The potential benefits and limitations of
the use of saltbush on Mallee mixed
farms
Michael Moodie, March 2014
Mallee Sustainable Farming
The potential benefits and limitations of the
use of saltbush on Mallee mixed farms
Background
Saltbush (Atriplex nummularia) is well adapted to the Mallee environment and for this reason many
farmers have integrated saltbush into their mixed farming systems. While there are many benefits
of establishing saltbush plantations there are also some limitations of using it as a livestock feed
source. These factors need to be well understood by farmers who have adopted or are looking to
develop saltbush plantations on their mixed farms. Exploiting the benefits and managing the
constraints of saltbush is critical to achieve profitable returns from the considerable investment
required to establish saltbush plantations.
In this article, we report the scientific knowledge of the benefits and disadvantages of using
saltbush as a livestock feed source. Furthermore, we also outline the results from a recent scientific
study into the potential profitability of integrating old man saltbush into mixed farming systems in
the Victorian and South Australian Mallee.
Adaptability
Atriplex nummularia is suitable for use in arid zones with 200-400 mm mean annual rainfall and are
considered to be amongst the most heat tolerant of the terrestrial dicotyledon’s (Ben Salem et al,
2010). As a C4 plant, growth tends to be higher in summer and autumn where temperatures are
higher (Norman et al., 2009a). However saltbush can also withstand low temperatures of -10 to -12
degrees C for a few hours.
Old man saltbush is well adapted to deep silty-clay soils with low to moderate salinity (2-50 dS/m)
(Masters et al., 2007), and can reach the water table up to 10 m below the ground surface (Ben
Salem et al, 2010). However saltbush has little tolerance of persistent waterlogging in the root zone
(Barrett-Lennard, 2003).
Grazing
The growth patterns of old man saltbush complement annual pastures systems where annuals are
dead and of poor nutritional value during the hottest months (Papanastasis et al, 2008). Under
ideal conditions saltbush should be grazed once a year for 1-2 month duration (Ben Salem et al,
2010). Saltbush required recovery periods where it is rested from grazing and cannot support
intensive and continuous grazing (Le Houerou, 1992).
Saltbush cannot be used efficiently as a ‘living haystack’ as plants need to be grazed annually.
Research has shown that shrubs that are not heavily grazed for a short period of time at least once
per year tend to drop leaves and not grow as fast as grazed plants (Wilmont and Norman, 2006).
Furthermore, the research showed that after three years of management by heavy annual grazing
(in Autumn) there was the same amount of biomass by the following summer as there was on ungrazed sites.
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Mallee Sustainable Farming
The potential benefits and limitations of the
use of saltbush on Mallee mixed farms
Feed quality
Overall the edible parts of saltbush are high in ash and crude protein but low in energy (Ben Salem
et al, 2010). Abou El Nasr et al (1996) found that sheep fed fresh old man saltbush achieved 150%
of their maintained nitrogen requirements. The crude protein (CP) content of the edible dry matter
(EDM) of old man saltbush ranges 10 and 25% and is usually above 15%. However much of the CP
comprises non-protein compounds such as nitrates, glycinebetaine and proline(Ben Salem et al,
2010). The non-protein compounds may be converted into microbial protein in the rumen,
however the extent to which this occurs depends on the availability of metabolisable energy
(Pearce et al, 2010) as without sufficient energy these compounds are excreted in the livestock
urine.
The metabolisable energy (ME) of old man saltbush EDM is low and provides only low to moderate
energy to sheep (Ben Salem et al, 2010). The high levels of soluble salts in the EDM (high ash
content) mean that there is a low digestible organic matter in the dry matter (DOMD)and therefore
animals need to consume high levels of EDM to meet their energy requirement (Masters et al,
2005ab, Norman et al, 2009b). Furthermore the high levels of salts can limit voluntary feed intake
(VFI) so that animals may not be able to eat enough energy to maintain weight and the high salt
level incurs a metabolic energy cost to process and can lower the efficiency of digestible energy by
10% (Arieli et al., 1989, Masters et al., 2005 a,b).
Saltbush EDM produces adequate fiber for livestock production. The cell wall fiber (NDF) varies
between 30 and 45% EDM and the lignocellulose fraction (ADF) ranges from 15-29% (Ben Salem et
al, 2010).
The high salt content of old man saltbush limit’s the voluntary feed intake of livestock as sheep stop
eating salty forage after they have ingested approximately 200 g of salt in a day (Masters et al
2005ab). The concentration of salt in saltbush is commonly above 250 g/kg DM and at this
concentration a 50 kg mature whether (one DSE) will stop ingesting after about 800 g of foliage
(Ben Salem et al, 2010). This consumption is 250 g less than that what is required for one DSE to
maintain live weight (Ben Salem et al, 2010).
The high salt content of salt bush leads to high water consumption by livestock. Correal et al
(1992) found that ewes consumed 6-8 L/day in autumn and 7-10 L/day in summer while being fed
old man saltbush.
Most of the salt within saltbush is sodium chloride and potassium chloride, however saltbush also
contains high levels of sulphur (S), magnesium (Mg), calcium (Ca) and phosphorus (P) (Ben Salem
et al, 2010). While most of these minerals are present in concentrations above the recommended
intake for ruminants, the complex interactions between minerals mean that livestock grazing only
saltbush may be pre-disposed to mineral imbalances (Masters et al., 2007). Research has shown
that sheep grazing saltbush for an extend period of time without supplementation could develop
Mg, Ca and P deficiencies. Furthermore sheep grazing saltbush alone could suffer sulphide toxicity
which in turn can result in copper deficiency. However when combined with an annual pasture
system saltbush may provide a valuable source of S to livestock (Ben Salem et al, 2010).
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Mallee Sustainable Farming
The potential benefits and limitations of the
use of saltbush on Mallee mixed farms
Old man saltbush appears to be a valuable source of vitamin E. A study by White and Rewell (2007)
found that 58% of weaner sheep flocks in the Mediterranean climate area’s of Australia had vitamin
E deficiency in autumn. The strategic use of oldman saltbush could help address this problem (Ben
Salem 2010).
Old man saltbush forage also contain anti-nutritive secondary compounds such as tannins, oxalates,
saponins and alkaloids (Ben Salem et al, 2010). However the level of secondary compounds in
saltbush forage appears to be low enough to avoid negative effects (Ben Salem, 2010).
Animal production
Animals grazing saltbush need supplementary feed sources such as grains, hay or inter-row
pastures to increase the metablosable energy on offer to livestock (Atiq-ur-Rehman et al., 1999).
Research by Hassan and Abdel-Aziz (1979) found that sheep needed to be fed a minimum of 150 g
per head per day of barley to maintain live weight while grazing saltbush. Where production is the
objective, sheep grazing in saltbush plantations need to be supplemented with high levels of hay
and or grain. Hopkins and Nicholson (1999) suggest that lambs can obtain acceptable carcass
weights (21-22 kg) when grown on saltbush and supplemented with either oat grain or Lucerne
hay over a ten week finishing period, however the challenge is the potential substitution by animals
of the saltbush with grain supplements resulting in minimum consumption of saltbush.
Inter-row pasture growth supplements the energy requirements of sheep grazing saltbush
Research has identified that high salt diets (such as that provided by grazing saltbush) can lower
proportions of fat and increase proportions of lean meat compared to sheep grazing either grainhay based diet or a pasture-stubble paddock (Walker et al 1971, Kraidees et al 1998, Pearce et al
2008 ab). For sheep production, the benefits of using saltbush to alter carcass composition maybe
achieved during a strategic finishing or backgrounding phase prior to feedlotting (Pearce et al,
2010)
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Mallee Sustainable Farming
The potential benefits and limitations of the
use of saltbush on Mallee mixed farms
Senesced pastures are low in vitamin E and over the summer and autumn months in Mediterranean
environments, saltbush provides an avenue to increase livestock vitamin E intake (Pearce et al
2010). A study by Pearce et al (2005) found that the muscle of sheep that had grazed saltbush had
high vitamin E levels, the meat was redder days 4 and 5 of ageing and colour was lighter than meat
from pasture fed lambs. Other than colour, research has not demonstrated any significant
improvements or detriments for eating quality in terms of flavour and aroma, tenderness, juiciness
and overall acceptance (Pearce et al, 2008 a,b). However the high vitamin E content of meat from
sheep fed saltbush is an important selling point because the level is equivalent to some vegetables,
oils, nuts, green leafy vegetables and fortified cereals which are common food sources of vitamin E
(Traber, 1999).
Saltbush can also have positive effects on fibre production. Research has found that sheep
consuming diets high in sodium chloride grew more wool per unit of digestible organic matter
intake (Thomas et al 2007b). Furthermore, the high sulphur levels in old man saltbush may
improve wool growth (Franklin-McEvoy et al 2007, Norman et al, 2009).
Management benefits
Anecdotal evidence suggest that saltbush plantations on mixed farms can provide a range of
benefits which have not been quantified through research. Monjardino, Bathgate and Llewellyn (in
press) proposed that such benefits could include:
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
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reduced erosion risk through ability to contain stock during peak cropping times
heightened value during times of drought
increased laming rates from extra shade and shelter
reduced methane generation and parasitic activity from bioactive activity in the rumen.
Farm Profit
The economic consequences of including old man saltbush plantations on a typical farm in the
Victorian and South Australian Mallee was investigated through the Mallee Evercrop Project. The
Mallee MIDAS model was used to assess the profitability of forage shrubs on a typical 3000 ha
mixed farm with dune-swale soil types. The results of the economic modelling analysis are
reported in Monjardino, Bathgate and Llewellyn (in press). The key findings of this research is
outlined below.
Saltbush was selected as a profitable enterprise option on 1% of the typical farm’s area. The most
profitable fit for shrubs appears to be on heavier soil types that are not the best for cropping but
can support reasonable inter-row pasture growth. Saltbush is utilised in February and March and
grazing saltbush was found to be a more profitable option for filling the summer/autumn feed gap
than supplementary feeding with hay, wheat, lupins or oats.
On the typical farm with 80% of the area used for cropping, including shrubs did not impact overall
farm profit. However at lower cropping area’s the farm with forage shrubs economically
outperformed that without, mostly due to the extra feed to sustain livestock over the summer
months (Figure 1).
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Mallee Sustainable Farming
The potential benefits and limitations of the
use of saltbush on Mallee mixed farms
As copping intensity increases, whole farm profit declines due to low crops yields on the poorest
soils. Where farms have a higher proportion of marginal soil types, forage shrubs could be
relatively profitable at 7% of the farm area. These results indicate that forage shrubs have a larger
profitable niche in less productive soils and farms of the Mallee.
The study looked at what the potential value of saltbush plantations would be if some critical
management considerations could be altered. The key finding of this analysis were:





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Lowering the establishment cost of saltbush plantations by $100 per hectare would only
increase the profitable area of shrubs by only 1%
Improving saltbush organic matter digestibility from 60 to 75% grew the forage shrub area
by 13% on the standard farm and 11% on a marginal farm with a profit gain of $6 ha in both
farms.
There would be no gain from increasing saltbush growth rate unless digestibility was
greater than 70% organic matter digestibility.
A decrease of up to 5% in dry matter total ash of saltbush leaves could potentially increase
shrub area by 5% without much affecting profit.
Having a higher quality understory (such as standing cereal or higher legume content) could
increase the optimum shrub area by 2%.
The optimum proportion of shrubs on the farm is highly influenced by commodity prices. If
long term wheat prices were only $175/t then 10-20% of the farm could be profitably
planted under shrubs. Similarly high lamb and wool price would favour high shrub plants of
10% of farm area.
This modelling highlights a potential role for saltbush plantations in mixed Mallee farming systems
and it is notable that this result occurs despite other potential NRM or animal health benefits not
being captured in the economic analysis.
Figure 1. Whole farm profit of a typical Mallee farm with or without saltbush and different levels of
crop area. Source Monjardino, Bathgate and Llewellyn (in press).
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Mallee Sustainable Farming
The potential benefits and limitations of the
use of saltbush on Mallee mixed farms
Conclusion
Overall forage shrubs provide a valuable feed source during a time of year when pasture
production and quality is low. Forage shrubs support livestock to be carried over the dry months at
a time when there is a heavy reliance on supplementary feeding. Consequently farmers are able to
increase stocking of the farm or reduce supplementary costs or both. This increased flexibility can
help spread the risk in a particularly volatile environment (Monjardino, Bathgate and Llewellyn (in
press).
Acknowledgements
Funding for this project was provided by GRDC and the Australian Government through the
Northern Victorian Grain and Graze Project and the Future Farm Industries CRC Evercrop project.
Thankyou to Rick Llewellyn and Hayley Norman of CSIRO for assisting sourcing of literature used in
the development of this article.
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