Soil salinization

Salinization Salinization from irrigation
Ioannis Daliakopoulos)

What is Salinization?

Soil salinization occurs when water-soluble salts accumulate in the soil to a level that impacts on agricultural production, environmental health, and economics. In the early stages, salinity affects the metabolism of soil organisms and reduces soil productivity, but in advanced stages it destroys all vegetation and other organisms living in the soil, consequently transforming fertile and productive land into barren and desertified lands

Where does it occur?

It is estimated that salinization affects around 3.8 million ha in Europe3. There are different causes of salinization but irrigated areas in particular can be affected by salinization. It is estimated that 25% of irrigated cropland in the Mediterranean area is affected by moderate to high salinization leading to moderate soil degradation4. Projected temperature increases and changes in precipitation characteristics in the Mediterranean are only likely to enhance the problem of salinization.


Map:  Saline (EC > 4 dScm-1 within 100 cm soil depth) and sodic (Na/T > 6% within 100 cm soil depth) soils as primary and secondary limitations to agricultural use and areas of seawater intrusion in the European Union5

What causes it?

Natural processes

The accumulation of salts in the soil can occur through natural processes such as physical or chemical weathering and transport from parent material, geological deposits or groundwater. It can also occur due to parent rock constituents, such as carbonate minerals and/or feldspars or as a result of the one-time submergence of soils under seawater. Sea level rise also induces seepage into areas lying below sea level. In arid areas, saline soils are formed due to evapotranspiration and lack of rainfall to flush the soils. Finally, wind in coastal areas can blow moderate amounts of salts inland.

Human activities

Human activities can cause salinization through the use of salt-rich irrigation water, which can be exacerbated by overexploitation of coastal groundwater aquifers causing seawater intrusion, or due to other inappropriate irrigation practices, and/or poor drainage conditions. The excessive use of water for irrigation in dry climates, with heavy soils, causes salt accumulation because they are not washed out by rainfall. The process occurs in cultivated areas where irrigation is associated with high evaporation rates and a clay texture of the soil. The practice of waterlogging without adequate drainage has also become a serious cause of soil salinization. Waterlogged soils prevent leaching of the salts imported by the irrigation water.

Causes  Location
Naturally induced saline soils Spain, Hungary, Slovakia, Greece, Austria, Bosnia, Serbia, Croatia, Romania and Bulgaria
Artificially induced salinization, such as irrigation Italy (e.g. Campania and Sicily), Spain (e.g. the Ebro Valley), Hungary (e.g. Great Alfold), Greece, Cyprus, Portugal, France (West coast), the Dalmatian coast of the Balkans, Slovakia and Romania. Also in North Europe countries (e.g. Denmark, Poland, Latvia, and Estonia).
Sea-level rise and surface seawater seepage and seawater infiltration into the groundwater Western Netherlands, Belgium, North-eastern France, and South-eastern England


How can it be measured or assessed?

The table below lists key indicators of soil salinization, the purpose of the indicator and methods used or measuring or assessing soil salinization.

 Indicators   Purpose Methods
Electrical Conductivity (EC) Assess salt content Salinity sensors and sampling electromagnetic induction to measure Electrical Conductivity
Exchangeable Sodium Percentage (ESP)   Measure the concentration of sodium relative to the other exchangeable cations ESP = Exchangeable {(Na)/(Ca + Mg + K + Na)} x 100
Sodium Adsorption Ratio (SAR)   Measure of the sodicity of soil, as determined from analysis of water extracted from the soil. SAR = Exchangeable {(Na)/(Ca + Mg)-0.5}

Salt profile  

Assess vertical distribution of salt Any of the above

Potential salt sources 

Measure/estimate EC, SAR, ESP of irrigation water, groundwater and seepage water  Any of the above

Remote sensing indices  

Find proxy spectral indicators that can assist in soil salinity mapping Water absorption bands in the SWIR (short-wave infrared wavelength bands) and NIR (near infrared wavelength bands) 7

Field symptoms  

Detect salinity in affected areas visually Poor condition or absence of vegetation, presence of salt-tolerant weeds, areas that take longer to dry or the presence of unnatural colour soil crusting (white or dark)

How can it be protected or restored?

Practices to control soil salinity include improving drainage, minimising saline water irrigation, leaching salts, isolating salts, growing halophytes, and employing good soil/water management (drip irrigation, irrigation scheduling, seedbed placement, applying organic matter). Drainage is a primary method of controlling soil salinity.

Technology SLM category1
Leaching (provided good drainage conditions) A
Surface water flushing


Drip irrigation S, A
Increase of irrigation water every 3-4 watering events A, M
Irrigation with saline water at less sensitive growth stages A
Mixing of saline/non-saline water M, A
Alternate/cyclic irrigation with saline and freshwater A, S
Alternative water resources (e.g. reuse of wastewater) S, M
Desalination of irrigation water S, M
Mechanical removal of salt surface salt crust A, S
Careful use of machinery (no heavy machinery) M
Green manuring - mulching with manure A
Use of compost or other organic soil amendments A, M
Mulching with leaves/bark or other material S, A
Use of inorganic amendments (e.g. Si, CaSO4.2H2O, H2SO4) A
Biological reduction (phytoremediation or bioremediation) A, V, M
Introduction of salinity-hypoxia tolerant plants  M, V
Land use change from irrigated to rainfed M, V, A
Implementation of drainage systems S
Intervention to the nutrition of plants (e.g. fertilisers) A
Drought pre-treatment of seedlings or seeds with NaCl A
Grafting seedling on proper rootstock A
Inoculation with mycorrhizal associations A
Biopriming with Trichoderma harzianum A
Pre-sowing (or pre-plant) irrigation A, M

 A: Agronomic; M: Management; S: Structural; V: Vegetative; Adopted from Panagea et al., 20166. Always consult with local experts before implementing as limitations may apply.


Rainwater harvesting





Rainwater harvesting: A network of gutters channels rainwater to a metal tank, and is later used for irrigation  Biological soil amendments: Mycorrhiza supplement in the form of grey aggregates used during tomato transplantation  Green manuring: Sorghum seeded in June and incorporated in the ground as in August using a tille

Case Study Experiment

How does it interact with other soil threats?

As salinity is responsible for the structural collapse of soil aggregates into their components it is closely linked to other soil degradation issues. Salinity is often associated with prolonged wetness and lack of surface cover and therefore increases the vulnerability of soils to erosion. Salt interacts with animals and plants, changing the ecological health of land, streams and estuaries. The greatest threat to biodiversity is from the loss of habitat both on land and in water. 

How does it affect soil functions?

  • Biomass production - soils in salt-affected landscapes are less fertile and produce less biomass than non-saline soils resulting in less soil organic carbon (SOC) and in turn more erosion, which further accentuates SOC losses due to the dominance of plant inputs in the accumulation of organic matter.
  • Storing/filtering/transforming - salinization affects a series of environmental interactions leading to reduced water infiltration and retention resulting in increased water runoff and erosion
  • Gene pool - soil biodiversity and microorganism activity declines as EC increases, thus impacting important soil processes such as respiration, residue decomposition, nitrification, and denitrification.
  • Physical heritage - damage to water supply infrastructure as well as transport infrastructure from shallow saline groundwater hinders the functions of soil as a physical medium for build development.
  • Cultural heritage - the removal and re-deposition of archaeological artefacts as well as through the burial of archaeological artefacts under eroded sediments

Front Page Salinization2

FactSheet SalinizationFrontCover

Presentation Slides Fact Sheet








1 Jones, A., Panagos, P., Barcelo, S., Bouraoui, F., Bosco, C., Dewitte, O., Gardi, C., Hervás, J., Hiederer, R., Jeffery, S., 2012. The state of soil in Europe -a contribution of the JRC to the European Environment Agency’s Environment State and Outlook R- SOER 2010.
2 Tόth, G., Montanarella, L., and Rusco, E. (eds.), 2008. Threats to soil quality in Europe. EUR 23438 EN. Institute for Environment and Sustainability, Land Management and Natural Hazards Unit, Office for the Official Publications of the European Communities, Luxembourg, 162pp.
3 Stanners, D., Bourdeau, P., others, 1995. Europe’s environment: the Dobris assessment, in: Europe’s Environment: The Dobrís Assessment. Office for Official Publication of the European Communities.
4 Mateo-Sagasta, J., Burke, J., 2011. Agriculture and water quality interactions: a global overview. SOLAW Background Thematic Report - TR08.
5 Tsanis, I.K., Daliakopoulos, I.N., Koutroulis, A., Karatzas, P., Varouchakis, E., Kourgialas, N., 2015. “Soil Salinization” in “Soil threats in Europe: Status, methods, drivers and effects on ecosystem services” Editors: Stolte, J., Tesfai, M., Øygarden, L., Kværnø, S., Keizer, J., Verheijen, F., Panagos, P., Ballabio, C., Hessel, R. EUR 27607 EN; doi:10.2788/488054
6. Panagea, I. S., Daliakopoulos, I. N., Tsanis, I. K., & Schwilch, G. (2016). Evaluation of promising technologies for soil salinity amelioration in Timpaki (Crete): a participatory approach. Solid Earth, 7(1), 177.
7 Metternicht, G., Zinck, J., 2003. Remote sensing of soil salinity: potentials and constraints. Remote Sensing of Environment 85, 1–20. doi:10.1016/S0034-4257(02)00188-8

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