Multispecies grasslands produce more yield from lower nitrogen inputs across a climatic gradient

High-yielding forage grasslands frequently comprise low species diversity and receive high inputs of nitrogen fertilizer. To investigate multispecies mixtures as an alternative strategy, the 26-site international ‘LegacyNet’ experiment systematically varied the diversity of sown grasslands using up to six high-yielding forage species (grasses, legumes, and herbs), managed under moderate nitrogen inputs. Multispecies mixtures outyielded two widely used grassland practices: a grass monoculture with higher nitrogen fertilizer, and a two-species grass-legume community. High yields in multispecies mixtures were driven by strong positive grass-legume and legume-herb interactions. In warmer sites, the yield advantage of legume-containing multispecies mixtures over monocultures and the high-nitrogen grass increased. Improved design of grassland mixtures can inform more environmentally sustainable forage production and may enhance adaptation of productive grasslands to a warming climate.