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SOLUTION 3

Dense saltbush plantings

 

3.4  Level of confidence in dense saltbush plantings

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How reliable is the information

Overview

Dense plantings of saltbush was one of the first saltland pasture options developed in Australia and it follows that both researchers and farmers are reasonably confident in their understanding of where to best establish saltbush, which species for which regions, how to manage them for production and other benefits, the likely animal performance, and the associated economics.

In other words, the strengths (persistence, water use, out-of-season feed) and weaknesses (cost, animal nutrition limitations and profitability) of using such plantings are reasonably well understood.

Adaptation

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 susceptible to waterlogging than to drought conditions. Trials in Western Australia have shown that survival of river saltbush becomes threatened if the average depth to the watertable in summer is less than about 0.9m, and as the average ECe in the subsoil (25-50cm) increases to more than 40dS/m. The greatest growth of river saltbush occurs with average ECe values in the subsoil of 7 to 13dS/m and average depths to the watertable of 1.6-2.2m.

The adaptation of Old man saltbush was not tested in the WA trials, but experience suggests that its tolerance to salinity will be similar to River saltbush but its tolerance of shallow watertables may be slightly less on account of its deeper root system.

While saltbush will survive in land of ‘severe’ salinity (subsoil ECe values 16–32dS/m), better growth will occur in land of ‘high’ salinity (subsoil ECe values of 8–16dS/m). For sites with average ECe values below 8dS/m the recommendation would be for less dense plantings of saltbush and with more focus on improved under-storey – as outlined in Saltland Solution 4.

In addition, average watertables in summer should be deeper than 0.9m for densely planted saltbush, and should be deeper than 1.2m for saltbush with under-storey (Saltland Solution 4).

Establishment

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. The influence of soil type is strong, with direct seeding much more likely to succeed if there is a ‘sandy’ surface soil. Direct seeding is no longer recommended on heavy-textured soils because of the high risk of establishment failure

Value as sheep feed

There has been a considerable research focus on the value of saltbush as a stock feed. Much of the criticism of saltbush pasture in the 1990s was related to its low nutritional value. As a sole diet, saltbush poses challenges for grazing animals because of its relatively low energy content and high salt concentrations. Part of the nutritional ‘difficulty’ is that standard laboratory tests of digestibility can greatly over-estimate feeding value because the soluble salt content (which can be 20% or more of the dry weight) is measured as part of the digestible fraction but contains no nutrition and restricts intake when it reaches 8-10% of the diet.

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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 early case studies were largely based around the growth of dense saltbush stands with an unimproved annual under-storey.

An example

On the property ‘Maro Creek’ in the northern agricultural region of South Australia, saltbush plants are typically planted in single rows, 1.5 m apart within rows and 3 m apart between rows. A 4 m row spacing every sixth row is used for vehicle access and mustering, and this results in a planting at a density of approximately 2100 plants per hectare. During the late 1990s, approximately 200ha of old man saltbush were established. “The saltbush paddocks have become a very valuable part of our farming system,” say Ted Bear and Martin Wilkinson. They maintain the condition of stock, providing green feed in autumn when it is most valuable. They take the pressure off bare paddocks and make it much easier to spell the newly seeded pasture paddocks, allowing pastures to get off to a good start. And they help free up land more suited to cropping. Also the ability of saltbush to cope with extended dry periods is one of its great strengths.
“In dry years the saltbush has proved its worth, effectively drought-proofing the sheep enterprise on the farm.” 

Read the full story  

Below are links to a range of farmer case studies from across southern Australia where saltbush (either dense plantings or saltbush with improved under-storey) has become an integral part of the farm operation. The case studies are dominated by WA and SA examples as this is where the most extensive saltland plantings exist. There are also some multiple entries with stories from the same farm told for different audiences, or at different times.

PURSL Conference Proceedings


SGSL Case study booklet – “Insights” published in 2003 

  • David Millsom from Pyramid Hill, Victoria
  • Ian Walsh from Cranbrook, WA
  • Tony York from Tammin, WA
  • Ashley Lewis from Wickepin, WA



SALT
Magazine



Have a Yarn Series (Western Australian SGSL trial sites)

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Risks and challenges

Establishment

Establishment failure is the greatest on-farm risk with saltland pastures. Although the economics are now in favour of saltbush, there is no doubt that the high costs of establishment with nursery-raised seedlings and the risk of potential failure (especially with direct seeding) are still a major disincentive for many farmers. Improved success with direct seeding (potentially using conventional farm seeding equipment, seed treatments, and better weed control strategies) will be needed if this is to change.

Weeds

Established saltbush plantations are largely immune to weed invasion because of the competitive advantage perennial shrubs have over annual weeds. However, young saltbush plants are susceptible. Direct seeded sites are at most risk, but during the early stages, nursery-raised seedlings are also susceptible to weed competition.

Sea barleygrass and annual ryegrass are perhaps the most common weeds, but slender iceplant is becoming a major weed on saltland, particularly the heavier land of the valley floors in the eastern and northern wheatbelt of WA. Iceplant has high oxalate concentrations in the leaves which are potentially toxic to sheep, however animals are unlikely to graze iceplant unless the saltbush has been almost totally defoliated. Strategies to control this weed within stands of saltbush could affect the economics. Preliminary field experiments suggest that it can be controlled by pre-emergent applications of Oxyfluorfen.
Note - the Future Farm Industries CRC accepts no liability for farmers using this chemical.

Overgrowth

If saltbush plantings are not grazed frequently enough, then under good growth conditions the plants can grow out of the reach of grazing sheep. Further growth will then be concentrated above the sheep grazing height. 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 in dense plantings and is rarely undertaken. This is only a minor problem as long as the saltbush are grazed annually. Some leaves that are not grazed (ie above sheep height) does allow for on-going water use by the saltbush even if heavily grazed.

Pests

Rabbits and kangaroos find saltbush palatable and can damage seedlings. Locusts can rapidly defoliate saltbush at any stage. Saltbush established by direct seeding is extremely vulnerable to red-legged earthmite (Halotydeus destructor) and preventative measures should be considered standard practice. Saltbush is generally in dynamic equilibrium with native birds, insects and other potential pests which it might host. It is possible that the impact of some of these might increase if large areas were planted to a saltbush monoculture.

Variation in palatability

Because saltbush plantings are essentially wild populations (with the exception of clones such as ‘Eyres Green®’) there can be great variation between plant size, shape, growth rate and palatability. Research has not yet identified the cause of palatability differences. For example, palatability was not related to levels of digestibility, crude protein, ash, oxylates or nitrates. However, sheep maintain better growth rates when eating the preferred plants.

Mustering

Sheep can be difficult to muster in dense saltbush plantings, particularly when the bushes have grown above sheep height. Leaving unplanted ‘laneways’ through dense saltbush plantings makes access and stock management easier.

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Prospects

Recent research

The SGSL research has greatly increased our insights into the best options for managing saltland, including dense saltbush plantings. The SGSL animal grazing experiments at Tammin and Yealering, WA, are highly relevant to dense saltbush plantings.

Establishment research
A major joint venture (including AWI, MLA, FFI CRC, DAFWA, DPIV, NSW DPI and Kings Park Botanic Garden) is investigating improved establishment techniques for a range of species that have traditionally proven difficult, including 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) that may enhance establishment of saltbush by direct-seeding. A key challenge 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.

The following preliminary results are available:

  • ‘Tweaking’ the seed combined with better sowing techniques. Early results from this work shows: (a) river saltbush has a requirement for light during germination and that this requirement can be met by priming the seed in gibberellic acid, and (b) germination in old man saltbush can be improved by priming with salicylic acid and kinetin. Early results suggesting benefits from the removal of bracts has not been replicated. Preliminary results from a field site at Meckering, WA, suggest that the seed treatments can improve the success of establishment with a cone seeder with old man saltbush but not with river saltbush. The seed in this work was precisely planted in a sandy soil at a depth of 1cm, a depth not previously been regarded as possible.
     
  • Use of herbicides. The case for pre-emergent herbicides to control competing grasses (especially sea barleygrass and annual ryegrass) was first made in 1997 on the basis of strong benefits with the niche seeder using Phenylcarbamoyloxy-2-N-ethylpropionamide. The new work is suggesting that if the seed can be buried, then some of the grass specific herbicides that were previously not suitable because the saltbush seeds were not buried may now be ‘back in the frame’.



Old man saltbush germplasm selection

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. Preliminary morphological screening is occurring using material from two sites. This will demonstrate the variability and heritability of traits, and may identify lines for early cloning and production of seed.

Future Prospects

Dense saltbush is a relatively unspecialised option recommended mainly for sites with high salinity (8-16dS/m) and low waterlogging risk. Such sites are quite hostile for most plants and so there are few alternatives if farmers wish to establish a saltland pasture.

The combination of relatively high establishment costs and the relatively limited productivity available from the high salinity levels at these sites restricts the potential to make a profit from dense saltbush plantings.

The potential for a breakthrough in direct seeding, to reduce the cost of establishment, is explored above, but without such an advance, the prospects for dense saltbush plantings across large areas is limited. In the short term, the greatest prospects for dense saltbush plantings seem to be on farms with:

  • small saline areas with high salinity but low waterlogging potential;
  • annual farm rainfall between 3000 and 400mm;
  • average winter temperatures above 13oC; 
  • a priority for amenity and environmental protection; and
  • the need for only a modest outlay for planting sufficient nursery raised seedlings to cover the saline site.
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