Effect of three tillage systems on weed flora in a 3-year rotation with four crops

Field experiments were conducted to determine the effect of tillage on the dry weight, frequency (PF), density (PD) and species composition of the weed population. Three tillage systems (CT: conventional tillage, MT: minimum tillage and NT: no tillage) were compared in a 3-year rotation [wheat-vetch (green manure) cotton-barley]. Decreases in PF, mean PD and number of species were observed under NT because in this system the soil remains undisturbed, and conditions art not suitable for seed germination. In contrast, annual weeds had a higher PF under the CT system, because they mainly propagate by seed and soil tillage creates more favourable growth conditions; thus they also had a higher PD. The hight st PF and PD were found for the species Sinapis arvensis and Solanum nigrum. Perennial weeds had higher PD under the NT system, because their roots cannot be destroyed by soil tillage, The number of species was not altered in CT and MT, but was decreased in NT. In winter crops, annual species under CT and MT, and perennial species under NT were observed. In cotton crops, perennial species under CT and MT, and annual species under NT were observed. The mean PD of weed species in the first crop followed the sequence NT > MT > CT and in subsequent crops followed the reverse sequence CT > MT > NT.