Modelling perennial ryegrass (Lolium perenne) persistence and productivity for the Upper North Island under current and future climate

The objective of this study was to predict the future performance of perennial ryegrass in the Upper North Island, New Zealand. The Basic Grassland model, BASGRA, was used with historic, current and future daily climate data as input, and soil water holding capacity, to predict changes in perennial ryegrass performance in space and time. The study focussed on land of ≤7° slope north of the town of Tokoroa and considered two potential warming pathways to the end of the 21st century. Persistence was defined as the time in years for the ryegrass sward to decline to 50% ground cover. The results for the two climate pathways were largely consistent with each other. Persistence should remain in the medium category (2.5-3.4 years, 10-12 t DM/ha) for the rest of this century for Bay of Islands, Whangarei, South Waikato/Tokoroa, and Rotorua. Persistence is predicted to change from medium to predominantly low (0-2.4 years, <10 t DM/ha) for Far North, Dargaville, DairyFlat/Rodney, Waiuku/Pukekohe and northern and central parts of Waikato. Coastal regions of Bay of Plenty were predicted to be poorly suited to perennial ryegrass and to remain so into the rest of the century. Large parts of the Upper North Island that are currently borderline for perennial ryegrass are predicted to become unsuitable for the species.