Measurement of Pasture Growth, Parameterization for Tropical Grass and Validation of the GrassGro Model

Abstract

The GrassGro model was evaluated using 1995 experimental data from the Temperate Pasture Sustainability Key Program conducted at the Big Ridge 2 experimental site at CSIRO's "Chiswick" farm. The experiment was designed to measure changes in feed on offer (∆FOO) using the exclosure technique on three pasture types: Phalaris ('Phalaris aquatica'), Phalaris-white clover ('P. aquatica-Trifolium repens') and 'degraded' (a mixture of C₃and C₄pasture species). The model was calibrated for daily growth rate (DGR) and ∆FOO under grazed and ungrazed conditions for the three pasture types. The parameters for phalaris and white clover pastures supplied with the model were accepted for simulation. A set of model parameters was developed for 'Eleusine tristachya', which was the major contributing species in the 'degraded' pasture. ... Once calibrated, the model was used to simulate the pasture growth under different climatic regimes (Cooma, Armidale and Canberra) and choice of lambing time for matching animal demand to the pasture supply on the Northern Tablelands of New South Wales. The simulated results agreed well with the information provided by various sources.