3.10. salinisation of soils
The soil is a basic resource for agriculture, its quality being the most important feature. It is often the case in semi-arid areas that salts were deposited in earlier geological eras. When these deposits are subjected to irrigation, the soil become more saline and the quality is adversely affected. In addition to this, in climates where evapotranspiration is high, the problem gets worse because of the shortage of water. The absence of percolation brings about an increase in salt concentration close to the surface and the land eventually becomes useless. Irrigation systems which use little water enhance the formation of saline areas in the surrounding areas, and the systems become fragile, there being a serious risk of salts invading the zone if the water supply is not continuous and the soil deteriorates completely. (Puigdefabrégas, 1995).
Salinisation affects 25% of the irrigated land in the European Mediterranean (Szabolcs, 1990). In the particular case of Spain, salinisation is widely spread along extensive areas of the coast, mainly in the South East and inland regions.