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SOLUTION 9

Sub-tropical grasses with limited salinity tolerance

 

9.5  Establishment & management of sub-tropical grasses

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Choosing the right varieties

None of the varieties of Kikuyu or Rhodes grass reported here have been selected for salinity tolerance and the relative salinity and waterlogging tolerances of existing varieties have not been documented so specific advice for saline sites is not possible. [Note – there are some Rhodes grass varieties that have been selected for use on sandy soils with saline irrigation water in the Middle East, but they have not been tested on saline sites in Australia]. We suggest that farmers use varieties that have been proven locally as well-adapted to non-saline land as the seed will be easily available and there will be local experience to draw on.

Rhodes Grass Varieties

Pioneer (also known as commercial Rhodes grass) was introduced from South Africa in 1903. It is an early-flowering, erect plant with moderate leafiness and is probably the most drought-resistant variety. It runs to head quickly throughout the growing season, so its feed quality drops quickly. It has been superseded by Katambora.

Katambora is later flowering than Pioneer, so remains more leafy and productive into autumn. It is also finer leaved, more stoloniferous and perhaps more drought resistant.

Callide, released in 1963 is later flowering than Katambora, is less cold-tolerant and needs a higher rainfall than Pioneer or Katambora, but is more palatable and can be more productive than Pioneer or Katambora under conditions of higher fertility.

Finecut is a recently released variety that has been selected for its improved grazing qualities. It has fine leaves and stems, is early flowering, of uniform maturity and high yielding. Finecut was derived from Katambora.

Topcut is a recently released variety developed from Pioneer that has been selected for improved haymaking qualities. It has fine leaves and stems, is early flowering, of uniform maturity and is high yielding.

Nemkat is a recently released variety bred from Katambora types.

Kikuyu Varieties

Whittet – the only commercially available variety and is a proven soil stabiliser with good quality summer feed when well fertilised and heavily grazed.


Rhodes grass and kikuyu respond well to high nitrogen conditions – to meet this nitrogen demand requires that the pasture contains a strong legume component. The most appropriate companion legumes will be determined by the climate and the salinity and waterlogging levels at the site. See also Saltland Solution 10.

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Weed and pest control

Established stands of kikuyu and Rhodes grass are strongly competitive against weeds. In the right conditions both, but especially kikuyu can choke out all other competition, including desirable companion species. However, both kikuyu and Rhodes grass are much less competitive as seedlings, and this is likely to be especially the case if sown into saline sites. In such a location, it is likely that other species which would normally be easily out-competed by the sub-tropical grasses will be advantaged by the saline conditions and compete much more vigorously.

Weed control during the establishment phase is critical for all sub-tropical grass-based pastures, and even more so in saline situations. The likely weeds will differ from region to region and depend on the sowing time, but as with new pastures for non-saline areas, weed control on the site should commence in the year prior to sowing.

Most of the problem weed species on saline sites will be annuals and it will be essential to reduce their seed set in the spring of the year prior to pasture establishment if autumn sowing is planned. Autumn sowing may not be ideal for the sub-tropical grasses in southern Australia, but if they are sown as part of a shotgun mix on saline sites, there will be many compromises to account for the range of species in the mix, and autumn sowing is often selected. There are no selective herbicides that can remove annual grasses from these sub-tropical based pastures so site clean-up in the previous spring is critical.

For spring sowing (probably the best option for these frost-sensitive species), there is more latitude with weed control because a knockdown herbicide followed by direct drilling will give the sub-tropicals a full growth season before annual weeds reappear. However, as discussed above, when shotgun mixes are sown on saline sites the selection of weed control and sowing times will affect which species get the best chance to establish.

Ensure that pre-planting weed control does not produce a bare site over summer, as salinity levels will increase in the surface soil, making subsequent establishment of sown pastures more difficult. This is doubly the case if the site is erosion prone.

If other weeds common to saline areas (such as Juncus or rush species, or summer growing grasses such as marine couch that are harder to control than the annual weeds) are present on the site, there may be specific management requirements to control them so seek advice from a local agronomist before implementing a weed control program.

Neither Rhodes grass nor kikuyu are particularly susceptible to attack by insect pests or diseases and usually no specific control measures are required. On the other hand, if legumes are included in the pasture mix, insect attack, especially from red legged earth mite and lucerne flea are highly likely and control measures will be needed.

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Establishment techniques and timing

Spring sowing is probably best for the sub-tropical grasses, at least for non-saline situations where most experience exists. However, if these sub-tropicals are sown as part of a shotgun mix, many compromises will need to be made between the needs of the different species.

There are significant management issues associated with the incorporation of subtropical grasses into shotgun mixes. If sown with more salt-tolerant species such as tall wheatgrass or puccinellia, these sub-tropical grasses with limited salinity tolerance will occupy the least saline and/or waterlogged areas. To begin with, the temperate species are best sown in autumn, while the sub-tropicals are best sown in spring, or even summer in northern NSW.

Once established, the different species can also have different management requirements and grazing needs – for example, kikuyu can tolerate consistently hard grazing that would lead to most other perennial grasses being grazed out. The choice of temperate or sub-tropical grasses for such a shotgun mix will depend on local conditions – the sub-tropical grasses are not suited to cold conditions or Mediterranean conditions with low summer rainfall, although the ‘additional’ soil water that is often associated with saline sites can allow the sub-tropicals to persist in lower rainfall zones.

As a general rule, in the warmer areas with summer rainfall, then spring (sometimes summer in northern NSW if good rain falls) sowing is recommended practice. This is to advantage the sub-tropical grasses if they are expected to make a major contribution to pasture production.

In areas where the sub-tropicals might be expected to make a smaller contribution (compared to temperate species), then making a recommendation between autumn and spring sowing is more difficult. It should be recognised that it is generally a waste of seed (ie money) to sow sub-tropical grasses in the autumn (when soil temperatures are too low to stimulate germination) as part of a mixture and expect them to germinate in the following spring and survive the competition from the species sown in autumn. To see an interview about a case from Narrabri in northern NSW, click here.

Depending on the site and available equipment, both kikuyu and Rhodes grass can be direct drilled, or sown into a conventional seedbed, as long as the sowing depth does not exceed about 5 - 10 mm for Rhodes grass or 20 mm for kikuyu. Direct drilling is usually preferred as saline sites often have high erosion potential. Rhodes grass seed is extremely ‘fluffy’ and difficult to sow through conventional machinery as the seeds ‘bridge’ in the seedbox. Pelleting the seed overcomes this problem, but it is expensive. One common solution is to mix the seed with fertiliser and then broadcast it, followed by harrowing and/or rolling to ensure seed/soil contact – another is to sow the Rhodes grass through the grain box of a combine, with the seed mixed with a ‘carrier’ such as sawdust, sand or killed grain. On small areas kikuyu can be vegetatively established, using 1 runner/cutting per square metre.

In summary, the best time to establish these sub-tropical grasses is after a knockdown spray to kill the existing weeds. However, there are so many factors to consider with shotgun mixtures, the needs of the sub-tropical grasses will rarely be the critical factor because they will only be suited to the margins of most saline sites.

There are some other consideration for seeding:

  • Seeding depth – Rhodes grass requires precise, shallow seeding at 5-10mm at 1 - 2 kg/ha, while kikuyu has a comparatively larger seed and can be sown from 10-25 mm at 1- 4 kg/ha.
     
  • Seed quality of Rhodes grass varies widely and needs to be checked at the time of purchase, while kikuyu seed normally has excellent germination.
     
  • Rhodes grass seed is light and fluffy and difficult to handle using conventional seeding machinery, either use a ‘carrier’ like sand or fertiliser or use coated seed.

 

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Fertilisers

Like the temperate perennial grasses, the sub-tropicals perform best if well supplied with nitrogen, and so the inclusion of legumes with some salt- and waterlogging-tolerance in the seed mix is usual. Winter annual legumes are generally most likely to be compatible with the sub-tropical grasses because they do not have to compete with the aggressively growing summer-actives. The range of suitable legumes is covered in Saltland Solution 10 – Legumes for saltland, but there are no outstanding candidates for inclusion with sub-tropical grasses. 

There are standard recommendations for fertiliser use on sub-tropical grasses  in those districts where they are commonly used as pasture species. As there is no specific information about the fertiliser needs of these species on saltland, the only solution is to assume that the recommendations for non-saline land are applicable. As with pastures on non-saline land, a current soil test of the area is the best approach to sorting out a sensible fertiliser and soil ameliorant (lime or gypsum) requirements.

At the time of sowing, a ‘starter’ fertiliser with added nitrogen will be more effective than superphosphate alone because saline sites usually have a history of very low legume content so there will not be a strong bank of soil nitrogen for the grass seedlings to access. After establishment, either N fertiliser or a strong companion legume will be needed if these grasses are to perform anywhere near their potential.

In practice, fertiliser applications on saline sites are often overlooked, as placing expensive inputs onto lowly productive sites can be poor economics.

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Grazing options and management

Well researched grazing management guidelines are available for the sub-tropical grasses. For more information, see Kikuyu,  Managing kikuyu for milk production, and/or Rhodes Grass and/or Department of Primary Industries & Fisheries: Rhodes Grass - because of their widespread use in non-saline grazing systems. With a little adjustment to account for the fragile nature of many saline sites, these same principles can be applied to saltland situations. The general rules for grazing sub-tropical grasses, modified for saltland situations include:

  • Careful grazing is needed during the establishment year as Rhodes grass in particular is susceptible to being pulled out by grazing livestock. Keeping the grazing pressure low will also allow these species to spread vegetatively and thicken up the stand if establishment has been less than ideal.
     
  • Grazing over winter will be minimal if the sub-tropical grasses are the main pasture species as growth will be virtually non-existent, but also because most saline sites are waterlogged to some degree over winter and early spring and can be highly susceptible to pugging damage;
     
  • Once firmly established, the grazing requirements for kikuyu and Rhodes grass are quite different;
     
  • Kikuyu is highly suited to heavy grazing, either via continuous stocking or short rotations. The underground or surface stolons are very resistant to being pulled up by grazing animals, and if not grazed heavily, a heavy mat of unpalatable stolons will develop and smoother all competitive or companion species. The problem is that the soils on most saline sites cannot stand such heavy grazing pressure, and neither can most of the other species that might be sown on a saline site in the more salty areas where kikuyu will not have colonised, and where the soils are likely to be even more fragile. Finding a grazing compromise in these situations can be difficult. Because there are usually environmental and amenity benefits being sought from saltland pastures, the grazing management is likely to be more conservative than for similar pastures on non-saline land. For kikuyu, this will mostly mean it is not grazed frequently enough or heavily enough to keep its feed quality high.
     
  • The grazing management recommendations for Rhodes grass are similar to the temperate perennial pasture grasses than kikuyu. Once established, and especially in reasonably fertile situations, Rhodes grass can be set-stocked as long as the stocking rate is not so high that the stolons get pulled out by the grazing animals. This is a particular problem on light soils. Rhodes grass is very suited to rotational grazing and such an approach is much more likely on saline sites where maintaining groundcover is at least as important as forage production for livestock.
     
  • For both kikuyu and Rhodes grass, grass dominance is encouraged by the sort of undergrazing that is often preferred on fragile, saline sites. This makes it doubly difficult for legumes to make a significant contribution to the pasture in saline situations as they struggle with both the salinity and the highly competitive grasses.
     
  • For both kikuyu and Rhodes grass, the stands thin out, they can be thickened up by spelling for a growing season, and this thickening up will be assisted by fertiliser application.
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Animal nutrition issues

Both sheep and cattle will perform well on these sub-tropical grasses if the sward is kept vegetative. For kikuyu and Rhodes grass, typically the growing leaves would have a digestibility in the low 60%s (ME of ~9 MJ/Kg dry matter) but the stems are much less digestible – say 6 - 7 MJ/Kg.

There have been some rare reports of kikuyu poisoning in New Zealand, Queensland, New South Wales and Western Australia. It is an unusual disorder, but occurs sporadically in cattle. In most cases the outbreaks have followed the introduction of livestock to paddocks that had been spelled for a period and which had become quite lush or rank. It can also occur in pasture that receives good summer rain after being fertilised, and is growing vigorously.

It is unlike to be a problem in situations where kikuyu makes up only part of the suite of species growing at the different salinity and waterlogging levels across a saline site which has been sown to a shotgun mix.

The WA Department of Agriculture and Food have a useful Farm Note (No. 29/2004), entitled “Perennial Grasses – Potential Grazing Issues”.

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