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A Revolution in Land Use

A Revolution in land use

What will it take to save the basin?

Current options and future prospects for managing dryland salinity

Why we need a revolution in land use

Lessons from ecology

Agriculture and the environment

Setting targets

Dryland salinity is a serious problem affecting many parts of Australia, including the Murray- Darling Basin, one of our most important river systems. In 1999, CSIRO Land and Water released a report for the Murray Darling Basin Commission called Effectiveness of Current Farming Systems in the Control of Dryland Salinity. It outlined the causes and extent of salinity in the Basin and identified that for much of the Basin, current farming systems, even when implemented with best practice, cannot control salinity. This report continues the story by investigating the capability of various options to deal with salinity and the prospects for new solutions from research, development and innovation. Such innovative solutions, which may lead to revolutionary new ways to use our land, will need to be incorporated into the landscape not only to help counter the growing problem of salinity but also to maintain native biodiversity and community well-being.

What will it take to save the basin?

No single land-use option will halt the growth of salinity and the loss of native biodiversity in our land and rivers. We need to develop and deploy a suite of novel land uses that are matched to the diverse climate, soils, and hydrological conditions of the Basin. These land uses, in combination, need to deliver leakage rates past the root zone that approach those of natural vegetation. This will require radical change to land use, incorporating the following features.
  • Commercially driven tree production systems and/or new tree species, to be developed for large areas of the current crop and pasture zones of the Basin. These would include trees to produce fruits, nuts, oils, pharmaceuticals, bush foods and forestry products such as specialty timbers, charcoal, and biomass energy.
  • New farming systems made up of novel mixes of all the best current annual and perennial plants, the best agronomy, companion plantings, rotations and combinations.
  • New forms of cereals, pulses, oilseeds and forages selected or bred for characteristics that substantially reduce deep drainage and nitrogen leakage.
  • Refined land assessment tools that best locate trees, other perennial plants, high-value annuals, and native species to meet water quantity and quality targets, and biodiversity goals.
  • New tools for land managers to monitor leakage past the root zone, and change land use accordingly.

To realise this vision, we will need to pioneer the development of a new landscape, a mosaic of tree crops driven by large-scale industrial markets such as biomass fuels and high-value annual crops, as well as mixed perennial-annual cropping systems, and areas devoted to maintaining those elements of native biota dependent on native vegetation. Devising the optimal placement of these land uses in terms of salinity control, productivity and maintenance of native biodiversity will require a robust understanding of landscape process and ecosystem function, and good maps of landscape properties, particularly salt storage and groundwater flow.

While a vision for the Basin is emerging, many of the components described above do not yet exist. A substantial new research and development effort is needed that tackles the redesign of farming systems and their integration into the landscape as a whole. This needs to combine biophysical and economic studies that deliver innovative designs well matched to soil, climate and catchment circumstances including biodiversity; on-farm measurement and improved land assessment techniques; modern genetic improvement techniques; and a participatory process that engages all land managers.

Back to top

Current options and future prospects for managing dryland salinity

There is no single, viable, land-use system capable of controlling leakage over the Basin as a whole. The following list summarises various options that can help control leakage. Some are available now and others, as noted, have realistic prospects but require additional research. Further to successfully integrate these options into the landscape as a whole will demand a significant research effort in the maintenance and restoration of the native biota and of ecosystem function. Research is also essential to develop incentives for incorporating maintenance and restoration of biodiversity into these current options and future prospects.

Annual cropping

This is the preferred economic option but it is ineffective in attaining leakage targets except in a small proportion of the Basin. There is little opportunity for agronomic research to reduce leakage by the magnitude required.

Opportunity cropping

Rotations of winter and summer crops that are sensitive to the water conditions of soil make a useful contribution in those parts of the Basin with significant summer rainfall. Opportunity cropping is a relatively mature area in research agronomy. An applied research effort over the next 5–10 years on suitable crop/soil/rainfall combinations could yield improved systems in terms of salinity control and profitability.

Phase farming

This is effective when the lucerne phase is long enough to dry the subsoil and the cropping phase is terminated before leakage recommences. Reductions in leakage of 50–70% are associated with reduced profitability. This is a mature area of agronomic research and systems are well advanced and available. Research over the next five years should overcome dependence on lucerne and fine-tune the application of phase farming to improve profitability and drainage outcomes.

Companion farming

Over-sowing annual cereals into perennial forages/pastures holds promise of significantly reducing leakage beneath the root zone. Research is needed over at least 5–10 years on species and agronomic practice to provide viable systems.

New agricultural plants

Some potential exists to select or breed long season, perennial and/or deep-rooted cultivars of current crop and fodder plants that may substantially reduce deep drainage, and to fit these plants into new farming systems. This will require a substantial and well-focused research effort over the next 5–25 years.

Organic farming

While the demand for organic produce is growing in the marketplace, organic farming is not necessarily any more effective than annual cropping in controlling leakage beneath the root zone. However phase farming, companion farming and agroforestry practices that reduce leakage are in harmony with the organic philosophy and are therefore more likely to be adopted.

High rainfall tree products

These products are effective in reducing leakage, and profitable, but their proven potential is currently limited to a small proportion of the Basin. Long-term research (10–30 years) is needed to extend profitable forestry to a larger proportion of the Basin in a way that maintains water yield.

Low rainfall tree products

While this is potentially the most effective landuse option for managing salinity by reducing leakage, it is not commercially viable due to a lack of markets to drive reforestation and/or revegetation at the necessary scale. A very significant, well-focused research effort over the next 30 years will be essential to develop: new markets; tree crops to produce fruits, nuts, oils, pharmaceuticals; bush foods; and forestry products including specialty timbers, charcoal, carbon credits and bio-mass energy applications.

Agroforestry

Agroforestry can be more profitable than tree crops alone, but its effectiveness depends on the proportion planted to trees, and on the skill of locating trees in the right parts of the landscape. Further research is needed to determine which tree/crop/pasture mixtures can reduce leakage to acceptable levels and continue to give economic return. This research should provide solutions over the next 30 years. It will build on and benefit from work essential to the development of commercial tree crops and new agricultural plants.

Perennial pastures

Perennial pastures leak less water beneath the root zone than annuals, but higher rainfall, winter dominance, acid and shallow soils, and grazing pressure all compromise their potential across the southern half of the Basin. Research and development should focus on ameliorating subsoil and on deeper rooting species.

Saltland farming

Saltland farming allows for soil stabilisation and provision of stock feed but makes little long-term contribution to managing the watertable, reducing salt loads to rivers and therefore to water quality. Identifying species and management practices that make best use of such land is important because of the huge areas that will be affected by salt, but the impact of this research on controlling land and river salinisation will be relatively small.

Back to top

Why we need a revolution in land use

Five years ago the salt problem was just another topic for scientific meetings and loss of biodiversity was regarded as a nature conservation issue. Today, it is front-page news and high on the political agenda. This prominence has elicited different responses. Hydrologists are relieved that the community is at last beginning to share the burden of their message on salinity. Landholders have the disquiet of knowing that they may be both responsible and the major casualty. Agricultural scientists find the doom and gloom a bit much. The dedication and skill of their predecessors has seen many seemingly intractable problems overcome in the past. Why not this one? Ecologists have documented the decline and loss of biodiversity and the change in ecosystem processes and are concerned that salinity and loss of biodiversity are often treated as completely separate issues. They are not, as salinity is an extremely visual manifestation of the loss of major elements of biodiversity and change in ecosystem process.

Agriculture has flourished over much of the world for thousands of years, despite the changes wrought when virgin land comes under the plough. But in southern Australia, the signs of an uncertain future surfaced within ten years of the first trees being ring-barked. Railway engineers found that the reservoirs they constructed to supply water to locomotives became too salty to use.

By 1897, astute observers were making the connection between clearing native vegetation and fresh creeks becoming salty. Twenty years later, an analysis was published that described the relationship between clearing and salinisation with surprising clarity, although the underlying processes were somewhat misunderstood. A description of the problem that accurately captured the fundamental issues was published in 1924.

Figure 1. The salinity in the Murray River at Morgan (close to the off-take for Adelaide's water) has been rising slowly for 80 years and is forecast to rise more quickly over the next 100 years.

Figure 1. The salinity in the Murray River at Morgan (close to the off-take for Adelaide's water) has been rising slowly for 80 years and is forecast to rise more quickly over the next 100 years.

Source: Murray-Darling Basin Ministerial Council (1999)

This newfound understanding was not translated into action. Agriculture continued to expand and became the foundation of a prosperous economy. At the same time, more water has been leaking below annual crops than the aquifers can deliver to rivers. As aquifers fill and watertables rise, the deep and ancient stores of salt are lifted to the soil surface, killing much of the remaining native vegetation and its associated fauna, while the salt is carried into rivers.

This publication does not go back over the causes of the salinity problem. They are well dealt with in its predecessor report, Effectiveness of current farming systems in the control of dryland salinity, which concluded that:

  • current farming systems are the fundamental cause of the dryland salinity problem;
  • under best management practice, the leakage from most agricultural land still far exceeds the capacity of the landscape to shed the excess water;
  • for most of the country we do not have profitable systems to replace existing land use;
    and
  • even if we did introduce very different farming systems immediately, it will be a long time before we see an improvement in salt trends.

This volume looks to the next 20 to 50 years. If today's agriculture is the root cause of dryland salinity, can we envisage a new agriculture in better harmony with Australia's unique landscape?

Back to top

Lessons from ecology

We often hear that Australian farmers imposed a European agriculture completely unsuited to Australian soils and climate. This is not entirely fair. All human societies that have forsaken a hunter-gatherer existence have based their civilisations on annual seed-bearing plants such as wheat, rice and maize. It is not the European heritage of agriculture that is at odds with this land, but the replacement of native perennial plants with annuals.

The strategy of the annual plant is to match its life cycle perfectly with the favourable growing season and to survive the harsh times as seed. This made the annual a perfect candidate for domestication because its large seeds favour the survival of the next generation. For example, the wheat plant packages half its total biomass as starch and 70% of its nitrogen as protein in its seed. Perennial plants cannot match this bounty. The strategy of the perennial is to survive, not sit out, the hard times. They need deep roots to tap the last of the water and frequently, woody stems so that they can lift their canopies above their annual competitors.

Figure 2. Salt exports and trends in river salinities 1975?95: tonnes per km2 per annum. The salt levels in many major river systems are rising.

Figure 2. Salt exports and trends in river salinities 1975–95: tonnes per km2 per annum. The salt levels in many major river systems are rising.

Source: Murray-Darling Basin Ministerial Council (1999)

Perennials have to survive greater pressures from parasites and grazers. Many perennial plants produce structures and chemicals as protection. This investment in infrastructure and defence, and its associated maintenance requirement, diverts resources that could be used for new growth. Even though a perennial may capture more water and nutrients than an annual, the harvestable proportion of digestible energy and protein falls short.

The annual is more suited to intensive agriculture. Ploughing and herbicides remove competitors and allow a perfect match between the season and the plant's requirements. The productivity of the annual and its apparent wastefulness are linked. Typically 5–15% of the long-term average rainfall gets past the roots of annual plants, whereas less than 1% escapes the native perennial vegetation.

For most landscapes, leakage past the root zone of native vegetation approaches the capacity of the groundwater systems to deliver water to rivers (discharge capacity). For the annual cropping zone of the Basin, leakage beneath the root zone for annual crops and pastures translates to between 15 and 130 mm per year, while the landscape capacity to drain groundwater to rivers is of the order of 0.5–10 mm per year.

Figure 3. Areas threatened by dryland salinity.

Figure 3. Areas threatened by dryland salinity.

Source: Land and Water Resources Research and Development Corporation (1998)

Back to top

Agriculture and the environment

The removal of vast areas of native vegetation (in some cases over 95% of areal extent) has resulted in 5–15% of rainfall leaking past the root zone over agricultural land. This has caused the changes in land and river salinity shown in Figures 1, 2 and 3 and the widespread loss of biodiversity, and changes to ecosystem processes. The salinity level of waters of the Loddon and Avoca rivers is already above the desirable Australian limits for drinking for most of the year. The Warrego, Condamine-Balonne, Border, Macquarie and Namoi rivers are predicted to join this category in 20 years, and the Lachlan, Castlereagh and Murray (at Murray Bridge) within 50 years.

The paucity of data makes it difficult to predict the area of land expected to be salinised or what of our natural heritage we stand to lose. Groundwater monitoring has been conducted over almost half the 107 million ha Basin. Groundwater is rising under at least 15 million ha of the Basin. About 0.3 million ha of land were salt-affected by 1996, and this is expected to rise to 6–9 million ha before a new hydrologic equilibrium is reached.

If we are to have any impact on these trends, we will need to introduce perennial species into agricultural landscapes. Given that perennials are less conducive to intensive agriculture, the task will be difficult. In the following pages we examine the options and their prospects. However, before looking at the options, we need to be clear about the targets we set ourselves over the next 20 to 50 years. We also need a comprehensive assessment of leakage rates under current farming systems and how they vary throughout the Basin.

Back to top

Setting targets

No strategy can work until we have set targets to measure its performance. Three suggested targets are described below.

Mimic the bush

A first target is to try to reach the leakage rates of the original vegetation. This is the target required to avoid and/or reverse salinisation. We aim to retain a productive landscape by mimicking the hydrological function of native vegetation with economically viable species.

Due to the vast quantities of salt already mobilised by rising water tables, reversing the salt trend to the state that existed before clearing is not possible. We can limit the spread of salinity by creating a productive landscape that mimics the water use patterns of the original bush. However without profitable tree crops, especially in low rainfall areas, the only way to do this is to revert to native vegetation with serious implications for agriculture and rural communities.

Nevertheless native vegetation and re-vegetation has a most important role in salinity control. Maintenance of remnant native vegetation throughout the basin is a key target in order to conserve and maintain biodiversity and ecosystem services in conjunction with salinity control. The integration of native vegetation into landscape design is critical to halting further loss of species and ecosystem function. On our present path we can expect to lose 50% of avifauna from the basin over the next 50–100 years. Solutions, which mimic the ecosystem functions of the bush, will be important to both salinity control and protection of landscape biodiversity and function.

Protect the land

A second target is to ensure that recharge levels remain less than the discharge capacity of a catchment. The discharge capacity is the amount of water that the groundwater aquifers can carry — water that will eventually be delivered to a stream. The discharge capacity is set at the point of lowest transmissivity, where the aquifer becomes shallow, narrows or decreases in permeability. As long as the recharge rate is less than the discharge capacity, watertables will not rise to the surface, and land and infrastructure will not be lost to salinity.

This target is made difficult by our inability to measure both leakage and discharge capacity with reasonable accuracy. Discharge capacities have been calculated for only a few catchments, and fall somewhere between one half and one tenth of our best estimates of current leakage rates beneath land used for agriculture.

Protect the rivers

A third target is to keep the salinity of the streams below a certain threshold, say 800 EC, which is the Australian limit for desirable drinking water.

This target is the most relevant for the Basin, and also the easiest to measure. Even though millions of hectares of farmland are threatened by salinity, the major cost to the community will come from declining river quality for domestic water supply and irrigation.

Individual leakage targets would have to be determined for each catchment, but for most, targets should not exceed the catchment's discharge capacity, which will rarely exceed about 1% of rainfall. For the Basin, this means leakage rates beneath the root zone of land use should be less than 0.5–10 mm per year, depending on the amount of rainfall, its distribution, and catchment properties. Any increase or decrease in recharge affects stream salinity, and the size of the impact will depend on the salinity of the groundwater.

Figure 4. Dominant land use within the Basin.

Figure 4. Dominant land use within the Basin.

Source: Modified from Walker et al (1999). Effectiveness of Current Farming Systems in the Control of Dryland Salinity

It is essential to consider time lags within the system. In many areas, the salt discharge is rising and will continue to rise even after recharge has been reduced. In local-scale groundwater systems, the salt discharge may continue to rise for a decade or more. In larger intermediate and regional-scale systems, the rise could extend to hundreds of years no matter what we do (Figure 6). Unfortunately, large-scale groundwater systems dominate the Basin (Figure 4).

There is an important distinction between salt from dryland and irrigation sources. The Salinity and Drainage Strategy for irrigation areas includes a system of salt credits, which are tradeable pollution rights. If managers of an irrigation area need to put more salt into the river from drainage systems, they are responsible for the cost of engineering works that can intercept a similar quantity of salt downstream.

Figure 5. There is a time lag between a change in vegetation and the response of the groundwater.

Figure 5. There is a time lag between a change in vegetation and the response of the groundwater.

The Salinity Audit published by MDBC in 1999 predicts that most of the future salt discharge into river systems will come from dryland catchment sources, undermining existing plans to protect irrigation areas. For this reason the following pages focus on land-use options for dryland catchments.

Figure 6. Distribution of local, intermediate and regional scale aquifers in the Basin.

Figure 6. Distribution of local, intermediate and regional scale aquifers in the Basin.

Source: National Land and Water Resources Audit (2000)

Figure 7 summarises the problem we face. If dryland agriculture as we know it today does not change, land and native biodiversity will continue to be lost to salinity and rivers will become saline — path A in Figure 7. If we push current land-use systems to their limit of efficiency, we are likely to follow path B — buying time but ultimately losing the battle. We already recognise that path D, a return to the pristine state, is unattainable. On the following pages we briefly evaluate the potential of improving current systems before examining the options for moving down path C.

Figure 7. Which path do we take?

Figure 7. Which path do we take?

Source: Walker et al (1999). Effectiveness of Current Farming Systems in the Control of Dryland Salinity

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Back to Contents

COPYRIGHT

© 2000 CSIRO Land and Water.

To the extent permitted by law, all rights are reserved and no part of these publications covered by copyright may be reproduced or copied in any form or by any means except with the written permission of CSIRO Land and Water.

IMPORTANT DISCLAIMER

To the extent permitted by law, CSIRO Land and Water (including its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using these publications (in part or in whole) and any information or material contained in them.

A Revolution in land use

What will it take to save the basin?

Current options and future prospects for managing dryland salinity

Why we need a revolution in land use

Lessons from ecology

Agriculture and the environment

Setting targets

Dryland salinity is a serious problem affecting many parts of Australia, including the Murray- Darling Basin, one of our most important river systems. In 1999, CSIRO Land and Water released a report for the Murray Darling Basin Commission called Effectiveness of Current Farming Systems in the Control of Dryland Salinity. It outlined the causes and extent of salinity in the Basin and identified that for much of the Basin, current farming systems, even when implemented with best practice, cannot control salinity. This report continues the story by investigating the capability of various options to deal with salinity and the prospects for new solutions from research, development and innovation. Such innovative solutions, which may lead to revolutionary new ways to use our land, will need to be incorporated into the landscape not only to help counter the growing problem of salinity but also to maintain native biodiversity and community well-being.

What will it take to save the basin?

No single land-use option will halt the growth of salinity and the loss of native biodiversity in our land and rivers. We need to develop and deploy a suite of novel land uses that are matched to the diverse climate, soils, and hydrological conditions of the Basin. These land uses, in combination, need to deliver leakage rates past the root zone that approach those of natural vegetation. This will require radical change to land use, incorporating the following features.
  • Commercially driven tree production systems and/or new tree species, to be developed for large areas of the current crop and pasture zones of the Basin. These would include trees to produce fruits, nuts, oils, pharmaceuticals, bush foods and forestry products such as specialty timbers, charcoal, and biomass energy.
  • New farming systems made up of novel mixes of all the best current annual and perennial plants, the best agronomy, companion plantings, rotations and combinations.
  • New forms of cereals, pulses, oilseeds and forages selected or bred for characteristics that substantially reduce deep drainage and nitrogen leakage.
  • Refined land assessment tools that best locate trees, other perennial plants, high-value annuals, and native species to meet water quantity and quality targets, and biodiversity goals.
  • New tools for land managers to monitor leakage past the root zone, and change land use accordingly.

To realise this vision, we will need to pioneer the development of a new landscape, a mosaic of tree crops driven by large-scale industrial markets such as biomass fuels and high-value annual crops, as well as mixed perennial-annual cropping systems, and areas devoted to maintaining those elements of native biota dependent on native vegetation. Devising the optimal placement of these land uses in terms of salinity control, productivity and maintenance of native biodiversity will require a robust understanding of landscape process and ecosystem function, and good maps of landscape properties, particularly salt storage and groundwater flow.

While a vision for the Basin is emerging, many of the components described above do not yet exist. A substantial new research and development effort is needed that tackles the redesign of farming systems and their integration into the landscape as a whole. This needs to combine biophysical and economic studies that deliver innovative designs well matched to soil, climate and catchment circumstances including biodiversity; on-farm measurement and improved land assessment techniques; modern genetic improvement techniques; and a participatory process that engages all land managers.

Back to top

Current options and future prospects for managing dryland salinity

There is no single, viable, land-use system capable of controlling leakage over the Basin as a whole. The following list summarises various options that can help control leakage. Some are available now and others, as noted, have realistic prospects but require additional research. Further to successfully integrate these options into the landscape as a whole will demand a significant research effort in the maintenance and restoration of the native biota and of ecosystem function. Research is also essential to develop incentives for incorporating maintenance and restoration of biodiversity into these current options and future prospects.

Annual cropping

This is the preferred economic option but it is ineffective in attaining leakage targets except in a small proportion of the Basin. There is little opportunity for agronomic research to reduce leakage by the magnitude required.

Opportunity cropping

Rotations of winter and summer crops that are sensitive to the water conditions of soil make a useful contribution in those parts of the Basin with significant summer rainfall. Opportunity cropping is a relatively mature area in research agronomy. An applied research effort over the next 5–10 years on suitable crop/soil/rainfall combinations could yield improved systems in terms of salinity control and profitability.

Phase farming

This is effective when the lucerne phase is long enough to dry the subsoil and the cropping phase is terminated before leakage recommences. Reductions in leakage of 50–70% are associated with reduced profitability. This is a mature area of agronomic research and systems are well advanced and available. Research over the next five years should overcome dependence on lucerne and fine-tune the application of phase farming to improve profitability and drainage outcomes.

Companion farming

Over-sowing annual cereals into perennial forages/pastures holds promise of significantly reducing leakage beneath the root zone. Research is needed over at least 5–10 years on species and agronomic practice to provide viable systems.

New agricultural plants

Some potential exists to select or breed long season, perennial and/or deep-rooted cultivars of current crop and fodder plants that may substantially reduce deep drainage, and to fit these plants into new farming systems. This will require a substantial and well-focused research effort over the next 5–25 years.

Organic farming

While the demand for organic produce is growing in the marketplace, organic farming is not necessarily any more effective than annual cropping in controlling leakage beneath the root zone. However phase farming, companion farming and agroforestry practices that reduce leakage are in harmony with the organic philosophy and are therefore more likely to be adopted.

High rainfall tree products

These products are effective in reducing leakage, and profitable, but their proven potential is currently limited to a small proportion of the Basin. Long-term research (10–30 years) is needed to extend profitable forestry to a larger proportion of the Basin in a way that maintains water yield.

Low rainfall tree products

While this is potentially the most effective landuse option for managing salinity by reducing leakage, it is not commercially viable due to a lack of markets to drive reforestation and/or revegetation at the necessary scale. A very significant, well-focused research effort over the next 30 years will be essential to develop: new markets; tree crops to produce fruits, nuts, oils, pharmaceuticals; bush foods; and forestry products including specialty timbers, charcoal, carbon credits and bio-mass energy applications.

Agroforestry

Agroforestry can be more profitable than tree crops alone, but its effectiveness depends on the proportion planted to trees, and on the skill of locating trees in the right parts of the landscape. Further research is needed to determine which tree/crop/pasture mixtures can reduce leakage to acceptable levels and continue to give economic return. This research should provide solutions over the next 30 years. It will build on and benefit from work essential to the development of commercial tree crops and new agricultural plants.

Perennial pastures

Perennial pastures leak less water beneath the root zone than annuals, but higher rainfall, winter dominance, acid and shallow soils, and grazing pressure all compromise their potential across the southern half of the Basin. Research and development should focus on ameliorating subsoil and on deeper rooting species.

Saltland farming

Saltland farming allows for soil stabilisation and provision of stock feed but makes little long-term contribution to managing the watertable, reducing salt loads to rivers and therefore to water quality. Identifying species and management practices that make best use of such land is important because of the huge areas that will be affected by salt, but the impact of this research on controlling land and river salinisation will be relatively small.

Back to top

Why we need a revolution in land use

Five years ago the salt problem was just another topic for scientific meetings and loss of biodiversity was regarded as a nature conservation issue. Today, it is front-page news and high on the political agenda. This prominence has elicited different responses. Hydrologists are relieved that the community is at last beginning to share the burden of their message on salinity. Landholders have the disquiet of knowing that they may be both responsible and the major casualty. Agricultural scientists find the doom and gloom a bit much. The dedication and skill of their predecessors has seen many seemingly intractable problems overcome in the past. Why not this one? Ecologists have documented the decline and loss of biodiversity and the change in ecosystem processes and are concerned that salinity and loss of biodiversity are often treated as completely separate issues. They are not, as salinity is an extremely visual manifestation of the loss of major elements of biodiversity and change in ecosystem process.

Agriculture has flourished over much of the world for thousands of years, despite the changes wrought when virgin land comes under the plough. But in southern Australia, the signs of an uncertain future surfaced within ten years of the first trees being ring-barked. Railway engineers found that the reservoirs they constructed to supply water to locomotives became too salty to use.

By 1897, astute observers were making the connection between clearing native vegetation and fresh creeks becoming salty. Twenty years later, an analysis was published that described the relationship between clearing and salinisation with surprising clarity, although the underlying processes were somewhat misunderstood. A description of the problem that accurately captured the fundamental issues was published in 1924.

Figure 1. The salinity in the Murray River at Morgan (close to the off-take for Adelaide's water) has been rising slowly for 80 years and is forecast to rise more quickly over the next 100 years.

Figure 1. The salinity in the Murray River at Morgan (close to the off-take for Adelaide's water) has been rising slowly for 80 years and is forecast to rise more quickly over the next 100 years.

Source: Murray-Darling Basin Ministerial Council (1999)

This newfound understanding was not translated into action. Agriculture continued to expand and became the foundation of a prosperous economy. At the same time, more water has been leaking below annual crops than the aquifers can deliver to rivers. As aquifers fill and watertables rise, the deep and ancient stores of salt are lifted to the soil surface, killing much of the remaining native vegetation and its associated fauna, while the salt is carried into rivers.

This publication does not go back over the causes of the salinity problem. They are well dealt with in its predecessor report, Effectiveness of current farming systems in the control of dryland salinity, which concluded that:

  • current farming systems are the fundamental cause of the dryland salinity problem;
  • under best management practice, the leakage from most agricultural land still far exceeds the capacity of the landscape to shed the excess water;
  • for most of the country we do not have profitable systems to replace existing land use;
    and
  • even if we did introduce very different farming systems immediately, it will be a long time before we see an improvement in salt trends.

This volume looks to the next 20 to 50 years. If today's agriculture is the root cause of dryland salinity, can we envisage a new agriculture in better harmony with Australia's unique landscape?

Back to top

Lessons from ecology

We often hear that Australian farmers imposed a European agriculture completely unsuited to Australian soils and climate. This is not entirely fair. All human societies that have forsaken a hunter-gatherer existence have based their civilisations on annual seed-bearing plants such as wheat, rice and maize. It is not the European heritage of agriculture that is at odds with this land, but the replacement of native perennial plants with annuals.

The strategy of the annual plant is to match its life cycle perfectly with the favourable growing season and to survive the harsh times as seed. This made the annual a perfect candidate for domestication because its large seeds favour the survival of the next generation. For example, the wheat plant packages half its total biomass as starch and 70% of its nitrogen as protein in its seed. Perennial plants cannot match this bounty. The strategy of the perennial is to survive, not sit out, the hard times. They need deep roots to tap the last of the water and frequently, woody stems so that they can lift their canopies above their annual competitors.

Figure 2. Salt exports and trends in river salinities 1975?95: tonnes per km2 per annum. The salt levels in many major river systems are rising.

Figure 2. Salt exports and trends in river salinities 1975–95: tonnes per km2 per annum. The salt levels in many major river systems are rising.

Source: Murray-Darling Basin Ministerial Council (1999)

Perennials have to survive greater pressures from parasites and grazers. Many perennial plants produce structures and chemicals as protection. This investment in infrastructure and defence, and its associated maintenance requirement, diverts resources that could be used for new growth. Even though a perennial may capture more water and nutrients than an annual, the harvestable proportion of digestible energy and protein falls short.

The annual is more suited to intensive agriculture. Ploughing and herbicides remove competitors and allow a perfect match between the season and the plant's requirements. The productivity of the annual and its apparent wastefulness are linked. Typically 5–15% of the long-term average rainfall gets past the roots of annual plants, whereas less than 1% escapes the native perennial vegetation.

For most landscapes, leakage past the root zone of native vegetation approaches the capacity of the groundwater systems to deliver water to rivers (discharge capacity). For the annual cropping zone of the Basin, leakage beneath the root zone for annual crops and pastures translates to between 15 and 130 mm per year, while the landscape capacity to drain groundwater to rivers is of the order of 0.5–10 mm per year.

Figure 3. Areas threatened by dryland salinity.

Figure 3. Areas threatened by dryland salinity.

Source: Land and Water Resources Research and Development Corporation (1998)

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Agriculture and the environment

The removal of vast areas of native vegetation (in some cases over 95% of areal extent) has resulted in 5–15% of rainfall leaking past the root zone over agricultural land. This has caused the changes in land and river salinity shown in Figures 1, 2 and 3 and the widespread loss of biodiversity, and changes to ecosystem processes. The salinity level of waters of the Loddon and Avoca rivers is already above the desirable Australian limits for drinking for most of the year. The Warrego, Condamine-Balonne, Border, Macquarie and Namoi rivers are predicted to join this category in 20 years, and the Lachlan, Castlereagh and Murray (at Murray Bridge) within 50 years.

The paucity of data makes it difficult to predict the area of land expected to be salinised or what of our natural heritage we stand to lose. Groundwater monitoring has been conducted over almost half the 107 million ha Basin. Groundwater is rising under at least 15 million ha of the Basin. About 0.3 million ha of land were salt-affected by 1996, and this is expected to rise to 6–9 million ha before a new hydrologic equilibrium is reached.

If we are to have any impact on these trends, we will need to introduce perennial species into agricultural landscapes. Given that perennials are less conducive to intensive agriculture, the task will be difficult. In the following pages we examine the options and their prospects. However, before looking at the options, we need to be clear about the targets we set ourselves over the next 20 to 50 years. We also need a comprehensive assessment of leakage rates under current farming systems and how they vary throughout the Basin.

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Setting targets

No strategy can work until we have set targets to measure its performance. Three suggested targets are described below.

Mimic the bush

A first target is to try to reach the leakage rates of the original vegetation. This is the target required to avoid and/or reverse salinisation. We aim to retain a productive landscape by mimicking the hydrological function of native vegetation with economically viable species.

Due to the vast quantities of salt already mobilised by rising water tables, reversing the salt trend to the state that existed before clearing is not possible. We can limit the spread of salinity by creating a productive landscape that mimics the water use patterns of the original bush. However without profitable tree crops, especially in low rainfall areas, the only way to do this is to revert to native vegetation with serious implications for agriculture and rural communities.

Nevertheless native vegetation and re-vegetation has a most important role in salinity control. Maintenance of remnant native vegetation throughout the basin is a key target in order to conserve and maintain biodiversity and ecosystem services in conjunction with salinity control. The integration of native vegetation into landscape design is critical to halting further loss of species and ecosystem function. On our present path we can expect to lose 50% of avifauna from the basin over the next 50–100 years. Solutions, which mimic the ecosystem functions of the bush, will be important to both salinity control and protection of landscape biodiversity and function.

Protect the land

A second target is to ensure that recharge levels remain less than the discharge capacity of a catchment. The discharge capacity is the amount of water that the groundwater aquifers can carry — water that will eventually be delivered to a stream. The discharge capacity is set at the point of lowest transmissivity, where the aquifer becomes shallow, narrows or decreases in permeability. As long as the recharge rate is less than the discharge capacity, watertables will not rise to the surface, and land and infrastructure will not be lost to salinity.

This target is made difficult by our inability to measure both leakage and discharge capacity with reasonable accuracy. Discharge capacities have been calculated for only a few catchments, and fall somewhere between one half and one tenth of our best estimates of current leakage rates beneath land used for agriculture.

Protect the rivers

A third target is to keep the salinity of the streams below a certain threshold, say 800 EC, which is the Australian limit for desirable drinking water.

This target is the most relevant for the Basin, and also the easiest to measure. Even though millions of hectares of farmland are threatened by salinity, the major cost to the community will come from declining river quality for domestic water supply and irrigation.

Individual leakage targets would have to be determined for each catchment, but for most, targets should not exceed the catchment's discharge capacity, which will rarely exceed about 1% of rainfall. For the Basin, this means leakage rates beneath the root zone of land use should be less than 0.5–10 mm per year, depending on the amount of rainfall, its distribution, and catchment properties. Any increase or decrease in recharge affects stream salinity, and the size of the impact will depend on the salinity of the groundwater.

Figure 4. Dominant land use within the Basin.

Figure 4. Dominant land use within the Basin.

Source: Modified from Walker et al (1999). Effectiveness of Current Farming Systems in the Control of Dryland Salinity

It is essential to consider time lags within the system. In many areas, the salt discharge is rising and will continue to rise even after recharge has been reduced. In local-scale groundwater systems, the salt discharge may continue to rise for a decade or more. In larger intermediate and regional-scale systems, the rise could extend to hundreds of years no matter what we do (Figure 6). Unfortunately, large-scale groundwater systems dominate the Basin (Figure 4).

There is an important distinction between salt from dryland and irrigation sources. The Salinity and Drainage Strategy for irrigation areas includes a system of salt credits, which are tradeable pollution rights. If managers of an irrigation area need to put more salt into the river from drainage systems, they are responsible for the cost of engineering works that can intercept a similar quantity of salt downstream.

Figure 5. There is a time lag between a change in vegetation and the response of the groundwater.

Figure 5. There is a time lag between a change in vegetation and the response of the groundwater.

The Salinity Audit published by MDBC in 1999 predicts that most of the future salt discharge into river systems will come from dryland catchment sources, undermining existing plans to protect irrigation areas. For this reason the following pages focus on land-use options for dryland catchments.

Figure 6. Distribution of local, intermediate and regional scale aquifers in the Basin.

Figure 6. Distribution of local, intermediate and regional scale aquifers in the Basin.

Source: National Land and Water Resources Audit (2000)

Figure 7 summarises the problem we face. If dryland agriculture as we know it today does not change, land and native biodiversity will continue to be lost to salinity and rivers will become saline — path A in Figure 7. If we push current land-use systems to their limit of efficiency, we are likely to follow path B — buying time but ultimately losing the battle. We already recognise that path D, a return to the pristine state, is unattainable. On the following pages we briefly evaluate the potential of improving current systems before examining the options for moving down path C.

Figure 7. Which path do we take?

Figure 7. Which path do we take?

Source: Walker et al (1999). Effectiveness of Current Farming Systems in the Control of Dryland Salinity

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Last updated: 30 August, 2012