> Soil and land management > Soil health and condition

Land salinity

In all agricultural regions, land salinity poses a threat to key assets such as wetlands, native vegetation and high quality agricultural land, as well as to infrastructure such as roads, sewage and buildings. Natural (or primary) salinity can be a feature of some soils and water bodies. However, human-induced (or secondary) salinity can arise where land use and management activities lead to increased intensity or extent of salinity in the landscape.

Land salinity occurs when there is an excess of salts in the soil or plant rootzone. Moderate to high levels are toxic to plants, while even moderately low levels can affect production. Land salinity can occur with or without the influence of groundwater.

Types of Salinity

Primary (Natural) Salinity

Many of South Australia’s soils are inherently saline, due to:

the presence of inland seas during the Pliocene-Miocene eras, which left behind marine sediments and salts
natural salt accumulation in the soil from rainwater when it evaporates
topography, with low-lying basins accumulating salt over time.

Dry saline land is a type of land salinity that occurs in soils with high levels of naturally occurring salt but is not associated with a shallow watertable. In mild situations, dry saline land can also be referred to as transient salinity, where salts are trapped within the soil profile (e.g., due to low permeability clay subsoil) and salts move up and down (with varying influence on plant rootzones) depending on seasonal conditions. In extreme cases, where naturally high salt concentrations extend to the soil surface and visibly affect plant growth, these areas of dry saline land are commonly called magnesia ground or magnesia patches. These are mainly found in the Eyre Peninsula.

Map showing the distribution of dry saline land (non-water table associated) across the South Australian agricultural zone. — Distribution of saline soils (non-water table induced) within South Australia’s agricultural soils. Source: DEW

Watertable-induced salinity is caused by the movement of salts from shallow, saline ground water into the plant root zone through capillary action. This is a natural feature in some of South Australia’s soils, but this process can be intensified through land management actions (secondary salinity) which increases groundwater recharge.

Secondary (Human-induced) Salinity

Dryland salinity is the term given to land salinisation associated with elevated watertables in non-irrigated areas. Historical clearance of native vegetation and replacement with dryland farming (shallow-rooted annual crops and pastures) means that less rainfall is used by plants and this can cause groundwater levels to rise in some situations. Elevated watertables can cause the movement and accumulation of salts towards low-lying areas where discharge of water and salt occurs at or near the soil surface, in plant rootzones, or to adjacent waterways. These changes to the landscape water balance can increase the intensity or extent of land salinisation and/or increase saline groundwater discharge to streams and rivers, including the River Murray.

Irrigation-induced salinity can occur where excess irrigation water is applied, relative to the crop water use and deep drainage, and rising shallow groundwater brings salts up into the plant rootzone.

Approximately 1.5 million hectares (14%) of cleared agricultural land in SA is affected to some degree by watertable – induced dryland salinity. The Upper South East is the most severely affected area in the State (approximately 200,000 ha). With the successful completion of the Upper South East Dryland Salinity and Flood Management Program, the drawdown effect associated with the drainage network has reduced the risk of salinity over an estimated area of more than 100 000 ha. This is a reduction of 50% of land affected in the Upper South East.