Assessing saline areas

Page last updated: Monday, 3 August 2020 - 1:21pm

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Dryland salinity can be assessed on-farm by observation and/or measurement.

Observation will usually give indications of salinity level, and measurement will give the information needed to implement effective management. Expensive management options justify more detailed assessment of the saline site.

The Department of Primary Industries and Regional Development recommends that any dryland salinity management is part of a whole farm, and preferably a whole catchment, water management plan.

For a snapshot on salinity and diagnosis, refer to the MyCrop Diagnosing salinity in cereals fact sheet. Detailed information is provided below.

Assessing the site

Observation

Observation is a cheap and easy way of assessing a site, but it does not always give the correct information needed to choose management options. We recommend using direct measurments to confirm the nature of a saline site.

Observations on the site include:

  • reduction in crop yields: when yields are depressed by 50% and soil sample results show elevated levels of salt then decisions can be made whether to continue cropping
  • pasture composition changes: clover reduces or disappears, and plants which can tolerate some salinity begin to appear: cotula, sea barley grass, iceplant, curly ryegrass, samphire (Figure 1)
  • saline areas are more waterlogged and stay wetter longer
  • bare patches appear: leaving a white crust on the surface in summer
  • satellite or aerial imagery shows high albedo (proportion of light reflected back from the surface) or repeated bare patches.
Graphic showing the salinity and waterlogging tolerance of plant indicator species
Figure 1 Indicator species in the salinity-waterlogging matrix

Observations at farm and landscape level include:

  • the site being on a valley floor or change of slope
  • the site being above a known hydrological barrier (bedrock highs or dolerite dykes)
  • other saline areas in similar landscape positions nearby.

Measuring or estimating soil salinity

We recommend using one or more of these measures or estimates across sites to guide expensive management options:

  • field measurement of a soil: water mix electrical conductivity, using a hand-held electrical conductivity meter
  • laboratory measurement of soil electrical conductivity, using an electrical conductivity meter
  • laboratory measurement of total dissolved solids (TDS)
  • field measurement of electromagnetic (EM) induction conductivity, using an EM device
  • remote sensing using an EM device
  • depth to watertable and salt content, and trend.

The two most common measures are electrical conductivity of soil samples – in the field or in a laboratory – or using an electromagnetic induction meter (EM) to 'map' salinity across the paddock (e.g. the EM38 or EM31). An EM map is particularly valuable to show variation of salinity across a site.

See measuring soil salinity for more detail.

Waterlogging and salinity

Waterlogging increases the susceptibility of plants to salt damage by causing the plant roots to become more permeable to salt, so that salt uptake into the shoots is vastly increased. To successfully grow in many saline situations, plants have to be tolerant of both waterlogging and salinity.

Assess the level of watrlogging using information in Diagnosing waterlogging.

Surface water management

A combination of grade banks upslope and shallow relief drains onsite can reduce waterlogging and increase production from saltland pastures.

Reducing the amount of time the soil is waterlogged or inundated improves root survival and plant growth with corresponding productivity gains from the understorey and saltbush species.

Mounding

Mounding has several advantages on some sites:

  • Mounds and the associated channels either side are a form of shallow relief drain. They can be used to drain water from the site.
  • Drainage from the mound is improved, providing a better environment for germination and young root growth.

Estimating risk

Estimate risk of changing salinity by measuring depth to the watertable, salinity of groundwater, and any trend in depth over at least 5 years. A shallow, rising watertable is a high risk.

See Monitoring groundwater for detailed information.

Consult a specialist to interpret measurements.

Diagnosing the severity of salinity

Using the assessment information above, land can be classified into salinity classes. The severity of salinity effects on plants varies with species, concentration in the root zone, interactions with waterlogging, soil type and management.

The classes accepted across Australia are in Table 1. See measuring soil salinity for conversion to other units.

Table 1 Salinity classes according to the estimated electrical conductivity of a saturated soil extract (ECe calculated from EC1:5), land and plant condition

Salinity class

Electrical conductivity of soil extract

ECe (mS/m)

Land and plant condition

Non-saline

<200

Land not affected.

Slightly saline

200-400

Ground surface is seasonally damp after extended periods of rain; there is a gradual change in pasture composition with reduced vegetation diversity and reduced growth and/or yield of crops and pastures often associated with a slight yellowing of the leaves; sensitive deep rooted species and salt sensitive legumes have reduced prodution (e.g. white and subclover, soybeans, chickpea); patches of salt tolerant species develop, such as sea barley grass (Hordeum marinum) or strawberry clover (Trifolium fragiferum); there is dieback in some trees; intermittent streams flow for longer.

Moderately saline

400-800

Ground surface is damp for long periods after extended periods of rain; many field crops and pasture species have severely reduced growth; there is a change in pasture composition to dominance by salt-tolerant species, including grasses; there is reduced vigour of less tolerant species such as strawberry clover; there is dieback in most trees; intermittent streams evolve to permanent streams; there is noticeable rising damp in buildings and some deterioration of roads.

Highly saline

800-1600

Ground surface is waterlogged or permanently moist and too salty for most field crops or lucerne. Halophytes are common; salt tolerant species (e.g. sea barley grass) may dominate large areas and only salt tolerant plants remain unaffected; trees are dead or dying; areas of bare soil have salt crusts; soil structure collapses with subsequent erosion; rising damp and salt efflorescence in buildings is common; there is major deterioration and crumbling of roads.

Severely saline

1600-3200

Halophytes dominate and only highly salt tolerant plants survive (e.g. Puccinellia ciliata and Atriplex spp.). There is decreased growth of most halophytes, some may show reddening of leaves and at the upper end of the range even highly salt tolerant species may be scattered and in poor condition. Most trees are dead, except for highly salt tolerant (e.g. Melaleuca spp.). Extensive bare areas have salt stains and/or crystals evident (on some soils a dark organic stain may be visible); topsoil may be flowery or puffy.

Extremely saline

>3200

Bare salt scalds and samphire (Halosarcia spp.) dominate. Some halophytes die; most have reduced growth.

Contact information

Justin Hardy
+61 (0)8 9892 8408
John Simons
+61 (0)8 9083 1128