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SOLUTION 9

Sub-tropical grasses with limited salinity tolerance

 

9.4  Level of confidence in sub-tropical grasses

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How reliable is the information?

Kikuyu and Rhodes grass have been widely used by farmers for decades though there have been few studies of the productive potential for these species in saltland. In other words, the performance of these species in non-saline situations is well known and reliable, but their performance on saltland is much less so. However, from extrapolation from non-saline land, combined with limited experiences on saltland, we can identify what is reasonably reliable, from what is not.

We can state reliably:

  • Rhodes grass and kikuyu have limited salt and waterlogging tolerance;
  • Rhodes grass and kikuyu are very widespread in the warmer areas of Australia and internationally, and therefore can be assumed to be fairly adaptable across a variety of soil types;
  • Both species have a strong ability to spread vegetatively and thicken up if initial establishment is patchy;
  • Under the right conditions these sub-tropical grasses can be highly productive over the warmer growing season;
  • The sub-tropical grasses are not salt accumulators and therefore will be nutritionally similar on mildly saline and non-saline land;
  • The general agronomy (establishment techniques, fertiliser needs, grazing management) of both species is well understood at least for non-saline situations;
  • Because these species are widely used on non-saline land, commercial seed supplies are reliably available.

There are other aspects to the use of sub-tropical grasses that reflect a relatively low level of confidence in our knowledge:

  • Pasture production from these sub-tropical grasses has rarely been measured in saline situations;
  • The ability of sub-tropical grasses to draw down mildly saline watertables (a demonstrated strength of saltbush and tall wheatgrass) has not been measured;
  • Although often used in shotgun mixtures, the role and appropriate management strategies for these mixtures (including sowing times, grazing management etc) have not been well documented.
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Farmer experiences

Both kikuyu and Rhodes grass are widely grown on non-saline land, in districts with warmer temperatures and summer rainfall, so numerous case studies are available for non-saline situations. There are not many documented case studies regarding the use of sub-tropical grasses on saltland, but given that these species are best suited to land with low to moderate salinity, farmer experiences can be extrapolated from non-saline to saline situations.

The Evergreen farming group in WA has a vision of "green farms all year round", using profitable perennial pastures and fodder shrubs to achieve this. They welcome new members and provide on-line access to a significant ‘library’ of information on perennial pastures including case studies, newsletters, fact sheets, budgets and research results. Several of the Sustainable Grazing on Saline Land (SGSL) grower network sites in WA used the ‘evergreen mix’ that includes a range of sub-tropical grasses. Typical of this approach was the experience of Deane Aynsely near Beverley in 350mm country east of Perth. This SGSL site consisted of 23ha of ‘relatively fresh’ land at risk of increased salinity, surrounding a 2ha salt scald. “Sub-tropical grasses planted in the saltbush/acacia interrows have been highly successful, particularly Rhodes grass.”

Another case study that has been documented by the SGSL initiative is from Geoff O’Neill’s property at Bellata in Northern NSW – see below.

The WA Department of Agriculture and Food has assembled 17 detailed farmer case studies around the concept of perennial pastures across the southern coastal region. For more information, see Evaluating Perennial Pastures. Many of these case studies are more focussed on the use of lucerne than on sub-tropical species, but they make useful reading in any case because they focus on incorporating perennials into the farming system. Case Study 9 (Mixed perennial plantings work on highly variable soil types) of the WA publication is summarised in the text box below. SALT magazine published a story titled “Gaining ground with sub-tropical grasses” which is an interesting case study with sub-tropical grasses from the north west slopes of NSW, but does not include consideration of salinity.

Glen Oliver, North Stirling Basin, WA

Glen Oliver’s farm is located in the North Stirling Basin; an internally drained farming region that is prone to salinity and waterlogging. Glen is a highly proactive farmer within this catchment and for more than 15 years he has been a great advocate for planting perennial grasses.

His 2000ha property is 45km east of Cranbrook and has an annual rainfall of 375mm. Around 40% is low lying with a saline water table of only 1 or 2 metres. It has therefore been imperative that he utilise as much rainfall as possible to minimise groundwater recharge. The property was first cleared in the 1960s and by the mid 1970s salinity issues started to emerge. Of the saline areas 440ha is planted to perennials.

After running many perennial pasture trials on his property, he prefers to now sow a mixture of perennials which vary in their establishment depending on his highly variable soil types.

In the process of increasing year-round ground coverage by better utilising his rainfall through the use of perennials;
he has managed to substantially increase his carrying capacity and he has so far increased his breeding ewe flock by 25%.

The trial paddock was sown to perennials in 2002. Varieties sown were: lucerne, tall wheatgrass, puccinellia, Rhodes grass, Balansa clover and saltbush. The seed was sown at a rate of 6.65kg/ha. The cost of seeding/ha was $44.70. (The tall wheatgrass and saltbush seed were harvested on-farm). The economics of this operation are outlined in Section 7.5 – How do the dollars stack up? 

To read the full story (pp42-45)

The SGSL program conducted many on-farm trials assessing pasture options for saltland. Projects in northern NSW tended to include sub-tropical grasses in the mix, as outlined in Geoff O’Neil’s story below.

Geoff O’Neils, Bellata, NSW

At Bellata, high soil chloride levels along with surface crusting due to sodicity had, in the past, severely limited crop and pasture production. The SGSL trial was seeking perennial pasture alternatives to better manage hostile subsoils and surface crusting and used a mixture of Katambora Rhodes grass, Bambatsi Panic, Gatton Panic, Lucerne, Burgundy Bean, plus snail and barrel medics.

“It’s a large open site with a heavy grey clay. These areas are like self-mulching concrete and we have always struggled to get enough growth off the site.” Despite some hurdles with establishment, now that the tropical grass pasture was thriving Geoff could see the advantages in high production and the benefits of improved soil health and moisture retention. “We hope this area is going to mean year-round feed at a much higher productivity. Our cuts and our first grazing have shown it will be something like 3 or 4 times more productive than the original pasture. The success of this pasture has us now assessing the rest of the farm and what’s been our traditional thinking there.”


Key learnings from this site

  • For the northern cropping zone, permanent pastures may be a viable alternative to cropping on soils dominated by significant levels of chloride salts and where soils set hard due to sodicity.
     
  • Tropical grasses help improve the soil health of degraded paddocks. They contribute organic matter through high production, cycle soil nutrients via a deep fibrous root system, and provide excellent ground cover. Tropical grasses form a more favourable environment for other pasture and legume species to grow in as litter helps to conserve soil moisture and limit soil dispersion.
     
  • An initial application of gypsum (prior to sowing) proved beneficial in breaking up the surface crust, and improving soil conditions for plant germination.
     
  • The establishment of tropical grass pastures is a major challenge as they require plenty of moisture through the establishment phase. Attempt to plant with good soil moisture reserves and when warm season rains are most likely to fall.
     
  • It is essential to include legume species in a tropical grass pasture mix. Legumes including medics and clovers will improve the value of the pasture and reduce the reliance on fertilisers.
     
  • The soil environment has quickly turned around in terms of moisture retention, increased organic matter and improved soil structure as a result of the permanent pasture.

Read the full story link, click here or see a short interview with Geoff, click here.

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Risks and challenges

Site selection

Because these sub-tropical grasses have only limited salinity tolerance, the primary challenge is correctly identifying suitable sites for these species. In practice, detailed diagnosis with salinity, waterlogging and watertable testing is rarely carried out especially for small sites. Instead, a shotgun mixture with one or more of these sub-tropical grasses is often sown indiscriminately across the site allowing the different species to find the most appropriate niches. These shotgun mixtures usually contain species that are more salt and waterlogging tolerant (such as tall wheatgrass and puccinellia) and legumes (such as lucerne, strawberry clover and balansa clover) in the hope that the individual species will establish and dominate that part of the saltland patch with the ‘right’ salinity and waterlogging balance.

Use in shotgun mixtures

There are significant challenges associated with the incorporation of subtropical grasses into shotgun mixes that also contain temperate species. If sown as part of a shotgun mixture with more salt-tolerant species, these sub-tropical grasses will occupy the least saline and/or waterlogged areas. This can be positive for the saline site as a whole, but can significantly complicate management because the different species can have different management requirements and grazing needs. For example, the temperate species are best sown in autumn which does not suit the sub-tropicals that need soil temperatures >15 degrees centigrade in order to germinate, and kikuyu can tolerate consistently hard grazing that would lead to most other perennial grasses being grazed out.

Establishment

The seed of Rhodes grass is fluffy and difficult to sow through conventional machinery unless pelleted, but pelleting is expensive. Both Rhodes grass and kikuyu are best established when the soil warms up in spring, but that time can coincide with a greater risk of the soil drying out.

Agronomic management

Rhodes grass and kikuyu both respond strongly to soil nitrogen. This can be supplied by either applied N fertiliser, or by having a legume component in the pasture – both these options are unlikely on salt-affected land where farmers are likely to restrict expensive inputs such as N fertiliser, and most of the potential companion legumes are even less salt- and waterlogging-tolerant than these grasses. In addition, legumes find it difficult to persist in kikuyu pastures unless they are heavily grazed to prevent a dense mat of kikuyu runners developing – winter-growing annual legumes have the best prospect as they do not have to compete with the summer-active grasses. Growth potential for the sub-tropical grasses is likely therefore to be considerably restricted on saltland both due to the salinity/waterlogging impacts and because of limited soil nitrogen.

Weediness

Kikuyu is a significant environmental weed in some regions of Australia and invades wetlands and native vegetation. However, it is already widely distributed across southern Australia, so additional weed risk from establishment in mildly saline situations is limited. Rhodes grass also has significant weedy characteristics as it is able spread rapidly by above ground stolons. Unlike kikuyu, Rhodes grass can be ‘controlled’ by heavy grazing, especially on light soils where the stolons can be pulled out by livestock.

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Prospects

Recent research

Although not as well serviced in Australia as the temperate perennial grasses, there is a wide range of information about all aspects of the management of sub-tropical grasses - including kikuyu and Rhodes grass.

Very little of the historical R&D has been focussed on using sub-tropical grasses on saltland. The Future Farm Industries CRC has an active R&D program that includes temperate and sub-tropical perennial grasses and a range of legumes for both saline and non-saline land. The CRC advocates “profitable perennials for Australian landscapes”. For more information , visit the The Future Farm Industries CRC website

However, most of the recommendations and guidelines for using sub-tropical grasses on saltland will rely on adapting guidelines already developed for non-saline sites. This increases the uncertainty associated with such recommendations, but groups such as Evergreen Farming have amassed an impressive suite of case studies and farmer/extension experience with these grasses and provide practical information on all aspects of sub-tropical grass pastures.

Future Prospects

Sub-tropical grasses with limited salinity tolerance have only a small role to play in the national response to saltland. They have a limited temperature range, rely on summer rainfall, can only tolerant low to moderate levels of salinity. There are overseas programs breeding more salt-tolerant varieties of Rhodes grass for the Middle East market and these need to be evaluated in saltland situations in Australia.

However, in the northern half of NSW, the northern agricultural region and south coast of WA, sub-tropical grasses are playing an increasing role in farm feed supplies. Extending the use of the sub-tropical grasses into land with low to moderate salinity is only a small step once the grasses have become accepted into a region’s general pasture options.

In the suitable climatic zones, shotgun mixtures containing these sub-tropical grasses with a suite of more and less salt-tolerant grasses and legumes will continue to be favoured by farmers as the revegetation method of choice for saltland. The niche for the sub-tropical grasses in a shotgun mixtures is the mildly saline margins of a salty area, and the surrounding non-saline land that might be included in the area fenced off around a saline scald. In these situations, the sub-tropical grasses are highly productive, especially if they can be combined with a suitable companion legume. Winter-growing annual legumes are the best prospect as they can grow (and fix nitrogen) when the sub-tropical grasses are dormant.

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