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SOLUTION

Saltbush & under-storey

 

4.4  Level of confidence in saltbush & under-storey

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How reliable is the information

Overview

Dense planting of saltbush was one of the first saltland pasture options developed in Australia and researchers and farmers are now confident in their understanding of saltbush species, establishment, management and the associated economics.

The focus on the under-storey in saltland systems, and the arrangement of saltbush plantings to specifically incorporate and encourage under-storey is a more recent development. While there is considerable knowledge about the individual species used as under-storey, it is the combination with saltbush and the degree of complementarity that is less well understood.

We can state reliably:

  • Saltbush (Atriplex species) are the perennial halophytes with the broadest range of adaptation to saltland in southern Australia. The two most common species are river and old man saltbush and both are generally more tolerant of drought than waterlogging. Old man saltbush is the species of choice for moderately saline soils where there is no or low waterlogging. It appears to have higher nutritive value than other saltbushes tested, it is long-lived and does not invade the inter-row spaces.
     
  • Establishment of saltbush from seed is less reliable than using nursery-raised seedlings. There are real trade-offs between reliability of establishment and cost of establishment. Direct-seeding is cheaper (around $100-150 per hectare) than planting nursery-raised seedlings (around $450 per hectare if using a contractor, but cheaper if done by the farmer). Current research is focusing on better ways of direct-seeding saltbush so this area could change quite dramatically over the next few years.
     
  • Across a wide range of situations, saltbush & under-storey has proven to be an economically viable saltland pasture. Economic gains tend to be greatest when the pastures are grazed in autumn and used to at least partly offset the need for hand feeding. The pastures also greatly increase the resilience of farms to withstand extreme events such as droughts and floods.
     
  • Because of the perennial saltbush component, these pastures are more reliable (ie. less dependent on current season rainfall) than annual pastures on non-saline land.
     
  • As a sole diet, saltbush poses significant challenges for grazing animals because of its relatively low energy content and high salt concentrations.
     
  • Saltbush also has some well established positives as a stock feed. It is green over summer, with high crude protein concentrations, when most other feed is dry. Being green, saltbush also provides vitamin E which can otherwise be a limitation for sheep on the dry pastures that occur in southern Australia in summer and autumn.
     
  • Even in quite dense saltbush stands, the under-storey will make up about half of the available livestock forage. As the density of saltbush is reduced, the contribution from the under-storey increases.
     
  • If the saltbush is able to use water over summer, lowering the watertable and increasing the leaching of salts from the soil surface, then conditions for the under-storey will be significantly improved. This means the under-storey species will be more productive, and/or less salt tolerant (ie. more productive and nutritious) species will be able to grow.
     
  • The greatest benefit from under-storey will occur if it contains a substantial legume content. The legumes can fix nitrogen for the benefit of the saltbush and the other under-storey species, as well as greatly enhancing the feed value for grazing animals.
     
  • On more saline sites in low rainfall areas, where legumes in the under-storey will either not survive, or will not be productive, then the economics favour allowing a volunteer under-storey. As legumes become a smaller component of the feed on offer there may be a need to supplement sheep with good quality hay in autumn. In higher rainfall areas tall wheatgrass and puccinellia can be sown. Over time, if the saltbushes are able to improve the surface soil conditions, then additional under-storey species can be added.

There are other aspects to the use of saltbush & under-storey that reflect a relatively low level of confidence in our knowledge:

  • At high salinity levels there is no advantage (and significant cost) for sowing over volunteer under-storey, but the threshold level where it is better to sow an under-storey has not been determined.
     
  • In practice, at high salinity sites where a sown under-storey may not be profitable, it is likely that volunteer under-storey will be dominated by sea barleygrass which has little nutritional value when dry and can pose a significant grass seed challenge for sheep. Dense saltbush planting may be a better bet but the threshold between the choices is not clear.
     
  • Individual animals vary in how long it takes them to include saltbush in their diet. Even after a month of grazing some animals will select a diet of 10% saltbush while flock-mates are consuming 60% saltbush. A new research project is underway to develop simple management tools to reduce variation in saltbush intake within and between flocks.
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Farmer experiences

As the story about the benefits of saltbush with improved under-storey has taken hold, case studies have increasingly reflected the use of saltbush in alley systems with legume under-storey. However most of the early case studies were largely based around the growth of dense saltbush stands with an unimproved annual under-storey. We now know that the reported benefits of saltbush were actually the combined benefits of saltbush and whatever under-storey was available.

The SGSL initiative has provided a rich mixture of farmer experiences with saltbush & under-storey systems. The large amount of saltland in low rainfall situations throughout the WA wheatbelt provides a concentrated focus on saltbush & under-storey. However, there is considerable experience building up in  areas of SA, VIC and NSW.

The case studies demonstrate that the saltbush component well established and quite stable across the country, though in some locations direct-seeding is preferred, while in others nursery-raised seedlings seem to give a better result. To complement this, most of the SGSL site work was about what to sow in the under-storey. Sub-tropical grasses, tall wheatgrass, puccinellia, lucerne, annual legumes, annual grasses etc were all trialled.

One of the unexpected benefits from moving focus from the dense saltbush solution to the less saline and waterlogged environments typical of the saltbush & under-storey solution has been an ability to focus more on saltbush species with the highest nutritive value. When saltbush research pioneer Clive Malcolm conducted his research in the 1970s, the research focus was mainly on the highly saline and more waterlogged landscapes and the shallow rooted species river saltbush became the main species of choice. Recent SGSL research has shown that river saltbush has a lower nutritive value than old man saltbush but with the focus moving towards the saltbush & under-storey, and less saline and waterlogged sites, they have been more suited to the growth of the deeper-rooted old man saltbush anyway.

Western Australian SGSL trial sites (Have a Yarn Series)

Though not included in the SGSL series above, perhaps the most effective advocate for saltland pastures in general and saltbush & under-storey in particular has been Michael Lloyd from Lake Grace. Major SGSL research sites were located on farms at Tammin and Yealering in WA and those farmers also have a very positive story to tell. For more information, see Making the most of saltbush forage and Saltbush more hardy than many think

South Australian SGSL trial sites

Wolford Parsons from the Yorke Peninsula, SA, has also been a major advocate for better saltland management, especially the use of saltbush & under-storey. Other SA farmers have also been successful with saltbush systems. For more information, see Challenge of rehabilitating a saline site ultimately rewards.

Though not as widely used in Victoria and NSW (because much of the saltland is too wet or too cold for saltbush, making tall wheatgrass and puccinellia better options for the perennial component of saltland pastures), there are some examples of effective use by farmers of the saltbush & under-storey option.

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Research experience

The focus by researchers on the saltbush & under-storey package began with a paper presented to the 1998 PUR$L conference by Barrett-Lennard and Ewing titled ‘Saltland pastures? They are feasible and sustainable – we need a new design’. The paper articulated the different roles for the saltbush rows and the under-storey pasture.

  • The saltbush would be mainly responsible for the transpiration of groundwater, the lowering of watertables and the reduction of surface soil salinity to enable better growth of the annual under-storey species. They would also decrease water and wind erosion.
     
  • The annual, under-storey species would be mainly responsible for the production of forage for livestock and subsequent generation of farm income.

With this understanding of the role of under-storey, R&D that was largely abandoned because of findings in the early 1990s that sheep fed saltbush gained weight but lost condition, and due to the very low livestock returns during that time, was revitalised.

The SGSL (Sustainable Grazing on Saline Lands) initiative joined the CRC Salinity to undertake a series of projects looking at aspects of the saltbush & under-storey system. These included water use, planting density for the saltbush, sown vs volunteer under-storey, supplementation, and rotational grazing vs set stocking. The conclusions from this research were:

  • Water use. The growth of saltbush can increase the depth to watertablewhere there are local grounwater flow systems, but achieving such benefits on a paddock scale requires plantings on a paddock scale. The draw-downs may be small (around 0.5 m) but they can have substantial benefits if the result is increased salt leaching from the surface soil allowing the under-storey plant base to change from mostly sea barleygrass to annual ryegrass with a substantial legume content. Saltbush will only use the saline groundwater in summer when less saline sources of soil water have been used. Grazing strategies can assist. If the saltbush has maximum leaf area over summer to maximise water use and is then grazed in autumn, after the highest evaporative demand of summer has passed. Saltbush has very little capacity to control groundwater in winter when evaporative demand is low. There may therefore be situations where plant water use needs to be complemented with surface water management strategies.
     
  • Planting density for saltbush. Saltbush can be planted at very high densities (eg.planting on a 1 x 1m grid equates to 10,000 plants per hectare). However, such dense plantings are quite uneconomic with plant-to-plant competition producing very small plants. The research suggests that with dense stands of saltbush a good rule of thumb is to plant at no more than about 1000 stems per hectare (ie. plants on a 3.3 x 3.3m grid). The SGSL research showed that saltbush do not use water at distances beyond about 6m from the plant, so a good solution for saltbush and understorey is to plant double rows of saltbush with alleys of about 10-12m wide. Double rows 2m apart, with the plants 2m apart in the row, and an alley of ~10m would equate to a saltbush planting density of roughly 600/hectare.
     
  • Sown versus volunteer under-storey. On most saltland, the volunteer under-storey is dominated by annual grasses (especially sea barleygrass), and this is of low nutritive value after the plants have ripened and set seed. Sowing under-storey provides the opportunity to increase the energy value of the under-storey by adding legumes to the mix. In turn the legumes fix nitrogen to allow growth of higher quality grasses. On soils capable of growing annual legumes (ie. with low salinity) there will be substantial gains from sowing under-storey and the combined (saltbush plus under-storey) feed will be suitable for growing animals (in winter/spring when the under-storey is green) and maintaining animals (in summer/autumn when the under-storey is dead). However, with soils that are too saline to grow legumes and high quality grasses, the combined feed lacks energy, and will only be suited (at best) to the maintenance of sheep, unless salt tolerant perennial grasses can be sown.
     
  • Rotational versus set stocking. There may be benefits to pastures and productivity from rotational grazing but it requires increased labour to manage the animals. Rotational grazing enthusiasts suggest that one of the major problems with set stocking compared to rotational grazing is that the former can lead to the elimination of the higher value/more palatable plants from a stand. In our work there were some signs that set stocking did result in the loss of some desirable plants compared to rotational grazing but the results (achieved over only 2 years) were not extremely strong. Perhaps combining mobs to increase stocking density without need for extra fencing is a viable option.
     
  • Supplementation. Saltbush does not have high levels of digestible energy and its high salt content restricts intake. These two factors combine to ensure that with a diet of saltbush alone, mature animals are unlikely to maintain liveweight. The solution that animals grazing saltbush generally adopt is to mix their feed sources, taking advantage of saltbush’s strengths (high crude protein concentrations, essential minerals and other useful compounds like vitamin E) and overcoming its energy and salt weakness through consumption of under-storey biomass. When the annual under-storey senesces in summer, the energy value declines over time, especially after rainfall events. It is important to monitor stock condition score and provide an energy supplements (ie. grain or good quality hay) when the under-storey is exhausted or if the nutritive value of the under-storey is poor. Metabolic requirements of the livestock will determine supplementation requirements and work is continuing to develop simple rules of thumb. At this stage it is not recommended that pregnant or lactating animals are fed saltbush-based diets for extended periods of time without extensive and careful supplementation.
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Risks and challenges

Establishment of saltbush

Establishment failure is perhaps the greatest on-farm risk with saltland pastures. Planting out nursery-raised saltbush seedlings reduces the risk of failure, but significantly increases the cost. Where direct-seeding of saltbush is possible then it provides a significantly cheaper option. However, at this stage direct-seeding is only recommended for lighter textured soils, or where there is a sandy layer over clay. There is a significant research focus on direct-seeding of saltbush so recommendations might change dramatically in the future.

Establishment of under-storey

Apart from the general risks (lack of rain, weed competition, too salty or waterlogged, insects) associated with pasture establishment, there are no particular issues with the main under-storey annual pastures species as they are widely used outside of saltland situations. For the perennial species - refer to the relevant section in the Solutions section of this website.

Weeds

Young saltbush plants, especially if direct-seeded are very susceptible to weed competition, even if the saltland site seems to be devoid of growing plants. Sea barleygrass and annual ryegrass are perhaps the most common weeds, but slender iceplant is becoming a major weed on saltland, particularly on the heavier land of the valley floors in the eastern and northern wheatbelt of WA. Controlling these weeds to allow the saltbush to establish will automatically improve the situation for the under-storey species.

Overgrowth

Under good growth conditions the old man saltbush plants can grow out of the reach of grazing sheep if they are not grazed hard at least annually. Regrowth after grazing will then be concentrated above the sheep grazing height, exacerbating the problem. Grazing with cattle can assist because of their greater grazing height and ability to break down taller stems. Mechanical pruning/slashing to restore the stand back to sheep grazing height is expensive and difficult and therefore is rarely undertaken.

However, this is only a minor problem as long as the saltbush is hard grazed annually. Sheep quickly learn how to pull down or reach the higher branches. In addition, leaving some leaves that are not grazed (ie. above sheep height) does allow for on-going water use by the saltbush. If sheep are left in a saltbush stand with limited available feed on offer to pull down the highest saltbush branches they may also need to have an energy supplement of hay.

Pests

Rabbits and kangaroos find saltbush palatable and can do a lot of damage to seedlings. Locusts can rapidly defoliate saltbush at any stage. Saltbush established by direct seeding is extremely vulnerable to red-legged earth mite (Halotydeus destructor) and preventative measures during establishment should be considered standard practice.

Maintaining saltbush & under-storey pastures

Established saltbush stands are very hardy, resisting drought, salinity and frost. Unless weakened by waterlogging (especially over summer), then persistence of saltbush stands is usually good. The under-storey is more vulnerable because it has to persist from year to year or re-establish each year which is  difficult in sites with higher salinity levels. The main challenge therefore with established saltbush & under-storey pastures relates to how to effectively graze (and supplement) the combination of saltbush & under-storey to maximise under-storey production and persistence, and to give the best whole-farm outcomes.

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Prospects

Recent research

The SGSL initiative greatly increased understanding of the best options for managing saltland. It had a major focus on saltbush and under-storey systems, with grazing experiments at several locations in the WA wheatbelt. For more information, see Sustainable Grazing on Saline Lands WA 1 Research Project and Sustainable Grazing on Saline Lands WA2 Research Report.

Saltbush and under-storey is now the primary saltland management recommendation for the extensive saltland areas in the eastern wheatbelt of WA where rainfall is too low for most of the perennial grasses. SGSL research has shown that this option is profitable under a wide range of assumptions, providing the establishment costs are controlled. At higher salinity sites, a volunteer under-storey may be more profitable (equally productive but at lower cost) than sowing improved species because the cost of seed is avoided and at high salinity levels, the sown species will not perform well.

With SGSL completed, there are three major research activities within the Future Farm Industries CRC focussed on the saltbush and under-storey system:

  1. A joint venture with Kings Park Botanic Garden, WA, is investigating improved establishment techniques for a range of species that have traditionally proven difficult. These include native grasses, sub-tropical species and saltbush. The saltbush work is focused on the use of better sowing techniques and seed treatments (bract removal, seed coatings and seed pre-treatment) which might enhance establishment of saltbush by direct seeding. A key challenges is to improve the seed treatment and sowing technology to the point were it will be possible to move from the highly specialised niche seeders (rarely owned by individual farmers) towards the more widely available commercial machinery such as cone or air seeders. This research has shown some promising results and major changes in the recommendations for saltbush establishment may emerge. For more information, see Establishment proves challenging for warm-season perennials.
     
  2. The Future Farm Industries CRC is undertaking research into the selection of improved lines of old man saltbush. Approximately 450 families of saltbush have been collected from around Australia and planted at five locations. For more information, see Saltland pastures can pay in WA. Preliminary morphological screening is occurring using material from two sites. This will demonstrate the variability and heritability of traits, and might identify lines for early cloning and production of seed.
     
  3. The biggest effort relating to saltbush and under-storey is into improved under-storey species. Developing a salt-tolerant legume presents a challenge which is much greater than for grasses. Legumes are inherently less salt-tolerant than grasses, however an annual variety of the legume Melilotus has some promise. In addition, there also needs to be a salt tolerant rhizobium bacterium and this needs to be able to form a symbiotic relationship with the legume under saline conditions. The options are more limited and the CRC is now actively searching for better rhizobia that are capable of persisting with Melilotus in saline soils.

 

Future Prospects

Saltbush and under-storey is the recommended use for land of moderate salinity and low waterlogging in the 300-400mm average rainfall zone of southern Australia. However the economics of applying this option in the low rainfall zone needs careful planning and management.

The SGSL economics theme modelled saltland pasture systems in WA, SA, Vic and NSW and showed that saltland pastures could be profitable in all States. The system modelled in WA was saltbush and under-storey, while perennial grasses were the basis of the saltland systems in SA, Vic and NSW. The increases in profit from better saltland management were greater in high rainfall areas (Western Victoria and central NSW) than in WA and SA. This modelling confirmed the conclusions drawn from across the SGSL grower network sites in WA that the highest risk of failure and lowest profitability occurred with saltland pastures in the low rainfall areas where saltbush and under-storey is the primary option. Most success occurred in the medium and high rainfall districts where there is a greater selection of suitable pasture species and potential for higher pasture production and utilisation.

Despite the challenging economics, saltbush and under-storey is the Saltland Solution with the best prospects for productive use of saltland. This is because:

  • a high proportion of the total saltland in Australia is in the WA wheatbelt;
  • the land has a low opportunity cost;
  • farmers have a strong track-record with the solution;
  • green feed in autumn has such a premium value in this strongly Mediterranean climate; and
  • the improvement in visual amenity (compared with bare saline land) is a strong driver for farmers.
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