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Sub-tropical grasses with limited salinity tolerance


9.3  What are the benefits from sub-tropical grasses?



Rhodes grass and kikuyu are highly productive sub-tropical grasses, capable of yields in excess of 20t of dry matter per hectare under high rainfall and high fertility. In practice however, yields will be much lower than this on non-saline land, and lower still if salinity and/or waterlogging are present – though definitive studies have not been carried out.

For both kikuyu and Rhodes grass, production falls substantially as salinity increases because of their limited salinity tolerance. When salinity levels reach the upper level of the moderate salinity range (8 dS/m), production will probably be negligible, partly because of the direct effect of the salinity on these grasses, and partly because of strong competition from other, more salt-tolerant species. This competition may come from species such as tall wheatgrass that were sown as part of a shotgun mix, or from ‘weed’ species invading the saline area.

Countering this trend is the fact that the growing season on saltland is typically greater than for surrounding soils because of the greater water supply. If Rhodes grass and kikuyu have access to moisture over summer on land with low to moderate salinity, then production can be high. Most likely though, production on saltland will be small due to the effect of salinity and the generally low nitrogen status of saline areas – although even small yields can be valuable if produced ‘out of season’ when green feed is not available on other parts of the farm.


Water use

Both kikuyu and Rhodes grass are deep rooted, summer growing species and therefore are able to use much more water over summer than their more temperate, winter growing relatives. We are not aware of any studies that have reported comparative water use for these species in saline situations, but from other research and anecdotal evidence, we can conclude:

  1. Saltland pastures can have a significant effect on local water use, primarily because there is an increase in evapo-transpiration under well managed saltland pastures compared to untreated controls. This is likely to be the case for sub-tropical grasses because they are both deep rooted and summer active, as long as the soil water is only mildly saline. In addition, there is clear evidence that under favourable circumstances (watertable shallow but not overly saline) saltbush and tall wheatgrass (and possibly other perennial saltland species) can draw directly from the groundwater and further lower the watertable.
  2. As a result of the soil water use by saltland pastures, the salt content of the upper soil layers can be further reduced by rainfall leaching, potentially keeping the site suitable for species that are not very salt tolerant, such as kikuyu and Rhodes grass. Most research on this topic has been with saltbush stands that draw down the watertable and can then support a less salt-tolerant under-storey, and in suitable situations, the sub-tropical grasses should behave similarly.
  3. Within saltland pastures, water use will tend to be least by annual species and those perennials (such as puccinellia) that dry off over summer, and greatest by pasture species (such as saltbush and the sub-tropical grasses) that grow actively over summer.
  4. Trees will use more water (soil water and from the watertable) than pastures if the groundwater is not so saline as to prevent roots from accessing it. Direct comparisons between saltland pastures and trees are rare, but work in central NSW has confirmed that trees on saltland can increase water use and lower the watertable which should dramatically reduce surface run-off and salt export from saline sites.

Amenity & environmental

Farmer case studies have consistently shown that while profitability is the major consideration in the way successful farmers run their businesses, it rarely dominates the decisions associated with managing saltland. This is partly because most farms have salinity on only relatively small areas (the national average is about 20ha per farm but in the eastern states it is more likely to be 10ha), and partly because saltland is a highly visible ‘blight’ on the farm landscape.

Groundcover is the key to most of the amenity and environmental benefits from revegetating saltland, and both Rhodes grass and kikuyu are capable of rapid spread via stolons. For the environment this involves reducing surface soil evaporation and salt build-up, protecting the soil from erosion, and as the basis for re-establishing some plant and animal biodiversity. Amenity value comes from establishing green and growing plants on previously bare or weedy saline scalds.

However, while that is true in general for saline sites, those sites that will support Rhodes grass and/or kikuyu are only mildly saline and will not usually be bare unless they have been seriously overgrazed. It is more likely that such sites will have been invaded by waterlogging- or salinity-tolerant weed species so the amenity and environmental gains may be relatively minor.

Even if such a site is bare, groundcover can be quickly re-established on this class of saltland simply by fencing and conservative grazing without the expense associated with pasture establishment. In other words, if groundcover and amenity are the primary motivations behind rehabilitating saltland that is suited to sub-tropical grasses, then there are cheaper alternatives. These species should only be considered if establishing a productive pasture on the saltland (as well as amenity or environmental gains) is one of the objectives.

There is increasing recognition of the role that saltland pastures can play in improving catchment outcomes and this is translating into institutional support for saltland pastures, including the sub-tropical grasses because of the environmental and amenity values they provide. Many organisations that support both agriculture and natural resource management are providing financial support and technical assistance to assist farmers to assess their saltland, and to revegetate it for productive or conservation purposes. Such assistance is on a state by state or catchment by catchment basis, so local enquiry is essential.


How do the $$$s stack up?

The Sustainable Grazing on Saline Land (SGSL) program showed that across southern Australia, saltland pastures could provide a profitable investment. The final report from the SGSL Economics Theme stated “Introducing improved pasture species to salt-affected land to increase the feed value for livestock is profitable across a broad range of environments, production conditions and commodity price assumptions, according to the results of this study.”

There are few studies that have looked specifically at the economic returns from sub-tropical grass based pastures on saltland – one exception is from Glen Oliver’s property in the North Stirling Basin. A summary of the economics is shown below or click here to read the full story.

Economic assessment, North Stirling Basin, NSW

The total annualised stocking rate on the 26ha of perennial pasture studied on Glen Oliver’s farm in the North Stirling Basin, NSW was 3.6 DSE/ha and produced 121kg of sheep meat valued at $148 per hectare. In addition 16kg of greasy wool at a value of $54 was grown by the ewes and weaners.

This resulted in a gross margin of $150/ha, which rises to $200/ha when net value of tall wheatgrass seed is added – seed is harvested annually from the case study paddock. These figures include pasture establishment costs and they compare very favourably with the profitability for production from non-saline land in the Great Southern of WA.

[Note - the contribution from the sub-tropical grasses in the mix is probably relatively minor given that the site is harvested for tall wheatgrass seed]

More generally, however, the profitability of saltland pastures is complex because up to half the benefits typically come from saltland pastures providing ‘support’ for the cropping and grazing on the rest of the farm. This may be out-of-season feed allowing a higher stocking rate across the rest of the farm; the additional grazing resource allowing more cropping while maintaining stock numbers; shelter (at least with saltbush) for lambs or off-shears sheep; and perhaps also increased value of their real estate asset when the salinity problem is seen to be manageable. In addition, many farmers establish saltland pasture to improve the amenity value of their working and living environment, and to achieve that aim will accept a lower rate of return than they would demand of other on-farm investments.

Notwithstanding these benefits, the SGSL program clearly identified several factors that can undermine the profitability from saltland pastures, and we can apply these general conclusions to the sub-tropical grasses:

  • Infrastructure costs can be a relatively significant factor for any saltland pasture if fencing and water are required for a small site;
  • Establishment costs are a primary determinant of profitability and can vary greatly for different saltland systems (in the SGSL program, the variation across 20 farm sites in WA was from $77 to $324/ha). In general, the costs of establishing a pasture based on sub-tropical grasses will be similar on saline or non-saline sites;
  • Risk of  failure is significantly higher than for non-saline pastures, particularly if the site is waterlogged or sodic (as is often the case), as well as being saline. Sowing sub-tropical grasses is inherently more risky because they have to be sown in spring when soil temperatures are rising and soils are often drying out, and this risk may be increased on saline sites;
  • Pasture productivity – for most plants, including the sub-tropical grasses, the saltier the site, the lower the pasture and animal production that can be expected;
  • Nutritive value of the pasture – many saltland species contain either salt or other compounds in the leaves that help them survive the inhospitable saline environment, but that can be detrimental to grazing animals. The sub-tropical grasses do not have any of these limitations so nutritionally, we can expect them to be similar to their non-salt-tolerant relatives;
  • Product prices – the cost of ongoing inputs such as fertiliser or supplements and the prices paid for meat and wool products will always impact on the ‘bottom line’ of any pasture system and the sub-tropical grasses are no exception.

In conclusion, the sub-tropical grasses are likely to be profitable if used in the appropriate, mildly saline circumstances. However, these circumstances (ie warm temperatures, summer rainfall, mild salinity, limited waterlogging and reasonable soil fertility) are not widespread.