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SOLUTION 4

Saltbush & under-storey

 

4.2  Most likely situations for saltbush & under-storey

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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. Saltbush & under-storey 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 are likely to thrive. As this is a mixed option, some compromises are necessary, but overall for saltbush & under-storey, these factors are summarised in Figure 4.10. 

Figure 4.10 Most likely situations for saltbush & under-storey.

Subsoil salinity/ depth to watertable matrix

 Winter

Summer 

 

 

Drivers of plant zonation

  • Halophyte (saltbush) and non-halophytes (under-storey) with differing tolerances to waterlogging.
  • Compromises required!
  • Saltbush growth in summer assisted if roots can access groundwater;
  • Most likely rainfall - 300 - 400 mm for annual under-storey, and 350 - 450 mm for perennial under-storey

 


Key to symbols

red dot

This is the zone most preferred by saltbush and where it is highly recommended;

Small Dot

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

red ring

Saltbush will most likely survive in this zone, but its growth will be poor and therefore it is not recommended.

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Common indicator species

Identifying sites that are suited to the saltbush & under-storey mixture involves finding a compromise between where saltbush will grow and where the sown under-storey species can make a significant contribution (ie. more so than a volunteer under-storey). Indicator species such as curly ryegrass that can tolerate sites with high salinity are indicative of locations that will be too salty for the under-storey species. Indicator species (such as cotula, marine or saltwater couch, puccinellia or samphire) that can tolerate high levels of waterlogging are indicative of sites where the saltbush is likely to struggle.

In between these two extremes, there are some species, that if present, are likely to indicate the ideal mix of salinity and waterlogging for a saltbush & under-storey pasture. These include capeweed, annual ryegrass (Figure 4.11), sea barleygrass (Figures 4.12), barley grass (Figures 4.13), annual legumes (such as woolly clover – Figure 4.14 or burr medic – Figure 4.15). SALTdeck was produced by the SGSL initiative to assist with the identification of the 50 most common saltland species. These can be viewed individually on this website or ordered from the Saltland Genie.

Capeweed was not included in SALTdeck because it has quite low salinity tolerance.

It must always 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. history of grazing management, cultivation, herbicide use, and impact of recent weather events, especially out of season rainfall). Similarly, sites with large bare areas may be too salty and/or too waterlogged for saltbush & under-storey, 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.

Figure 4.11 – SALTdeck identification card for annual ryegrass, a common indicator of land suitable for saltbush & under-storey. 

Figure 4.12 – SALTdeck identification card for sea barleygrass, a common indicator of land suitable for saltbush & under-storey. 

Figure 4.13 – SALTdeck identification card for barley grass, a common indicator of land suitable for saltbush & under-storey. 

Figure 4.14 – SALTdeck identification card for woolly clover, a common indicator of land suitable for saltbush & under-storey. 

Figure 4.15 – SALTdeck identification card for burr medic, a common indicator of land suitable for saltbush & under-storey.

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Salinity and waterlogging requirements

Salinity

For soils with high summer salinity levels (subsoil ECe values of 8-16 dS/m) and low levels of winter waterlogging, dense saltbush plantings are recommended because at these salinity levels, there is little chance of a productive under-storey.

Saltbush & under-storey becomes the recommended option for sites of moderate summer salinity (subsoil ECe values of 4-8 dS/m) in the 300-450 mm rainfall zone, but it can also be recommended for sites of low summer salinity (subsoil ECe values of 2-4 dS/m) if the rainfall is too low to support perennial grasses.

Waterlogging

Much saltland can also be waterlogged, at least for part of the year. Despite being highly salt tolerant, saltbushes are relatively sensitive to waterlogging and inundation, especially if it is prolonged or if it occurs during periods of high temperature. Some under-storey species (eg. balansa clover) are highly waterlogging tolerant, while others (eg. burr medic) are more like saltbush. As a package, saltbush & under-storey is not suited to highly waterlogged sites because the saltbush will not survive.

It is generally recommended that saltbush & under-storey be established at sites where watertables are deeper than ~0.3 m in winter and deeper than ~1.5 m in summer. Old man saltbush is generally more sensitive to waterlogging than river saltbush (watertables should be more than 0.5 m in winter).

As well as a watertable maintained below 0.3-0.5 m in winter, good surface water management can also be critical for the successful establishment and long term survival of the saltbush component of the pasture. This means choosing sites that have either 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 furrows associated with the mounds can further assist surface water movement from the site. However, layout design is critical. Mounds in a herringbone layout can decrease waterlogging, but mounds on the contour that collect runoff can make a waterlogging problem worse (see Figure 4.16).

 

Figure 4.16. Use of herringbone mounding 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.

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Soil and climatic requirements

Overall, the climatic requirements for the under-storey species are less precise than for saltbush, so the saltbush & under-storey combination is restricted to those areas where saltbush is suited.

Rainfall

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

Temperature

Saltbush grows optimally when daytime temperatures are warm (in the range of 30oC). 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 10oC; with old man saltbush some growth can still occur in winter.

The overall result is that saltbush & under-storey is not recommended for saline sites in the colder and/or wetter areas across southern Australia. In these areas, the perennial grasses such as tall wheatgrass and puccinellia are usually better options.

Soils

Saltbush tend 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 heavier 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. By far the most restricting soil issue for saltbush is waterlogging.

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