Modification of the ammonium acetate extractant for the determination of exchangeable cations in calcareous soils
1998
Normandin, V. | Kotuby-Amacher, J. | Miller, R.O.
Neutral normal ammonium acetate (NH4C2H3O2) is the extractant predominately used to determine exchangeable cations in agricultural soils. On calcareous soils containing calcium carbonate (CaCO3), this method over estimates exchangeable calcium (Ca). A study was conducted to evaluate five method variables: extractant pH, extraction ratio (soil to extractant), shaking time, shaking vessel, and extractant volume. Modifying these variables, soils formerly utilized in the Western States Proficiency Testing Program were extracted and analyzed for Ca, sodium (Na), magnesium (Mg), and potassium (K). Results indicate that the extraction ratio significantly increased the amount of extractable Ca in soils containing more than 0.5% CaCO3. As the soil:extractant ratio decreased, the amount of measurable Ca increased. The concentration of Ca in noncalcareous soils remained constant in extraction ratios greater than 1:5. Additionally, the pH of the NH4C2H3O2 significantly altered the Ca concentration of the calcareous soils. As pH increased from the prescribed value of 7.0 to 9.0, extractable Ca decreased significantly. Increased extractant pH had little effect on exchangeable K, Mg, and Na for the soils tested. Further analyses with 30 soils indicate an NH4C2H3O2 extractant of pH 8.5 extracted equivalent amounts of K, Mg, and Na independent of the CaCO3 content.
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