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SOLUTION 7

Vegetatively established grasses

 

7.4  Level of confidence in vegetatively established grasses

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How reliable is the information?

Marine couch and saltwater couch have been used by farmers with saltland for decades but there have been few serious studies of the productive potential for such saltland pastures. Many of the conclusions drawn about the vegetatively established grasses have been drawn from an extensive research project undertaken with Distichlis by RIRDC (the Rural Industries R&D Corporation) and published in 2002.

More recently there has been a PhD study focusing on the relative merits of kikuyu, marine couch, saltwater couch and Distichlis (‘NyPa turf’) as turfgrasses when irrigated with saline water (EC 13 dS/m).

The following information can be stated reliably:

  • Marine couch, saltwater couch and Distichlis are extremely salt- and waterlogging-tolerant;
     
  • Marine couch and saltwater couch are widespread and are therefore very adaptable – the same conclusion can probably be drawn for Distichlis, but it has not yet been widely tested around Australia;
     
  • Under the right conditions these vegetative grasses can provide good groundcover and some grazing in situations that would otherwise be unproductive or actively contributing to environmental damage;
     
  • Seed production either does not occur (the commercial Distichlis plants are clones, and all male), is very poor (saltwater couch) or the seeds can have poor germination ability (marine couch);
     
  • The vegetatively established grasses are not salt accumulators and therefore can be expected to be nutritionally similar to their non salt-tolerant relatives;
     
  • Because of the need to establish these species from ‘cuttings’, they are one of the more expensive options for the restoration of saltland;
     

The following information indicates where only a low level of confidence can be provided:

  • Establishment can be patchy, but the reasons for this are unclear;
  • Actual levels of pasture production from these vegetative grasses have rarely been measured;
  • Little is known about the agronomic management (weed control, fertiliser use) of these grasses;
  • Animals will graze these species but animal performance levels have not been reported.
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Farmer experiences

Because of the expense in establishment, these plants tend to be used mostly in horticulture as turf grasses in situations where the soil is saline, or where only saline water is available for irrigation. A good example of this is the use of saltwater couch on a golf course in Western Australia where the ‘irrigation’ water is as salty as half strength seawater. Under these conditions, saltwater couch has thrived. This story was featured in SALT magazine.

Marine couch has been widely used in Queensland, and some research results have been published, but farmer experiences have been poorly recorded. For more information, visit the CRC for Plant~based Management of Dryland Salinity website. In one example, the Barrett family from central Queensland have reported “By 1915 the land was cleared, and scalding started to appear by the mid-1930s. Landholders in the area recognised the problem and quickly planted varieties of salt-tolerant species such as marine couch and saltbush gathered from the Capricorn coast. This has saved a lot of our property, since these have spread across the salt-affected areas since then.”

The Mathews at Wickepin have been using the NyPa genotypes – especially NyPa Forage for a number of years but the results have not been widely publicised.

Richard Gunner’s case study (the Coorong, South Australia) appeared in SALT magazine, Issue 8. Richard had been exploring the use of NyPa forage because “the plant we really want is one that can withstand winter inundation, tolerate groundwater saltier than the sea and is palatable and nutritious for cattle. Over the past few years we have become very interested in a clone of Distichlis spicata that comes from Florida and has been selected for its forage qualities.”

The value of the vegetatively established grasses for the most salty areas is discussed by farmers and advisors at Manilla in northern NSW.

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Risks and challenges

Genetic variation. These salt-tolerant grasses can show exceptional diversity within a species – for example marine couch has from 10 to 30 chromosome pairs and its morphology ranges from short (<5 cm) mat-forming ecotypes to tall (~40 cm), erect ecotypes, with fine-textured to coarser leaves. Flowers vary from short compact ovoid panicles to longer narrower ones.

Given this level of genetic and morphological variation, similar variation in salt tolerance within species is to be expected. Success on the ground is likely to be highly dependent on genotype and therefore (if possible), vegetative material should be collected from sites that are similar to the intended establishment area, and that has the plant characteristics that are required.

Sources of germplasm. In general, there has not been enough consistent demand to develop continuous, or commercial supplies of planting material. Many farmers have collected their own supplies from other saline environments and allowed stands to thicken up over time. Distichlis is commercially available but if the couch grasses are required, then the best place to start is with the turf-grass genotypes as these types will at least be readily accessible and have had some selection applied.

Agronomic management. Because little is known about the agronomic management (weed control, fertiliser use) of these grasses, no firm guidelines can be provided. In reality, the productive potential of the highly saline/waterlogged sites where these vegetative grasses might be established is usually quite low, making it unlikely that the addition of further inputs would be economic outside of turf-grass situations. If the capability of the site is high enough to justify inputs such as weed control or fertiliser, then more productive grasses such as puccinellia or tall wheatgrass should probably be investigated. These grasses have the great advantage of being available from commercial seed suppliers.

Weediness. These vegetatively established grasses can be quite ‘weedy’ – in fact, if they did not have strong colonising ability, they would not be suited to saltland areas. Saltwater couch and marine couch are natives, and therefore do not have to be tested for their weediness as do imported plants. Weediness assessment has been carried out on the ‘NyPa’ Distichilis before it was allowed to be marketed as a turf and pasture grass for salt- degraded lands. The weed assessment noted that the saltgrass (Distichlis), in its native North American environment, “has spread to the irrigated lands, and become a pest in ditches, cotton fields, and other crops in the United States”. It is extremely widespread, occurring as far north as Canada and in subtropical environments such as Hawaii. The assessment further states that the grass “has adapted to a range of soil conditions ranging from intertidal river mouth deltas and hyper-saline saltflats to only mildly saline or alkaline soils. The grass can, once established, survive extreme annual droughts and is extremely competitive in very wet soils but is normally associated with inundated soils.”

In balance, this weed risk was deemed to be outweighed by the environmental benefits of revegetating saltland. However, these grasses should be used cautiously where there is local potential for them to become pests – primarily in irrigated areas where inundated soils and irrigation channels can provide an ideal environment.

Establishment. Studies with Distichlis have shown that establishment into previously grassed areas is problematic because of competition. Where the competition was removed by spraying with a knock down herbicide the establishment rate was good (80% survival) - however, establishment was poor where there had been no spraying with only 30% survival. Similar experiences are likely with the other vegetative grasses.

Cost. While the actual costs associated with establishing these grasses have not been documented, establishment is time consuming and expensive because the plants have to be propagated vegetatively and planted individually. This effectively makes broadacre establishment unlikely. In reality, intensive plantings of these grasses in southern Australia have been (and will likely continue to be) limited to amenity plantings (such as golf courses) and to small saltland areas on farm where costs and returns are not the primary considerations.

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Prospects

Recent research

Both historically and currently, there has been very little research carried out with these vegetatively established grasses.

A comprehensive experimental program and literature review was conducted by RIRDC when the NyPa Distichlis was introduced to Australia in the 1990s.

Modern research on marine and saltwater couch is focusing primarily on the value of marine and saltwater couch as turf-grasses. Three Australian groups that have been active in this area are:

  1. Don Loch and colleagues, from Queensland Department of Primary Industries and Fisheries, Redlands Research Station, Cleveland, Queensland.
  2. Tim Colmer and colleagues from the University of Western Australia.
  3. Bill Semple from the Department of Land and Water Conservation in NSW.

Future prospects

The high cost associated with vegetatively established species means that these grasses have very limited prospects in strictly commercial grazing operations. For such highly saline and waterlogged areas, Saltland Solution 6 (Puccinellia), or Saltland Solution 1 (Fence and exclude from grazing), or Saltland Solution 2 (Fence and volunteer pasture) may be more suitable alternatives.

As indicated by the current research efforts, the future prospects for the vegetatively established grasses are stronger as amenity or turfgrasses. It is likely that amenity areas will have increasingly restricted access to ‘fresh’ water and will focus more on using recycled and saline water sources. In these situations, these vegetatively established grasses can be ideal, and the high cost of establishment per hectare is not such a consideration.

However, as discussed in Production, there are saline sites where saltwater or marine couch will already be present and if grazed appropriately, can make a significant contribution to the ‘volunteer’ pasture. Top