Cover crops as a weed management strategy in Mediterranean horticulture: evidence from field experiments in Portugal

Sustainable intensification of horticultural systems requires effective weed management strategies that reduce reliance on synthetic herbicides while maintaining crop productivity. Agroecological practices, particularly the use of multispecies cover crops, are increasingly recognized as promising tools to reconcile weed suppression with environmental sustainability. This study assessed the effects of multispecies winter cover crop on weed dynamics in Mediterranean horticultural systems in central Portugal. Field experiments were conducted in two locations over two consecutive seasons (2023/2024 and 2024/2025) in industrial tomato and one season in chilli pepper and broccoli Bimi. Cover crop-based soil management was compared with conventional management without cover crops. Weed communities were assessed at three stages: before cover crop termination (T0), one month after main crop planting (T1), and before harvest (T2), using fixed transects to quantify ground cover, phenological development, and species composition. In tomato, cover crop management significantly reduced weed ground cover and delayed weed phenological development at T0 and T1, whereas differences were not detected at T2. In contrast, in Bimi and chilli pepper, effects on weed ground cover were weak or absent, although early-season phenological delays were observed in Bimi. Across crops, cover crops modified weed community structure by reducing the dominance of highly competitive species and promoting a more even distribution of relative abundance, particularly during early crop stages. The weed suppressive effects of cover crops were crop-dependent, with stronger responses observed in the multi-year tomato system. These findings indicate that multispecies cover crops function primarily as early-season modulators of weed dynamics and should be considered a complementary component of integrated weed management in Central Portugal horticultural systems.