The termination of agricultural production in intensively managed fields leads to the succession of weed communities and to changes in the vegetation cover and food supply for animals. We studied a population of the common vole on a regularly managed alfalfa field in southern Moravia (Czech Republic) during two and a half consecutive years. When the field was set aside, the vegetation cover transformed significantly and we studied the same vole population for the next three years. Multi-annual variation in population size disappeared; maximal abundances decreased, and mean body size tended to be lower in the weed-filled habitat. We observed conspicuous seasonal patterns in the proportion of breeding females, sex ratio and in litter size variation; however these patterns did not depend on the field management regime. The set-aside field had a strong effect on vole population dynamics; however, other well-designed studies are needed to distinguish between the possible causal processes (immigration, natality or survival) of the observed changes.