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This article in SSSAJ

  1. Vol. 35 No. 5, p. 763-767
    Received: Sept 2, 1970
    Accepted: June 18, 1971

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Potassium Removed from Some Southern Brazilian Soils by Exhaustive Cropping and Chemical Extraction Methods1

  1. V. Oliveira,
  2. A. E. Ludwick and
  3. M. T. Beatty2



Soils from the orders Alfisol, Inceptisol, Mollisol, Ultisol, and Oxisol contained exchangeable K (neutral 1N NH4OAc) and boiling 1N HNO3 extractable K varying from 31 to 358 ppm and 62 to 652 ppm, respectively. Total K varied from 1,780 to 14,200 ppm. Quantities absorbed from each soil by 7 cuttings of perennial ryegrass (Lolium perenne) in the greenhouse ranged up to 13 times that of exchangeable K and up to 5 times that of HNO3-extractable K. Total plant uptake represented 3.5 to 29.7% of total soil K. In no soil did K become limiting in the first four cuttings. However, except for the Mollisols, uptake decreased abruptly in the later cuttings, indicating very little “slowly” available K. Even though exchangeable K and K removed by strong acids were highly correlated with plant uptake (r = 0.744** to 0.881**), all extractants greatly underestimated actual plant-available K under intensive cropping. Total soil K did not significantly correlate with plant uptake (r = 0.211).

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