Irrigation salinity

Irrigation salinity is the rise in saline groundwater and the build up of salt in the soil surface in irrigated areas. Inefficient irrigation or applying more water than the plants can use means that this excess water leaks past the root zone to groundwater (recharge). This excess water can cause the watertable to 'mound' under irrigation areas and in some cases the ground becomes waterlogged.

How does irrigation salinity occur?

The major causes of irrigation salinity include over-irrigation of farm land, inefficient water use, poor drainage, irrigating on unsuitable or 'leaky' soils, allowing water to pond for long periods and allowing seepage from irrigation channels, drains and water storages. This increases leakage to the groundwater system, causing the watertable to rise, which may mobilise salt that has accumulated in the soil layers.

When the saline watertable rises to within two metres of the surface, evaporation concentrates salt at the surface. As the soil becomes waterlogged vegetation and crops die because they have limited access to oxygen. Soil saturation is compounded by periods of heavy rainfall, but drought helps improve the situation.

Irrigation salinity will be made worse where the water that is being applied to the irrigated area is derived from already salty rivers, as is now the case in many inland areas.

What are the impacts of irrigation salinity?

Agricultural production in irrigated areas of NSW is worth over $1.5 billion a year. Salinity poses a serious threat to the economic and social future of the people and towns that rely on irrigated farming for income, and to the broader community that rely on this produce.

What is being done?

The major irrigation corporations in NSW have taken a lead in managing irrigation salinity. The control of irrigation salinity requires the coordinated management of groundwater at the district and farm scale. Land and Water Management Plans contain strategies for integrated natural resource management in irrigation areas and have been operating in some of the major private irrigation districts for many years. More information can be found on the NSW Irrigator's Council website

The Land and Water Management Plans for the large irrigation areas like the Murray (Murray Irrigation Area) and Murrumbidgee ( Murrumbidgee Irrigation Limited) are now incorporated in catchment blueprints, which are part of Catchment Action Plans.

Regional water sharing plans are also being prepared under the Water Management Act 2000.

What can I do to manage irrigation salinity?

Prevention

The main strategy for controlling irrigation salinity is to implement water-use efficiency measures coupled with good irrigated farming practices. Only the quantity of water that can actually be used by the crop should be applied to the land.

To reduce water usage in irrigation areas requires improvements to irrigation infrastructure and technology, as well a better matching of crops, such as rice, to suitable soil types. Some specific management and engineering practices that are implemented by irrigators include:

Land Management Practices

  • Avoiding over-irrigation of crops by using techniques such as drip irrigation, soil moisture monitoring and accurate determination of water requirements.
  • Good crop selection - use deep-rooted plants to maximise water extraction.
  • Minimising fallow periods, since bare soil aids water infiltration.
  • Adopting crop rotation to help minimise fallow periods. "Break crops" such as cannula, lupins and peas improve soil structure and fertility.
  • Avoiding deep-ripping and over tillage to minimise infiltration of water.
  • Good soil management - maintain satisfactory fertility levels, pH and structure of soils to encourage growth of high yielding crops.
  • Maximising soil surface cover using multiple crop species with different growth habits.
  • Mulching exposed ground to help retain soil moisture and reduce erosion.
  • Establishing and maintaining trees and shrubs on the property and public lands.

Engineering Measures

  • Implementing subsurface drainage systems to intercept water infiltrating below the plant roots.
  • Implementing surface drainage systems to collect and control water entering and/or leaving the irrigation site.
  • Use large bores, or bore fields to draw down the regional watertable and maintain it below the root zone.
  • Disposing of saline waters in special evaporation basins, or in other approved ways.

Treatment

Where salinity is increasing as a problem on an irrigated farm, it may be necessary to select crop varieties that have a greater tolerance to salt. Examples of salt tolerant species are listed in Productive Use of Salt-affected Land (Book4DrylandSalinity.pdf, 258KB). Where the land is severely salt-affected, it may be more economic to take the land out of production.

The implementation of engineering measures such as subsurface drainage and groundwater pumping, referred to above, can reduce the watertable to below the root zone and allow salt-affected land to be brought back into production.

Assessment and planning

Assessment and planning strategies to manage irrigation salinity are broadly the equivalent to those outlined in Dryland Salinity.

Reference and resources

  • The Department of Primary Industries (formerly NSW Agriculture) has produced a series of fact sheets on irrigation salinity management, as well as a web based guide on using saline water for irrigation.

  • The Glovebox guide to salinity contains information on the identification and management of irrigation salinity in the Murray and Murrumbidgee catchments.
  • This is available on the CRC for Plant Based Management of Dryland Salinity website

  • The CSIRO program Sustainable Irrigation Systems is developing innovative irrigation delivery applications, more productive and efficient irrigated cropping systems, and drainage technologies that help improve water demand management and the quality of return flows from irrigation.

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Page last updated: 26 September 2013