Natively retained sulfate and its effect on the acid buffering capacity of andosols

Ninety-one soils from non-agricultural Andosols in Japan were analyzed for natively retained SO42− (phosphate-extractable). Retained SO42− ranged from 0.4 to 63.5 mmol kg−1, and correlated with the active Al content. Sulfate adsorption isotherms of 22 soils were determined to estimate the lowest concentration of atmospherically-deposited SO42− to be adsorbed by each soil. This varied among the Andosols, ranging from 0.01 to 0.8 mmol l−1; as a consequence, some soils had difficulty in adsorbing deposited SO42− due to the large amounts of SO42− already retained. From multiple regression analysis, SO42− adsorption capacities of Andosols were shown to depend largely on the form and the amount of active Al.