SGS Pasture Theme: Effect of climate, soil factors and management on pasture production and stability across the high rainfall zone of southern Australia

The Sustainable Grazing Systems (SGS) National Experiment (NE) Pasture Theme explored factors that influenced annual herbage accumulation and perennial grass and legume content across the NE sites, in the high rainfall zone (HRZ, >600 mm/year annual rainfall) of southern Australia using multi-variate analysis and the SGS Pasture Model. Annual rainfall was a poor predictor of annual herbage accumulation. The length of growing season accounted for 30% of the variation in annual herbage accumulation. Much of the remaining 70% of variation in annual herbage accumulation was explained by soil Olsen P, the proportion of native species in the pasture and stocking rate, together with interactions among other factors including legume content. Simulated effects of set stocking and rotational grazing on herbage accumulation using the SGS Pasture Model, predicted that rotational grazing was unlikely to result in large increases in herbage accumulation. In contrast, it was predicted that the adoption of deep-rooted C₃ and C₄ perennial grasses could provide useful increases in herbage accumulation. Perennial grass content and basal cover were both significantly influenced by growing season length (P <0.001), grazing method (P <0.001) and an interaction between stocking rate and soil pH (P = 0.002). These analyses suggested that to maintain or improve the perennial grass component of a pasture at medium-high stocking rates, it was crucial to adopt grazing strategies that included rotation or resting. Perennial grass percent also significantly (P<0.001) increased in response to ameliorating the soil pH. Legume content of pastures significantly (P<0.001) increased in response to set stocking and increased stocking rate. To be botanically stable and productive, sown pastures based on perennial grasses in the HRZ of southern Australia will need to be grazed at high stocking rates (15-23 DSE/ha) in combination with rotational grazing or resting, and with adequate soil P. Additional gains in production and stability could be obtained by ensuring an adequate legume component, including a C₄ perennial grass and ameliorating soil acidity. Pastures based on native perennial grasses may require lower soil P and more conservative stocking rates, depending on species.