Basic Information | International Commission on Irrigation & Drainage (ICID)

Waterlogging and Soil Salinity

Waterlogging refers to the saturation of soil with water. Soil may be regarded as waterlogged when the water tableof the groundwateris too high to conveniently permit an anticipated activity, like agriculture. Crops need air to a greater or lesser depth in the soil. Waterlogging of the soil stops air getting in.

The practice of irrigation results in consumptive uses of water through evapotranspiration, leaving behind salts concentrated in a smaller volume of water. In irrigated agricultural land, waterlogging is often accompanied by soil salinity as waterlogged soils prevent leaching of the salts imported by the irrigation water.

Salts are a major water quality factor in choosing disposal options for subsurface drainage in arid irrigated areas. Salinity can restrict the urban or agricultural re-use of drainage water, as it is the most significant long-term water quality concern for managing irrigated agriculture in arid zones. Salinity has not been noted as a serious concern with subsurface drainage waters from humid areas. This is generally due to the higher rainfall, higher dilution capacity in surface waters and lower initial salt content in the soil.

Drainage of irrigated land serves two purposes: to reduce waterlogging and to control and reduce salinization. Subsurface drainage water from arid areas always has a higher salinity than the supply water, a higher proportion of Na and Cl, an increased hardness and a higher sodium adsorption ratio (SAR). The higher salinity and higher levels of specific ions often reflect the characteristics of the soil through which the irrigation water has percolated. This in turn is influenced by the shallow groundwater quality, by the ionic composition of the irrigation water, and by the irrigation efficiency. Salt species are also influenced by a number of interdependent, multi-phase chemical interactions. A full salinity appraisal is an essential component of any subsurface drainage water re-use or disposal scheme.