One way of preventing crop weeds is to reduce soil seed banks. Does introducing a perennial plant cover in a crop rotation system help reduce soil seed bank and weed density in subsequent crops? In order to answer this question, a Tall fescue perennial cover was introduced in a crop rotation system. Changes in soil seed bank were determined by counting germinated and non-germinated seeds. The number of germinated seeds on the ground was fairly low (2 346 to 7 877 seeds/m2), with important variations from one year to the next, depending on plant species present in the plant cover and their seed set. In spite of these variations, the perennial plant cover helped reduce the number of seeds belonging to certain weed species that are harmful for cereal crops.