Are these the best plant choice?
Puccinellia and other salt tolerant species are cheaper to establish and likely to be more productive for livestock. Get professional advice before making large investments in these vegetatively established grasses.
Other options for these sites
Waterlogging can be reduced in several ways, and this may result in more profitable options for land use.
Occurrence of the three species
Marine couch (Sporobolus virginicus) is a C4 perennial grass with a worldwide distribution in latitudes ranging from tropical to temperate. It occurs over much of the Australian coastline, bordering sandy beaches, salt marshes and mangroves. There are native and alien Sporobolus species in Western Australia (Genus: Sporobolus – link to FloraBase). Sporobolus virginicus is native.
Saltwater couch (Paspalum vaginatum) is native to the Americas and parts of WA, where it grows in tropical and subtropical regions (a C4 plant). It has been introduced throughout the other tropical areas of the world, where it is sometimes an invasive weed. It is also cultivated as a turf grass in many places (Wikipedia).
Distichlis (Distichlis spicata) is native to the Americas, where it is widespread. It has been introduced to other continents and has naturalized in many environments. It is extremely salt tolerant.
Description of the three species
Marine couch
Marine couch (Sporobolus virginicus) is a rhizomatous, stoloniferous, tussocky perennial grass (Figure 1). It grows to 0.1–0.5m high. The flowers are green–purple, and present from January to December.
It grows in a similar ecological niche to saltwater couch, having high tolerance to waterlogging and moderate tolerance to salinity.
It tolerates pH of 5–9.
Marine couch occurs as morphologically distinct variants and chromosomally distinct races. The plants vary from short prostrate, mat forming to tall erect ecotypes, with fine-textured to coarse leaves.
Typically, the leafy culms emerge from creeping, branched rhizomes. The leaf blades are flat, and taper to a fine point. They occur almost opposite each other on the culms, which have alternate long and short nodes. The flowers (which can occur throughout the year) occur on lead-coloured spike-like panicles, that are 2–8 cm high and 5–10 mm wide. The leaves have salt glands.
Saltwater couch
Saltwater couch (Paspalum vaginatum) is a semi-aquatic stoloniferous and rhizomatous C4 perennial that develops dense swards. It flowers on a 2 or (rarely) more branched seed head; flowers are mostly in late spring through to autumn.
Saltwater couch has a V-shaped seed head (see photo) similar to water couch (Paspalum distichum) with which it is frequently confused. Distinguished from Paspalum distichum by the shiny, not hairy, glumes (hand lens needed to see this) and growth in very saline areas (Figure 2). P. distichum is not tolerant of highly saline conditions, but nevertheless grows in quite salty places.
Distichlis
Is available in Australia as NyPa ForageTM, a male clonal selection that can only be established with vegetative material. It does not produce seed. Distichlis spicata is a deep-rooted low growing erect to semi-erect perennial that forms dense swards (Figure 3)). It spreads by stolons and new shoots from nodes on rhizomes. Its specialised roots and salt glands enable this plant to thrive in saline soil and water. Distinguished by alternate striate, stiff, pointed leaves and extensive root system.
Other selection
Benefits
Production
Despite the lack of bulk, these three grasses can provide useful grazing, depending on the genotype and form.
Farmers report that both sheep and cattle will graze the vegetatively established grasses.
Often saline sites remain wet with actively growing plants when the rest of the farm contains only dry, carry over feed – this greatly increases the ‘value’ that any saltland pastures can contribute in a whole farm system.
Overall production is usually low – of the order of 1t/ha over the growing season – though in good seasons with added fertiliser, production is ecpected to be much higher.
Animal nutrition issues
Both sheep and cattle will graze these vegetatively established grasses, which are often the only green material available on farms in southern Australia in summer and autumn. This production of out-of-season feed is one of the primary benefits saltland pastures provide to a grazing enterprise.
General observations are:
- There are no known nutritional problems associated with grazing these vegetatively established grasses. They do not accumulate salt, but rather have glands on the leaves that exude salt. Plants that accumulate salt (such as saltbush) can be nutritionally challenging for livestock because of both the high salt content in the diet and the various compounds in the plant material that allow the plant cells to function in the presence of high internal salt concentrations.
- As with all grasses, forage quality (both protein concentration and digestibility) decreases with increasing age of the plant material. Long rests between grazings are best for the plants, but produce lower quality feed, while short rests are best for the animals but can reduce the persistence of the plants.
- Forage quality can be improved by the use of fertiliser, but on highly saline, waterlogged and poorly productive land, such fertiliser applications may not be economic.
- Summer-growing grasses (whether salt-tolerant or not) are not as nutritious for livestock as cool season grasses. They tend to have higher fibre content (lower digestibility) and lower protein concentrations. Distichlis has been recorded to have from 6 to 17% protein and from 45 to 60% digestibility – the higher nutritive values were associated with applications of N and K fertiliser.
Water use
These grasses grow on saline and waterlogged sites, and they are active during the warmer seasons when water use can be expected to be relatively higher – this will be especially true if there is good groundcover and a high leaf area index (ratio of leaf area to soil surface area). However, the preferred sites are usually discharging saline water, and evapotranspiration of the plants is unlikely to dry the surface.
If the intent is to dry the site, we recommend a combination of surface and subsurface water management, and other plant species.
Amenity and environmental
Increasing ground cover increases amenity and environmental benefits.
Increased ground cover reduces surface soil evaporation and salt build-up, protecting the soil from erosion, and re-establishing some floral and faunal biodiversity. Amenity is improved by establishing green and growing plants on previously bare saline scalds.
Marine couch, saltwater couch and Distichlis are all used as turf (or amenity) grasses because of their ability to colonise saline sites, and to establish a full mat of groundcover so their amenity value can be high.
Vegetated areas – compared to bare saltland – have greatly increased soil microbial activity and biomass, but still substantially below the levels found in non-salt-affected pastures.
Site conditions
We recommend measuring salt and waterlogging levels on each site before deciding on species and management. These three species prefer waterlogged and moderately saline sites.
Common indicator species
The most suitable areas to establish these vegetative grasses will be very wet (boggy) in winter and may be relatively bare (but still wet or at least moist) in summer.
The most common indicator species would be sea barley grass, cotula, curly ryegrass and perhaps puccinellia in the most waterlogged and saline situations.
Salt tolerance
These grasses are highly salt-tolerant, but assessing the differences in salt tolerance between the
species is not easy. Results vary between trials, between species and between accessions within species.
Research in Queensland has shown that marine couch, saltwater couch and Distichlis have relatively similar ranges of salt tolerance, but are highly variable within each species. For example, for marine couch, saltwater couch and Distichlis irrigated with saline water and cut every two weeks for 12-16 weeks, the following ranges of salinity in the irrigation water reduced shoot dry weight by 50%:
- Marine couch: 12 to 37dS/m (in other words, the most salt-tolerant accession had its yield reduced by 50% when the irrigation water had 37dS/m, while the least salt-tolerant accession required only 12dS/m in the irrigation water to reduce growth by 50%).
- Saltwater couch: 13–40dS/m (depends on accession).
- Distichlis (NyPa Forage): 27dS/m.
To indicate how salt tolerant these species are, kikuyu had a 50% decrease in shoot dry weight when irrigated with water of EC 4–5dS/m.
Field observations in NSW have shown that both marine couch and saltwater couch can survive with exceptionally high surface (0–10cm) soil salinities (ECe values of 40-100dS/m).
Waterlogging tolerance
All plants in this category are highly waterlogging tolerant so it is unlikely that any expense associated with improving surface water management would be worthwhile.
Potentially, improved surface water management (reduced waterlogging) may render a site more suited to a less waterlogging tolerant (but potentially more productive and easier to establish from seed) alternative such as tall wheatgrass.
Land capability
These three species will grow on a broad range of soil types if the site is waterlogged and saline.
Climatic requirements
These vegetative grasses are all C4 species (i.e. subtropical grasses that have little ability to grow at temperatures below about 15°C). They prefer climates with:
- mild winters and low levels of frost
- warm to hot summers
- medium to high rainfall (more than 400mm annual rainfall)
These species will not be as productive in cold, frosty locations, although marine couch and saltwater couch have performed well on saline sites in inland New South Wales, and Distichlis has been used commercially in the south-west of Western Australia.
Management
Picking the right species and varieties
There is extensive diversity within these vegetatively established species – for example marine couch 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. This does not apply to the commercial Distichlis cultivar (NyPa Forage), which is a clone.
Given this level of genetic and morphological variation, similar variations 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 have the plant characteristics that are required.
Distichlis ‘NyPa Forage’ has been best studied under Australian conditions and is now available through Elders.
There is also a native species Distichlis distichophylla (Australian saltgrass) which is listed as endangered in NSW. Australian saltgrass is a spreading perennial grass, in the form of a loose, prickly clump of spreading underground stems (rhizomes). The foliage is distinctive, with a row of thin stiff leaves to 50 mm on each side of the stem. It often grows with marine couch (Sporobolus virginicus), and is best-distinguished in summer when in flower or seed.
Marine couch is a halophytic perennial grass with a world-wide distribution ranging from tropical to temperate latitudes. Saltwater couch was introduced into SA from South Africa in 1935 as a forage for salt affected areas. By 1945, it was being used in WA for similar purposes.
In general, there has not been the consistency of 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, though this can be a slow process. Distichlis is commercially available, but if marine or saltwater couch 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.
Establishment
The vegetatively established saltland species are all quite similar in that they are creeping, relatively fine-leafed grasses that spread via rhizomes (stems creeping along below the soil surface) or stolons (stems creeping along the soil surface) and often have both.
These grasses have to be propagated vegetatively and planted individually, making broadacre establishment costly and time consuming. However, as each of these plants spreads laterally by rhizomes and/or stolons, it should be possible to establish relatively continuous stands by planting vegetative material at relatively wide spacings, protecting the material from grazing and allowing the plants to ‘fill in’ the bare patches. This is especially true where the site is not already supporting other grasses that will compete strongly with the sown species.
Planting system
Planting vegetative material is quite expensive per hectare, making this method most suited to small areas of saltland, or where time is not critical – widely spaced plants can be established and allowed to gradually spread.
Distichlis has been planted – the harvested, vegetative material – with modified vegetable planters: two adapted broccoli vegetable planters planting rhizomes in previously ripped lines. This system was relatively labour intensive, needed two people to dig and prepare rhizomes and to operate the tractor and planter, planting at about 2 ha/day.
Distichlis across southern Australia spreads at approximately one metre per year under suitable conditions, though this rate tends to slow with time. Rates of spread can be very slow in heavy-textured highly saline soils.
Time of planting
The planting window can be very narrow and the risk of failure can be higher than for non-saline sites.
These grasses do not grow at temperatures below about 15°C. Late autumn or winter planting is not usually successful. Spring planting is more suitable, but waterlogged over winter and early spring can be a problem.
Late spring planting in many situations may not give the planted material sufficient time to establish before the sites dry off in summer.
Weed control
Weed control is still a major issue for establishment of these grasses. Where weeds are likely to be a problem, use a knockdown herbicide.
Grazing options and management
Most of this information is from field observations:
- There is limited grazing value over winter, because these warm season grasses grow very slowly in winter, and most sites suited to these grasses will be heavily waterlogged and therefore highly susceptible to pugging damage.
- The vegetatively established grasses seem to be able to tolerate extremely heavy grazing, provided they are allowed time to recover.
- Under continuous stocking in summer, the grazing pressure can be extreme and the grasses will eventually get eaten out.
- Rotational or tactical grazing allows plants to recover and persist.
Economics
Establishment is time consuming and expensive because the plants have to be propagated vegetatively and planted individually.
Production on highly saline and waterlogged sites will usually be modest.
This effectively makes establishment viable for only amenity plantings (such as golf courses) and small saltland areas on farm where costs and returns are not the primary considerations.