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RESEARCH PRODUCT

Weed suppression in cover crop mixtures under contrasted levels of resource availability

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Cover crop (CC) mixtures appear as a promising agroecological tool for weed management.Although CC supress weed growth by competing for resources, their suppressive effect undercontrasting levels of soil resource availability remains poorly documented. A two field: yearexperiment was conducted to investigate the weed suppressive effect of four CC mixtures.They were composed of 2 or 8 species including or not legume species and compared to abare soil control. The experiment included two levels of irrigation and nitrogen fertilisation atCC sowing. The objectives were to assess (i) weed and CC aboveground biomass response toCC mixtures and resource availability, (ii) the weed suppressive effect of CC mixtures across agradient of CC biomass and (iii) weed community response to CC mixtures and resourceavailability. CC and weed biomass were mainly influenced by interactions between CCmixtures and fertilisation and between CC mixtures and irrigation, with contrasted effectsbetween field: years. Nitrogen fertilisation increased biomass of non-legume based CCmixtures but this only resulted into a further reduction of weed biomass of little biologicalrelevance. Legume-based CC mixtures suppressed weeds to a greater extent without nitrogenfertilisation in year 2 but not in year 1, possibly due to contrasted initial soil nitrogenavailability (lower in year 2). Weed biomass generally benefited more from irrigation than CCmixtures. Among the 33 weed species recorded, weed communities in each plot weredominated by wheat volunteers, Geranium dissectum, Veronica persica and Echinochloa crusgalli, whose biomass varied depending on the interaction between year, CC mixture andresource availability. Our results revealed that competitive outcomes between CC mixturesand weed species were driven by a complex interaction between resource availability andspecies traits. Further experiments focusing on plant traits should improve our understandingof weed: CC competitive outcomes under various levels of resource availability.