Comparison of soil solution extraction procedures: Effect on solute chemistry

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Abstract
A study was undertaken to evaluate the effect of five methods of soil solution extraction on solute chemistry. The methods evaluated were high speed centrifugation, immiscible displacement, column equilibration/vacuum extraction, and 1:1 and 2:1 solution:soil water extractions. Solutions were analyzed for pH, major cations and anions, silicon, and dissolved inorganic and organic carbon. Solute concentrations followed a general trend of centrifugation > immiscible displacement > column equilibration ≈2:1 extract ≈1:1 extract. Solution pH varied up to 3 units depending on the method employed. A significant soil type times method interaction also occurred indicating that the extraction methods differ with soil type. The coefficients of variation averaged over all solutes for each method ranged between 0.079 and 0.130. This study shows that the method of choice for a given experimental design must be carefully evaluated for each soil.