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SOLUTION 6

Puccinellia based pastures

 

6.4  Level of confidence in puccinellia based pastures

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How reliable is the information?

Puccinellia based pastures are probably the most widely adopted saltland pasture system in Australia – there are at least 200,000 ha of puccinellia based pastures in the Upper South East and Coorong districts of SA.

Research into solutions for saltland in Australia have focussed primarily on 4 of the saltland options – ie. puccinellia, tall wheatgrass, dense saltbush plantings, and saltbush with under-storey. As a result, there is more research information on these options than any of the others, and there is more documented farmer experience. These factors combine to underpin the reliability of the information presented here about puccinellia based pastures.

For example, puccinellia based pastures are the only saltland option with well researched recommendations about fertiliser types and rates.

Puccinellia based pastures are a very reliable option in the right conditions (e.g. Upper South East of SA; other similar environments in WA; niches in Victoria and NSW – see also Most likely situations) and there is great deal of confidence in the establishment and management of these pastures.

It is important to get the site selection right, because while puccinellia can grow on sites without waterlogging and relatively high salinity, it is a poor competitor on such sites and can be out competed by other annual or perennial grasses. As such, puccinellia has minimal weed risk, and won’t dominate a sward like tall wheatgrass can.

The ‘sweet spot’ for puccinellia is when the surface salinity level is quite high (say 20-30dS/m – similar to saltbush), but with a substantially shallower watertable (ie more waterlogging) than saltbush can tolerate.

Importantly, as part of the underlying confidence in the puccinellia option, there are no known detrimental grazing issues – puccinellia does not accumulate salt in the leaves in the way many other saltland pasture species do.

Supply of seed is sometimes an issue as both supply and market demand can be very variable. Dry years in the Upper South East of South Australia (the primary seed source) reduce the opportunity for farmers to harvest significant quantities of seed. Farmer demand for seed varies with the weather, livestock prices, and the extent to which catchment based agencies are actively supporting the establishment of saltland pastures for production and environmental benefits.

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Farmer experiences

Because puccinellia pastures have been extensively adopted over large areas of the Upper South East of South Australia, there are numerous farmer case studies that cover many aspects of puccinellia based pastures. Some examples include: 

“Evolution of saltland management in the farm system”  
“Compressing history – many hands bring many experiences”  
“Integrating puccinellia with pigs”  
“Of droughts and flooding rains”  
“Puccinellia proves its place”  
“Pulling the plug”  
“Reclaiming productivity with puccinellia”  
“Getting the most out of puccinellia and tall wheatgrass”  
“Fitting saltland into the whole farm system”  
“Rising to the challenge” 

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Recent research

The Sustainable Grazing on Saline Land (SGSL) program and the CRC Salinity carried out a major R&D effort into saltland pasture systems and options. A network of five major research projects was run across southern Australia from 2001 to 2007. One of these research sites was located in the upper south east of SA and concentrated on puccinellia based pastures. Specific objective of the puccinellia research were:

  1. To develop grazing management strategies for puccinellia based pastures to maximise pasture and animal productivity, pasture persistence and the sustainability of the whole system;
  2. To determine the financial return from the systems under investigation;
  3. To understand the environmental impacts of these saline grazing systems; and
  4. To determine the optimum rate and timing of fertiliser applications for puccinellia pastures.

The conclusions were:

  • The puccinellia-based pasture options were the standout performers - essentially the best option for the Upper South East of SA. The puccinellia based pastures were significantly more productive than the unimproved pastures, both in terms of pasture and animal production. The addition of balansa clover made them even more productive.
     
  • The project confirmed local producer knowledge that balansa clover is excellent in the year of establishment, but ‘fades out’ dramatically over the next season or two. Carefully planned grazing management designed to especially favour balansa clover did not significantly slow the decline. The project showed that there is a very clear threshold of 10-15 dS/m (ECe) - balansa clover cannot persist in paddocks where this salinity threshold is exceeded at either seed set in spring or germination in autumn.
     
  • It might be best to promote puccinellia in a similar manner to saltbush – with and without legume understorey. For more information, see Saltland Solution 3 – Dense saltbush plantings and 4 – Saltbush and understorey. The “puccinellia with legume understorey” option would only be recommended for sites where balansa clover has a reasonable chance of regeneration – say below 16dS/m (the beginning of the ‘severe’ salinity category).
  • The economic assessment of these puccinellia based pasture options for the Upper South East of SA has confirmed that this pasture type can be highly profitable. In addition, measures of persistence and biodiversity value indicate these to be sustainable pasture options for the longer term.
     
  • The two grazing management strategies employed (continuous vs strategic) did not result in significantly different levels of plant and animal production - there were some small indications that strategic grazing may have resulted in slightly higher levels of balansa clover in the pasture sward, but overall grazing method seems to play only a minor role in the composition of puccinellia based pastures.
     
  • Nitrogen fertiliser significantly increased biomass production in puccinellia based pastures, but only when applied at levels above 25kg/ha. This result presents a significant challenge to extension – current practice is to apply small nitrogen dressings, but these gave the poorest responses. In addition, while larger nitrogen applications gave a better response per unit of nitrogen, the analyses within this project indicate that applying nitrogen to puccinellia is only marginally economic, except if wool prices are high. This makes recommendations about “the optimum rate and timing of fertiliser applications” problematic.
     
  • The case for developing a pasture legume for saltland that can replace the need for nitrogen fertiliser in puccinellia based pastures is very strong. The salt and waterlogging tolerant legume Melilotus may be a better option than balansa clover but this option is still being researched. Puccinellia based pastures respond well to nitrogen fertiliser, but it is only economic at high wool prices.
     
  • In line with other sites, this project confirmed that the average per hectare value of saltland pasture (puccinellia in this case) is highest when the area per farm is small, and while larger areas can be profitable, the increase in whole farm profit becomes smaller with each added hectare of saltland pasture.

In WA, the principles of zonation between puccinellia and tall wheatgrass were examined in a PhD project (completed in 2008). This work showed that puccinellia had far greater tolerance to salinity under waterlogged conditions than tall wheatgrass. Under saline/waterlogged conditions, puccinellia formed roots that contained aerenchyma (hollow roots that act like “snorkels” conveying oxygen to the root-tips); it also had a barrier at the root surface that reduced the rate at which oxygen leaks out of the aerenchyma into the surrounding soil. Tall wheatgrass had neither of these adaptations.

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Risks and challenges

Establishing puccinellia based pastures is ‘standard management’ for saltland in the Upper South East of SA, and most of the dedicated research on puccinellia based pastures has been carried out in that region. Therefore, the level of knowledge in the farming and farm advisory community is much higher than for other regions in Australia that might have saltland suitable for puccinellia based pastures. This inevitably means that the risks and challenges for puccinellia are lower in South Australia than for the other states where there is not the same amount of ‘local knowledge’. This consideration means that farmers outside SA may need to trial puccinellia on smaller areas before trying larger paddocks, although there are factsheets available on puccinellia for WAVictoria as well as for SA.

Puccinellia has a small seed and therefore a small seedling. This means that early growth (after emergence) is slow and the seedling is a very poor competitor against weeds. Seedlings of sea barleygrass (often the dominant species on saltland suited to puccinellia) are much larger and grow more quickly, and if not well controlled, can overwhelm puccinellia. Good weed control is essential prior to sowing and after emergence.

In addition, the slow seedling growth means that there must be minimal grazing in the first year as the plants need to be given time to tiller out and establish a sward that will be competitive with weeds in following years. It follows that puccinellia poses minimal weed risk because it is not at all competitive on sites with lower levels of waterlogging and salinity - high tolerance to waterlogging is puccinellia’s most characteristic adaptation.

Sourcing good quality seed can be a challenge as not much seed has been harvested in last few years due to dry conditions in the Upper South East of SA. Furthermore, the grower group in SA that was responsible for much of the seed supply, has disbanded, so significant market failure in this area is possible.

There are no major animal nutrition/management challenges with puccinellia based pastures because puccinellia does not accumulate salt, it is highly palatable even when it has hayed off, and the seeds are small and non-invasive. 

Weed control, grazing management and fertiliser use are the primary, on-going management challenges.

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Prospects

Current research

Puccinellia along with tall wheatgrass have long been the mainstay grasses for revegetating saline discharge areas, particularly in the eastern states and SA. Dense saltbush plantings and saltbush with under-storey have been the preferred solutions in the generally lower rainfall deeper watertable saltland sites in WA. However, work by the CRC Salinity brought a focus to other grasses, some of which exhibit even higher salt tolerance than puccinellia.

The Salinity CRC screened a range of legumes for salinity and waterlogging tolerance - see Students and salt (page 5 of Focus on Salt Issue 35) and Saltland Solution 10 - Legumes for saltland, and the evaluation of grass species is a continuation of that work. Grasses are generally more salt-tolerant than legumes, so the salinity levels used to challenge the grasses have been twice as high as that used for the legumes.

In these trials, puccinellia growth was reduced by 18% when grown at a salinity level of 24 dS/m. One of the native grasses tested (rats-tail couch or Sporobolus mitchellii) had a similar salinity tolerance to puccinellia, with a 16% reduction in growth when grown at a salinity level of 24 dS/m. A range of other grasses have been identified with salt tolerances falling between puccinellia and tall wheatgrass.

The challenge for on-going research is to identify species that combine high production potential with high tolerance to salinity and waterlogging.

Future prospects

There are currently no major research projects focussing on puccinellia pastures, but this must be balanced against the fact that puccinellia based pastures have probably received more research attention than any other saltland option with the possible exception of saltbush.

This lack of current research is not a negative reflection on the future prospects for puccinellia based pastures in Australia. It is much more a reflection of the fact that salinity research has declined in all southern states in recent years as risk estimates have been lowered and the run of dry years since the turn of the century has dramatically slowed the rate of salinity expansion and the area of waterlogged/saline land.

Puccinellia based pastures will continue to be the mainstay ‘saltland pasture’ in the Upper South East of South Australia. Puccinellia based pastures will continue to find limited niches in WA, Victoria and NSW, but in those states, puccinellia will much more often be part of a saltland pasture mix than a pure puccinellia based pasture.

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