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Encyclopedia > Soil salination
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Visible salt deposits on the former bed of the Aral Sea
Visible salt deposits on the former bed of the Aral Sea

Soil salination is the accumulation of free salts to such an extent that it leads to degradation of soils and vegetation. Image File history File links Unbalanced_scales. ... Image File history File links Broom_icon. ... ImageMetadata File history File links Download high resolution version (1600x1200, 569 KB) Summary Abandoned ship on the bed of the Aral Sea. ... ImageMetadata File history File links Download high resolution version (1600x1200, 569 KB) Summary Abandoned ship on the bed of the Aral Sea. ... The Aral Sea (Kazakh: Арал Теңізі (Aral Tengizi), Uzbek: , Russian Аральскοе мοре) is a landlocked endorheic sea in Central Asia; it lies between Kazakhstan in the north and Karakalpakstan, an autonomous region of Uzbekistan, in the south. ... Retrogression and degradation are two regressive evolution processes associated with the loss of equilibrium of a stable soil. ...


Salination is a natural process that results from:

  • high levels of salt in the soils.
  • landscape features that allow salts to become mobile (movement of water table)
  • climatic trends that favor accumulation

Salt is a natural element of soils and water. The ions responsible for salination are: Na+, K+, Ca2+, Mg2+ and Cl-.
As the Na+ (sodium) predominates, a salinised soil is also a sodic soil. For other uses, see Salt (disambiguation). ...


Over eons, and as the world’s soils became established, the soil salt levels declined to a very livable minimum. As the soil fertility increased, the remaining salt, not flushed or leached out by rain, was chelated into the nooks and crannies of the humic acid molecules constituting most of the "fertility" in rich fertile soil. Look up eon, Eon, EON in Wiktionary, the free dictionary. ... Humic acid is one of the major components of humic substances which are dark brown and major constituents of soil organic matter humus that contributes to soil chemical and physical quality and are also precursors of some fossil fuels. ...


In some areas (for example in Australia), salinity is an inherent situation (enormous amounts of salts are stored in the soils). However, human practices have increased the salinity of top soils by bringing salt to the surface through disrupting natural water cycles, by allowing excess recharging of groundwater and accumulation through concentration. Annual mean sea surface salinity for the World Ocean. ... Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of geologic formations. ...


One of the best examples of excess salination was observed in Egypt in 1970 when the Aswan High Dam was built. The change in the level of ground water before the construction had enabled soil erosion, which led to high concentration of salts in the water table. After the construction, the continuous high level of the water table led to the salination of the arable land. Map showing reservoir The hydroelectric power station of Aswan Dam Aswan is a city on the first cataract of the Nile in Egypt. ... Groundwater is any water found below the land surface. ... Severe soil erosion in a wheat field near Washington State University, USA. Erosion is the displacement of solids (soil, mud, rock, and so forth) by the agents of wind, water, ice, or movement in response to gravity. ... To meet Wikipedias quality standards, this article or section may require cleanup. ...


Salinity from drylands can occur when the water table is between two to three metres from the surface of the soil. The salts from the groundwater are raised by capillary action to the surface of the soil. This occurs when groundwater is saline (which is true in many areas), and is favored by land use practices allowing more rainwater to enter the aquifer than it could accommodate. For example, the clearing of trees for agriculture is a major reason for drylands in some areas, since deep rooting of trees has been replaced by shallow rooting of annual crops.


Salinity from irrigation can occur over time wherever irrigation occurs, since almost all water (other than natural rainfall) contains some dissolved salts. When the plants use the water, the salts are left behind in the soil and eventually begin to accumulate. Since soil salinity makes it more difficult for plants to absorb soil moisture, these salts must be leached out of the plant root zone by applying additional water. This, in turn, can lead to rising water tables, requiring drainage to keep the saline groundwater out of the root zone. If the water table rises too high, then natural soil evaporation will begin to draw the salts back upward into the soil profile. The problem is accelerated when too much water is added too quickly due to inefficient water use such as over-irrigation, applying more than is required for leaching, using bad estimates of evapotranspiration and poor system design, and is also greatly increased by poor drainage and use of saline water for irrigating agricultural crops. These practices result in the concentration of salts. Irrigation is the artificial application of water to the soil. ... Evapotranspiration (ET) is the sum of evaporation and plant transpiration. ... Drainage is the natural or artificial removal of surface and sub-surface water from a given area. ... Biosalinity is the study and practice of using saline (salty) water for irrigating agricultural crops. ...


Salinity in urban areas often results from the combination of irrigation and groundwater processes. Cities are often located on drylands, leaving the rich soils for agriculture. Irrigation is also now common in cities (gardens and recreation areas).


The consequences of salinity are

  • detrimental effects on plant growth and final yield
  • damage to infrastructure (roads, bricks, corrosion of pipes and cables)
  • reduction of water quality for users, sedimentation problems
  • soil erosion ultimately, when crops are too strongly affected by the amounts of salts.

Salinity is an important land degradation problem. One way to prevent excess salination would be the use of humic acids, especially in regions where too much irrigation was practiced. In soils with excess salts, humic acids can fix anions and cations and eliminate them from the root regions of the plants. A type of plant that is of particular interest for those in areas affected by soil salinity is the saltbush, which is able to tolerate saline conditions and draws salt up into its leaves. Severe soil erosion in a wheat field near Washington State University, USA. Erosion is the displacement of solids (soil, mud, rock, and so forth) by the agents of wind, water, ice, or movement in response to gravity. ... Humic acids are those organic compounds found in soil that are insoluble in acidic conditions. ... An anion is an ion with negative charge. ... A cation is an ion with positive charge. ... Species About 100-200 species, including: Atriplex alaskensis (Alaska Orach) Atriplex californica Atriplex calotheca Atriplex canescens Atriplex confertifolia Atriplex coronata (Crownscale Saltbush) Atriplex glabriuscula Atriplex hortensis (Garden or Red Orache) Atriplex halimus Atriplex heterosperma Atriplex hymenelytra Atriplex laciniata (Frosted Orache) Atriplex lentiformis Atriplex littoralis (Grass-leaved Orache) Atriplex longipes ( Orache...


From the FAO/UNESCO Soil Map of the World the following salinised areas can be derived [1] .

Africa
Near and Middle East
Asia and Far East
Latin America
Australia
North America
Europe

69.5
53.1
19.5
59.4
84.7
16.0
20.7

The reclamation of saline soils is discussed in Salinity control. Salinity control of soils in (irrigated) agricultural land // Controlling the problem of soil salinity, reclaiming salinized agricultural land. ...



References

  1. ^ R.Brinkman, 1980. Saline and sodic soils. In: Land reclamation and water management, p. 62-68. International Institute for Land Reclamation and Improvement (ILRI), Wageningen, The Netherlands.

See also

Soil Salinity is a major environmental issue in Australia, chiefly affecting agricultural lands in many areas of W.A. (Western Australia) Much of central Australia was at one time a shallow inland sea. ... Salinity control of soils in (irrigated) agricultural land // Controlling the problem of soil salinity, reclaiming salinized agricultural land. ... This article or section is missing references or citation of sources. ... Soil acidification is the buildup of hydrogen cations, also called protons, in the soil. ... A saline seep is formed through excess water entering into the ground, which eventually raises the water table. ... Geohumus is a commercial product, made in Germany, which is used for soil improvement. ... Species About 100-200 species, including: Atriplex alaskensis (Alaska Orach) Atriplex californica Atriplex calotheca Atriplex canescens Atriplex confertifolia Atriplex coronata (Crownscale Saltbush) Atriplex glabriuscula Atriplex hortensis (Garden or Red Orache) Atriplex halimus Atriplex heterosperma Atriplex hymenelytra Atriplex laciniata (Frosted Orache) Atriplex lentiformis Atriplex littoralis (Grass-leaved Orache) Atriplex longipes ( Orache...

External links

  • Soil salinity, provides free downloads of articles and software on land drainage for soil salinity control.

Notes


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