Final Site Report Western Australia

Summary

Grazing systerns in the high rainfall zone of southwest Australia involve beef, dairy and to a lesser extent prime lamb and wool production on annual-based pastures. Typically these pastures comprise of subterranean clover and ryegrass which has been invaded by cornrnon pasture weeds. Up to a third of the agricultural land within this part of Australia is threatened by salinisation. The salt originates from the ocean and is deposited inland at a rate of 20 to 200 kg/halannurn by prevailing winds.

In combination with poor drainage, this process has resulted in up to 10,000 tonnes of salt being stored under every hectare in the southwest of Western Australia. This salt along with the groundwater is rising as a consequence of replacing the deep-rooted native vegetation with shallow-rooted crops and pastures. The original native vegetation maintained a hydrological balance by utilising excess winter rainfall at other times of the year. However, once this vegetation was replaced by shallow rooted species this balance was upset and the groundwater began to rise at rates between 0.15 and 1.5 m/annum.

If current agricultural practices continue, potentially 6.1 million ha of land will be affected by dryland salinity once the groundwater reaches a new equilibrium. Not only will dryland salinity affect agricultural production, but it will also have a negative impact on water resources, infrastructure (e.g. roads and towns) and native flora and fauna (e.g. freshwater wetlands). Farrners with the support of the comrnunity are faced with the enormous challenge of replacing current agricultural systems with ones that are both productive and sustainable. Previous research has shown that pastures in the high rainfall zone, whether based on either perennial or annual species, will require integration with trees to restore the hydrological balance. By contrast, perennial pastures alone may be able to restore the balance in the less than 600 rnrn rainfall zone.