Page 20 - Curriculum Visions Dynamic Book

Salt pollution
Salt can build up in soils making it impossible for crops to grow. Soil scientists called
the build up of unwanted salt salinisation.
It is a form of salt pollution.
All waters contain dissolved salts. In most cases these salts are good for plants, providing essential minerals for growth. However, in
dry areas salts can build up if the land is not irrigated properly.
Why soils become salty
Salt occurs in nature from rainwater, the decay of dead plants, river water that soaks into the soils after floods, and the weathering of rock. The salt is absorbed by humus and clay particles in the soil to provide a reserve bank of nutrients for plants to use in their growth. However, too much salt can cause problems. Thus in most parts of the world, bouts of heavy rainfall and floods that soak right through the soil are vital in helping to
Rainfall
flush surplus minerals away.
In dry regions, farmers disturb
the natural balance by irrigating the land for long periods each year. Many use water drawn from underground supplies that are nearly saturated with salts. The farmers may be tempted to save precious water by putting only enough water on the soils to provide sufficient moisture for the plant roots. As a result the surplus minerals never get flushed away. Indeed, they are often drawn back up to the surface
as the water in the soil evaporates. You can see salt-polluted, or saline, soils because they have
white salt crystals on their surface.
 The irrigation water applied to fields in arid areas often has been pumped from underground supplies, or aquifers, and these can have a very high concentration of salt.
 Under normal conditions, rainwater flushes out the salt from fields. In a desert, there is not enough rainfall to do this. Thus, the only plants that will grow are those that will tolerate salty soils.
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