Irrigation - Australian Agriculture Assessment 2001 - Summary
Summary
Natural resource challenges facing agriculture
Australian agriculture feeds the nation with a diverse range of produce, contributes $17.6 billion every year to export earnings as raw and processed products, and employs approximately 400 000 Australians—generating national and regional wealth.
Australia's natural resources underpin our agricultural industries. Climatic variability, largely infertile and highly erodible soils, the chemistry of those soils, their salt stores and pH are all key factors affecting sustained productivity.
Agricultural activities can be broadly grouped into:
- produce quality—covering issues of food safety, meeting market specifications, processing, marketing, selling and transport (not covered by the Audit);
- production—covering issues of rotations, enterprise mix, varieties and trends in yield performance; and
- natural resource maintenance and protection—covering issues of on-farm resource management and off-farm impacts.
On-farm practices link these activities and are crucial to delivering natural resource outcomes.
The Standing Committee of Agriculture in Australia defined sustainable agriculture as:
'the use of farming practices and systems which maintain or enhance the economic viability of agricultural production; the natural resource base; and other ecosystems, which are influenced by agricultural activities' SCA 1991
The guiding principles for sustainable agriculture were stated as:
- farm productivity is sustained or enhanced over the long term;
- adverse impacts on the natural resource base of agricultural and associated ecosystems are ameliorated, minimised or avoided;
- residues resulting from the use of chemicals in agriculture are minimised;
- the net social benefit derived from agriculture is maximised; and
- farming systems are sufficiently flexible to manage risks associated with the vagaries of climate and markets.
These succinct definitions imply the need to manage agricultural systems to be both profitable and environmentally sound, through adoption of efficient and environmentally benign management practices.
Australian Agriculture Assessment 2001 objectives
To provide information to:
- understand the links between natural resource condition and production—to maximise sustainable agricultural production;
- document the condition of natural resources used in agriculture—to maintain and protect the natural resource base on which agriculture depends; and
- determine off-farm exports and fluxes of sediments, carbon and nutrients—for quantifying the off-farm impacts of agriculture on public resources, rivers and estuaries.
Australian Agriculture Assessment 2001 assessed key factors related to natural resource sustainability, including:
- soil loss off-farm and through our rivers to estuaries and marine environments through water-borne soil erosion;
- nutrient balance, incorporating an assessment of all inputs and outputs in the production cycle;
- soil chemistry—particularly pH and soil nutrient status; and
- transport and delivery of nutrients through regional river networks.
To underpin this assessment, the Audit has compiled Australia's first integrated soil properties information system (the Australian Soil Resources Information System) for agricultural landscapes as a framework for assessing condition, change and trends of change in agricultural landscapes, and to assist in managing soils.
Australian Agriculture Assessment 2001 should be read in conjunction with other Audit assessments:
- water balance and the onset of dryland salinity are covered in Australian Dryland Salinity Assessment 2000 (NLWRA 2001a);
- water use and water use efficiency are covered in Australian Water Resources Assessment 2000 (NLWRA 2001b);
- Australia's Rangelands are covered in Tracking changes: Australian Collaborative Rangeland Information System (NLWRA 2001c).
Impacts of land use on native vegetation, and catchments, rivers and estuaries are covered in separate Audit reports. A related report—Australians and Natural Resource Management 2001—details the economic benefits that agriculture delivers to the Australian economy and the costs of resource use, particularly off-farm.
Landscape nutrient balances
Agriculture has doubled the productive capacity of agricultural landscapes. This capacity is determined by changes in water and nutrient availability and was assessed by mapping modelled water, carbon and nutrients balances and distribution of the major stores and fluxes; and determining how stores and fluxes respond to changes in agricultural inputs.
Net primary productivity (a measure of plant biomass gain) is an integrated measure of the coupled water, carbon, nitrogen and phosphorus balances. Distribution broadly follows rainfall patterns and is also influenced by air dryness, light and agricultural inputs. Net primary productivity strongly controls carbon stores in plants, litter and soil. Net primary productivity averages 0.96 Gt of carbon each year for the Australian continent. Nearly 60 Gt of the total continental carbon is stored as plant biomass (45%) and soil carbon (55%).
Agricultural nutrient inputs have increased continental net primary productivity by 5%; the mineral nitrogen store by 13% and the mineral phosphorus store by 8%. These increases have occurred over less than a quarter of the continent (since more than 75% of Australia is rangelands, national parks, or other largely natural and intact vegetation). Addition of nutrients and the use of legumes and irrigation water has increased agricultural productivity, nearly doubling pre-European stores of carbon, organic nitrogen and organic phosphorus. Soil mineral nitrogen, plant-available phosphorus, and nitrogen and phosphorus concentrations in soil water have also increased by up to a factor of five. These increases are concentrated in southern agricultural regions of Australia.
Harvested product is relatively small component of the continental net primary productivity and landscape stores of carbon, nitrogen and phosphorus. Nutrients applied to agricultural landscapes can exceed those required to achieve optimum production levels and in some regions are approaching diminishing returns. Attention to nutrient balance on farm will lead to more cost-efficient agriculture and fewer off-farm impacts.
Nutrients leaking from farms can lead to enriched rivers, estuaries and nearshore marine zones. Priority needs to be given to managing farm nutrient inputs more efficiently to counter increasing associated environmental costs.
Farm-gate nutrient balance
Nutrient management is a critically important issue for Australian agriculture. A balanced supply of all essential plant nutrients is required to sustain productivity and maintain soil fertility status on farm. Nutrient leakages off-site (especially nitrogen and phosphorus) can degrade the quality of water resources with enrichment of waterways leading to problems such as algal blooms.
In the higher rainfall, more intensively managed areas, Australia's surface soils have become more fertile following a long history of fertiliser application, but areas of soils with potentially low or marginal soil phosphorus, sulfur and potassium levels occur within the agricultural zone of all States. Australian soils are generally well endowed with calcium and magnesium.
A major shift in fertiliser consumption in Australia occurred during the 1990s, with a doubling of nitrogenous fertiliser use. The reasons for this upsurge is most likely associated with a range of factors including:
- higher nitrogen demands in more intensively cropped rotations;
- failure of pasture legumes to persist;
- varietal changes and adoption of minimum tillage practices;
- as a result of declining protein levels in wheat a growing awareness by farmers of the increased quality and yields obtainable from increased fertiliser applications; and
- the introduction of premium prices for higher protein wheat.
Farm-gate nutrient balances differ across Australia's regions. Balances for nitrogen, phosphorus, sulfur, and calcium are mainly neutral (inputs = exports) or moderately positive (inputs > exports) across much of the southern agricultural zone. At the gross regional farming scale, this suggests that levels of these nutrients are generally being maintained in soils. Potassium and magnesium balances are usually negative (inputs < exports) indicating that soil reserves are being progressively depleted.
In intensive industries with high nutrient use, such as sugar cane, dairying and horticulture, nitrogen and phosphorus balances were assessed as positive (inputs > exports). Highly positive (inputs > exports) nutrient balance indicate a likelihood that nutrients are moving off-farm to streams and groundwater.
Mainly negative nutrient balances were derived for the subtropical regions, suggesting nutrient depletion is occurring on these soils, many of which are naturally fertile. This implies that close attention to nutrient status needs to be maintained from a productivity perspective, so that soils retain their nutrient status.
Overall, attention needs to continue to be paid at a higher level in Australian agriculture to nutrient status, monitoring and tracking changes in all farming systems. This needs to be done with dual objectives—maximising yields on-farm and minimising export of nutrients off-farm, with the consequent impacts on the quality of water bodies.
Soil acidity
Soil acidification looms as a major soil degradation issue in all Australian States. The Audit estimates that 50 million and 23 million hectares of Australia's agricultural zone are already experiencing impacts from soil acidity in surface and subsoil layers respectively and that these are probably markedly affecting yields. Large areas of acidic soils occur in New South Wales, Western Australia, Victoria, and Tasmania.
Farmer awareness of the insidious nature of this issue has been heightened by research and extension programs in some States. However, awareness is by no means universal. Soil acidification is a cost of productive agricultural systems—whether from nitrogen fixation by legumes in mixed pastures or crop rotations, or from the increased use of nitrogen fertilisers.
In the absence of remedial lime applications, (which neutralise acidity) it was estimated that from 29 to 60 million hectares will reach the limiting soil pH value of 4.8 within 10 years, and a further 14 to 39 million hectares will reach the pH value of 5.5, where growth of sensitive plant species is impaired.
Currently, approximately 2 million tonnes of lime are applied to agricultural land each year and use is generally increasing. It has been estimated that from 12 to 66 million tonnes of lime is required to adjust Australia's existing acidic soils to pH values of 4.8 and 5.5 respectively, with a further 3 to 12 million tonnes needed each year to maintain soil pH status in a satisfactory range. These estimates indicate the imperatives for coordinated extension activities across industry groups, agribusiness and government.
Land degradation problems arising from induced acidification are mostly reversible by applying lime. Other management solutions can be used where liming is not a viable option. In northern Queensland banana plantations, improvements in nitrogen and residue management reduced the need for lime.
Other opportunities include stock management and attention to the use of perennials in the pasture management cycle.
Erosion
Water-borne soil erosion is a major and continuing issue for Australian agriculture and catchment management and impacts on river, estuary and marine resources. It causes unsustainable losses of soil for agriculture that in some areas far exceed (up to 50 times) rates of soil development.
Hillslope erosion (sheet and rill erosion) remains high in Australia's tropical northern regions, particularly at the onset of the wet season, and especially in the semi-arid woodlands and arid interior. Maintaining vegetative cover, minimising soil disturbance and building sediment-trapping wetlands and riparian areas remain imperatives.
Gully erosion while inactive in many previously formed gullies, persists as the major erosion process affecting river condition in southern and eastern Australia. Sediment from these previously active gullies has affected about 10 000 kilometres of stream length in the Murray - Darling Basin alone. These rivers, now with coarse sand accumulations in stream beds, exacerbating flooding and smothering habitat of Australia's native fish.
Active gully erosion is still occurring in northern Queensland and in south-western regions of Western Australia. Changes to agricultural practices that minimise gully erosion is an imperative, from both on- and off-farm perspectives.
River bank erosion is a major problem. Extensive lengths (120 000 kilometres) of riparian vegetation along eastern Australia's rivers and streams are degraded and require rehabilitation. Where these landscape resources are intact, they protect the integrity of banks against erosion. Priority areas include much of the Murray - Darling Basin, South Australia and south-western regions of Western Australia.
Sediment delivery to streams, rivers, estuaries and near shore marine zones is high in many catchments. Deposition of sand and suspended sediments in streams and rivers is worst in the Murray - Darling Basin, coastal regions of New South Wales, south-east Queensland and the south west of Victoria.
From a near shore marine and estuary perspective, approximately 90% of suspended sediment loads reaching marine and estuarine environments is derived from 20% of agricultural catchments particularly in coastal regions of Queensland and New South Wales.
For the Great Barrier Reef Lagoon, about 25% or 12 million tonnes of sediment delivered to streams is discharged each year on average across all contributing catchments. This is predicted to be approximately three times greater than natural loads, with consequent impacts on estuaries and marine fisheries, seagrasses and near shore coral reefs. However for catchments such as the Burdekin and Fitzroy, loads can be more than 20 times natural loads
National, State and regional priorities for natural resources management can now be re-appraised in the light of these findings (e.g. soil loss on farm is irreversible and impacts that occur off-farm which will continue for many generations). Catchment management and industry priorities, particularly in terms of implementing improved practice are essential. Total impacts are likely to be equal to, if not greater than, those of dryland salinity. It is imperative that soil management targets hillslope, gully and river bank erosion in the areas identified by this assessment.
Nutrient loads to Australian rivers and estuaries
Nearly 19 000 tonnes of total phosphorus and 141 000 tonnes of total nitrogen are exported to Australia's coast each year from areas of intensive agriculture: highest exports are in northern Queensland, Moreton Bay and New South Wales.
Total nutrient loads from river basins are partly dictated by sediment load and therefore basin size—the bigger the basin, the bigger the load. Smaller basins can export large loads if they have high export rates due to high slopes and intense rainfall; increases in population, or changes in land use and management.
Efficiency of phosphorus delivery from Australia's rivers to the coast varies from as low as 3% in the Murray - Darling Basin to over 90% in Tasmania.
The major sink for phosphorus is floodplain sedimentation, but reservoir sedimentation (both nitrogen and phosphorus) and riverine denitrification (nitrogen only) can account for substantial proportions.
Priorities for reducing river and estuarine nutrient loads vary—large relative increases in river nutrient loads do not always coincide with large total exports, and estuaries differ in their sensitivity to increases in nutrient loading particularly because of differences in residence times and tidal flushing.
Targeted erosion control and soil management provides a significant contribution to managing the supply of nutrients with much of the nutrient accompanying increased sediment loads to most rivers.
Where a large part of the increase is caused by increases in either surface run-off loads or point source discharges, close attention needs to be paid to fertiliser application, animal waste retention on-farm, and sewage treatment plant and septic tank effluent management.
Agricultural practice
Australian agricultural industries have continuously implemented new or innovative practices. In more recent years, farmers have adopted:
- improved crop rotations;
- reduced tillage and stubble retention/incorporation by the grains industry (to reduce wind and water soil erosion and improve soil health);
- green trash blanketing by the sugar industry (to add flexibility to harvest and reduce soil erosion); and
- potassium fertiliser and lime use in agricultural systems of Western Australia (identified as significant nutritional limitations).
The Audit assessment of farming practices across all agricultural industries has demonstrated how `best management practice' is an evolving part of agriculture. Industry has a commitment to development and adoption of best management practice. A key agent for change will be linking practices and environmental stewardship to improvements in farm business profitability.
Ways forward
Australian agriculture has shown its capacity to adapt and innovate in response to environmental challenges. Australian farmers are conscious of the need to manage their natural resources sustainably, delivering a `clean and green' product and working hard to manage their activities within the broader context of catchment management. Continuous improvement in practice is the framework to deliver sustainable outcomes.
Australia could enhance its capacity to deliver both productivity outcomes on-farm and environmental benefits off-farm with:
- continued definition and improvement of best practice and tracking of implementation;
- leadership in monitoring and reporting from industries and their research and development corporations;
- soil management including soil erosion control and revegetation of riparian lands; and
- increased attention to soil fertility, pH and nutrient balance.
All these issues are best addressed through partnerships between industry groups, agribusiness, research and development corporations and government. Australian Agriculture Assessment 2001 has provided the information basis to improve natural resource management by Australian agriculture.
It remains for Australian agriculture and its support groups to keep this information current as a basis for tracking progress and setting priorities.
Australian Natural Resources Atlas
Access to information on natural resources provides opportunities for increased awareness and informed debate. This access has been improved through internet and database technology. The interactive web-based Australian Natural Resources Atlas (Atlas) presents Audit products at scales from local to regional to national.
The Atlas provides information to aid decision making across all aspects of natural resource management. It covers the broad topic of water, land, agriculture, people and ecosystems. The Atlas presents information by geographic region (national, State, regional) and by information topic. Users of the Atlas can prepare a map—using the `make a map facility'—or search hundreds of reports in a matter of seconds.
The Australian Natural Resources Data Library supports the Atlas with links to Commonwealth, State and Territory data management systems.
The outputs of Australian Agriculture Assessment 2001 have been reported in the Agriculture and Land topics of the Atlas.
Audit reports
NLWRA 2001a, Australian Dryland Salinity Assessment 2000, a theme report for the National Land and Water Resources Audit, Canberra.
NLWRA 2001b, Australian Water Resources Assessment 2000, a theme report for the National Land and Water Resources Audit, Canberra.
NLWRA 2001c, Tracking Changes. Australian Collaborative Rangeland Information System, a theme report for the National Land and Water Resources Audit, Canberra.
Australia-wide and regional information |
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Link to monitoring data  |
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