Human Impacts on Soil: Salinization

The extension of irrigation and the use of a wide range of different techniques (e.g. drawing wells, by pumping, building dams, canals, drains, spraying and so on) for water abstraction and application can lead to a build up of salt levels in the soil through the mechanism of raising the ground water enough to the ground surface for capillary rise and subsequent evaporative concentration take place. It is obvious in semi-arid areas.

Besides that, water seep laterally and downwards from irrigation canals so that further evaporation takes places.

And the construction of dam and barrages control water flow which create a large reservoir from which further evaporation takes place.

In coastal area, over-pumping of ground water provokes sea-water incursion since fresh water has a lower density than sea water. It can further increase the salinity of ground water.

With shallow soil profile and irrigation water without proper drainage system may stimulate more evaporation from the irrigated areas and more accumulation of salt in the soil profile.

The consequences of salinity: high sodium concentration in soil leaves the soil structureless and impermeable to water and unfavourable to root development. The poor soil structure and toxicity cause the death of plant directly. The osmotic pressure causes osmotic movement of water from the cell towards the more concentrated soil solution. This leads to cell collapse and plant succumbs.

Removal of salt can be done by improved drainage or by the addition of quantities of fresh water to leach the salt out of the soil. Both solutions involve considerable expense and pose severe technological problems in areas of low relief and limited fresh-water availability.

Conversion involves the use of chemical to convert harmful salts into less harmful ones. E.g. gypsum is added to sodic soils to convert caustic alkali carbonates to soluble sodium sulphate and relatively harmless calcium carbonate.

Other possible measures include the...