Underestimation of Available Phosphorus by Resin-Bicarbonate and Olsen Tests in Calcareous Soils treated with Gypsum
2009
Chien, S.H. | Austin, E.R. | Calvo, C.G.
In the present study, Olsen [0.5 M sodium bicarbonate (NaHCO3), pH 8.5] and resin-bicarbonate (HCO3) tests underestimated available phosphorus (P) in calcareous soils treated with gypsum (CaSO4). The reaction of CaSO4 and HCO3 - ion or resin-HCO3 to form calcium carbonate (CaCO3) precipitate reduced the strength of the Olsen NaHCO3 extractant and resin-HCO3 strip for P extraction. The iron (Fe) oxide-impregnated filter paper (Pi strip) was independent of CaSO4 influence and thus correctly estimated soil-available P with respect to plant response to soil-available P. Two greenhouse experiments were conducted with maize and wheat grown on calcareous soils treated with different rates of CaSO4. The results confirmed that Olsen and resin-HCO3 tests should not be used to measure available P or labile P in the P fractionation scheme in the calcareous soils containing significant amounts of gypsum.
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