Effects of lime and two incubation techniques on sulfur mineralization in a forest soil

Abstract

Limed and unlimed mor humus was incubated at 15°C in an open system and a closed one to evaluate the sulfur mineralization capacity in a Norway spruce stand in southern Sweden. Samples were collected 6yr after dolomitic lime (8800 kg ha −1) had been applied to determine the long-term effect of liming on sulfur mineralization. The open-incubation columns were periodically leached with a simulated throughfall solution, lacking sulfate. Soil in the open and closed incubation vessels was destructively sampled and extracted with distilled water. Extracts and percolates were analyzed for NO 3 −1, SO 4 2− and total S. Soil microbial activity was monitored as CO 2 evolution. The open incubation resulted in a higher net S mineralization in both the limed and control humus; i.e. 24.47 vs 14.17 and 13.60 vs —0.60μg SO 2− 4-S g −1 dw 82 days −1, in the control and limed treatment respectively. Nitrate formation was mainly affected by the liming itself, and differences related to incubation technique were only observed in the control treatment. Limed humus had a lower net S mineralization regardless of the incubation technique used. Organic S leaching from the open incubation columns was higher in the limed treatment than in the control, 17.6 and 6.9μg Sg −1dw 82 days −1, respectively. Limed humus had the highest microbial activity irrespective of the incubation technique. Immobilization of sulfate seemed to be greater in the limed incubation than in the control. The fact that the organic C-to-S ratio was lower in the limed percolation water than in the control also indicates that such a difference exists.