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UNIT 2

Saltland Basics

 

2.5  The case for managing discharge

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The appearance of dryland salinity has been observed on farms across southern Australia since the early part of the 20th Century. As early as 1924, the association between clearing native vegetation and the on-set of dryland salinity was reported in the scientific literature.

The National Land & Water Resources Audit (2000) reported on the extent of existing salinity and the inevitability of dryland salinity being an on-going feature of the agricultural landscape. Prior to this there were only sporadic efforts to understand and manage saltland in Australia. The Audit recommended that all state salinity strategies contain explicit plans that included the ‘living with salinity’ option.

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Where does discharge occur?

While it is difficult to estimate the actual area of dryland salinity that will occur in a catchment, it is relatively easy to map where it could possibly occur. Because it is caused by saline groundwater rising towards the soil surface and into the root zone, dryland salinity tends to occur in the lower parts of the landscape. However groundwater can also form perched watertables where the lateral flow is interrupted by geological features, break of slope or man made structures such as roads. Often salinity interacts with waterlogging on saltland soils, as this interaction can have additional adverse effects on plant growth and survival.

Where the landscape is very flat, such as over much of the South West of Western Australia and the Upper South East of South Australia, the area affected by dryland salinity can be extensive. However, in many other areas dryland salinity appears as relatively small ‘patches’ scattered along the lower parts of the local landscape. The result is lots of farms, each with small areas of dryland salinity.

The survey of farmers with saltland undertaken by the Australian Bureau of Statistics (ABS) found that there was about 2 Mha of saltland reported by farmers as showing signs of dryland salinity, scattered across nearly 20,000 farms – simplistically an ‘average’ of 100 ha per farm. However, salinity is not democratic so the impact of salinity on different farms is highly variable. Most farms have relatively small areas affected, but some farms have very large areas.

At about the same time as the ABS study, a survey of woolgrowers across Australia found that 41% of all farms had areas affected by dryland salinity. While the salinity estimates from the two surveys cannot be directly compared, the woolgrower survey concluded that because of the areas per farm are not normally distributed, a mean value should not be calculated, and that using the median figure was more appropriate – in this case the median, or middle value was about 20 ha.

The unevenness of distribution of saltland across farms can be even more apparent in a severely affected state like Western Australia. The Land Monitor database (determined from LandSat imagery) suggests that the median farm in Western Australia is 2.8% salt affected. However the same dataset shows that the most severely affected 10% of farmers have more than 18% of the farm salt affected.

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Opportunities for productive use

The National Dryland Salinity Program commissioned the first comprehensive assessment of the ‘opportunities’ that saline land and water resources in the landscape might provide. In 2000 the Options for the Productive Use of Salinity(OPUS) project explored in detail a large range of possibilities, including various saltland pastures, saltland forestry, aquaculture, algae/seaweed, date palms and salt/mineral extraction options. The conclusion from the OPUS project was that most of the possibilities were very limited. The only realistic possibility was the development of saltland pastures for the existing grazing industries.

Since the OPUS project was completed a small number of salt/extraction enterprises have continued and there have been further trials with saline aquaculture. However, the prospects still appear to lean strongly towards saltland agronomy.

Although there had been limited research into saltland grazing systems during the 20th Century, farmers across the country had been ‘experimenting’ with saltland pasture and grazing options. Insights, a publication from the Sustainable Grazing on Saline Land (SGSL) initiative, presented the stories of 10 farmers who were actively tackling their saline land. These were inspirational stories of farmers who had strong pride in the appearance of their farms, had found that actively managing saltland fitted well into their farming systems, and were positive about their future in the grazing industries.

Seventeen issues of SALT Magazine have also carried a consistently positive message from farmers managing saltland.

Since Insights was published, SGSL and the CRC Salinity built a strong case (with economic, social and environmental aspects) for better managing saline land.

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Advantages for farmers

The 2007 publication Prospects for profit and pride from saline land concluded that the economic prospects from saltland pastures are good, and in some cases excellent. Saltland pastures on medium and high capability saltland can be both productive and profitable. The extent to which such prospects can be realised by individual farmers will vary according to regional, local and property characteristics, the levels of soil salinity and waterlogging, the plant systems selected and management priorities. Importantly, the report concludes that there are no profitable options for saltland of the lowest capability (i.e. the most salty and/or waterlogged), so the identification of these land classes and their exclusion from saltland revegetation programs is an important part of any investment strategy.

Duty of care, personal pride from improving the visual amenity of the farm, and satisfaction in overcoming a serious challenge are also very significant motivators for landholders. Even with severely degraded land, preventing further deterioration and off-site damage is important.

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Advantages for catchment managers

A recent salinity report in NSW compared the pros and cons of recharge and discharge management. It concluded that management interventions (including those assisted by public funding) on and near discharge sites should be the first response in all catchments unless the source of the recharge is both rigorously identified (generally an expensive exercise) and relatively close to the discharge site (i.e. one is dealing with a local groundwater flow system).

The study found:

  • Identifying specifically where recharge is occurring (and therefore where intervention will be effective) is inherently difficult, while identification of discharge sites is relatively simple.
     
  • Discharge sites are typically small (~2% of the study catchment) while recharge areas are large and diffuse, potentially allowing much greater investment per hectar on the discharge sites to achieve an improved catchment outcome.
     
  • The chance of getting a negative outcome from recharge management (e.g. a reduction in fresh, surface water flows, or no impact) is high, while the chance of getting a negative outcome from improved management of discharge sites is low.
     
  • Management interventions that prove to be ‘incorrect’ can be identified relatively quickly on discharge sites as the impacts are local. However, for recharge management, many years (or decades) might pass before the ineffectiveness of an intervention is determined, making adaptive management impossible.
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Difficulties and risks

Saltland sites, especially if waterlogging is an additional feature, are inherently difficult to manage well. Fencing saltland to prevent uncontrolled grazing is always part of best practice because stock preferentially camp on and graze the salty sites removing much of the vegetation, increasing surface evaporation and thereby further concentrating salts at the soil surface.

If an intervention on saltland is primarily to achieve social or environmental goals (which tend to relate to the appearance of the site), the risks are relatively minor once sites are fenced off from grazing.

The major risks associated with grazing saltland are financial:

  • The risk of ‘establishment’ failure on saltland is much higher than for conventional sites. Seeds of salt-tolerant species (for example saltbush) can be quite sensitive to waterlogging and salinity, and conventional sowing equipment is often not well suited to saltland species.
     
  • The frequent combination of salinity and waterlogging often means that the opportunity to sow or plant the saltland pasture is brief following opening rains. This is exacerbated when saltland pasture is generally seen as a low priority compared to establishing the farm’s main crops and/or pastures.
     
  • Where the area of saltland is small, the capital cost of fencing and providing water can mean that an economic return is a very distant prospect.
     
  • Depending on the site, the combination of salinity and waterlogging, and the effectiveness of establishment, the production achieved from a saltland pasture may not be sufficient to provide a significant return on the investment. Saltland pastures cost as much (or sometimes more) to establish as conventional pastures, but can have significantly lower productive potential.

In summary, establishing saltland pastures is rarely the next best investment opportunity on a farm from a purely economic perspective. In most cases farmers are seeking some financial return, combined with social and environmental benefits.

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