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Soil acidity - Management of risk

Soil acidity can be corrected with lime, however overall lime application rates have been well below the estimated annual acidification rate. Between 2015 and 2018 about 100,000 t of lime was applied in SA p.a. but this needs to increase to 200,000 t p.a. to correct current rates of acidification. More importantly, about 3 million tonnes of lime is required immediately in SA to raise current topsoil pH to 5.5.

Acidity can also be ameliorated by incorporation of calcareous or alkaline clay or by use of alkaline irrigation water. The use of deeper rooted perennial plants and effective management of soil nitrogen can reduce the rate of acidification.

Future challenges

Soil acidification will continue to increase unless the level of remedial action is significantly improved.

Soil acidification is becoming an increasing issue in cropping districts due to high levels of production and increased use of nitrogenous fertilisers. In recent years it has been confirmed that the extent of acid soils in cropping areas is expanding, particularly on sandier, non-calcareous soil types. Sub-surface (below 10 cm depth) acidity is more widespread than previously recognised, and is a significant issue in the Mt Lofty Ranges, Kangaroo Island and South East.

DEW is working in partnership with industry groups, PIRSA and Landscape boards, to develop and deliver programs and projects to:

Improve land manager understanding and awareness of soil acidity, its causes and treatment options
Conduct soil pH testing (including spatial paddock pH mapping) and lime application trials in districts suspected or confirmed to have newly emerging soil acidity
Re-test previous monitoring sites
Test additional sites to assess the extent of surface, subsurface acidity and stratification.

An improved understanding of the rate of topsoil and subsoil acidification under various land uses and land management systems and soil types is required. In addition, a better understanding of the impacts and treatment of soil acidity, especially in the sub-soil, are required, as well as programs that increase the recognition and management of acidity by land managers.

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