M. M. Mortland,
  3. K. Lawton and
  4. B. G. Ellis2

Abstract

Abstract

Soil fractions from six soils known to vary in ability to supply K to field crops were cropped intensively in greenhouse experiments. All soils and soil fractions were Mg-saturated prior to conducting the experiments. The K content of the clay and of the silt was linearly correlated with the logarithm of the K uptake for each fraction, except for the silt fraction of one soil. No correlation was noted between the uptake of K and the K content of the entire soil. In equilibrium experiments, K in solution in 1.0n MgOAc after 90 days was linearly correlated to the K content of the clay. A similar correlation was obtained with the entire soil. The different pattern of K release during cropping tests as compared to the equilibrium studies is attributed to rate processes which would govern release during cropping, but which would not be a factor in the equilibrium experiment. X-ray analyses indicated the formation of expanding lattice clays upon the removal of interlayer K by cropping. Large amounts of K were removed from the coarse clay (2.0–0.2µ), intermediate amounts from the medium clay (0.2–0.08µ), and small amounts from the fine fraction (<0.08µ). This differential release of K by the different size clay fractions can be explained by a decrease in the activity of interlayer K when the K content of the clay is decreased.

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