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

BackgroundAccurately determining exchangeable base cations is critical for assessing base cation depletion in acid forest soils, where various extraction methods may yield different results.AimThe aim was to quantify differences in the effectiveness of BaCl2, NH4OAc (pH 7), and Cohex methods in extracting base cations from acid forest soils and to assess the feasibility of establishing transfer functions.MethodsExchangeable 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 BaCl2- and NH4OAc(pH 7)-extractable base cations for 199 O, 200 B, and 200 BC horizon samples was also evaluated.ResultsBaCl2 and NH4OAc(pH 7) extracted similar amounts, although differences were observed for Ca2+ and Mg2+ in the O horizon, where BaCl2 extracted approximate to 1.3 times more Ca2+ and approximate to 1.05 times more Mg2+. Geochemical modeling suggested that the recovery of Ca2+ and Mg2+ in the NH4OAc(pH 7) extracts was incomplete. Transfer functions were developed for the prediction of BaCl2-extractable Ca2+ and Mg2+ from NH4OAc(pH 7)-extractable amounts in the O horizon. In the mineral soil, Cohex differed significantly from other methods, especially for K+, extracting only approximate to 50% in the C horizon.ConclusionsBoth BaCl2 (ISO 11260) and NH4OAc(pH 7) are effective for quantifying exchangeable cations in acid forest soils, though NH4OAc(pH 7) requires correction for Ca2+ and Mg2+ in the O horizon. The one-step Cohex extraction is less suitable, particularly due to its low K+ recovery.