Four-species grass-clover mixtures demonstrate transgressive overyielding and weed suppression over 3 years and across 31 sites

摘要

The use of multi-species mixtures has been proposed as one strategy to improve agricultural sustainability in grassland systems. We conducted a co-ordinated continental-scale field experiment at 30 sites across Europe and one in Canada to investigatethe relative resource utilisation (measured as aboveground biomass yield of the sown species) of monocultures and four-species mixtures in experimental grassland plots. Over all sites and years, comparisons of the yield of sown species (weeds excluded) demonstrated strong yield benefits associated with mixtures. Average annual yield of the mixtures was better than the best-performing monoculture in 79% of mixtures and at about 70% of sites, with an average yield ratio of 1.18 (mixture yield/best monoculture yield). By year 3, mixtures contained a median percentage of weed biomass of 3% and, thus, were much more resistant to weed invasion than monocultures (median = 32% weeds after 3 years). The yield benefits were quantitatively related to sward evenness, and were robust to changes in the relative abundance of the four component species. These benefits established quickly (within the first year), persisted for at least 3 years, and were evident across sites with very different soils and climatic conditions.