Calcium content of liming material and its effect on sulphur release in a coniferous forest soil

Soil columns with O + A (Experiment I) or O horizons (Experiment II) from a Haplic Podsol were incubated at 15 degrees C for 368 and 29 + 106 days, re spectively. Three types of liming material differing in Ca-2+ content, i.e. calcium carbonate (CaCO3), dolomite (CaMg(CO3)(2)) and magnesium carbonate (MgCO3), were mixed into the O horizons in equimolar amounts corresponding to 6000 kg of CaCO3 per ha. In the limed treatments of Experiment I, the l eaching of dissolved organic carbon (DOC) and the net sulphur mineralizatio n (estimated as accumulated SO42- leaching corrected for changes in the soi l pools of adsorbed and water extractable SO42-) increased with decreasing Ca2+ content of the lime and increasing degree of lime dissolution. In rela tion to the control treatment, only the MgCO3 treatment resulted in a signi ficantly higher net sulphur mineralization. In Experiment I the net sulphur mineralization was 4.06, 1.68, 0.57, and 2.14 mg S in the MgCO3, CaMg(CO3) (2), CaCO3 and control treatment, respectively. The accumulated SO42- leach ing in Experiment II during the first 29 days was 1.70, 0.74 and 0.48 mg S in the MgCO3, CaMg(CO3)(2) and control treatment, respectively. In the two experiments there were consistently significant positive correlations betwe en leached amounts of SO42- and DOC. It was concluded that net sulphur mine ralization was strongly connected to the solubilization of the organic matt er (DOC formation) and that pH and/or Ca2+ ions affected the net sulphur mi neralization through their effects on organic matter solubility.