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SOLUTION 9

Sub-tropical grasses with limited salinity tolerance

 

9.1  Sub-tropical grasses in a nutshell

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A quick summary

Like the temperate perennial grasses with limited salinity tolerance, the sub-tropical grasses included in this Saltland Solution have commercial seed supplies, have some salinity and/or waterlogging tolerance and are widely used in non-saline pastures. Kikuyu can be established from seed or from vegetative plantings, but is included in this Saltland Solution rather than with the vegetatively established pastures because unlike marine couch, saltwater couch and Distichlis, it can be established from seed, and because it has only limited tolerance to salinity.

As with the temperate grasses with limited salinity tolerance, these sub-tropical species can have an important place in saltland management because salt-affected land is often either very patchy, or varies from non-saline land around the edges of a saltland site to highly-, severely- or extremely-saline land in the centre. Small or highly variable sites are particularly suited to shotgun mixtures rather than trying to establish a single species across the site.

There are a number of sub-tropical grasses available in Australia, but of these, our investigations suggest that only 2 species have sufficient salinity and waterlogging tolerance to be considered as Saltland solutions. These are kikuyu (Pennisetum clandestinum) and Rhodes grass (Chloris gayana) which are the focus of this Saltland Solution even though local shotgun mixtures often include other sub-tropical species with lower salinity tolerances – for example, Bambatsi panic seems to be a good bet for the hard-setting clays in northern NSW and is reputed to have some salt tolerance.

There is limited experience (producer or research) with growing these sub-tropical grasses on saline sites, but they are widely grown on non-saline land in northern NSW and in the south coast and northern agricultural regions of WA and it is in these districts that they are most likely to be useful for saline sites. On the other hand, if they are not successfully grown on non-saline land in your district they are unlikely to grow well on saline sites, where they must deal with the added stresses of salinity and waterlogging.

Kikuyu has a much wider range of climate tolerance than Rhodes grass and is widely grown in nonsaline areas of southern Australia, including the Southern Coast of WA, Kangaroo Island and Upper South East of SA and the South West  and  Gippsland Districts in Victoria.

Kikuyu and Rhodes grass will grow well in soils of low salinity (ECe 2-4 dS/m) and also into the moderate salinity (ECe 4-8 dS/m) range. Both are spreading grasses: Rhodes grass has runners (stolons) while kikuyu has both runners and rhizomes (underground runners). This spreading habit means they will spread vegetatively to fill-in gaps which is an advantage on saline sites as soil salinity can inhibit recruitment from seed. However, kikuyu’s strongly creeping habit means that over time it can dominate mixed swards and is often sown in non- saline situations without other grasses because of this. Rhodes grass is more suited to mixed swards.

New salt-tolerant varieties of Rhodes grass are available, but these were predominantly developed for the Middle Eastern market and for irrigation with brackish water on well drained soils, rather than poorly drained saline soils in southern Australia. The performance of these ‘salt tolerant’ varieties has yet to be evaluated in southern Australia.

Sub-tropical grasses require warm soils (soil temperature >15oC) to germinate plus total weed control during establishment as the seedlings compete poorly with weeds. Sowing time varies from mid- to late August in the northern agricultural regions in WA to early, or even late summer in northern NSW.

Where these sub-tropical grasses with limited salinity tolerance can be used on and around saltland, they have the great advantage of producing green feed over summer, a commodity that is often rare on the rest of the farm.

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History

These sub-tropical grasses have no significant history as saltland species, but during the latter part of the 20th Century, as the number and area of saline patches increased, these species have been included in ‘shotgun mixtures’ with other, more salt-tolerant species on saltland. This is particularly the case in central and northern NSW, where sub-tropical grasses were already common in pasture mixtures because of the warmer temperatures and predominance of summer rainfall. Much of the extension information available for Rhodes grass is from Queensland where it is widely used for non-saline land.

More recently, perennial grasses (both temperate and sub-tropical) have started to be more widely accepted in WA where annuals have traditionally dominated. The WA Department of Agriculture and Food Evergreen Farming group have been strongly advocating the use perennials, including sub-tropicals for both the northern agricultural region and for the south coast of WA, for both saline and non-saline pasture mixtures. There is significantly less opportunity for sub-tropical species in Victoria and SA because of temperature limitations.

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Species identification

Both kikuyu and Rhodes grass are relatively easy to identify. SALTdeck was developed in the Sustainable Grazing on Saline Ground (SGSL) program to assist farmers and advisors to identify the 50 most common species associated with saltland, including kikuyu and Rhodes grass – see Figures 9.1 and 9.2. SALTdeck cards can be viewed on this website .

Rhodes grass (Chloris gayana) is a sub-tropical/summer active perennial grass, so named because Cecil Rhodes distributed seed throughout Zimbabwe (then Rhodesia) and South Africa. It is a tufted grass that sends out strong, above ground runners (stolons), allowing it to spread rapidly. This can be a great advantage on saltland where soil salinity often inhibits recruitment from seed. It has a very characteristic seed head that looks like the fingers of a hand – see Figure 9.1.

Kikuyu (Pennisetum clandestinum) is a highly stoloniferous (ie creeping) sub-tropical grass, widely used as a domestic lawn species. In agriculture, kikuyu is the base pasture for much of the dairy industry in northern NSW and southern Queensland. If not heavily grazed (or mown), kikuyu can form dense swards to 50cm in height. The seed heads are hidden (thus the name clandestinum) but when in flower, the male stamens are highly visible – see Figure 9.2. The creeping nature of kikuyu makes it ideally suited to low to moderate salinity land, where it can ‘thicken up’ if initial establishment from seed is limited. 

 Figure 9.1 - SALTdeck card showing the photo and text sides of Rhodes grass

Figure 9.2 - SALTdeck card showing the photo and text sides of kikuyu.

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