Mallee Seeps Decision Tree

A tool for the identification and rehabilitation of Mallee Seeps

What is a Mallee Seep?

A Mallee Seep is an area affected by a localised perched water table that brings water and salt to the surface soil layers that can result in surface ponding and bare saline scalding over time.

This should not be confused with other forms saline land degradation, such as:

as each has unique critical driving factors and therefore require different management strategies to overcome them.

The first thing you should do is determine whether you have a Mallee Seep. Click the link below to read our quick guide on how to accurately identify a Mallee Seep.

Mallee Seeps Decision Tree

Do you have a Mallee Seep?

Mallee Seeps should not be confused with other forms of saline land degradation that have very different causes and will require different management strategies. These include:

Mallee Seep

A Mallee Seep is defined as an area affected by a localised perched water table (sitting above tight clay layers) that bring water and salt to the surface, leading to land degradation.

Regional Groundwater Salinity

Regional Groundwater Salinity involves areas of shallow saline regional water systems (within 5-10m of the surface) in the Upper South East of SA and on River Murray tributary lines that cause saline degradation in surface layers.

Regional Creek-line Salinity

Regional Creek-line Salinity are areas of saline land within or adjacent to existing creek-lines whose water is often highly saline and emanating from higher catchment areas.

Dry Saline Land

Dry Saline Land (magnesia land) are saline patches that are not formed due perched or regional water tables, but rather salt rising to the surface from subsoil clays, becoming worse after log dry periods.

What stage of Seep Development are you in?

It’s important to analyse which stage of seep development that your land or area is currently in. In order to appropriately assess the stage, you should analyse your Discharge Zone (seep affected area) and compare with the following characteristics:

Early Mild Phase

The “Early Mild Phase” can present as:

small areas of increased plant growth,
waterlogged areas with machinery trafficking issues,
dominant ryegrass invading crops and pasture areas,
plant stress and poor growth beginning in the centre of affected areas, as plant roots begin to find excess water, which may be fresh or saline.

Intermediate Moderate Phase

The “Intermediate Moderate Phase” developes with:

expanding areas of no crop/pasture germination,
plants around edges becoming stressed and dying,
bare patches that begin to scald out in dry periods, and
salt tolerant volunteer species may begin to establish thorughout area, and
extended periods of surface ponding after rainfall at some sites.

Established Severe Phase

Over time these will grow into the “Established Severe Phase”, consisting of;

large, bare, degraded, unproductive saline scalds,
white salt crystals in a dry crusty surface, or blackened topsoils when wet,
areas that may continue to expand depending on landscape and seasons.

What is the salinity level of the perched water table?

You can calculate the salinity level a number of ways, but our recommendation is to dig a hole to the perched water table and test a water sample for salinity.

If you don’t have a salinity meter then take a sample (from the perched water table – not from surface water or open dam) to your local environmental office.

Tasting the water can also give a reasonable indication, as if it tastes fresh or at a level that you would still feed to livestock, then it is likely in the Low to Medium range, but saltier than this would be in the High to Very High range. Taste at your own risk!

For a more detailed explanation of the salinity testing process, see our water testing video.

What happens if you dig a hole and can’t find a water table?

Low to Medium

<16 dS/m or <10,000 ppm

High to Very High

>16 dS/m or >10,000 ppm

Your decision tree results

Development Phase

Early Mild Phase

Water Salinity Level

Low to Medium Salinity

Key Comments

These areas are often showing very high production even in very dry years due to the plants access to water in the rootzone. If left unmanaged they can quickly grow into large scalded areas, particularly with a medium salinity water table, as salt can rapidly find its way to the surface over the summer/autumn if no cover is established. However, if swift, targeted action is taken, then production losses and significant land degradation can be avoided altogether.

Discharge Zone Management

Often these areas begin as waterlogged zones after wet periods that retain emit moisture throughout the growing season and beyond. Letting these wet areas bare out and bake over summer can rapidly bring salt to the surface and rapid degradation. One strategy is to sow summer crops on these patches – even straight after winter crop harvest – such as sorghum and millet, to maintain cover and use water over the summer/autumn period and stop salt wicking to the surface. These crops can be cut prior to the following winter crop seeding, and will tend to regenerate or reshoot in the following seasons right where they are needed above the perched water table while it still exists. This can stop seep scalds forming, with minimal disruption to your normal cropping program.

Sow lucerne over and just around affected area to lower water table and prevent lateral spread of water table and seep. If small, scalded areas are forming then spread 10-15cm sand over these patches before sowing the lucerne. This will help it establish and keep the surface from accumulating salt. Maintain lucerne and crop through it with the paddock crop each year.

Interception Zone Management

Sow lucerne in a targeted strip of about 20m wide around the discharge zones as close as possible to the affected area. This will both intercept lateral water flows into the perched water table as well as directly lower it. Maintain lucerne and crop through it if required. While you may question the hassle of establishing lucerne, you must also consider the amount of highly productive land that is under threat, often much larger than first thought. Lucerne can be sown through and is quite adaptable to do its vital role within existing farming systems.

Recharge Zone Management

Any deep sand amelioration with ripping, spading, delving, claying and the mixing in of manures or other organic matter etc, resulting in higher water retention and plant water utilisation will have a positive impact on reducing recharge, but will not have as dramatic affect as the water interception achieved with deep rooted perennials.

If it works for your farming system and paddock and you get a season with favorable conditions, then establishing lucerne over a larger portion of the recharge zone will significantly increase the rate at which the perched water table dries up and ceases to be affected by high rainfall periods and events.

Extra Resources