Weed control under increasing cover crops diversity in tropical summer and winter.

Description of the subject. Weed pressure is a main biotic constraint in tropical agriculture. Cover crop mixtures have increased in popularity to limit weed growth through competition for shared resources, but the relationship between cover crop diversity and weed suppression is still under debate. Objectives. This study aimed to assess the impact of increasing cover crops diversity (one to four species) on weed control during two growing seasons (tropical summer and winter) in Reunion Island. Methods. Weed control was expressed regarding ground cover by weeds and weed aboveground dry mass and linked to cover crop traits in the mixtures during four months of growth. Results. While cover crops reduced weed ground cover and dry mass by 60% and 68% on average in summer and winter, respectively, a higher number of cover crops species within a mixture did not increase mean weed control but decreased weed control variability in summer. Additionally, cover crop traits explaining weed control differed between growing seasons. In summer, weed control was mainly explained by the final cover crop aboveground biomass and leaf area (depletion strategy). In contrast, weed control was mainly explained by the cover crop rate of increase in ground cover (obstruction strategy) in winter. Conclusions. Using functional traits to characterize cover crop mixture enables us to identify mixture of species and traits adapted to different growing conditions. Despite being limited to one service, future studies could use this approach to assess the relationship between diversity and the multifunctionality of cover crop mixtures