Soil Salinization

SALINISATION is the accumulation of soluble salts of sodium, magnesium and calcium in soil to the extent that soil fertility is severely reduced.
SALINITY is the degree to which water contains dissolved salts. Salinity is usually expressed in parts per thousand or grams per thousand grams. Normal seawater has a salinity of 33 parts per thousand. This rises to 40 parts per thousand in the Red Sea.

Salinisation is the process that leads to an excessive increase of water-soluble salts in the soil. The accumulated salts include sodium, potassium, magnesium and calcium, chloride, sulphate, carbonate and bicarbonate (mainly sodium chloride and sodium sulphate). A distinction can be made between primary and secondary salinisation processes. Primary salinisation involves salt accumulation through natural processes due to a high salt content of the parent material or in groundwater. Secondary salinisation is caused by human interventions such as inappropriate irrigation practices, e.g. with salt-rich irrigation water and/or insufficient drainage. 

Sodification is the process by which the exchangeable sodium (Na) content of the soil is increased. Na+ accumulates in the solid and/or liquid phases of the soil as crystallised NaHCO3 or Na2CO3 salts (salt “effloresces”), as ions in the highly alkaline soil solution (alkalisation), or as exchangeable ions in the soil absorption complex (ESP). 

Soil salinisation affects an estimated 1 to 3 million hectares in the enlarged EU, mainly in the Mediterranean countries. It is regarded as a major cause of desertification and therefore is a serious form of soil degradation. Salinisation and sodification are among the major degradation processes endangering the potential use of European soils.

Methodology

Two major data sources are available to delineate areas at risk of salt accumulation in Europe: The European Soil Database (ESDB, 2004) and the map of salt affected soils in Europe compiled by Szabolcs (1974). Szabolcs’ map was of pressing importance in the 1970s because the salinity and alkalinity of soils hindered the satisfactory agricultural utilisation of lands in many regions.

To delineate an updated map of salt affected soils in Europe, items from the two databases were selected that have characteristics of salt affected or potentially salt effected soils. Potentially salt affected refers to soils that are at present not or to a very low degree saline or alkaline, but where human intervention (irrigation) may cause their considerable salinisation and/or alkanisation/sodification (Szabolcs, 1974).

The information on salinity and alkalinity, available directly or through pedotransfer rules in the ESDB, is described in detail by Baruth et al. (2006). In the WRB (World Reference Base) soil names that give information about salinity are Solonchaks, "salic" soils, or "petrosalic" soils. Three Classes of salinity are proposed:

• low: ECse < 4 dS/m (deciSiemens per metre)

• medium: 4 < ECse < 15 dS/m

• high: ECse > 15 dS/m
  with EC: electrical conductivity of the soil saturation extract from the root zone.

In the WRB, soils having alkaline characteristics are Solonetz, "natric" soils, or "sodic" soils. Three classes of alkalinity are proposed for further analysis:

• low: ESP < 6%

• medium: 6 < ESP < 15%

• high: ESP > 15%
  with ESP, exchangeable sodium percentage.

References (Citations):
Tóth, G., Adhikari. K., Várallyay, Gy., Tóth, T., Bódis, K. and Stolbovoy, V. 2008. Updated Map of Salt Affected Soils in the European Union. In. Tóth, G., Montanarella, L. and Rusco, E. (eds.) 2008. Threats to Soil Quality in Europe EUR 23438 EN 151 pp Luxembourg: Office for Official Publications of the European Communities. pp. 65-77

Salinisation, also known as alkalisation or sodification, is often associated with irrigated areas where low rainfall, high evapotranspiration rates or soil textural characteristics impede the washing out of the salts which subsequently build-up in the soil surface layers. Irrigation with high salt content waters dramatically worsens the problem.

In coastal areas, salinisation can be associated with the over exploitation of groundwater caused by the demands of growing urbanisation, industry and agriculture. Over extraction of groundwater can lower the normal water table and lead to the intrusion of marine water. Natural disasters in coastal areas, such as tsunamis, can cause severe salinisation problems with several years of low fertility of the affected soil before recovery. In Nordic countries, the de-icing of roads with salts can lead to localised salinisation.

Salinity is one of the most widespread soil degradation processes on the Earth. According to some estimates, the total area of salt affected soil is about one billion hectares. They occur mainly in the arid–semiarid regions of Asia, Australia and South America. In Europe, salt affected soil occurs in the Caspian Basin, the Ukraine, the Carpathian Basin and the on the Iberian Peninsula. Soil salinity affects an estimated 1 million hectares in the European Union, mainly in the Mediterranean countries, and is a major cause of desertification. In Spain 3% of the 3.5 million hectares of irrigated land is severely affected, reducing markedly its agricultural potential while another 15 % is under serious risk. 

Read more at: https://esdac.jrc.ec.europa.eu/themes/soil-salinization#:~:text=Salinisation%20is%20the%20process%20that,soil%20fertility%20is%20severely%20reduced.