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. 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. ... Map of area around the Aral Sea. ... 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^- A magnified crystal of a salt (halite/sodium chloride) In chemistry, a salt is any ionic compound composed of positively charged cations and negatively charged anions so that the product is neutral and without a net charge. ...

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 soil salinity by changing the natural balance of the water cycle, by allowing excess recharging of groundwater and accumulation through concentration. Salinity is the saltiness or dissolved salt content of a body of water. ... 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. 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. ... Modern arable agriculture typically uses large fields like this one in Dorset, England. ...

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. High-altitude aerial view of irrigation in the Heart of the Sahara (, ) Irrigation (in agriculture) is the replacement or supplementation of rainfall with water from another source in order to grow crops. ... 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...

See also

• Salting the earth
• Soil acidification

Salting the earth refers to the practice of spreading salt on fields to make them incapable of being used for crop-growing. ... Soil acidification is the buildup of hydrogen cations, also called protons, in the soil. ...

External links

• A scholarly paper on land salinization – does not address the historical issue.