Net sulphur mineralization in forest soils as influenced by different lime application rates

Long-term effects of liming on net sulphur mineralization in coniferous forest O horizons were studied in three laboratory experiments by an open incubation technique, in which net sulphur mineralization was estimated from the accumulated SO42− leaching during the incubation period. Soil from two Swedish field experiments was used; Hasslöv (56°24′N, 13°00′E) and Norrliden (64°21′N, 19°46′E), which were limed 6–10 and 24 years before soil sampling with dolomite (CaMg(CO3)2) and calcium carbonate (CaCO3), respectively. The lime application rates were 0, 0.16, 0.35 and 0.88 kg m−2 of dolomite, and 0 and 0.5 kg m−2 of calcium carbonate. The net sulphur mineralization at Hasslöv 7 years after liming, decreased with increasing lime application rate (5.20, 4.93, 4.53 and 3.36 μg S column−1 day−1) while the soil respiration (CO2 release) increased in the two highest lime treatments. The observed inverse relationship between net sulphur mineralization (mineralization–immobilization) and soil respiration, the 0.16 kg m−2 treatment being an exception, indicated an increase in sulphur immobilization at increasing lime application rates. The control (0) and 0.88 kg m−2 treatments at Hasslöv were studied both 6, 7 and 10 years after liming. An inverse relationship between net sulphur mineralization and soil respiration could be shown on all three occasions. The results obtained in the Norrliden experiment 24 years after liming were more ambiguous than those of the Hasslöv experiment, but similar trends with respect to net sulphur mineralization and soil respiration could be traced during the latter part of the Norrliden experiment.