ABSTRACT
Land degradation, a decline in the quality of the land caused by human activities, has become a major global issue (Eswaran et al., 2001). More than half of the dry areas worldwide are affected by land degradation (Dregne and Chou, 1994). Although water erosion is the dominant human-induced soil degradation process, an extent of 0.8 million km2 suffers from secondary salinization caused by land mismanagement, with 58% of these in irrigated areas alone, and nearly 20% of all irrigated land is salt affected (Ghassemi et al., 1995). The main source of salt in soils comes from the weathering of rocks and primary minerals, either formed in situ or transported by water and=or wind. Main causes of salinity development are irrigation with saline water; disturbance of the water balance between rainfall, on the one hand, and stream flow, groundwater level and evapotranspiration, on the other; groundwater rise caused by forest clearance, overgrazing, and cutting bushes; water percolation through saline materials; and intrusion of seawater. If the groundwater traverses saltbearing rocks, then there is a risk that the overlying formations be salt-contaminated. These factors cause and=or enhance salinization, sometimes in association with alkalinization. The latter leads to the formation of sodic soils, although these can also result from the desalinization of salt-affected soils that are poor in divalent cations. Following the slogan that ‘‘prevention is better than cure,’’ it is
argued that mapping salinity hazard might be more useful than mapping salinity itself, hazard being defined as ‘‘potential threat to humans and their welfare’’ (Smith, 2000).
