- Trial Rationale
- Steps Taken
- Lessons Learnt
- Looking Forward
The current lack of information on ways to regenerate saltbush has been a barrier to improving forage grazing systems. Although saltbush has been used effectively to reclaim land degraded by soil erosion, rising salinity or waterlogging, it has still not met expectations as a feed source for livestock, delivering poor financial returns for farmers.
Many established saltbush plantations are over-grown, too dense to manage effectively and too tall for livestock to feed on. Densely planted saltbush also limits pasture understorey growth resulting in poor diet variation and a lack of biodiversity. Landholders with old, overgrown saltbush are seeking guidance on ways to improve the grazing potential of their plantations.
Corrigin landholder Lex Stone became involved in the project through discussions with the Corrigin Farm Improvement Group (CFIG). CFIG provided support to assist Lex to explore options to manage old saltbush stands. Geoff White of Goomalling had previously been involved with Wheatbelt NRM’s sustainability advisory group. “When we put in the initial application to investigate saltbush regeneration, we learnt of another similar project with CFIG. Wheatbelt NRM asked us to work together on this project,” Geoff said.
The purpose of this trial was to:
- Demonstrate that regeneration can increase and improve feed availability for livestock;
- Show how regeneration of saltbush can improve production by increasing understory biomass; and
- Provide landholders with a number of options to turn old saltbush into a useable, profitable and manageable resource.
The trial was designed by Curtin University of Technology (Curtin) and delivered with the combined efforts of Greening Australia, Curtin, CFIG, the landholders (Geoff White and Lex Stone) and Wheatbelt NRM.
The layout and regeneration treatments applied at each site were slightly different.
The site on Geoff’s Goomalling property was previously planted with alternate rows of Oldman Saltbush (Atriplex nummularia) and River Saltbush (Atriplex amnicola) with two-metre inter-rows. The plants were moderately overgrown with natural recruitment after not being grazed effectively since they were planted some years before
The site was laid out in late March 2016 with four treatments, 120 m long, of fodder shrubs that comprised two rows of Oldman Saltbush and two rows of River Saltbush. These were split into four sampling blocks along each treatment. Plots included two rows of both Oldman and River Saltbush rows (22.5 m), treated with one of the four treatments including:
- Cut to 50 cm;
- Cut to 1 m; and
- Left as control.
The cutting was done using chainsaws, which was labour intensive but was the only option available. Initial samples of both Oldman and River Saltbush were taken from the site in April 2016. Biomass samples were taken in September 2016 to measure growth over the late autumn and winter and again in January and March 2017 to determine spring and summer growth. Final cuts were taken in early July 2017 because Geoff needed to use the study site to feed his sheep. The plots were therefore assessed for available feed biomass before the sheep were provided access to the site.
This site, belonging to Lex, was previously planted with three rows of Oldman Saltbush (8 m width) with inter-rows large enough to be cropped (28 m) resulting in very little natural recruitment in the inter-rows. Cutting was done with a specially made tree cutter and mulcher from the neighbouring Sandalwood plantation. The saltbush stands themselves however, had become overgrown. The treatments tested in Corrigin included:
- Cut to 50 cm; and
- Left as control.
No initial sampling took place at Corrigin, but the baseline biomass was estimated from the ends of each of the rows after the treatments were imposed. Biomass samples were then taken in October 2016 to measure growth over the late autumn and winter and again in December 2016, June and October 2017. The site was grazed by experienced sheep (have grazed saltbush before) for 1 week periods 2-3 times during the trial.
The River Saltbush at Goomalling had not grown above 1.2 m prior to the experiment. Therefore, no treatments had any feed above 1.2 m throughout the trial period. Rolling River Saltbush severely constrained its growth in the first year, and even by July 2017 it still had significantly less feed available than any of the other treatments (Figure 1). There were no significant differences between the available feed in the other treatments. All treatments in River Saltbush showed a significant increase in March 2017, but by July 2017 the control had decreased to levels below what they were at the start of the experiment. It is suggested that the increase in March 2017 in all treatments was due to significant summer rainfall, and that subsequent dry weather until June led to a drop in leaf matter in the control treatment. It is unknown why this occurred only in the control treatment.
The Oldman Saltbush at Goomalling showed a similar increase in available biomass in March 2017 as seen in the River Saltbush, particularly in the control treatment. In both the ‘rolled/ squashed’ and ‘cut to 0.5 m’ treatments applied to Oldman Saltbush, the amount of feed available above 1.2 m was negligible following the start of the experiment, highlighting that all the new growth was available to grazing sheep. In the treatment ‘cut to 1 m,’ the amount of feed above 1.2 m was negligible in the October and January measurements, but one year after cutting, the amount of feed above 1.2 m had increased to near where it was at the start of the trial.
The availability of energy-rich pasture complements the high protein content of saltbush to provide livestock with a balanced diet, improving meat and wool quality (Emms and Revell 2014). Due to the exceptional year in 2016, vegetation cuts of the understorey were taken back to Curtin in late August where they were dried and assessed for % legume, % grass and % herb content before being ground and analysed for nutritional value. The pasture cuts showed no significant difference in composition between the forage shrub treatments, although there was slightly less pasture biomass available in the ‘control’ and ‘rolled/squashed’ treatments and more in the treatment cut to 0.5 m (Figure 2).
In 2017, with the dry growing season, only limited understorey was available and therefore no cuts were made. “We didn’t think about the differences in the seasons,” said Technical Advisor Dr Sarita Bennet from Curtin. “The first year was quite wet and the second year was dry with a lot of leaf drop. There was however still enough food on offer for the sheep to survive and the farmer relied on the saltbush when the rest of the farm had very little grazing left.”
The ‘cutting to 0.5 m’ treatment presented the most encouraging treatment for regenerating Oldman Saltbush at the Corrigin site, with accessible biomass below 1 m steadily increasing at each assessment period until October 2017. The most marked growth occurred over summer between December 2016 and January 2017 (Figure 3). While ‘rolled/squashed’ Oldman Saltbush recovered well over summer and ended up with higher biomass below 1 m compared to the ‘control’ by October 2017, this biomass was low over spring and significantly lower than the ‘cutting to 0.5 m’ treatment throughout the trial’s duration.
Lex said he noticed positive changes to saltbush stands in all the treatments applied. “There was significant regrowth, which appeared to have more vigour than previous biomass on offer to livestock. There was however very little influence on understory ground cover,” he said.
Participants agree that this trial was a good first step towards improving grazing opportunities on marginal land in the Wheatbelt. “Future collaboration with more groups in other areas is a likely step forward,” said Sarita. “It would be beneficial to run a similar project on a larger scale for longer to have extended periods of controlled grazing. Next time we would weigh the sheep before and after grazing the saltbush to determine weight gain. In this trial, the dry season in the second year meant we didn’t have a chance to set it up property to look at that.”
The key learning from the trial for Lex was confirmation that managing saltbush does improve the vigour and grazing capacity of fodder for livestock. His next step is to compare the live weight gain and condition scores in sheep grazing on the managed saltbush verses unmanaged stands to carry out a proper economic analysis for return on investment.
The physical ability to cut or roll old saltbush stands is a limiting factor that farmers would need to consider. Rolling is a much cheaper and easier method compared to cutting as there are no machines specifically made for cutting saltbush and therefore it can become a labour intensive and/or expensive method. “Due to the significant machinery costs associated with mulching saltbush stands, we would like to investigate how the stands perform using a road verge tree trimmer, which would do a similar job to see if the results would produce the same outcome,” Lex said.
“We will certainly change the way we manage established saltbush. In the past we have let them grow, however we would instead not plant them so close, and keep them under 1.5 m in height using a tree lopper.”
Emms, J. and Revell, D. 2014. ‘Perennial forage shrubs – from principles to practice for Australian farms.’ Future Farm Industries Cooperative Research Centre (CRC). http://www.news.uwa.edu.au/201407086815/opinion/future-farm-crc-farewell