Salinization

Salinization: the build up of water-soluble salts in soil.

Why is salinization a resource concern?

Since Salinization causes excess salts to build up in soils this limits the growth of crops by limiting their ability to take up water.

What causes salinization?

Salinization may occur naturally or because of conditions resulting from management practices. Salinization will occur on the soil surface when the soil are under these conditions:

• the presence of soluble salts, such as sulfates of sodium, calcium, and magnesium in the soil

• a high water table - The water table lies underground and is the level at which the soil and gravel are completely saturated with water.

• a high rate of evaporation - Causing salt crystals to be left behind on the soil surface.

• low annual rainfall

Where does it take place?

Salinization often takes place in areas such as:

• the rims of depressions and edges of drainage ways

• at the base of hills or slopes,

• in flat, low-lying areas surrounding sloughs and shallow bodies of water. - These areas receive additional water the high water table, which evaporates, causing the salts to be left on the soil surface.

How does this affect Irrigation?

The soil surface becomes partially impermeable and dried out, stopping water from infiltrating soils. This causes water to lie on top of soil flooding land.

How does this then affect agriculture?

Salts in the soil increase the efforts by plant roots to take in water. High levels of salt in the soil have a similar effect as drought by making water less available for uptake by plant roots. Few plants grow well on saline soils; therefore, salinization often restricts options for cropping in a given land area.

Briefly: How can it be combated?

Reducing the severity and extent of soil salinity is primarily a problem of water management. Water management can be addressed in two ways:

• By managing the area contributing excess water to the soil (recharge area)

Or

• By managing the area where the excess water comes to the surface (discharge area).

 

Case study: The Murray-Darling Basin in Australia

Causes:

Deep beneath the ground, in the Murray Darling Basin, there is naturally salty groundwater. In some places saltier than the sea water, this salty groundwater flows into the river and eventually down to the Murray mouth and out into the ocean.

Prior to agricultural development, farming areas were covered by native vegetation that soaked up the rainfall. This meant, less water moved through the soil and into the salty groundwater. By clearing native vegetation and planting irrigated crops, the amount of water moving into the salty groundwater has increased. This has pushed more groundwater into the river, making it more salty. The excess water irrigates down to the subsoil, eventually the water table rises bringing salt to the surface.

Effects:

If there's too much salt in the water it can cause problems. Salinity can:

• Damage equipment by corrosion which comes with a big cost of repair or replacement

• Have impacts on native vegetation especially on floodplains and wetlands

• Agricultural land suffers too since crops and animals have difficulty surviving with low water.

• Without plant roots to hold the soil in place, the soil washes away causing terrible erosion of land.

• Irrigation presents another problem. Crops are grown using water that's poured over them. Too much water however will infiltrate into the water table causing it to rise every year Australia loses large areas of farming lands to salt.

• The salt from the rising water top causes walls to crumble at their bases.

• Roads, paths, pools and other infrastructure crack and lose their structure.

What is being done to combat the problem?

1. Governments have been working together to manage salt for almost 30 years. For each ton of salt added to the Murray we have to find a way to take salt out, the process is similar to a salt budget.

2. South Australia's salinity management program includes a range of strategies, such as:

• More efficient irrigation the land management salt interception schemes - salt interception schemes work by pumping salty water out before it enters the river

• Salinity zoning policy - the salinity zoning policy aims to minimize the salinity impact from new irrigation developments. They achieve this through planting deep-rooted trees, grasses or crops that can suck up the water out of the ground. This will lower the water table and allow the salt to go back down into the ground below the root zone.

 

 

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