REVERSIBILITY OF SOIL SOLUTION ACIDITY AND OF SULFATE RETENTION IN ACID FOREST SOILS

To quantify the effects of reduced sulfate input on the chemistry of s oil solution and soil S storage in acid forest soils, an experiment wi th undisturbed soil columns from two different sites was implemented. The acid cambisol of the Solling is subjected to a high sulfate input and especially the B-horizon has a high sulfate content. On the contra ry, the podzol of the Fuhrberg site is subjected to low input and has low sulfate content. Undisturbed soil columns were taken from both sit es and were irrigated at 6-degrees-C with a precipitation rate of 3 mm d-1 over 10 mo. In treatment No. 1, an artificial throughfall with pH 5.2 and reduced sulfate load (45 mumol L-1) was applied. In treatment No. 2, an artificial througfall representing a high sulfate depositio n (427 mumol L-1, pH 3.2) was used. In case of the Solling soil, the p H of soil solution was unaffected by treatments during the entire expe riment. Alkalinity of the soil solution was slightly increased in trea tment No. 1 at a depth of 20 cm. While treatment No. 1 resulted in a r eduction of the sulfate concentrations of the soil solution in the top soil, sulfate concentrations were unaffected at a depth of 40 cm. The B-horizon of the Solling soil prevented deacidification of the soil s olution by desorption of previously stored sulfate. In case of the Fuh rberg soil, treatment No. 1 resulted in reduced sulfate concentrations of the soil solution even in deeper soil layers with concentrations a pproaching input levels. The pH of the solution was slightly elevated and the alkalinity of the solution increased. Organic S compounds in t he soil seemed to have no influence on sulfate release in either soils .