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This article in SSSAJ

  1. Vol. 27 No. 1, p. 41-43
    Received: Mar 21, 1962
    Accepted: Aug 3, 1962

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Inability of the Kjeldahl Method to Fully Measure Indigenous Fixed Ammonium in Some Soils1

  1. B. A. Stewart and
  2. L. K. Porter2



In the course of some N fractionation studies in soils, inconsistencies resulted between the summation of the N fractions and the total soil N. In some, but not all, soils the summation figure exceeded by 25% the Kjeldahl figure. This inconsistency was especially noted in one soil that contained as much as 55% of the total N as indigenous fixed ammonium. A question was thus raised about the accuracy of the Kjeldahl procedure to measure indigenous, clay-fixed ammonium.

When soils were treated with HF before Kjeldahl analyses, the difference between the summation figures and the modified Kjeldahl results was < 5%. These results leave little doubt that on soils which contained from 11 to 55% of the total N as fixed ammonium the HF pretreatment increased the total N recovered.

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