A comparison of the productivity and nutritive value of multispecies swards to perennial ryegrass monocultures and permanent pastures

Reducing reliance on fertiliser nitrogen (N) is key to enhancing the sustainability of temperate grassland systems. Multispecies swards (MSS) have the potential to reduce the need for inorganic N inputs while enhancing herbage yields. Therefore, the objectives of this thesis were i) determine herbage productivity, nutritive value and species contributions to herbage dry matter (DM) from four swards - perennial rye grass (Lolium perenne L.) (PRG), permanent pasture (PP), a six species (6S) and a twelve species sward (12S) under both grazing and plot-scale experimental conditions. ii) investigate the effects of establishment method and nutrient input type on sward productivity, nutritive value and contribution of species to herbage DM. In the grazing experiment, PRG received 170 kg N ha-1 yr-1, PP received 135 kg N ha-1 yr-1 and MSS received 70 kg N ha-1 yr-1. In the plot experiment, similar N rates were applied, except for PP, which received 70 kg N ha-1 yr-1 with N applied as either inorganic N, cattle slurry, or a combination of both. Two establishment methods for sown swards were evaluated: direct drilling and conventional cultivation. The findings across both experiments indicate that MSS can produce higher herbage DM yields with reduced N inputs compared to PRG and PP. In the plot study, establishment method had no impact on herbage DM production. However, as inorganic N was replaced with cattle slurry, the productivity of PRG and PP reduced, whereas both MSS were unaffected by nutrient input type. In the grazing experiment, despite being managed at a higher pre-grazing herbage mass compared to PRG and PP, MSS maintained comparable nutritive val-ue to PRG, while PP exhibited lower overall herbage nutritive values. Herbage from both MSS had higher overall mineral concentrations compared to PRG and PP. In the grazing experiment, the proportional contribution of herb species to herbage DM declined across years, while the contribution of grass increased. In the plot experiment, both establishment method and nutrient input type in-fluenced the nutritive value of the swards and could be mainly attributed to the changes in botanical composition observed across the different treatments. The findings of this thesis indicate the incorporation of MSS into intensive grazing systems can substantially reduce inorganic N fertiliser requirements without compromising herbage productivity or nutritive value.