Extending the pasture model in the GRAZPLAN decision support system to evaluate management practices for maintaining improved pastures

Summary

The aims of this project were to

(i) improve our understanding of the factors influencing early growth in pastures, and

(ii) use this understanding to improve the ability of the GRAZPLAN pasture model (as used in the GrassGro decision support tool) to predict changes in pasture composition.

The improved model will be valuable in predicting the impact of pasture management practices on the sustainability and profitability of grazing enterprises in southern Australia. Graziers frequently experience a loss of legumes and perennial grasses from pastures. These pastures are invaded by less productive annual grasses and broadleaf weeds. In the Sustainable Grazing Systems Key Program, experiments are underway at a number of sites to devise strategies to arrest the decline in pasture composition and productivity.

However, determining strategies for the long-term sustainability of grazing systems cannot be achieved quickly or economically by experimentation alone. GrassGro can be used to evaluate the long-term outcomes of pasture management strategies provided that changes in pasture composition can be simulated adequately. In many situations, GrassGro simulates compositional changes realistically. However, there are also some cases where the model fails to predict actual pasture change. This project comprised experimentation and modelling to develop an improved version of the GRAZPLAN pasture model so that it can be used more reliably in developing sustainable and profitable pasture management practices for the grazing industries.