A COMPARISON OF EXTRACTANTS FOR THE DETERMINATION OF CATION-EXCHANGE CAPACITY AND EXTRACTABLE CATIONS BY A MECHANICAL VACUUM EXTRACTOR

The present study was undertaken to compare extracting solutions for the determination of cation exchange capacity (CEC) and extractable cations in mineral soils with pH >7.0. Standard procedures (e.g., 1.0 M NH4OAc, pH 7.0) cause discrepancies in these determinations in calcareous soils. Three soils (1 calcareous, 2 noncalcareous) ranging in pH (0.01 M CaCl2) from 7.2 to 8.0 were extracted using 7 different extractants. The extractants were 1.0 M NH4OAc (pH 7.0 and 8.2), 1.0 M NH4Cl (unbuffered and pH 8.4), 0.1 M BaCl2 (unbuffered and pH 8.2), and 0.4 M NaOAc/0.1 M NaCl/60% ethanol (pH 8.2). Soils were leached over a 16-h extraction time in a mechanical vacuum extractor. Ammonium-N in the soil was determined by an automated distillation-titration method using the Kjeltec Auto 1030 Analyzer. Calcium, Mg, K, and Na were determined by inductively coupled plasma-atomic emission spectroscopy. The BaCl2 extractant gave the highest CEC values. There was very little difference in CEC or exchangeable cations between buffered and unbuffered solutions of each extractant.