Vegetatively established grasses

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 vegetatively established grasses, these factors are summarised in Figure 7.4. 

Figure 7.4 Most likely situations for vegetatively established grasses.

Key to symbols
	This is the zone most preferred by vegetatively established grasses and where they are highly recommended;
	Vegetatively established grasses are one of the possible options for this zone but it is outside its preferred conditions;

Common indicator species

The most suitable areas to establish these vegetative grasses will be very wet (boggy) in winter and may be relatively bare (but still wet or at least moist) in summer. The most common indicator species would be sea barleygrass, cotula, curly ryegrass and perhaps puccinellia in the most waterlogged and saline situations (see Figures 7.5 to 7.8). 

 Figure 7.5 - SALTdeck card showing the photo and text sides for cotula.

 Figure 7.6 - SALTdeck card showing the photo and text sides sea barleygrass.  

 Figure 7.7 - SALTdeck card showing the photo and text sides for curly ryegrass.  

 Figure 7.8 - SALTdeck card showing the photo and text sides for puccinellia.

Salinity and Waterlogging requirements

Salt tolerance. These grasses are highly salt-tolerant, but assessing the differences in salt tolerance between the species is not easy. Results vary between trials, between species and between accessions within species – this is in line with the highly variable genetic make up and growth habit discussed in Risks and challenges. Research in Queensland has shown that marine couch, saltwater couch and Distichlis have relatively similar ranges of salt tolerance, but are highly variable within each species. For example, for marine couch, saltwater couch and Distichlis irrigated with saline water and cut every two weeks for 12-16 weeks, the following ranges of salinity in the irrigation water reduced shoot dry weight by 50%:

• Marine couch: 12 to 37 dS/m (in other words, the most salt-tolerant accession had its yield reduced by 50% when the irrigation water had 37 dS/m, while the least salt-tolerant accession required only 12 dS/m in the irrigation water to reduce growth by 50%).
• Saltwater couch: 13–40 dS/m (depends on accession).
• Distichlis (‘NyPa Forage’): 27 dS/m.

To indicate how salt tolerant these species are, kikuyu had a 50% decrease in shoot dry weight when irrigated with water of EC 4–5 dS/m.

Field observations in NSW have shown that both marine couch and saltwater couch can survive with exceptionally high surface (0-10 cm) soil salinities (EC_e values of 40-100 dS/m).

Waterlogging tolerance. All plants in this category are highly waterlogging tolerant so it is unlikely that any expense associated with improving surface water management would be worthwhile unless prolonged inundation is a problem.

If improved surface water management is desired for other reasons (such as preventing surface scalding or making grazing possible) and that management reduces the waterlogging at the site, this may in fact reduce the competitive ability of these vegetatively established grasses. Potentially, improved surface water management (reduced waterlogging) may render a site more suited to a less waterlogging tolerant (but potentially more productive and easier to establish from seed) alternative such as tall wheatgrass.

Soil & climatic requirements

Land capability.  While these grass species all tolerate high salinity and high waterlogging, there is little information about the field conditions (soil type, salinity down the profile, depth to watertable etc) to which they are best suited. Anecdotal information relating to Distichlis indicates that the plants grow well over a range of soil types but seem to establish better and spread faster in sandy soils.

Climatic requirements. These vegetative grasses are all C4 species (ie sub-tropical grasses that have little ability to grow at temperatures below about 15^oC). This temperature requirement also applies to germination (not relevant in most cases for saltland) and to vegetative establishment.

The widespread use of marine couch on saltland in Queensland is in line with the warm season growth pattern of these vegetative grasses. These species will not be as productive in cold, frosty locations; notwithstanding this, both marine couch and saltwater couch have been shown to perform well on saline sites in inland NSW and Figure 7.9 shows that in Western Victoria near Hamilton the volunteer pasture with a significant proportion of marine couch produced 2 - 4 t/ha of dry matter depending on the salinity of the plots. Distichlis has been used commercially in the south-west of WA but experience in the Upper South East of SA has shown disappointing growth potential as it would appear Distichlis needs regular daily temperature above 30 degrees C for good growth.

Because these plants are most suited to moist/waterlogged conditions, high levels of plant cover require climatic conditions that can provide significant periods of wetness – so, all else being equal, we would expect much better growth at 700 mm rainfall, than at 400 mm. However, actual rainfall is not always a good indicator as saltland sites (ie sites where these plants are likely to be suited), usually have a shallow watertable and are low in the landscape, so the moisture requirements of the plants can be provided by a combination of rainfall, water run-on to the site, and contributions from the shallow groundwater.

In other words, these vegetative grasses are likely to be suited to a range of soil types, but rely on there being a combination of salinity and waterlogging during the year to keep them competitive with other species. Once established, they will tend to grow in niches where there is little competition from more vigorous species such as tall wheatgrass.