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SOLUTION 3

Dense saltbush plantings

 

3.2  Most likely situations for dense saltbush plantings

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Landscape niche

All plants have landscape niches or zones (combinations of climatic and soil conditions and management) where they are most competitive or where they will perform best. Saltland plants are the same, each tending to have a particular set of climatic (rainfall, temperature etc) and soil (salinity, waterlogging) factors which determine where they will be able to survive, and where they are likely to thrive. For saltbush, these factors are summarised in Figure 3.5. 

Figure 3.5 Most likely situations for dense saltbush plantings.

Subsoil salinity/ depth to watertable matrix

Winter

Summer 

 

 

Drivers of saltbush zonation 

  • A halophyte and so does best with some salinity.
  • Sensitive to waterlogging but can survive a higher watertable in winter than summer.
  • Growth in summer assisted if roots can access groundwater.
  • Summer grower, doesn’t like cold.
  • Rainfall 300-400 mm

 


Key to symbols

red dot

This is the zone most preferred by samphire and where this Saltland Solution is highly recommended.

Small Dot

Saltbush is one of the possible options for this zone but it is outside its preferred conditions;

red ring

Samphire will most likely survive in this zone, but its growth will be poor and uncompetitive with other plant options.

Western Australia has the largest areas of saltland suited to saltbush. However, saltbush is highly relevant to the drier saline sites in SA, Vic and NSW. For more information, see Getting the best from old man saltbush and Saltbush for saline land.

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Common indicator species

Analysis of the indicator species growing on the transect trials of the WA2 project (part of the Sustainable Grazing on Saline Land initiative showed the following salt tolerance of common indicator plants (from lowest to highest): capeweed (Arctotheca calendula) < annual ryegrass (Lolium rigidum) < cotula/water buttons (Cotula coronopifolia) < iceplant (Mesembryanthemum crystallinum) < curly ryegrass (Parapholis incurva) < puccinellia (Puccinellia ciliata) < samphire (Halosarcia spp.).

It must be noted that indicator plants can be misleading, especially those at the lower end of salinity tolerance. There may be many reasons (other than salinity) why a particular plant species is present at a particular location, eg. grazing management, cultivation, herbicide use, the impact of recent weather events (especially out of season rainfall). Consequently, the presence of combinations of indicator plants will improve confidence in the site diagnosis. Annual plants (like iceplant) are likely to be better indicators of current conditions than perennial plants (like puccinellia and samphire).

Saline areas that support plants in the salinity tolerance range from capeweed to sea barleygrass are most likely to be suited to saltbush with under-storey. Plants in the range from sea barleygrass to ice-plant are more likely to indicate sites suited to dense saltbush plantings. SALTdeck cards showing some common indicator species are presented in Figures 3.6 to 3.10 below. SALTdeck cards can be viewed on this website or they ordered from the Land Water and Wool website.

Figure 3.6 – SALTdeck identification card for annual ryegrass, a common indicator of land suitable for saltbush. 

Figure 3.7 – SALTdeck identification card for cotula, a common indicator of land suitable for saltbush. 

Figure 3.8 – SALTdeck identification card for curly ryegrass, a common indicator of land suitable for saltbush. 

Figure 3.9 – SALTdeck identification card for ice-plant, a common indicator of land suitable for saltbush. 

Figure 3.10 – SALTdeck identification card for sea barleygrass, a common indicator of land suitable for saltbush.

Sites with large areas of samphire are likely to be too salty and/or too waterlogged for either dense saltbush plantings, or for saltbush with under-storey unless the waterlogging can be corrected.

Similarly, sites with large bare areas may be too salty and/or too waterlogged for saltbush, but such a diagnosis can be misleading if the site is part of a larger paddock and has bare areas as a result of overgrazing and stock camping rather than the bare areas being a true indicator of excessive salinity or waterlogging.

At present we regard ice-plant as a poor indicator, especially in Western Australia where it is becoming a more common weed in cropping paddocks.

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Salinity and waterlogging requirements  

Salinity

Dense saltbush plantings are recommended for soils with subsoils (25-50cm) of ’high’ salinity (ECe values 8–16dS/m). The higher the soil salinity, the greater the salt concentration in the saltbush and the greater the need for fresh water and supplementary feed when grazed. Dense saltbush plantings will grow and provide better feed at lower salinity levels. However from an economic perspective this would generally be a sub-optimal use for the land unless other grazing benefits such as shade and shelter are particularly important.

Waterlogging

Much saltland can also be waterlogged, at least for part of the year. Despite being highly salt tolerant, saltbush is relatively sensitive to waterlogging and inundation particularly if it is prolonged or if it occurs during periods of high temperature. For more information, see Getting real about salinity. It is generally recommended that dense saltbush plantings be established at sites where watertables are deeper than 0.3m in winter and deeper than 0.9m in summer [See section 3.2a]. Saltbush is able to access groundwater at this depth, but it requires less saturated conditions in the surface soil. Old man saltbush is generally more sensitive to waterlogging than river saltbush (watertables should be more than 0.5m in winter and more than 1.1m in summer).

As well as a watertable maintained below 0.3-0.5m, good surface water management can also be critical for the successful establishment and long term survival of saltbush. This means choosing sites that either have limited inundation, or that can be easily modified so that surface water is not retained on the site. Planting the saltbush on mounds is a common method of reducing inundation, and the furrows associated with the mounds can further assist surface water movement. Arranging the mounds in a herringbone or fishbone pattern, with the rows sloping towards the natural drainage line, can greatly assist surface water flows from the site – see Figure 3.11. Tall plants will generally survive inundation better than short plants.

 

Figure 3.11 Use of herringbone design to alleviate waterlogging on a saline scald. (A). Saltbush rows ‘on the contour’ hold water back and become waterlogged. (B). Saltbush rows directed towards the drainage line in a herringbone layout shed water and alleviate waterlogging. For more information, see Saltbush establishment guide.

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Soil & climatic requirements

Soils

Saltbush tends to grow best on soils that are lighter than heavy clays. In particular, direct seeding is only possible if the soil is sandy/loamy, or if there is a sandy/loamy layer over a heavy clay.

Soil acidity seems to be only a minor inhibiting factor for saltbush, except at extreme levels. Saltbush prefers alkaline soils and has decreased growth in acutely acid soils, though the evidence supporting this is largely anecdotal.

  • Poor growth of river saltbush has been reported on a saline/waterlogged/acid site near Wundowie, WA.
     
  • In Clive Malcolm’s original trials of the adaptation of saltbush and bluebush, after 5 months growth the second poorest saltbush growth was at a site with a sub-soil pH less than 4.0.
     
  • In the SGSL experiments at Wubin, WA, there were indications that growth rates in old man saltbush were decreased as the groundwater pH decreased from ~3.6 to ~3.2.

There may also be other soil nutrient issues but research has not yet been undertaken. However, waterlogging is far and away the most significant soil limitation for saltbush growing on saline land.

Rainfall

The suitable rainfall range for saltbush stands is approximately 250-450mm. Below this range, the low production potential and high risk of establishment failure make dense saltbush plantings an uneconomic proposition. Above this rainfall range, there is a high likelihood that waterlogging will be a major constraint for saltbush. Good stands tend to be found in areas with 300-400mm average annual rainfall.

Temperature

Saltbush is a summer grower and optimum growth occurs when daytime temperatures are in the range 30-35oC. Conversely, plants are usually dormant or slow growing during the colder months. With river saltbush little growth is evident when the mean daily temperature is below 13oC; with old man saltbush some growth can still occur in winter.

Anecdotal evidence suggests that old man saltbush has better tolerance to temperature than river saltbush and will withstand quite severe frosts.

The overall result (especially with river saltbush) is that saltbush is not recommended for saline sites in the cooler and/or wetter areas across southern Australia. Perennial grasses such as tall wheatgrass and puccinellia are better options.

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