Field experiments were conducted in the experimental farm "La Higueruela" (CSIC) that, for the last 9 years has been managed with three crop rotations and two tillage systems (no-tillage and conventional tillage). The crop rotations were barley-->vetch, barley-->sunflower, and barley monoculture. The results showed a increase in the number of different weeds species: Amaranthus albus, Anacyclus clavatus, Arabidopsis thaliana, Dmba verna, Papaver rhoeas, Portulaca oleracea, Scandix pecten-veneris, Torilis nodosa and Veronica triphyllos. On the contrary, the presence of Polygonum aviculare and Raphanus raphanistrum was higher in the plots under conventional tillage system. As regards crop rotations, the number of seeds or fruits of A. thaliana, Convolvulus arvensis, D. verna and T. nodosa were greater in the plots with barley-->vetch rotation, Chenopodium album in the plots with barley-->sunflower rotation and S. pecten-veneris in those with barley monoculture.