Annual dynamics of soil organic matter in the context of long‐term trends

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.