Optimisation of perennial ryegrass, white clover and plantain mixtures for maximum dry matter yield in an intensive pasture system

Traditional methods used to formulate pasture mixtures provide limited ability to identify the optimum mixture of constituent species. This study used a simplex design approach to identify an optimum mixture of perennial ryegrass, white clover and plantain for maximum dry matter (DM) yield in an intensive pasture system. Three monocultures and seven mixtures of the three species were chosen based on a simplex centroid design, sown at two sowing rates (1000 and 2000 seeds/m²) and grown with or without N fertiliser (275 kg N/ha) at Lincoln, New Zealand. Swards were rotationally grazed by sheep and irrigated. Yield after 14 months was not affected by sowing rate, but rather on the relative abundances of species in the pasture mix and N fertilisation. The optimal proportions of species in the seed mix for maximum yield were 0.342 perennial ryegrass, 0.254 white clover and 0.404 plantain, sown at 1000 seeds/m² and fertilised with 275 kg N/ha. This combination produced a maximum yield of 29.9 t DM/ha. The optimal seed mix was equivalent to 8.3 kg perennial ryegrass, 3.6 kg white clover and 7.6 kg plantain (19.5 kg total seed/ha at the low sowing rate). However, perennial ryegrass and plantain became dominant in the mixtures at the expense of white clover over time, especially with N fertiliser. These changes in botanical composition meant that the optimal balance of species in the resultant pasture was 0.40 perennial ryegrass, no white clover and 0.60 plantain with 275 kg N/ha, and this combination yielded 28.7 t DM/ha