Dryland salinity

Dryland salinity is a natural process for soil, just like other processes such as wind erosion. Salinity degrades land by an increase in soil salt concentration in the environment, watercourse or soil in unirrigated landscapes, being in excess of normal soil salt concentrations in dryland regions.

Salinity refers to the movement and concentration of salt in the landscape and its associated detriment to land and water resources; dryland salinity refers to salinity in unirrigated landscapes. Salinity processes extend from local to regional scales and are driven by imbalances in the water budget that result, primarily, from agriculturally driven landscape change. There are two types of salinity:

There are two types of salinity. Primary salinity (natural salinity) and secondary salinity (induced salinity). (Nrm.qld.gov.au, 2013) Primary salinity naturally occurs in arid and saline environments such as salt lakes, marshes, pans and salt flats. Natural accumulation of salt in soils is an outcome from previous cycles of drainage, desiccation and sea winds. High levels of salt are often found in dry soils, more so than wet soils as it is diluted and washed through the soil profile. (Barry and Holwell et al., 2012).

Secondary salinity is a direct result of human interaction with the land, during development, agriculture and irrigation. Certain land practices have led to changes in the natural structure of the biosphere resulting in excess salting of the land, waterways and soils; thus having detrimental effects on biodiversity and the lands' productivity.

Factors such as climate, features of landscape, soils, drainage, aspect and the effects of human activities; all impact on the severity and occurrence of dryland salinity. Dryland salinity effects human and natural resources, such as native vegetation and crops, animals, infrastructure, agricultural inputs, biodiversity, aquatic ecosystems and water supply quality in the environment. Understanding dryland salinity requires a look at the water cycle. Water enters the soil from precipitation – this is called Infiltration; water may remain indefinitely within the spaces or pores between soil particles as soil moisture. Soil moisture may be lost to the surface or atmosphere directly, or through plant uptake – this is called evapotranspiration. Soil moisture may also continue to move downward to join the groundwater—this is called groundwater recharge. Recharge is most likely to occur when the amount of water that is available to the soil exceeds the soil’s capacity to store it (field capacity). Recharge may also occur by saturated flow when water bypasses the soil matrix as it moves to depth in macropores (e.g. root holes, fractures). Excessive recharge may raise the water table locally, or at a landscape scale. When brackish to saline groundwater intersects the ground surface and discharges, this is termed saline discharge. Areas of discharge are called saline seeps (when groundwater intersects the soil surface) or saline scalds (where water is lost by evaporation only). Groundwater discharge manifests in such problems as: reduced agricultural production, degradation of natural environment, reduced surface water quality, damage to infrastructure including roads, as well as soil erosion and denudation of land.

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