Simulating pasture growth rates in Australian and New Zealand grazing systems
B. R. Cullen A H , R. J. Eckard A , M. N. Callow B , I. R. Johnson C , D. F. Chapman A , R. P. Rawnsley D , S. C. Garcia E , T. White F and V. O. Snow GA Faculty of Land and Food Resources, University of Melbourne, Vic. 3010, Australia.
B Department of Primary Industries and Fisheries, Mutdapilly Research Station, Peak Crossing, Qld 4306, Australia.
C IMJ Consultants, Armidale, NSW 2350, Australia.
D Tasmanian Institute of Agricultural Research, University of Tasmania, Burnie, Tas. 7320, Australia.
E University of Sydney, Camden, NSW 2570, Australia.
F AgResearch, Lincoln Research Centre, Christchurch, New Zealand.
G AgResearch, Grasslands Research Centre, Palmerston North, New Zealand.
H Corresponding author. Email: bcullen@unimelb.edu.au
Australian Journal of Agricultural Research 59(8) 761-768 https://doi.org/10.1071/AR07371
Submitted: 4 October 2007 Accepted: 28 April 2008 Published: 29 July 2008
Abstract
DairyMod, EcoMod, and the SGS Pasture Model are mechanistic biophysical models developed to explore scenarios in grazing systems. The aim of this manuscript was to test the ability of the models to simulate net herbage accumulation rates of ryegrass-based pastures across a range of environments and pasture management systems in Australia and New Zealand. Measured monthly net herbage accumulation rate and accumulated yield data were collated from ten grazing system experiments at eight sites ranging from cool temperate to subtropical environments. The local climate, soil, pasture species, and management (N fertiliser, irrigation, and grazing or cutting pattern) were described in the model for each site, and net herbage accumulation rates modelled. The model adequately simulated the monthly net herbage accumulation rates across the range of environments, based on the summary statistics and observed patterns of seasonal growth, particularly when the variability in measured herbage accumulation rates was taken into account. Agreement between modelled and observed growth rates was more accurate and precise in temperate than in subtropical environments, and in winter and summer than in autumn and spring. Similarly, agreement between predicted and observed accumulated yields was more accurate than monthly net herbage accumulation. Different temperature parameters were used to describe the growth of perennial ryegrass cultivars and annual ryegrass; these differences were in line with observed growth patterns and breeding objectives. Results are discussed in the context of the difficulties in measuring pasture growth rates and model limitations.
Additional keywords: DairyMod, EcoMod, SGS Pasture model, simulation models.
Acknowledgments
We acknowledge the contribution of Karen Christie (University of Tasmania) in developing the initial Elliott simulations, and thank Dr Jay Tharmaraj (University of Melbourne) and Kevin Lowe and Tom Bowdler (Department of Primary Industries and Fisheries) for the pasture growth rate data that they provided. Dr Jeremy Bryant (AgResearch) provided assistance with the statistical analyses. This work was funded by Dairy Australia, Meat & Livestock Australia, and AgResearch, New Zealand. The New Zealand sites were funded by the New Zealand Foundation for Science, Research and Technology (contract C10X0319).
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