Abstract
When evaluating phosphate rock (PR) dissolution, previous to the extraction with sodium hydroxide (NaOH), dry soil samples with PR were extracted with three solutions to remove exchangeable and solution calcium (Ca) [sodium chloride (NaCl) 1 M, buffered NaCl with ethylenediaminetetraacetic acid (EDTA) (NaCl–EDTA), and NaCl buffered at pH 7 with triethanolamine (TEA) (NaCl–TEA)] for comparison with the extraction of soil samples without any prewash. In acidic soils, up to 51% of applied P was recovered during the NaCl extraction because of the high exchangeable acidity released during the extraction. In soils with exchangeable Ca>2 cmol(+)kg−1, high EDTA quantities also promoted PR dissolution. The NaCl–TEA solution efficiently removed Ca, avoiding PR dissolution and P retention by calcium hydroxide [Ca(OH)2] during the NaOH extraction. Thus, when evaluating PR dissolution we recommend the use of NaCl–TEA to remove Ca. We also recommend the same procedure when applying the Chang and Jackson fractionation to calcareous soils and soils submitted to PR application.
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