Farmers in the upper North Island are concerned about the poor productivity of their perennial ryegrass pastures beyond 3 years and suggest this is linked to a trend towards drier conditions for pasture growth during summer and autumn. To explore how conditions for pasture growth and survival have changed, trends in rainfall (measured and interpolated; c. 1954 to 2020), frequency of soil moisture deficit stress on pasture growth (1972-2020), and pasture growth rates (simulated 1977-2020, and measured c. 1979-2020) were compiled for summer-autumn months (November to April) for two Waikato locations: DairyNZ Ruakura/Scott Farm near Hamilton; and a commercial farm at Paratu Road between Morrinsville and Matamata. Significant negative linear trends were observed for interpolated rainfall (Paratu Road only), total stress days (both sites) and simulated pasture growth (both sites). No significant trend in measured pasture growth was observed for either site, suggesting adaptive management has cushioned the physical effects of harsher climatic conditions. The suite of adaptive management practices adopted on the Paratu Road farm is described. Analysis of decadal patterns indicated greater variability in rainfall in the decade 2011-2020 (coefficient of variation ranging from 32% to 36% depending on site and data source, versus ~ 22% in earlier decades) and a significantly higher number of stress days in the decade 2011-2020 compared with the 1970s and 1980s at Paratu Road. Further adaptation strategies will be needed to mitigate these most-recent trends, should they continue as predicted by climate change forecasts.
The persistence of both perennial ryegrass and white clover is challenged under summer-dry conditions. Future climate change projections indicate greater incidence and severity of summer moisture stress for many regions in New Zealand, and therefore, greater pressure on our traditional pasture base. The ‘Northland Diversified Forages Project’ aimed to identify alternative pasture species that provide an advantage in terms of dry matter yield, quality and/or timing of growth within a summer-dry environment, with a particular focus on legumes. A series of mown-plot trial and paddock demonstrations were established across a range of soil types to assess the potential of a wide variety of forage species. Perennial ryegrass and white clover both failed to persist, comprising less than 25% of the sward within 3 years of establishment. Cocksfoot demonstrated potential as a more persistent alternative to perennial ryegrass. However, whilst a range of legumes were successful at increasing the proportion of legume in the sward and total yield in the first year, significant challenges were identified in maintaining functional legumes across multiple years. This raises questions around whether we currently have the right species in New Zealand to adapt to a changing climate.
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