> Soil and land management > Soil health and condition > Soil acidity

Management of soil acidity risk

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Summary

Soil acidification is becoming an increasing issue in cropping districts due to high levels of production and increased use of nitrogenous fertilisers. Soil acidification will continue to increase unless the level of remedial action is significantly improved.

This page will help you understand:

commonly used management strategies
annual liming requirements and ‘catchup’ requirements
future management challenges.

Acidity management

Maintaining a surface soil pH above 5.5 (CaCl₂) is important for soil productivity and health. Once acidity develops, particularly at depth, it can be difficult and expensive to ameliorate.

Soil acidity can be addressed through:

the application of lime (calcium carbonate) which neutralises soil acidity
the incorporation of calcareous or alkaline clay into the soil
deep ripping or spading, which brings neutral or alkaline soils up from subsurface soil layers
changes to farming system (e.g. using deeper-rooted perennial plants or more acid tolerant crop varieties)
fertiliser management (e.g. changes to fertiliser type, timing and quantity, to minimise the leaching of alkaline nutrients)
use of alkaline irrigation water.

Lime application

The application of lime is one of the most widely used and effective methods for mitigating soil acidification. At the property scale, in areas that are potentially acidifying, regular paddock soil pH testing and liming is needed to ensure optimum crop and pasture production, and prevent increasing sub-surface acidification. Spatial paddock pH mapping and variable rate lime application can give the most cost-efficient treatment and management of soil acidity.

A truck carrying lime (calcium carbonate) across a dry paddock. — Lime application. Image Source: Brian Hughes

Lime Requirement	Definition	Aim
Annual	The amount of lime required to balance (neutralise) annual rates of acidification cause by production	No change in soil pH
Catch-up	The amount of lime required to treat historic acidification	Increase soil pH

Prior to 2018, lime application rates on agricultural land were below the estimated lime requirement to balance annual acidification. From 1999 to 2016, lime use was within the range of about 75,000 to 140,000 tonnes. Since 2016, annual lime use has more than doubled to a mean of 262,000 tonnes in 2022-2025, which is higher than the current lime requirement of about 200,000 tonnes per year.

However, more lime than this annual requirement needs to be applied to currently acidic soils to raise the pH to a fully productive level. This ‘catch-up’ lime requirement is estimated to be about 2.65 million tonnes.

Future challenges

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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