Salt affected soils are caused by excess accumulation of salts, typically most pronounced at the soil surface. Salts can be transported to the soil surface by capillary transport from a salt laden water table and then accumulate due to evaporation; they can also be concentrated in soils due to human activity. As soil salinity increases, salt effects can result in degradation of soils and vegetation.

Salinization is a 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.
• human activities such as land clearing and aquaculture activities.

Salinity from irrigation can occur over time wherever irrigation occurs, since almost all water (even 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 water in excess of plant needs is called the leaching fraction. Salination from irrigation water is also greatly increased by poor drainage and use of saline water for irrigating agricultural crops.

Salinity in urban areas often results from the combination of irrigation and groundwater processes. Irrigation is also now common in cities (gardens and recreation areas).

The consequences of salinity are

• detrimental effects on plant growth and 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.

Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License)