Long-term research has provided a great deal of information regarding the influence of management on the equilibrium dynamics of soil organic matter (SOM), although short-term dynamics remain largely uninvestigated. An improved approach to characterizing SOM dynamics in managed ecosystems would consider both short-term and long-term changes in content and composition. This approach and its implications are illustrated for an experimental site comparing agricultural management practices. Changes in soil C composition were assessed semiquantitatively using 13C natural abundance measurements, demonstrating their useful although rarely applied role in short-term studies. This information is a valuable complement to long-term data, since net differences since the site's inception fail to reveal a timeline marked by repeated changes in soil C content and composition. Such data are also useful for reinforcing and understanding long-term simulation models, which are typically driven by temporally dynamic events but are often fit against temporally sparse SOM data sets.