Forest soil sulfur in the Adirondack Mountains: Response to chemical manipulations

Chemical manipulations were conducted on plots during the growing seasons from 1991 through 1993 in four forest ecosystems (Woods Lake [WL], Pancake-Hall Creek [PHC], Huntington Forest [HF], and Pack Forest [PF]) in the Adirondack Mountains of New York. Sulfate was added as (NH₄)₂SO₄ (all sites at 1000 and 2000 mol_c ha^-1 yr^-1), H₂SO₄ (WL and HF at 1000 mol_c ha^-1 yr^-1), or (Ca,Mg)SO₄ (WL and HF at 1000 mol_c ha^-1 yr^-1). At WL and HF additional sets of plots were also treated with HNO₃ (1000 mol_c ha^-1 yr^-1). Soil solutions were sampled at 15 and 50-cm depths. Changes in the S constituents of the soil were evaluated by buried mineral soil bags installed below the forest floor. Additions of SO₄^2- increased solution SO₄^2- and total S and phosphate-extractable SO₄^2- in soil. Although organic S constituted >71% of the total soil S, no treatment effects on organic S were found. The response of SO₄^2- was not influenced by the form of addition. Extractable sulfate and soil solution SO₄^2- both increased with increases of (NH₄)₂SO₄. For the three hardwood sites (WL, PHC, and HF), there was a positive relationship (P<0.05) between soil solution SO₄^2- concentration at 15 cm and extractable SO₄^2- in soil bags, suggesting that these Haplorthod soils responded similarly to S inputs. For the Typic Udipsamment at PF, beneath red pine (Pinus resinosa Aiton), no such relationship was found. The similarity of response of Haplorthod soils suggests that similar soils across the Adirondack Mountains will show synchronous responses to S inputs.