However, species composition varied among years, probably related to differences in environmental conditions and field cropping histories. Weeds would have differently responded to the contrasts between crops seasons in the rainfall accumulated, which was higher in Exp. 1 (988 mm) than in Exp. 2 (678 mm). The same response was observed in previous research on sole crops in the Pampas [16], [22], [35], [36] and [37]. On the other hand, differences could also be related to the availability of propagules, since both experiments were performed in fields belonging to different farmers.