Sulfate retention and cation leaching of forest soils in response to acid additions

A vacuum extractor was used to examine the effects of increased SO₄ ^2- deposition on net S retention and cation leaching in 3 Maine Spodosols and an Illinois Alfisol. Columns were constructed using O horizons over upper B (Bh or Bhs) and lower B (Bhs or BC) horizons for the Spodosols and two depth increments of bulked soil (0-12 and 12-25 cm) for the Alfisol. Columns that received the high-S treatment retained a greater percentage of the added S than those that received the low-S treatment because of increased SO₄ ^2- adsorption in the former. High rates of net organic S mineralization were found for all soil types; no treatment effects were found for the amount of S mineralized. Trends in net S retention across soil type (within the same treatment) reflected increases in soil SO₄ ^2- from adsorption, as well as decreases in organic S from mineralization. When net S mineralization was removed from leaching losses of S, trends in net S retention closely reflected SO₄ ^2- adsorption differences. Because of the low SO₄ ^2- adsorption capacity of the Alfisol relative to the Spodosols, organic processes were more important in affecting net S retention for the Alfisol. Inorganic processes of S retention were more important for the 3 Spodosols studied. -from Authors