The
Mallee Farmer
FIGURE 1 Distribution of volumetric soil water under the shrubs compared with an adjacent annual crop on the 27 May 2008 (left graph) and the 12 November 2010 (right graph) at the Walpeup Enrich field experiment.
survival and growth, both before and after grazing. Changes in soil water under the forage shrubs are also being monitored by means of comparison with an adjacent annual crop system.
Preliminary findings
In the first autumn after planting, shrub survival was around 90% for all species, except for the Pink Bindweed and Tall Verbine. By autumn 2010, populations of Tall Verbine had declined further, with a mortality rate approaching 50%. Measurements in November 2010 after the site was grazed showed a continuing decline in the populations of Tall Verbine and Tree medic, but most notable was the dramatically low survival rate in the Creeping Saltbush. Recent data suggests that Creeping Saltbush has made a recovery with the survival percentage apparently improving to 58%; although this may reflect that this species is a biannual, with prolific seedling recruitment aided by above average summer rainfall recorded at Walpeup between the sampling times. Shortly before grazing the site in May 2010, edible biomass was assessed for all shrub species; Old Man Saltbush produced significantly more biomass (1800g DM/plant or approx. 4t DM/ha) than all other species. The Silver and River saltbushes also produced over 1000g DM/plant (2.5–3t DM/ha). On the other end of the scale, the Tree Lucerne, Tree Medic and Tall Verbine shrubs produced less than 62g DM/plant (0.15t DM/ha). Sheep showed a preference for grazing Tree Medic, Tree Lucerne, Emu Bush, Creeping Saltbush, Mallee Saltbush and Tall Verbine. However, all species with the exception of Fragrant Saltbush were well grazed by the end of the grazing period. The sheep had difficulties accessing all of the available feed on the Old Man Saltbush as it had grown out of their reach. Grazing some of the larger shrubs (Old Man Saltbush, Silver Saltbush and River Saltbush) could have
occurred earlier, perhaps even during the first autumn after establishment. Changes in soil water over time at the Walpeup Enrich trial site have shown that the forage shrubs are very effective at drying and maintaining a dry soil profile in comparison with an annual plant based system, such as annual cropping. The soil profile under the shrubs began to dry in September 2009, and has remained drier thereafter, compared with the annual crop system. The distribution of soil water down the profile has changed markedly since the introduction of forage shrubs In May 2008 before the planting of shrubs, there was little difference in soil water distribution, but by November 2010 (28 months after planting the shrubs) there has been a large divergence in distribution, with a drier profile under the shrubs compared with the annual crop system.
Where to next?
Measurements of shrub survival and growth will continue in 2011 when livestock will be introduced to the site a second time, and longer-term shrub
performance under grazing will be assessed. Relative preferences by sheep for the different shrub species will also be assessed – this is an important consideration since diet selection by animals can tell us about nutritional and ‘extra-nutritional’ effects of plants that cannot be easily measured in the laboratory. Assessments of conventional forage quality will also be conducted and together with the long-term survival and growth data, provide more conclusive information on which to base shrub selection for the Victorian Mallee environment. Shrub size and its early growth performance are important traits, but are unlikely to be the only criteria assessed when considering new forage species for grazing systems.
Acknowledgements
This project is supported by the Mallee Catchment Management Authority, through funding from the Australian Government’s Caring for our Country. The research was undertaken by the Department of Primary Industries (Future-Farming Systems Research Division) and was an initiative of the Future Farm Industries CRC.
Contact
Rob Harris. DPI T: (03) 5573 0963 E: Rob.harris@dpi.vic.gov.au
ABOVE Sheep grazing at one of the Enrich trial sites. OPPOSITE PAGE Measurements being taken for reporting.
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