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This article in SSSAJ

  1. Vol. 36 No. 1, p. 25-30
     
    Received: Jan 7, 1971
    Published: Jan, 1972


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doi:10.2136/sssaj1972.03615995003600010005x

Calcium Fluoride Formation During Extraction of Calcareous Soils With Fluoride: II. Implications to the Bray P-1 Test1

  1. G. W. Smillie and
  2. J. K. Syers2

Abstract

Abstract

Calcium fluoride formed during a 1-min extraction of calcite (50-2 µm) with the Bray P-1 reagent (0.03M NH4F/0.025N HCl) sorbed added P. Because of the problem in identifying minor components of a whole soil matrix by X-ray diffraction analysis, it was frequently difficult to positively identify CaF2 in residues following a 1-min Bray P-1 extraction of calcareous soils; CaF2 was, however, identified in a highly calcareous soil (59% CaCO3) following a 1-min Bray P-1 extraction. Added P sorbed by calcite and several calcareous soil horizons (containing more than 10% CaCO3) during 1-min and 24-hour extractions with the Bray P-1 reagent was not recovered in a subsequent 1M NaCl or 0.1N NaOH extraction. By comparison with the data obtained for calcite and noncalcareous soils, the P sorbed during the Bray P-1 extraction of calcareous soils was shown to be associated with CaF2 and not with CaCO3 or Al and Fe components. Formation of CaF2 and immobilization of P during a 1-min Bray P-1 extraction was demonstrated for a wide range of calcareous soils by comparing the amounts of added P recovered in subsequent NaCl and NaOH extractions with the amounts of added P recovered in NaCl and NaOH extractions subsequent to extraction with 0.03M NH4Cl/0.025N HCl. The low Bray P-1 estimates of “available” P, frequently reported for calcareous soils, may be attributed to the formation of CaF2 when the dilute HCl is neutralized by CaCO3.

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