A comparison of extractants for the determination of cation exchange capacity and extractable cations by a mechanical vacuum extractor

Abstract

Abstract 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 cat...