The importance of species selection in cover crop mixture design.
McKenzie-Gopsill A, Mills A (2022) The importance of species selection in cover crop mixture design. Canadian Weed Science Society/ Canadian Society of Agronomy Joint Annual General Meeting, Nov 14-17th 2022, Halifax NS, Canada
Plain language summary
Cover crops are being adopted into crop rotations as a way to increase diversity and provide natural benefits including reducing weeds. Recent studies have suggested biomass of cover crop mixtures may be more important than diversity for weed reduction. To investigate productivity and weed suppression of cover crops and mixtures of different cover crops researchers assessed 19 cover crop species and 19 mixtures of two or three cover crops grown over a full season in Atlantic Canada. More diverse cover crop mixtures provided greater productivity and weed suppression. Highly productive species grown individually and diverse mixtures provided the greatest suppression of weeds. Moreover, cover crop mixtures containing highly productive species resulted in the greatest diversity and weed suppression. Similarly, these mixtures provided the greatest year-over-year stability. Our results suggest that the effects of biomass and diversity on cover crop productivity and weed suppression differ by species. This highlights the importance of species selection in deciding which cover crop to use.
Cover crops are increasingly being included in crop rotations as a mechanism to promote diversity and provide agroecosystem services including weed suppression. Recently, cover crop mixtures have increased in popularity in an attempt to provide a greater diversity in ecological services as compared to monocultures. Several recent studies, however, have failed to detect a positive effect of cover crop diversity on biomass production or weed suppression. Here we assessed biomass productivity and weed suppression in 19 cover crops seeded as monocultures and 19 mixtures of varying species composition and functional richness (2- and 3-species mixtures) of full-season cover crops in Atlantic Canada. Cover crop biomass production and weed suppression varied by species identity, functional diversity, and species richness. As cover crop biomass increased regardless of diversity, weed biomass declined. Highly productive forbs and grasses provided the greatest weed suppression in monoculture. In line with previous observations, mixtures were on average not more productive nor weed suppressive than the most productive monocultures. We observed that the inclusion of the highly productive species buckwheat and sorghum-sudangrass in a mixture increased stand evenness, productivity, weed suppression and spatiotemporal stability. Taken together our results suggest that effects of diversity on mixture productivity and weed suppression are species specific. This further demonstrates the importance of species selection in cover crop mixture design.