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SOLUTION 6

Puccinellia based pastures

 

6.2  Most likely situations for puccinellia based pastures

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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 puccinellia, these factors are summarised in Figure 6.2. 

Figure 6.2 Most likely situations for puccinellia based pastures.

Subsoil salinity/ depth to watertable matrix

 Winter

Summer 

 

 

Drivers of puccinellia zonation

  • A halophyte and so does best with some salinity;
  • Very tolerant of waterlogging and can survive significant periods of winter inundation;
  • Winter grower, so cold-tolerant
  • Acts like an annual by ‘dieing off’ over summer to avoid the highest salinity levels
  • Rainfall 400+ mm

 


Key to symbols

red dot

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

Small Dot

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

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Common indicator species

Puccinellia is highly salt- and waterlogging- tolerant and is relatively non-competitive outside that zone. Therefore, the common indicators for the puccinellia zone are sea barley grass, curly ryegrass, beardgrass and samphire (shown below in figures 6.3, 6.4, 6.5 and 6.6), and there may also be patchy scalding across a site suitable for puccinellia. These can be viewed on this website .

Highly salt-tolerant species such as saltbush or bluebush will be absent from sites suitable to pucinellia because they cannot tolerate the waterlogging associated with such sites.

Figure 6.3 – SALTdeck identification card for sea barleygrass, a common indicator of land suitable for puccinellia 

Figure 6.4 – SALTdeck identification card for curly ryegrass, a common indicator of land suitable for puccinellia. 

Figure 6.5 – SALTdeck identification card for beard grass, a common indicator of land suitable for puccinellia.

Figure 6.6 – SALTdeck identification card for samphire, a common indicator of land suitable for puccinellia.

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Soil & climatic requirements

Puccinellia is a perennial grass that is highly salt-tolerant. It is the most salt-tolerant of the perennial grasses (along with marine couch and Distichlis). It is unique in both being highly waterlogging tolerant and able to withstand very dry summer conditions.

Although sea barleygrass, curly ryegrass and samphire are common indicator species, sites that are suited to puccinellia based pastures will often have significant bare areas because of the combination of waterlogging, salinity and dry summer conditions.

Puccinellia can withstand high salinities (ECe values) in the surface soil (0-10cm) in summer up to 50dS/m. Often, puccinellia sites are highly waterlogged over winter and during that time, surface soil salinities can be far lower. It is this lower winter salinity that makes balansa clover a potential partner in puccinellia based pastures. However, at this stage, both farmer experience and research results show that balansa will perform strongly in the year of sowing but will not persist. Pasture researchers believe that high surface soil salinity conditions during germination is the main cause of decline in balansa clover with time on saltland. Given this and the importance of balansa in the feed mix, we suggest that the puccinellia/balansa system be focused onto waterlogged saltland with ECe values less than 16dS/m.

Although it will tolerate a fairly wide range of soil pH values, it seems that puccinellia is particularly suited to alkaline or highly alkaline soils, or that it has a stronger competitive ability at those higher pH values. There is little scientific evidence to support this, but the fact that puccinellia based pastures seem to perform most strongly on the alkaline soils of the Upper South East of SA is strong circumstantial evidence.

Puccinellia is only recommended in the higher rainfall zones >350 mm across southern Australia. It is only at the higher rainfall levels that the combination of waterlogging and salinity most suited to puccinellia is likely to occur. At high salinity in lower rainfall zones, saltbush or saltbush and under-storey are likely to be more suitable options.

At a site near Kojonup, puccinellia colonised those areas with ECe values (0-30cm) of 22-24dS/m in winter and 22-28dS/m in summer, and the depths to watertable associated with occurrence were 8-13cm in winter and 94-104cm in winter. In contrast, tall wheatgrass colonised those areas where the ECe values (0-30cm) associated with occurrence were 8-11 dS/m in winter and 15-17 dS/m in summer, and the depths to watertable associated with occurrence were 15-20cm in winter and 108-119cm in summer – see Figure 6.5.

Puccinellia is substantially more waterlogging-tolerant than saltbush, and more salt-tolerant under waterlogged conditions than tall wheatgrass.

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Waterlogging and surface water management

Puccinellia has a great capacity to withstand winter inundation and waterlogging, making surface water management much less important. For other saltland pasture systems (eg saltbush), surface water management (the minimisation of waterlogging) is often a critical element underlying the success of the pasture system. 

Puccinellia and tall wheatgrass are often sown together as mixtures, but they rarely grow well in precisely the same places. Puccinellia will grow in significantly more waterlogged soils than tall wheatgrass and so is suited to areas where the watertable is shallower and the surface drainage less well developed. This can be seen in Figure 6.7 where despite sowing a mixture of puccinellia and tall wheatgrass, the resulting pasture was dominated by puccinellia in the low lying area and tall wheatgrass in the upper area where there was slightly better drainage. 

       

Figure 6.7 – segregation of puccinellia and tall wheatgrass when sown as a mixture in Western Australia (See the full story in the Dec 2006 SPA newsletter)

Puccinellia is tolerant to prolonged periods of winter-spring inundation (more than 3 months) as long as the plants are ‘tall’ enough to stay at least partially out of the water. Some landholders report that puccinellia actually benefits from extended flooding, provided plants are not totally submerged and surface water does not stagnate.

Puccinellia has three important adaptive traits that enable it to grow in saline waterlogged conditions. These are:

  1. The formation of aerenchyma - hollow channels in the roots that enable oxygen to diffuse down the inside of the root and therefore prevent oxygen starvation in the roots;
     
  2. The formation of a barrier in the roots that reduces the rate at which oxygen leaks out of the aerenchyma into the surrounding soil;
     
  3. The arrangement of root cells in a way that maximises the gas-filled spaces between the cells.
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