Salt-affected soils

Salt-affected soils are soils that contain considerable amounts of soluble salts.  They occur where evapotranspiration greatly exceeds precipitation, i.e. in arid and semi-arid areas.  Cations and anions accumulate in these soils and cause high salinity or alkalinity.  The accumulated ions include sodium, potassium, magnesium, calcium, chloride, sulphate, carbonate and bicarbonate.  A distinction can be made between primary and secondary salinisation processes.  Primary salinisation involves accumulation of salts through natural processes due to high salt contents in parent materials or groundwater.  Secondary salinisation is caused by human interventions such as inappropriate irrigation practices, e.g. with salt-rich irrigation water or insufficient drainage.

Primary salt-affected soils can be broadly classified in:

• Saline soils
  
• Sodic soils

The salts or exchangeable sodium in saline and sodic soils hinder crop growth.  For efficient crop production salts must be therefore leached from the root zone which is in itself problematic because irrigation water is scarce in most regions where these soils occur.  A further problem arises if the irrigation water is itself saline.  Drainage of the irrigation water always has to be ensured.  After the initial application of irrigation water for leaching of salts a regular water supply has to be maintained in order to sustain intensive cropping.  Generally sodic soils give much lower returns per unit irrigation water than saline soils because they require more water for their reclamation.