Management of Salt-Affected Soils - Practices of Irrigation and On-farm Water Management - page 275

8.2.1.4 Landscape Feature
In the landscape, soil salinity develops as excess water from well-drained recharge
zones moves to and collects in imperfectly to poorly drained discharge zones. The
buildup of excess water brings dissolved salts into the root zone of the discharge
area (Fig. 8.1 ) .
Fig. 8.1 Salinity development in discharge area
Salinity is more widely known and refers to the amount of soluble salt in a soil.
Unlike sodicity, movements of water influence salinity. Hence, salinity has been
related to clearing and irrigation development and results from changes of land use
and water movements in landscapes.
8.2.1.5 Climatic Condition
Soil salinity and related problems generally occur in arid or semiarid climates where
rainfall is insufficient to leach soluble salts from the soil (or where surface or internal
soil drainage is restricted). In humid regions, salt problems are less likely because
rainfall is sufficient to leach soluble salts from the soil, but even in higher rainfall
areas, salinity problems occur. In some areas with high water tables, problems may
occur with surface evaporation leaving salts to accumulate. Rainfall patterns can
influence the spread and severity of saline soil. Low rainfall and high evaporative
demand can stimulate capillary rise and hence high salt accumulation at the surface.
Under irrigated conditions in arid and semiarid climates, the buildup of salinity
in soils is inevitable. The severity and rapidity of buildup depends on a number of
interacting factors such as the amount of dissolved salt in the irrigation water and
the local climate.
8.2.1.6 Man-Made Activity
Man-made activity can stimulate the salinization process. One of the best examples
of excess salination was observed in Egypt in 1970 when the Aswan High Dam was