Determining Exchangeable Base Cations in Forest Soils: A Comparison of Three Methods

ABSTRACT Background Accurately determining exchangeable base cations is critical for assessing base cation depletion in acid forest soils, where various extraction methods may yield different results. Aim The aim was to quantify differences in the effectiveness of BaCl 2 , NH 4 OAc (pH 7), and Cohex methods in extracting base cations from acid forest soils and to assess the feasibility of establishing transfer functions. Methods Exchangeable base cations in 25 samples each from the O, B, and C horizons of the Swedish Forest Soil Survey were analyzed using all three methods. An additional dataset comprising BaCl 2 ‐ and NH 4 OAc(pH 7)‐extractable base cations for 199 O, 200 B, and 200 BC horizon samples was also evaluated. Results BaCl 2 and NH 4 OAc(pH 7) extracted similar amounts, although differences were observed for Ca 2+ and Mg 2+ in the O horizon, where BaCl 2 extracted ≈ 1.3 times more Ca 2+ and ≈ 1.05 times more Mg 2+ . Geochemical modeling suggested that the recovery of Ca 2+ and Mg 2+ in the NH 4 OAc(pH 7) extracts was incomplete. Transfer functions were developed for the prediction of BaCl 2 ‐extractable Ca 2+ and Mg 2+ from NH 4 OAc(pH 7)‐extractable amounts in the O horizon. In the mineral soil, Cohex differed significantly from other methods, especially for K + , extracting only ≈ 50% in the C horizon. Conclusions Both BaCl 2 (ISO 11260) and NH 4 OAc(pH 7) are effective for quantifying exchangeable cations in acid forest soils, though NH 4 OAc(pH 7) requires correction for Ca 2+ and Mg 2+ in the O horizon. The one‐step Cohex extraction is less suitable, particularly due to its low K⁺ recovery.