Soil Themes > Soil Salinisation
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.
More information about:
- Methodology for estimation of Saline and Sodic Soils
- Maps - Data
- Supporting Documents
|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. Salt affected soil can be divided into five main groups:
Salt affected soil often exhibits a white or grey salt crust on the ground. The pH of the soil is around 8.5 and the salt interferes with the growth of all but the most specially adapted plants (ED).
In Europe, the first two groups are the most significant. The factors that determine the accumulation of salt in a soil are as follows:
Salinity as an environmental stress and limiting factor for agriculture.
One of the main characteristics of salt affected soils is their temporal variability. Prolonged rainfall can lead to a temporary leaching of salt from the surface layers. In many salt affected areas, small ponds are dug to drain the saline water from the soil thus allowing limited agriculture on other parts of the land. The white deposits on the bank of the pond are evaporated salt crystals .
|The accumulation of salts, particularly sodium salts, are one
the main physiological threats to ecosystems. Salt prevents,
limits or disturbs the normal metabolism, water quality and
nutrient uptake of plants and soil biota. When water
containing a large amount of dissolved salt is brought into
contact with a plant cell, the protoplasmic lining will shrink.
This action, known as plasmolysis, increases with the
concentration of the salt solution. The cell then collapses.
In addition, sodium salts can be both caustic (corrosive) and
toxic (poisonous) to organic tissue. The nature of the salt,
the plant species and even the individuality of the plant
(e.g. structure and depth of the root system) determine the
concentration of soil-salt levels at which a crop or plants
will succumb. Examples of plants and crops with a high
tolerance to salt include bermuda grass, cotton, date palm,
peas, rape and sugar beet while apples, lemons, oranges,
potatoes and most clovers have a very low tolerance.
Salinization processes are near to irreversible in the case of heavy-textured soils with high levels of swelling clay. Although a combination of efficient drainage and flushing of the soil by water is often used, the leaching of salts from the profile is rarely effective.
Because the reclamation, improvement and management of salt affected soils necessitates complex and expensive technologies, all efforts must be taken for the efficient prevention of these harmful processes. Permanent care and proper control actions are required. Adequate soil and water conservation practices, based on a comprehensive soil or land degradation assessment, can provide an “early warning system” that provides possibilities for efficient salinity (or alkalinity) control, the prevention of these environmental stresses and their undesirable ecological, economical and social consequences.
Soil salinisation in coastal areas affected by tsunami tidal waves
|One of the long term effects of tsunami waves is the deposition of salty seawater on large flooded areas with consequent salinisation of soils.
Depending on the climatic conditions, these effects can be temporary and the soils may recover rapidly by washing out the infiltrated salt
deposits through heavy rainfall. In more arid or sub-humid areas the salinisation effects can on the other hand last for several years. Depending
on the type of crops cultivated in the area and their resistance to salinisation there can be serious consequences on long term agricultural
production and food security in the affected area.
The 9 magnitude earthquake that occurred at 00.58 UTC on 26th December 2004 at the interface between the India and Burma plates off the west coast of Northern Sumatra, Indonesia, triggered massive tsunamis that affected several countries throughout south and south east Asia (India, Bangladesh, Mynamar, Sri Lanka, Indonesia, Maldives and Thailand) as well as in East Africa (Somalia, Kenya, and Tanzania). The total inundated zone is estimated at ca. 60 000 sq. km. Soils of these areas have been affected by erosion and scouring that modifies the topography, land leveling and the elimination of bunds (for paddy fields), soil fertility losses when upper layer is washed away, deposition of salted sediment, salt infiltration and trash and debris accumulation. Recovery of the affected areas will require several years in some areas lacking sufficient rainfall for rapid outwash of accumulated salts and will be an additional burden to the local population.
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