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Calcium Fluoride Formation During Extraction of Calcareous Soils With Fluoride: II. Implications to the Bray P‐1 Test
Author(s) -
Smillie G. W.,
Syers J. K.
Publication year - 1972
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1972.03615995003600010005x
Subject(s) - calcareous , calcite , extraction (chemistry) , chemistry , soil water , calcareous soils , reagent , nuclear chemistry , fluoride , mineralogy , calcium carbonate , environmental chemistry , inorganic chemistry , geology , chromatography , soil science , paleontology , organic chemistry
Calcium fluoride formed during a 1‐min extraction of calcite (50‐2 µm) with the Bray P‐1 reagent (0.03 M NH 4 F/0.025 N 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 CaF 2 in residues following a 1‐min Bray P‐1 extraction of calcareous soils; CaF 2 was, however, identified in a highly calcareous soil (59% CaCO 3 ) following a 1‐min Bray P‐1 extraction. Added P sorbed by calcite and several calcareous soil horizons (containing more than 10% CaCO 3 ) during 1‐min and 24‐hour extractions with the Bray P‐1 reagent was not recovered in a subsequent 1 M NaCl or 0.1 N 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 CaF 2 and not with CaCO 3 or Al and Fe components. Formation of CaF 2 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 0.03 M NH 4 Cl/0.025 N HCl. The low Bray P‐1 estimates of “available” P, frequently reported for calcareous soils, may be attributed to the formation of CaF 2 when the dilute HCl is neutralized by CaCO 3 .