Weed community in crop rotation and in a 33-35-year winter wheat monoculture

The formation of weed communities in agricultural crops is determined by habitat conditions, soil fertility, and agricultural practice deployed. A multi-year experiment evaluated the species composition, the number and air-dry weight of weeds in winter wheat, the horizontal (layered) distribution of weeds in the canopy as well as values of Shannon-Wiener’s diversity index and Sørensen’s similarity coefficient in a weed community. Winter wheat was sown in a crop rotation: potato – winter wheat – peas – winter durum wheat and in a 33–35–year monoculture. Weed infestation indices were evaluated at the tillering stage and the milk maturity stage of winter wheat. At both developmental stages of winter wheat, an almost 3-fold higher number of weeds was recorded in the monoculture than in the crop rotation. Also, the air-dry weight of weeds was higher in the monoculture than in the crop rotation at both developmental stages compared. Weeds of the upper and middle levels accounted for 82–92.3% of the weed community in the crop rotation and for 98.5–100% in the monoculture. A higher value of the Shannon-Wiener’s biodiversity index was computed for the weed community from the crop rotation than from the monoculture. In turn, the Sørensen's similarity coefficient of the weed community reached 70–76% at the tillering stage and 68–78% at the milk maturity stage of winter wheat.