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UNIT 7

Saltland Toolbox

 

7.1  Saltland Capability

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‘Saltland’ explained

Although ‘saltland’ is clearly affected by salinity, it is often affected by other stresses: foremost amongst these is waterlogging, but saltland can also be affected by soil texture, extremes of pH, cemented pans in the soil, etc.

Salinity - All soils contain salts of various types. It is not until these salts build up in the soil to the extent that sensitive plants begin to be affected by the salt (most commonly sodium chloride) that land enters our classification of ‘saltland’.

In Table 7.3 land is described as ‘non-saline’ if it has a subsoil (25 - 50 cm) ECe (electrical conductivity of the saturated soil extract) of less than 2 dS/m. In general terms, as the salinity increases (ie as the ECe value increases) then the growth potential for both salt-sensitive and salt-tolerant plants declines. This happens quickly for salt sensitive plants, and more slowly for salt tolerant ones.

However, what plants will actually survive, and how much they will grow in a particular salt-affected soil is only partly determined by the actual salinity level in the soil. The other key factors that affect plant growth at a saline site include:

  1. Waterlogging – waterlogging reduces the oxygen available to plant roots, reducing the energy available in the roots to prevent uptake of salts. Some plants can be highly tolerant of soil salinity, but susceptible to waterlogging – old man saltbush is a good example of this. In general, the combination of salinity and waterlogging or inundation is far more damaging to plants than one or the other stress acting independently.
     
  2. Soil texture – it is more difficult for plants to extract water from clay soils, compared to sandy soils. Salt in soils has the effect of making it more difficult for plant roots to extract water because of the osmotic attraction between salt and water molecules. It is not surprising then that with similar soil salinities and depths to the watertable, plants are more severely affected in clay soils than in sandy soils. In Western Australia, a rule of thumb is that in sandy soils saltbush can be established from seed, while in clay soils, nursery-raised seedlings must be used because the conditions are more difficult.
  3. Seasonal variability - On sandy soils salinity will reach a peak in summer - autumn and then with the break in the season, salt will leach down the profile so that  the topsoil is relatively fresh. Under these circumstances balansa clover and other salt sensitive species can be grown successfully. Short season cultivars have been developed so that the balansa can flower and set seed before the soil salinity increases in spring.

In an attempt to develop and implement a common language for salt-affected land, the CRC Salinity introduced the concept of ‘saltland capability’.

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Saltland capability

‘Saltland capability’ refers to the specific ability of a salt-affected site to support plant growth year on year. Saltland capability is mostly affected by the levels of salinity and waterlogging on the site.

In general, we can distinguish between three levels of capability:

  • Saltland of high capability will have many options for productive systems, the severity of salinity and/or waterlogging will low to moderate, and the profitability of saltland pastures will be relatively high.
     
  • Saltland of moderate capability will have more limited options for productive systems, the severity of salinity and/or waterlogging will be moderate, and the profitability of saltland pastures will be low.
     
  • Saltland of low capability will generally not be suited to the growth of saltland pastures, the severity of salinity and/or waterlogging will be high to extreme, and the best option for this land will be to fence it off and allow it to revegetate naturally.

If one site is more hostile to plant growth than another, it is defined as having a lower saltland capability, regardless of whether that capability is most severely limited by salinity, or by combinations of salinity, waterlogging and soil texture.

This definition takes account of the fact that while salinity and waterlogging can by highly seasonally variable, the kinds of plants that a site grows year in, year out, are relatively unchanging. For example, a paddock that is growing samphire this year will probably be growing samphire next year – although the salt concentrations in the surface soil and the depth to the watertable may change dramatically with the seasons. Such a site has a low saltland capability and that is what leads it to grow samphire.  However, this is a generic definition and more site specific detail should be obtained with soil samples to determine the potential for site development. Seasonal variation in soil salinity and the nutrient status of the soil should be assessed. High salinity throughout the season and low fertility would indicate a site with low potential for productivity gains. Local knowledge and experience of others is also a great way to assess the potential of particular sites.

The saltland capability concept has been applied to each of the major salinity regions across southern Australia so that the local issues and conditions can be retained, but within a nationally accepted framework. Two examples are presented:


See also:

  • Central wheatbelt (WA)
  • Woolbelt & west midlands (WA)
  • Southern coast (WA)
  • Northern Eyre Peninsula, northern York Peninsula & mid-north (SA)
  • Southern Eyre Peninsula and Coorong (SA)
  • Southern York Peninsula, Kangaroo Island and the Upper South East (SA)
  • Adelaide Hills (SA)

For the above, see Saltland Prospects Part B


  • Northern Slopes (NSW)
  • Central slopes and plains (NSW)
  • Southern slopes (NSW)
  • Northern districts (Vic)
  • South-west districts (Vic)
  • Gippsland (Vic)
  • NAP region (Tas)

For the above, see Saltland Prospects Part C

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Saltland capability in southwest Victoria

Table 7.1. The ‘saltland capability’ concept applied to the saline situations in Southwest Victoria

SALTLAND
CAPABILITY

INDICATORS

RECOMMENDED PLANT SYSTEM 

PRODUCTIVE POTENTIAL 

LOW


 


 

Large areas of bare ground, salt crusting on soil surface. These are often areas of primary salinity adjacent to salt lakes (Class 3)

Fence separately, minimal grazing 

Low; pasture growth 4 t/ha, carrying capacity up to 3 DSE/ha mid-spring to late autumn. Sheep gain weight rapidly during spring but slowly during summer and autumn.

Highly prone to waterlogging and inundation, bare areas up to 1m2, variable salinity, salt couch, cotula and buckshorn plantain naturalized (Class 2)

Fence separately to encourage adapted volunteer species; puccinellia and tall wheatgrass can be sown if suitable volunteers are not present

Moderate; pasture growth 7 t/ha, carrying capacity up to 9 DSE/ha from mid-spring to late autumn. Sheep gain weight rapidly during spring but slowly during the dry conditions of summer and autumn.

Low-moderately saline, moderate waterlogging, ryegrass, and subclover not present (Class 1)

Tall wheatgrass, puccinellia with companion legumes; introduced grasses should not be sown close to waterways or primary saline sites

High; pasture growth 10 t/ha, carrying capacity 20 DSE/ha from mid-spring to late autumn. Sheep gain weight rapidly during spring but slowly during the dry conditions of summer and autumn.

HIGH

Low salinity, low-moderate waterlogging, waterlogging and salinity emerging (Class 0)

Tall fescue, tall wheatgrass and companion legumes

Very high; pasture growth 15 t/ha, carrying capacity 26 DSE/ha from mid-spring to late autumn. Sheep gain weight rapidly during spring but slowly during the dry conditions of summer and autumn.

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Saltland capability in the Northern and Eastern Wheatbelt of WA

Table 7.2 The ‘saltland capability concept applied to the saline situations in the Northern and Eastern Wheatbelt in Western Australia 

SALTLAND
CAPABILITY

INDICATORS

RECOMMENDED PLANT SYSTEM 

PRODUCTIVE POTENTIAL 

LOW


 


 

Scalded, inundated, high salinity, clay soils, samphire, curly ryegrass

Samphire

Low (less than 0.5 t/ha; not suited to grazing)

Patchy scalding, sea barleygrass, prone to waterlogging, mod-high salinity, samphire on more affected boundary

Dense saltbush

Low-moderate (0.5 to 1.0 t/ha; will maintain sheep if supplemented with good hay)

Morrel soils, moderately saline, low-moderate waterlogging, sea barleygrass, bluebush

Bluebush

Low-moderate (0.5 to 1.0 t/ha; will maintain sheep if supplemented with good hay)

Duplex soils, low-moderate salinity and waterlogging

Alleyed saltbush with under-storey

Moderate-high (0.7 to 2.0 t/ha; sheep will gain weight if annual legumes in under-storey)

HIGH

Ryegrass, low-moderate salinity, low waterlogging; subclover and capeweed disappearing, uneconomic for wheat, salinity emerging

Barley, salt-tolerant annual legume pastures

Moderate-high (barley yields up to 2 t/ha; annual legume pastures up to 3 t/ha; sheep will gain weight)

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