Highly accumulated sulfur constituents and their mineralogical relationships in Andisols from central Japan

To understand sulfur (S)-accumulating systems of Andisols in Japanese forests, this study examined the contributions of inorganic sulfate and organic S to S accumulation. The profiles showed high total S concentrations of 540 to 2240 mg S kg− 1. These high concentrations resulted in large pools of total S, ranging from 3370 to 8520 kg S ha− 1 to 1 m depth. The sulfate concentration determined using a method combining 0.1 M Na4P2O7 and 0.2 M acid ammonium oxalate extraction was higher than that determined by the conventional solvent Ca(H2PO4)2. The additional sulfate, likely dominated by the precipitate form in sulfate-bearing minerals and the occluded form in short-range ordered minerals, ranged in concentration from 0 to 850 mg S kg− 1 and accounted for 11% of the total S concentration. Values for Melanic Andisols (Melanudands) were larger than previously reported values for other soil orders. A significant correlation was found between the additional sulfate and soil mineral properties. These results suggest that the type of parent soil and its weathering degree are important in retaining additional sulfate. In the studied soils, approximately half of the accumulated S was inorganic forms of sulfate, with a ratio of organic S to inorganic sulfate of 55:45. The other half was organic S, 40% of which was the Al-associated form. Andisols have a high ability to consume acids by retaining sulfates and stabilizing organic S in the process of S dynamics.