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This article in SSSAJ

  1. Vol. 40 No. 5, p. 800-802
    Received: Jan 16, 1976
    Accepted: Mar 23, 1976

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Anomaly and Modification of pH-Acidity Relationship in the Double Buffer Method for Lime Requirement Determination1

  1. T. L. Yuan2



A break at pH 6.2–6.3 was observed recently in the linear titration curve of the buffer used in the double buffer method (Yuan, 1974). As a result, different pH-acidity relationships above and below this pH would have to be used in the lime requirement calculation. An attempt was made to investigate the possible cause or causes for the break. Suspected contamination of Cr2O72- in the K2CrO4 reagent originally used in the development of the method was investigated as was the effect of CaCl2 on buffering behavior of CrO42-. Although a completely satisfactory explanation of the anomaly was not obtained, it appears that higher purity of currently available K2CrO4 is involved. A modification of the buffer composition was made to give a linear curve with currently available chemicals so that the soil lime requirement can be more easily calculated. A table to show the soil buffering capacity based on a linear 1:1 pH-acidity relationship has also been added.

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