Abstract A simulation model was developed as a conceptual tool for organizing information on sulfur-cycling in a grassland ecosystem. The model successfully simulated the concentration of sulfur in shoots of two plant-functional-groups over the course of two growing seasons, and seemed to represent realistically such processes as microbial mineralization—immobilization, sulfate adsorption by soil, and nematode consumption. The greatest transfers of sulfur in the system were between soil sulfate and microorganisms. Various turnover rates were calculated, ranging from 3 × 10 −5 yr −1 (of the total labile sulfur) for the most resistant components of humus, to 10 yr −1 for the highly labile metabolic litter component. Only 2–4% of the total system-flux of sulfur was reapportioned among system components, indicating that the model system was near equilibrium.