4.4 Induced soil acidity
Induced soil acidity in large areas of agricultural land in NSW is predicted to worsen, but this trend can be reversed
Up to 20 million hectares of NSW agricultural land have acidic topsoils. In the absence of the application of lime, an additional 8–22 million hectares of the State's agricultural land is predicted to become highly acidic within 10 years.
In recent years, research and active extension programs on soil acidity have heightened farmers' awareness of the nature of induced soil acidification and its associated problems. The issue has not been widely recognised in the public arena, despite its potential to affect significant areas of NSW. This may be because the changes occur slowly, diffused across very large areas.
Status of Indicator
4.5 Area affected by acidity
Area affected by acidity in NSW is increasing.
Importance of the issue
Many NSW soils, including most of those along the coast, are naturally acidic. Lighter textured soils are at most risk of acidification as they are readily leached. Modern agricultural farming systems, such as the use of improved pasture species, legume-dominant pastures and the application of fertilisers, have accelerated acidification of soils or induced acidification of previously neutral soils (see EPA 2000a).
If left unchecked, soil acidification reduces pasture and crop growth, and can lead to a decline in vegetative cover and agricultural production. Soils affected by acidification extending into the subsoil layers pose serious problems for root development for plants and are difficult and costly to remediate (Pratley & Robertson 1998). As soil acidity becomes more severe, its impacts begin to extend beyond agricultural production, affecting plant vigour, reducing transpiration, and allowing more water to leak past the root zone. This contributes to waterlogging, groundwater recharge, dryland salinity, nitrate pollution of ground water, soil erosion, phosphate leakage into streams and damage to roads from rising watertables (NSW Agriculture 2001a).
The economic impact of soil acidification on farms in Australia is estimated to be 5–6 times higher than dryland salinity (NLWRA 2002). The value of lost production from acid soils in NSW is believed to be between $90 and $225 million per year. The additional costs of damage to ecosystems and community infrastructure have not been quantified (NSW Agriculture 1999).
Between 16 and 20 million hectares of agricultural land in NSW is currently estimated to be affected by acidic topsoils (NLWRA 2001a). As Map 4.5 shows, acid soils are mostly concentrated in a broad band extending southwards from the Central Tablelands. They are found in the prime cropping and pastoral zones of the Central and Southern Slopes under irrigation or in high rainfall areas (Helyar et al. 1990). Significant areas also occur on the North Coast where nitrogen-based fertilisers have been extensively used. Notable acidity occurs around Bathurst, Braidwood, Bega, Grafton and areas in the Central West, as well as the Northern Tablelands districts.
Map 4.5: Surface soil pH and acidification hazard for agricultural land in NSW
Source: DLWC data, as at 2002
The risk of further acidification of NSW lands is just as important as the current distribution of soil acidity. Some soils contain materials that help them to resist acidification and these are referred to as being 'well-buffered'. As part of the Soil Landscape mapping program by the Department of Infrastructure, Planning and Natural Resources, surface-soil buffering capacity has been determined, and overall acidification hazard mapped.
Map 4.5 shows the areas with highest risk of future acidification. These are believed to be broadly distributed but tend to be most common in the Southern Tablelands, the Central West and the South-western Slopes. However, currently available data does not allow determination of the full risk of further acidification across the State. Acid soil problems and hazards continue to be greatest in coastal areas, because of the light soils and high rainfall (see Map 4.5). The problem of induced soil acidification in coastal areas is, however, a different issue from acid sulfate soils (see Land 4.5).
Projections for future soil acidification risk (in the absence of lime applications) have indicated that the seriousness of the issue is increasing. The National Land and Water Resources Audit predicts an additional 5–17 million hectares of NSW agricultural land will become moderately acidic (pH 5.5) within 10 years. Another 8–22 million hectares is expected to reach highly acidic levels (pH 4.8) over the same period (NLWRA 2001a).
Response to the issue
Surface soil acidity and its associated problems are mostly reversible, but costly. It is important to note that surface soil acidification can lead to acidity in the subsoil, which is too expensive to treat for most agricultural land uses.
In 1997, the NSW Government allocated $7 million over three years to the Acid Soil Action (ASA) Program (NSW Agriculture 2001a). Of these funds, $4.9 million went towards the management of agricultural acidity. Further funding of $6 million was provided between 2000 and 2003.
The ASA Program aimed to improve management of acid soils in the tableland permanent pasture zones, often where economic constraints restrict the use of lime to treat them. The program also set out to correct soil acidity in the State's cropping, irrigation and horticultural areas. Two new programs were developed to assist farmers acquire the knowledge and skills needed to manage acid soils on their own farms: the ASA soil test interpretation program and the LANDSCAN course (NSW Agriculture 2001a).
In the first three years of the program, Northern and Southern Management Committees allocated funds to 60 community group projects and 30 research and advisory projects. The management committees comprise representatives from the farming community, the lime-crushing industry, catchment management boards and government agencies. The projects addressed the three key areas of the program: community education and extension; development of improved management systems; and community incentives for improved management of acid soils. Stakeholders contributed an additional $10 million to the program to further develop management systems for acid soils.
Estimates of soil pH, buffering capability and rates of acidification have been undertaken as part of the National Land and Water Resources Audit. This information is available to assist in managing soil acidity. For further information refer to Australian Agriculture Assessment 2001 (NLWRA 2001a).
For farmers, the most common way of treating soil acidity is to add agricultural lime (calcium carbonate) to the soil. The use of lime has increased markedly over the last 20 years, although its cost is often a limiting factor. Recent data from NSW Agriculture indicates that in 2001–02 approximately 600,000 tonnes of lime were applied in NSW, an increase of 160,000 tonnes over 1999–2000.
Effectiveness of responses
Soil acidification problems are now better defined but are still increasing. Research and active extension programs on acidity have improved farmers' awareness of the nature of induced soil acidification and its associated problems.
The increased application of lime by farmers in the areas targeted by the ASA Program indicates that government initiatives have had some success. Current prices, returns and policy settings, however, mean that there will continue to be large areas of agricultural land affected by soil acidity.
Landholders can treat soil acidity by applying lime where appropriate as well as minimising soil acidity by improved land management practices. These include minimum tillage, reducing legume dominance in pastures, matching nitrogen fertiliser inputs to crop requirements, and replacing annual with perennial crop species. NSW Agriculture has more information on practices to reduce soil acidity.
Government can continue to expand research and extension activities to assist in the management and remediation of soil acidity. Further improvements can be expected to follow from increased scientific understanding and research into better lime application techniques, amelioration of subsoil acidity, and improved agricultural management.
Improving understanding of off-site impacts from soil acidification may assist in heightening public awareness of soil acidity issues and help determine what priority actions are necessary.
2.1 Population and settlement patterns
4.1 Land-use changes
4.2 Soil erosion
4.3 Induced soil salinity
5.1 Freshwater riverine ecosystem health
5.3 Surface water quality
5.5 Groundwater quality
5.6 Marine and estuarine water quality
6.1 Terrestrial ecosystems
6.3 Terrestrial species diversity
6.6 Aquatic ecosystems
6.7 Aquatic species diversity
6.9 Aquatic harvesting