Saltbush plus understorey described
Saltbush plus understorey is now the option most recommended for low rainfall saline sites in the Western Australian grainbelt.
Saltbush belts with an understorey mix in alleys is a cheaper establishment option than dense saltbush plantings and allows easier vehicle access and livestock management.
The configuration often has about 500–600 saltbush plants per hectare but this can vary widely depending on the width of the belts and alleys.
Saltbush in this system has two main benefits:
- Saltbush uses water over summer, lowers the watertable and dries the soil surface, which:
- reduces the build-up of salt on the surface, and movement of salt offsite in runoff
- allows winter rain to leach salt from the shallow root zone of many understorey plants, improving the growing conditions and production.
- Saltbush provides green feed throughout the year but is of most value in autumn when most farms in the rainfall zone suited to this option will have only dry standing feed. It has been estimated that green feed in autumn in the WA wheatbelt has a value 10–times that of the same feed in spring. Saltbush provides protein, vitamin E and minerals, which are usually deficient in dry feed.
Understorey in this system also has two main benefits:
- The understorey provides a greater quantity and quality of feed than the saltbush
- The understorey provides good groundcover, which minimises erosion and evaporative concentration of salts at the soil surface.
See the farmer case studies – some with video.
Choosing species
Saltbush
Old man saltbush and river saltbush are the best saltbushes for this system – Anameka Saltbush™ is a selection of old man saltbush with higher nutritional value and palatability. Wavy leaf saltbush (introduced from Argentina) is often used when saltbush is established from seed rather than seedlings.
- Old man saltbush supports slightly better animal performance and does not spread into the inter-row. It does not tolerate waterlogging.
- River saltbush tends to be more tolerant of transient waterlogging.
- Wavy leaf saltbush is smaller and the easiest to establish from seed.
Understorey
The understorey species used in this option will grow best at low soil salinities (estimated subsoil ECe values of 2–4 dS/m) but may tolerate moderate salinity levels (estimated subsoil ECe values of 4–8 dS/m).
We recommend a mixture of:
- annual legumes – in order of importance: burr medic, balansa clover, sub-clover, lucerne and possibly messina
- grasses – depending on the salt and waterlogging levels, puccinellia, tall wheatgrass, Italian ryegrass, annual ryegrass.
Legumes provide nitrogen, which boosts saltbush growth. Burr medic is best in dry areas, balansa is better in wet areas, and messina is suited to waterlogged areas.
See pasture legumes and grasses for saline land for understorey species tolerances, and information about selecting the correct rhizobium for use on saline sites.
Benefits
Production
When saltbush has established and surface salt has been reduced, the understorey will typically produce 70–90% of the total edible dry matter when grazed in autumn.
The amount of feed depends on the site and management:
- The economic value of feed is highest in late summer and autumn, when dry annual pastures and stubbles have low feed value.
- Understorey can be grazed in winter and spring, with little damage to the saltbush.
Grazing saltbush plus understorey in autumn and early winter allows non-saline pastures to have grazing deferred until plants reach the target feed on offer of at least 500kgDM/ha.
Amenity and environmental
By far the most consistently reported benefit from establishing saltland pastures (including dense saltbush plantings) is visual amenity experienced by the farm family and local community.
Revegetation with saltbush and understorey can assist in reducing soil erosion and can enhance flora and fauna diversity by providing habitat to small local birds, lizards and other small animals. There is evidence of improved microbial activity in soils established to saltbush and understorey.
Saltbush (either dense plantings, or spaced rows with understorey) can provide a substantial low windbreak. These windbreaks can provide stock shelter and may improve survival of lambs and off-shears sheep in bad weather.
Suitable sites for this option
All plants have landscape niches or zones (combinations of climatic and soil conditions and management) where they are most competitive or where they will perform best. Saltbush and understorey plants are the same, each tending to have a particular set of climatic (rainfall, temperature, etc) and soil (salinity, waterlogging) factors which determine where they will be able to survive and are likely to thrive (Figure 1). As this is a mixed option, some compromises are necessary, but overall for saltbush and understorey, these factors are summarised below.
Common indicator species
Identifying sites that are suited to the saltbush and understorey mixture involves finding a compromise between where saltbush will grow and where the sown understorey species can make a significant contribution (i.e. more so than a volunteer understorey).
Indicator species such as curly ryegrass that can tolerate sites with high salinity are indicative of locations that will be too salty for the understorey species. Saltland indicator species (such as cotula, marine or saltwater couch, puccinellia or samphire) that can tolerate high levels of waterlogging are indicative of sites where the saltbush is likely to struggle.
In between these two extremes, there are some species, that if present, are likely to indicate the ideal mix of salinity and waterlogging for a saltbush and understorey pasture. These include capeweed, annual ryegrass, and annual legumes such as woolly clover or burr medic.
Indicator plants with low levels of salt tolerance can be misleading. There may be many reasons (other than salinity) why a particular plant species is present at a particular location (e.g. history of grazing management, cultivation, herbicide use, and impact of recent weather events, especially out of season rainfall). We recommend using other measures to check salt levels.
Sites with large bare areas may be too salty and/or too waterlogged for saltbush and understorey, but such a diagnosis can be misleading if the site is part of a larger paddock and has bare areas resulting from overgrazing and stock camping, rather than being a true indicator of excessive salinity or waterlogging.
Salinity
Saltbush plus understorey is the recommended option for sites of moderate salinity (subsoil ECe values of 4–8 dS/m) in the 300–450 mm rainfall zone, but it can also be recommended for sites of low salinity (subsoil ECe values of 2–4 dS/m) if the rainfall is too low to support perennial grasses.
Waterlogging
Much saltland can also be waterlogged, at least for part of the year. Despite being highly salt tolerant, saltbushes are relatively sensitive to waterlogging and inundation, especially if it is prolonged or if it occurs during periods of high temperature. Some understorey species (e.g. balansa clover) are highly waterlogging tolerant, while others (e.g. messina and burr medic) are more like saltbush. As a package, saltbush plus understorey is not suited to highly waterlogged sites because the saltbush will not survive.
For saltbush plus understorey we recommend:
- watertables deeper than ~0.3 m in winter and deeper than ~1.5 m in summer. Old man saltbush is generally more sensitive to waterlogging than river saltbush (watertables should be deeper than 0.5 m in winter for good old man saltbush production).
- draining surface water to improve establishment and long-term survival of the saltbush component of the pasture. This means choosing sites that have either limited inundation, or that can be easily modified so that surface water is not retained on the site.
- planting the saltbush on mounds to reduce the risk of inundation – the mounds and furrows should be in a herringbone layout to discharge water offsite.
- direct seeding saltbush on sandy/loamy soils, or if there is a sandy/loamy layer over a heavier clay – saltbush tends to establish more easily on lighter soils.
- using seedlings in clay soils – press soil around the seedling root ball to eliminate air pockets.
Saltbush prefers alkaline soils and has decreased growth in highly acid soils. We recommend soil testing before establishing saltbush plus understorey. Waterlogging is by far the most serious soil constraint for saltbush.
Climatic requirements
Overall, the climatic requirements for the understorey species are less precise than for saltbush, so the saltbush plus understorey combination is restricted to those areas where saltbush is suited.
Rainfall
The suitable rainfall range for saltbush stands is approximately 250–450 mm. Below this range, the low production potential and high risk of establishment failure make saltbush an uneconomic proposition, while above this rainfall range, there is a high likelihood that waterlogging will be a major constraint for saltbush.
Temperature
Saltbush grows optimally when daytime temperatures are warm (around 30°C). Conversely, plants are usually dormant or slow growing during the colder months. With river saltbush little growth is evident when the mean daily temperature is below 10°C; with old man saltbush some growth can still occur in winter.
Saltbush plus understorey is not the first recommendation for saline sites in the colder and/or wetter areas across southern Australia. In these areas, the perennial grasses such as tall wheatgrass and puccinellia are usually better options.
Establishing this option
To successfully establish saltbush with an understorey, choose the right species, use good seed or seedlings, control waterlogging, and use the right establishment methods. Guidelines for good saltbush plus understorey establishment are derived from farmer experience and research.
For more information view the separate page Establishing saltbush and understorey for dryland salinity management.
Management
Grazing
As with many other aspects of the saltbush plus understorey option, it is the saltbush that requires the more specialised management to ensure its productivity and persistence. Constant heavy grazing will eventually weaken and kill saltbush. Aim to leave about one third of leaf material on plants after grazing.
To a large degree, the annual understorey species behave the same on saltland as they do on other parts of the farm. Defer grazing until the plants are well established, then they can be rotationally grazed or set stocked. Do not graze those legumes that are aerial seeders (such as balansa clover and medics) during seed set.
Saltbush plus understorey pastures, like dense saltbush plantings, have been shown to thrive under a grazing management system that involves an annual crash grazing where the understorey is entirely consumed, and the saltbush is grazed back to the twigs in autumn when other farm feed sources have been exhausted. The saltbush provides protection from wind erosion needed to allow this hard grazing.
There is no advantage in saving saltbush-based pastures for less productive seasons as a living haystack or drought reserve. Old man saltbush drops a lot of leaves when left ungrazed in dry periods, and there is little advantage in deferred grazing between years. Saltbush that is not grazed at least annually may grow beyond sheep grazing height.
Animal nutrition
One of the great advantages of this saltbush plus understorey option is that some of the nutritional challenges associated with the saltbush are overcome by the understorey.
When sheep self-select a diet from a saltbush plus understorey pasture, they select a diet that optimises nutrient intake while minimising salt intake.
- In autumn, when the understorey is dry, sheep may select 30–40% saltbush in their diet.
- In spring, when the understorey is growing, sheep may select as little as 10% saltbush in their diet.
The saltbush component of saltbush plus understorey pastures provides a nutritional challenge to livestock because of the high salt concentration (20–30%) in the leaves. As salt in the feed increases, intake is decreased. Livestock grazing saltbush alone will not get sufficient nutrients for maintenance.
Across a range of environments, the new selection of old man saltbush – Anameka Saltbush™ – had a mean organic matter digestibility of 64%, crude protein of 19.5% and 25% ash. The nutritional profile and improved relative palatability are likely to increase voluntary intake, provide higher energy values and increased livestock productivity. This in turn should increase the effectiveness of understorey energy sources.
Water requirements
Provide unrestricted low-salinity water to animals grazing saltbush – this allows them to flush more salt and increase intake of plant material.
Resources
Barrett-Lennard, EG, Saltland Pastures in Australia – a practical guide.
Liddicoat, C and McFarlane, J, 2007, Saltland Pastures for South Australia, Department of Water, Land and Biodiversity Conservation Report No 2007/08. This is a product of the SGSL initiative, providing a wealth of information that will be of value beyond SA. viewed 11 November 2019. This downloads a 4.6 MB PDF.
Masters, David G., Benes, Sharon E., Norman, Hayley C. (2007). Biosaline agriculture for forage and livestock production. Agriculture, Ecosystems and Environment 119; 234–248.
Norman, HC, Masters, DG & Barrett-Lennard, EG, 2013, Halophytes as forages in saline landscapes: Interactions between plant genotype and environment change their feeding value to ruminants, Environmental and Experimental Botany, vol. 92, pp. 96–109.