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SOLUTION 8

Temperate perennial grasses with limited salinity tolerance

 

8.2  Most likely situations for temperate perennial grasses

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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 the perennial grasses with limited salinity tolerance (ie phalaris and tall fescue), these factors are summarised in Figure 8.1. 

Figure 8.1 Most likely situations for the temperate grasses with limited salinity tolerance.

Subsoil salinity/ depth to watertable matrix

 Winter

Summer 

 

 

Drivers of plant zonation

  • Non-halophytes so very limited salinity tolerance;
  • Some tolerance to waterlogging in winter
  • Summer growth assisted if access to low salinity groundwater
  • 300 mm rainfall during the growing season

 


Key to symbols

red dot

This is the zone most preferred by temperate perennial  grasses and where they are highly recommended;

Small Dot

Temperate perennial grasses are one of the possible options for this zone but it is outside their preferred conditions;

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Common indicator species

The ‘classical’ indicator species for saltland (such as sea barleygrass, marine or saltwater couch, water buttons etc) all tend to indicate levels of salinity and/or waterlogging that will exceed the tolerance of the temperate grasses such as phalaris and tall fescue. The indicator species already mentioned are likely to be towards the centre of a saline site, while the land suitable for phalaris or tall fescue may tend towards the edges of the site.

Around the edges of a saline site, the more likely indicator species for where phalaris and tall fescue might perform well will tend to be those species that are only tolerant of mild salinity and waterlogging – barleygrass, prairie grass, annual ryegrass or Yorkshire fog – as shown in Figure 8.2 to 8.5). These indicator species are quite widespread in mildly saline and non-saline environments and should be considered as weak indicators. SALTdeck has been produced to assist with the identification of the 50 most common saltland species. These can be viewed on this website or they ordered from the Land Water and Wool website.

Figure 8.2 - SALTdeck identification card for barley grass 

 Figure 8.3 - SALTdeck identification card for prairie grass 

Figure 8.4 - SALTdeck identification card for annual ryegrass 

Figure 8.5 - SALTdeck identification card for Yorkshire for Yorkshire fog

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Salinity and waterlogging requirements

Phalaris seems to be slightly more salt-tolerant than tall fescue but there is not a big difference – neither will be productive if soil salinity (ECe) exceeds about 6-8 dS/m and are better suited to soils with salinity levels of the order of 4 dS/m. As a general rule, waterlogging and salinity have additive effects on plants, so as the waterlogging at a particular site increases, it is likely that the salinity levels both phalaris and tall fescue can tolerate will decline but there is no specific data for these species.

Tall fescue can tolerate some winter waterlogging and short periods of flooding but it has only moderate drought tolerance compared to phalaris. Therefore, like phalaris, (but even more so), soil water-holding capacity becomes more critical to the overall suitability of tall fescue as average annual rainfall decreases.

For the temperate grasses considered here (phalaris, tall fescue), that are only tolerant of low to moderate salinity, surface water management can be critical. If surface water can be diverted away from the site at low cost, then it is likely that either these grasses will be more productive, or a larger proportion of the saline area will be suitable for them. There may be legal restrictions associated with diverting non-saline surface water away from a saline site in order to reduce inundation and waterlogging, especially where downstream flows are affected.

On the other hand, drainage options that include drawing water from a saline watertable can create disposal problems and are therefore heavily regulated in most jurisdictions – local advice is essential before planning any such drainage.

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Soil and climatic requirements

Soils

Phalaris can adapt to a wide range of soils from shallow, sedimentary soils to deep, self-mulching clays. However, it grows best on deep, heavy textured soils with good water-holding capacity and high fertility – or on lighter textured soils if there is a clay subsoil within 30cm of the surface to retain moisture. Suitable sites may be naturally fertile soils or those having received regular applications of phosphorus or sulphur fertiliser (or both), which promote good clover growth which will meet the high nitrogen requirements of phalaris.

Phalaris is most suited to alkaline and mildly acidic soils but is more sensitive to acidity than cocksfoot, perennial ryegrass or tall fescue and liming will be required if the soil has a pH (in calcium chloride) below 4.5 and high exchangeable aluminium (>5 mg/L). Most cultivars can withstand waterlogging over winter but not during the warmer months.

Soil water-holding capacity is not so critical to the overall suitability of phalaris as it has the ability to go dormant over summer. Grazing management is critical to persistence particularly in lower rainfall areas.

Tall fescue is suited to a similar range of soils to phalaris and like phalaris, grows best on medium to heavy textured soils that are naturally fertile or well fertilised. Tall fescue will tolerate acid soils and moderate levels of exchangeable aluminium, but is most productive when the pH (in CaCl) is between 5.0 and 8.0.

Climate (rainfall and temperature)

Without taking into account any additional soil moisture that might be available on a saline discharge site, (compared to a non-discharge area), the suitable range for phalaris may be defined as areas receiving more than 300 mm of effective rain between April and October (the main growing season). More southerly areas, with a higher incidence and greater reliability of cool season rainfall, can support phalaris in areas where the total rainfall may be only 450-500 mm/yr while in northern NSW 600-700 mm/yr is needed to ensure adequate rainfall during the growing season from autumn to spring.

Tall fescue is less drought-tolerant than phalaris, so in general, better soil moisture conditions are needed – either from better soils, underlying shallow groundwater, higher rainfall, or higher altitudes where evaporative demand is lower. While the tall fescue cultivars from Mediterranean-type environments are more winter-active and summer-dormant (like phalaris), those from more temperate areas in Europe and America are less active in winter but grow well over summer when moisture conditions are suitable. This effectively means that the summer-active types are not as suited as the Mediterranean types to the dry summer conditions in southern Australia and vice versa for the summer rainfall conditions in northern NSW.

Both phalaris and tall fescue are highly frost-tolerant (though phalaris generally has better growth rates through winter) and produce a significant proportion of their total annual production in spring.

The comments above about climate are independent of any interaction with salinity – saline sites generally have more water available to support a longer growing season than non-saline sites because of the high watertables. In conditions where the watertable is only mildly saline, both phalaris and tall fescue will be able to utilise some of that extra water and produce more dry matter than from adjacent, non-saline sites. This is clearly the case for Andrew Southwell (see farmer experiences) who has land with low to moderate salinity planted down to these perennial grasses and achieves a significantly higher stocking rate on his saltland compared to non-saline paddocks.

As salinity and/or waterlogging at a site increases, the suitability of phalaris and tall fescue quickly diminishes and tall wheatgrass becomes a more productive and persistent option.

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