Guideline Index

Chapter 7: Managing Limiting Soil Factors

7.5 Salinity

7.5.1 What is salinity?

When we refer to salinity in agriculture, we are referring to the level of salt in the soil and the soil solution.

The most frequently found salt in saline conditions is common salt, more correctly known as sodium chloride (NaCl). Other dominant salts found are sodium carbonate and sodium bicarbonate and to a lesser extent sulphates of sodium, calcium, magnesium and potassium and chlorides of calcium, magnesium and potassium.

Saline soils are those with sufficiently high levels of salt in the root zone to adversely affect plant growth.


High salt levels affect plant growth in two ways:

  • They reduce the plant’s ability to take up water (an osmotic effect).
  • They cause toxicities (usually chloride and sodium) and nutrient imbalances by changing the plant’s ability to take up a wide range of nutrients.

Natural saltland (primary salinity) existed in Australia before European settlement; however, the extent and severity of salinity has increased markedly due to changes in the management of land and water (secondary salinity).

7.5.2 The processes of salinity

The processes of salinity are shown in Figures 7.8 (dryland) and 7.9 (irrigation).

Rainfall or irrigation water can leave the soil surface in several ways. It can be used by plants or removed by runoff and evaporation. The remaining water seeps through the soil until it reaches a dense rock layer (often referred to as bedrock) or a clay or other hardpan layer that it cannot penetrate. The soil then begins to fill up with water, starting from this layer. The top of the saturated zone in the soil is known as the watertable. Recharge, or groundwater recharge, is the name for water added to the watertable in this way.

When the watertable rises to within 1 or 2 metres of the soil surface, the water can move into the plant root zone by capillary rise. Capillary rise occurs when drier soil on top of the watertable sucks up the ground water, similar to the action of a sponge. The capillary zone is the area above the watertable that is affected by capillary rise.

Figure 7.8  Processes and causes of dryland salinity
Figure 7.8 Processes and causes of dryland salinity

The height of capillary rise depends on the soil type. It is greatest in loam soils, which have a variety of particle and pore sizes. In sandy soils, there are bigger spaces and the force needed to lift water through them is greater. In clay soils, small pore size slows water movement.

As the watertable rises, the salts in the soil are dissolved. If capillary rise brings salty water into the plant root zone, the plants are affected by the salts. In extreme cases, capillary rise will bring the salty water to the soil surface. This is known as discharge. The salt makes it hard for the plants to take water from the soil, and the plants may show signs of water stress. Eventually, they may die of dehydration if the salinity levels are too high. Pastures suffering from the effects of salinity can become invaded by salt-tolerant weeds; and as salinity increases, the proportion of salt-tolerant grasses increases.

Figure 7.9   Processes and causes of irrigation salinity
Figure 7.9 Processes and causes of irrigation salinity

The early symptoms of salinity are often incorrectly thought to be caused by something else, such as waterlogging or a lack of fertiliser; and a yield loss of up to 30% can occur before definite signs of salinity become visible.

7.5.3 The causes of secondary salinity

The main cause of many of the secondary dryland salinity problems is the clearing of deep-rooted native trees from recharge areas. Trees and other large vegetation use and transpire much more water than pasture or cropping does. When these large plants are cleared from the recharge area, more water seeps into the watertable.

The main cause of irrigation salinity is poor irrigation methods, such as slow watering, that allow water to pond for long periods and seep into the soil. In addition, seepage from irrigation channels and drains and from dams results in recharge.

7.5.4 Soil classification and salinity measurement

Soils have been divided into five classifications to help identify the degree of the salinity problem. The classes range from very low to extreme levels of salinity and are named A+ (very low), A, B, C and D (extreme) – See Figure 7.10. Most of the Northern Victoria irrigation area is type A+ or A soil, but there are significant areas of classes B, C and D, particularly to the west. The growth of most pasture species is unaffected by salinity levels of class A or B soils. Only salt-tolerant plants like barley grass grow in class D soils.

Salinity is measured by determining the electrical conductivity (EC) of a water or soil sample. Electrical conductivity is a measure of the capacity of soil or water to carry an electric current. The main unit of measurement for soil salinity is deciSiemens per metre (dS/m). ECe (dS/m) is a salinity measure used by researchers that allows for the effect of soil texture on salinity. Further information about measuring salinity is provided in Chapter 9.2.10.

The estimated returns from applying irrigation water to dairy pastures growing on soils with different degrees of salinity are shown in Table 7.2. This shows how large an effect soil salinity can have on economic returns. Similar economic effects would occur with the application of fertiliser to the various classes of saline soil.

Table 7.2   Estimated returns from applying 1 megalitre of irrigation water to different classes of saline land (1992 data)  Source: Adapted from Norman et al. (1995).
Table 7.2 Estimated returns from applying 1 megalitre of irrigation water to different classes of saline land (1992 data)
Source: Adapted from Norman et al. (1995).

Soil salinity levels determine what grows in the soil and are a major reason for lower productivity. Lower salinity soils give better return for your money. Therefore, in salt-affected areas, it is important to know the classifications of your soil so areas of C and D class can be managed differently to the more productive A and B class soils.

7.5.5 What does salinity look like?

Salinity will affect plants differently depending on their stage of growth. They are usually most at risk during seedling emergence and early seedling growth. If salinity weakens them at an early stage in their growth, they are more prone to stress caused by other problems, such as poor soil structure, disease, insects, nutrient deficiencies, or waterlogging. Plants may die from the combined effect of several of these rather than just one.

The leaves of salt-affected plants can initially appear smaller and darker than normal. Shoot growth is also reduced. As salinity levels increase, the effects become more pronounced. Low germination rates and seedling deaths reduce establishment, and surviving plants grow more slowly. The tips of leaves can appear burnt, and this can spread until the whole leaf is yellow. The photos in Figure 7.10 show examples of A, B, C, and D soil salinity classes and the effect of their salt levels on productivity.


Figure 7.10a

Figure 7.10b

Figure 7.10c

Figure 7.10   Soil salinity classes A, B, C and D and their effect on productivity in the Kerang Irrigation Region of northern Victoria

Figure 7.10 Soil salinity classes A, B, C and D and their effect on productivity in the Kerang Irrigation Region of northern Victoria General pasture symptoms
  • Plant growth is poor and uneven.
  • Grasses dominate because they generally are more tolerant to salinity than clovers and other legumes.
  • Animals may lick and graze salty areas. General soil symptoms
  • White salt crystals may appear on bare soil surfaces in extreme cases.
  • The surface soil may remain moist and greasy.
  • Clay soils may appear loose and crumbly and when cultivated may have a soft and spongy texture.

7.5.6 Plant tolerance to salty conditions

The tolerance of the various pasture species to salinity does vary. In some cases, specific varieties may be recommended to assist more severe salinity problems because of their better tolerance to the particular conditions. Table 7.3 indicates the relative salt tolerance of some pastures and crops.


Table 7.3   Tolerance of some pasture and crop plants to various levels of salinity
Table 7.3 Tolerance of some pasture and crop plants to various levels of salinity

7.5.7 How can we best manage salinity?

The solutions to the salinity problem are not a matter of just treating the symptoms but of managing all the factors that influence the well-being of the water catchment.

As a whole, the community can help in lowering the watertable. Management of the whole catchment assists everyone’s problems and so benefits everyone. Some of the practices available are mentioned below.

Community surface drainage reduces accessions to the watertable as well as providing a wide range of benefits on farms. Surface drainage programs in irrigation areas provide financial and technical support to survey, design and construct subregional community drainage schemes.

Subsurface drainage removes excess water from below the ground surface. Common methods are groundwater pumping from suitable shallow aquifers (in irrigation areas) and tile or mole drainage (see Section 7.4.5).

Whole-farm plans can be used to protect and enhance environmental features while increasing farm profitability. A whole-farm plan is a drawing or photograph of the farm showing existing natural and built features and details of the improvements to be made on the property, such as fencing by soil salinity class, drainage plans, or improved irrigation management.

Trees strategically planted on recharge areas, along laneways and fence lines and on irrigation reuse systems and channel banks provide several benefits. A significant one is the consumption of ground water by the trees, which assists in lowering the watertable; others include providing shade and shelter for livestock, improving property values and providing wildlife habitat. In irrigation areas, incentives are sometimes available to producers and community groups for each of these four practices. For more information contact your regional catchment management authority or natural resource management group – See

As long as untreed recharge areas and irrigation practices continue to upset the natural water balance, the salinity problem will remain. Only when improved land and water management practices slow the rate of recharge to the groundwater system will it be possible to control salinity. Practices for managing dryland salinity

Salinity is not a widespread problem in dryland dairying areas at present. However, steps that dryland farmers can take to manage dryland salinity include:

  • Using more water in recharge areas by:
    • Retaining any remaining native vegetation.
    • Planting perennial pasture species, as they are deeper-rooted and use more water than annual species.
    • Replanting catchment areas with trees, which can be used for livestock fodder, firewood, posts and poles, sawlogs, honey, windbreaks, wildlife habitat, and erosion control.
  • Controlling grazing in recharge areas so that as much pasture growth as possible remains on the soil.
  • Fencing off saline areas and planting them in salt-tolerant trees or pasture species. These plants will help to keep the soil profile drier by using the saline water and will also help to prevent soil erosion, which often occurs on saline areas when the existing vegetation cover is killed by the salt.

In many cases, salinity in dryland areas is caused by problems on recharge areas that are not on the property on which the salinity occurs. In such cases, a catchment-wide approach to salinity management will be necessary, involving cooperation with neighbouring landowners and your local catchment management authority or natural resource management group. Practices for managing irrigation salinity

All irrigation farmers can take steps to improve irrigation management. These include:

  • Using a whole-farm plan for a structural approach to farm development.
  • Matching and monitoring the water application to the needs of pastures and crops.
  • Improving pasture and crop growth to use more soil water.
  • Watering paddocks in less than 6 hours.
  • Draining paddocks as quickly as possible after irrigation.
  • Reusing all drainage water in future irrigations.
  • Make sure that soil fertility and soil health is optimum
  • Minimise soil compaction
  • Monitor the soils salinity levels at various depths within the plants rooting zone (either by soil tests or installed monitoring devices e.g. gypsum blocks)

For more information on soil salinity refer to the Salinity Management Handbook, 2nd Edition.