b'14Effects of plant diversity on yield in intensively managedgrasslandsGrange G1 , 2 , Brophy C2 and Finn JA11Crops, Environment and Land Use Programme, Teagasc, Johnstown Castle EnvironmentResearch Centre, Wexford, Co. Wexford, Ireland2Dept of Mathematics & Statistics, Maynooth University, IrelandMulti-species grasslands mixtures offer an opportunity to increase sustainable production from intensively managed European grasslands. We investigate the effects of mixing species and functional groups with the aim of improving forage yield and yield stability.A simplex design including six species monocultures and 13 mixtures is sown in 2017 in a field experiment in the south-east of Ireland. Three functional groups are represented: grasses(Lolium perenne L., Phleum pratens L.); legumes (Trifolium repens L., Trifolium pratense L.)and herbs (Cichorium intybus L., Plantago lanceolata L.) and combined to create monocultures of all six species, as well as 2-, 4-, 5- and 6-species mixtures within 1, 2, and 3 functional groups respectively. All experimental plots receive 150 kg ha-1 of nitrogen fertiliser per annum and a Lolium perenne monoculture with 300 kg ha-1 of nitrogen included as a comparison, represents standard Irish management. Above-ground biomass is harvested following a simulated grazing protocol.We measure dry matter yield and separate subsamples to identify species proportions.The total annual above-ground yield is compared between each community, and we quantifythe effects of species richness, and functional group richness.58'