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Unit 4 - Plant and animal performance
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Unit 6 - Do the $$$'s stack up?
Unit 7 - The saltland toolbox
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UNIT 3

Can I trust the technology?

 

3.3 Confidence in saltland species

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Salt-tolerant pastures and fodders have been known for centuries, particularly in the Mediterranean region and arid lands of the Americas where animals have grazed on saline lands. While the basic plant physiological responses to salt have been long understood, development of more profitable salt-tolerant varieties and cultivars, and management techniques, has been relatively recent. There are 4 groups of salt-tolerant plants - shrubs, grasses, legumes and crops.

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Saltbush and other salt-tolerant shrubs

Pioneering work on saltbush (Atriplex species) and bluebush (Maireana species) commenced in Western Australia in the 1950s and continued under Clive Malcolm. Field trials with plant accessions from the Middle East, USA and other parts of WA were established in the 1960s, testing establishment techniques, grazing potential and sustainability. For more information, see Golden Pastures.

Broadacre establishment was developed with WA farmers who helped ensure that this was both practical and economical. This important feature of saltbush research recognised that salinity occurs on the complete range of soil types and conditions. About the only thing they have in common is low nutrient levels and the likelihood of waterlogging shortly after the break to the season.

Paddock trials showed a considerable increase in sheep grazing days on saltbush compared with unsown paddocks. A feature of saltbush is its ability to locally lower saline watertables, the amounts depending on the leafiness of the plants in summer, thereby enabling the development of relatively favourable conditions for establishment of less salt-tolerant grasses and legumes among the saltbush.

Clive Malcolm’s work identified the generally superior qualities of river saltbush (Atriplex amnicola), particularly in terms of growth rate, plant habit and recovery from grazing. However, he also found among river saltbush large variations in establishment rate from seed and biomass production, indicating that significant gains are to be made from selection and breeding programs. Oldman saltbush (Atriplex nummularia) is also regarded as a saltbush of major significance. It is deeper rooted and of higher nutritive value than river saltbush, and grows in slightly higher parts of the saline landscape.

Of all the saltland pasture options, there is probably the most high quality information about the shrubs - especially saltbush. Fact sheets on all aspects of saltbush establishment and management are available from state departments, the CRC Salinity (Future Farm Industries CRC) and the Saltland Pastures Association.

On this website there are 2 Saltland Solutions that provide specific detail on the use of saltbush on saltland – see Saltland Solutions 3 - Saltbush in dense plantings and Saltland Solution 4 - Saltbush and understorey.

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Grasses

The two most commonly used salt tolerant grasses, puccinellia (Puccinellia ciliata) and tall wheatgrass (Thinopyrum ponticum), have been applied in saline areas for about 50 years, particularly in WA, SA and Victoria. Tall Wheatgrass is no longer recommended in Victoria because of its weed risk assessment.

Puccinellia is the more salt and waterlogging tolerant of the two, but tall wheatgrass is capable of producing more biomass.

Many graziers have become wary of tall wheatgrass because of its lack of palatability, particularly if allowed to grow rank, and its tendency towards excessive ‘clumpiness’ which hinders farm traffic across paddocks. There has also been concern expressed in some areas about the potential for tall wheatgrass to become an environmental weed. The development of the cultivar Dundas has improved palatability. Farmers have gradually become more aware of the management needed to prevent tall wheatgrass from forming large clumps and minimise its weed risk. Part of the management challenge is that farmers will understandably often rank management of their least productive land near the bottom of their priorities.

Until recently, relatively limited research had been undertaken on puccinellia in Australia. Trials in SA had shown that the plant responds well to nitrogen and to rotational grazing, and wool growers were aware of the benefits of an effectively seed-free environment for lambs. However, there remained questions about the economics of extra investment or effort in puccinellia pastures until this was explored in the SGSL Program.

In addition, there is now some information available on the vegetatively established grasses with significant salt tolerance. One species which has attracted considerable research attention is the saltgrass distichlis. Australian trials with vegetatively propagated distichlis suggest that the plant grows best in moderately saline land with shallow water-tables. There has been little research conducted on other vegetatively propagated salt-tolerant grasses such as saltwater couch.

Given the very variable nature of saline sites there are also opportunities for many mildly salt-tolerant grasses, both temperate and sub-tropical.

The CRC Salinity has tested a wider range of potentially salt and waterlogging tolerant pasture and forage plants which would give farmers across Australia access to a greater range of species, and provide greater diversity and resilience in sown pastures.

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Legumes

Finding a productive and salt-tolerant legume is something of a holy grail for saltland farmers and researchers. However, legumes are usually much less salt-tolerant than grasses, apparently due to their relative inability to exclude the toxic salts that disturb enzyme activity once taken up into the plant. Furthermore, for legumes to achieve their potential they must ‘fix’ nitrogen, which means that not only do you need a salt tolerant legume, but also a salt tolerant rhizobia and a symbiotic relationship between the two. In other words, three quite unlikely phenomena need to converge, and so far they have largely failed to.

Unfortunately, subterranean clover, the most commonly sown pasture legume in southern Australia, has very low salt tolerance, and is among the first pasture species to disappear with the encroachment of salinity.

Saline sites tend to be seriously nitrogen deficient for pastures, and this in turn relates to the relatively low salt tolerance of most legumes. (This nitrogen deficiency can be greatly exacerbated by waterlogging which causes soils to become oxygen deficient and leads to nitrogen loss through the process of “denitrification”).

Research conducted in the 1990s led to the development of cv. ‘Frontier’ balansa clover, which captures balansa’s usual waterlogging tolerance, but with early maturing characteristics to avoid the failure of seed set as soil salinity levels rise in spring. Balansa is a tantalising prospect as it often performs exceptionally well in the establishment year, but even Frontier has proven unreliable in subsequent years. Research in South Australia has identified that germination of Frontier often occurs with season-opening rains when surface soil salinities are still high so establishment fails. On the other hand, sowing later, the opening rains have leached the salt from the soil surface can be highly effective.

Strawberry clover is recognised as a moderately salt and waterlogging tolerant perennial. While lacking the productivity of some alternative legumes, recent research shows that it displays excellent persistence in drought conditions.

Many other legume species are being researched by the Future Farm Industries CRC and several (especially Melilotus and burr medic) show promise as suitable species for moderately saline conditions in southern Australia.

These species stand out by combining relatively good (for a legume) salt tolerance with high levels of dry matter and have out-performed the control species, balansa clover, strawberry clover and lucerne. The suitability of Melilotus species has attracted considerable interest and lines are now available that have reduced levels of the toxin coumarin.

See also Saltland Solution 10 – Legumes for saltland

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Crops

Barley is the most salt-tolerant of the cereal crops and can provide economic returns from sites that can no longer produce wheat crops.

Researchers at the Future Farm Industries CRC are introducing both salt and waterlogging tolerance to wheat by crossing it to wild relatives such as sea barleygrass (Hordeum marinum) that has the exotic genes needed to enhance these tolerances.

This is relatively long term research which, even if successful, is unlikely to introduce cropping onto severely salt-affected land. However, there would be great rewards if it enabled profitable cropping on land that is currently marginal or unprofitable due to low to moderate salinity and/or waterlogging.

In parallel to this research, scientists at the Australian Centre for Plant Functional Genomics are researching the genetic make-up of both wheat and barley. They aim to modify crop plants in order to increase their productivity on saline soils. Successful breeding of salt-tolerant wheat in Australia was never going to be simple – largely because the locations in which salinity is a major problem are usually low in the landscape making waterlogging a companion constraint. In addition, it is likely that salt- and waterlogging tolerance is likely to be controlled by many genes. We expect that it could still take a while to identify all the relevant genes and learn how these can be manipulated together.

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