Dynamics of arable weeds communities in spring and winter wheat under different legume pre-crops during organic conversion

The transition from conventional to organic farming alters weed communities, their abundance, and competitive interactions with crops. This study assessed changes in annual arable weed communities in winter and spring wheat during the conversion from conventional to organic farming, in relation to different legume preceding crops: peas (P), soybeans (S), a vetch–oat mixture (VOM), and spring barley undersown with red clover (SB+RC). The results showed that during the conversion period, weed species richness, total weed emergence, and the abundance of harmful weed species increased. In the legume cropping years, SB+RC provided the most effective weed suppression, whereas soybeans were the least effective. Weed abundance and biomass were lower in winter wheat than in spring wheat, indicating greater competitive ability of winter wheat. Legume preceding crops generally increased cereal competitiveness and reduced weed biomass, while the effect of SB+RC on weeds differed from other legume treatments. The highest individual weed biomass was recorded for Galium aparine and Fallopia convolvulus , and by the end of the study the most abundant communities were dominated by G. aparine and Veronica arvensis . Overall, weed emergence, abundance, and community structure in cereal crops are strongly influenced by crop type, pre-crop effects, environmental conditions, as well as species-specific biological and ecological traits of weeds, underscoring the need for integrated and context-dependent management strategies.