Comparing Weed Abundance and Composition in Conventional Tillage vs. Early-Phase Conservation Agriculture Incorporating Winter Cover Crops

Conservation agriculture has been promoted as an alternative to conventional cropping systems to mitigate environmental pressures stemming from intensive tillage. Management practices in conservation agriculture can affect weed presence both within and between growing seasons. This study examined how recently adopted conservation agriculture, integrating no-till and cover crops, affected weed dynamics in a Mediterranean annual cropping system. Weed density, cover, richness, diversity and composition were compared between conventional and conservation agriculture during the inter-crop period and the early establishment of maize, the cash crop. Weed surveys were conducted in large-scale experimental plots during both sampling seasons over two consecutive years (2021-2022). During the inter-crop period, weed density was consistently lower in conservation agriculture than in conventional agriculture (10.1±1.9 vs. 63.0±14.4 plants m -2 in 2021, respectively), whereas weed cover responses varied between years. During the early maize establishment, conservation agriculture reduced weed density and cover (11.6±3.17 vs. 25.2±11.0 plants m -2 and 1.0±0.53% vs. 4.6±2.47% cover in 2022). Weed species richness was low (5-16 species) and varied across cropping systems, sampling seasons and years, while Shannon diversity was overall higher under conservation agriculture. Species composition and dominant species differed significantly between cropping systems and sampling seasons. Maize yield was similar between cropping systems, although a decrease was observed under conservation agriculture in 2022. This study highlights the importance of the transitional phase following conservation agriculture adoption, which is characterized by rapid changes in weed species composition. Furthermore, conservation agriculture demonstrates potential as a sustainable option for early-season weed control. • Weed dynamics rapidly change during the transition to conservation agriculture • Conservation agriculture reduced weed density and cover • Weed diversity in conservation agriculture equals or exceeds conventional cropping • Distinct weed communities thrive in conservation and conventional agriculture