Water, NaHCO3-, NaH2PO4- and NaCl-extractable SO42- in acid forest soils

A variety of different methods have been used for the determination of inorganic soil SO42- in the past, which makes it difficult to compare SO42- contents of soils. Sulfate was extracted with the four commonly used extraction solutions 0.5 M NaHCO3, 0.02 M NaH2PO4, 0.1 M NaCl and H2O from A-, Bw- and Bs-horizons of six acid forest soils. 5 g of field moist soil were percolated with a flow rate of 5 ml/h and percolations were repeated as long as SO42- was detectable in the percolate (< 0.5 mg SO4 . l-1). NaCl and NaHCO3 extracted highest amounts of total inorganic SO42- in A-horizons, but NaHCO3 caused analytical problems. NaHCO3 and NaH2PO4 yielded highest amounts in B-horizons. With the exception of Bs-horizons more than 70% of the total inorganic SO42- was H2O-soluble. Thus, if H2O-soluble SO42- is defined as reversibly bound, the greater part of the inorganic SO42- fraction can potentially be released, if SO42- deposition decreases.