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SOLUTION 3

Dense saltbush plantings

 

3.5  Establishment & management of dense saltbush plantings

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Choosing the right species and varieties

While selecting the right species and varieties can be important, in most situations, farmers establishing saltbush will have little practical control.

Species

The three most important saltbush species used in Australia are old man saltbush (Atriplex nummularia), river saltbush (A. amnicola) and wavy leaf saltbush (A. undulata). Mixtures of species are often sown with direct-seeding to reduce the risk of establishment failure. However, the grazing management of mixtures can be problematic. Nursery-raised seedlings are invariably planted as single species stands, usually river and/or old man saltbush.

Seed sources

Nearly all stands of saltbush are planted from what are essentially wild sources of seed. There having been limited attempts to select germplasm. In the 1980s, Clive Malcolm selected two lines of river saltbush for ease of establishment (‘Meeberrie’ and ’Rivermor’) and a line of old man saltbush seed termed ‘De Kock’ was also released at this time. Old man saltbush is octoploid, so it is likely to be exceptionally genetically diverse and specific traits will be difficult to maintain across generations. The pedigree of material sold today as descendents of the selections described above would have to be regarded as doubtful.

Clones

Tamlin’s Nursery in South Australia currently market a clone of old man saltbush called ‘Eyres Green’, claimed to have rapid recovery from grazing with good digestibility and high protein. Some farmers in WA have trialled ‘Clone 28’ from the river saltbush collection of the WA Department of Agriculture and Food. It produces a huge amount of dry matter but a lot of it is in woody shoots and the clone recovers poorly from grazing.

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Establishment techniques

Saltbush establishment guide

Before establishing dense saltbush plantings, significant planning is required. As discussed in Section 3.2c - Salinity & waterlogging requirements, the layout needs to ensure that surface drainage is not impeded and can be enhanced by planting mounds. In addition, mustering stock in dense saltbush plantings can be difficult unless the planting layout includes laneways at least 5m wide for vehicle and animal access.

Growing a good saltland pasture should be approached just as another agricultural activity and is based on many of the skills that you already use with other crops or pastures. Good site preparation, weed control, insect control, timing and grazing management is essential.

Establishment of any seed is a risky process. On non-saline land, germination and establishment success is routinely challenged by drought, frost, insect attack, and weed competition. On saltland, there are additional risks associated with salinity, waterlogging and inundation.

There are two ways of establishing saltbush: niche seeding (growing saltbush directly from seed) and the planting of nursery-raised seedlings with a tree planter.

Direct-seeding should only be used on soils with low to moderate salinity and a sandy surface soil. Nursery-raised seedlings are more versatile and can be grown on more saline soils and with a wider range of textures. If the site is suited to either method, then there is a trade-off between cost and reliability. If the site is large, then the lower costs associated with direct seeding might be compelling, but if the site is small the increased reliability of the seedlings could be a better option.

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Nursery-raised seedlings

Saltbush seedlings are available from a number of nurseries in WA and the eastern states. The seedlings are usually planted with a commercial tree planter

Method

  1. Spring of the year before planting. The site should be no more than highly saline, with an ECe in the subsoil of 8-16dS/m (See section 3.2a). On less saline sites other options, such as saltbush with improved under-storey, should be investigated. If the planting mounds are established prior to planting, make sure the mounds do not hold back the drainage of surface water. The layout should be designed to assist surface drainage (See section 3.2c). Red-legged earth mites love saltbush seedlings, and can be partly controlled in the spring of the preparation year by spraying as close as possible to the optimal TIMERITE® spraying date.
  2. Year 1 – Planting the saltbush. Wait until the risk from waterlogging has abated (August to October depending on location and climate). Apply a knockdown herbicide, cultivate and then plant the saltbushes. Monitor for red-legged earth mite and spray promptly as needed.
  3. Grazing. For dense saltbush stands with no under-storey, light grazing can commence in the first autumn after planting.

The cost of establishment using nursery-raised seedlings will depend on the price per plant, the density of planting, planting costs (including spraying and cultivation) and any costs associated with the pre-preparation of the site, plus the cost of providing infrastructure like fences and sources of stock water.

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Direct seeding of saltbush

Saltbush can also be established from seed using a niche seeder. The niche seeder places the seeds mixed with vermiculite at 2–3m intervals along the top of a raised M-shaped mound. The raising of the mound reduces waterlogging and the vermiculite acts as a mulch, reducing the movement of salt to the soil surface by capillarity.

Method

  1. Spring of the year before planting. The site should be no more than moderately saline (ECe in subsoil of 4-8dS/m) with a sandy surface soil. In the year before planting, spray-top with a knockdown herbicide to prevent seed-set by annual grasses. Plan the layout to ensure that the mounds established by the niche seeder will not hold back surface water and any additional surface water management structures are installed (See section 3.2c). Red-legged earth mite can be partly controlled in the spring before sowing by spraying as close as possible to the optimal TIMERITE® spraying date.
     
  2. Year 1 – sowing the saltbush seeds. Wait until the soil temperatures have warmed and the risk of waterlogging has abated (August-September depending on location and winter rainfall). Apply two knockdown herbicides – glyphosate four weeks before seeding, and SpraySeed® two days before seeding. Cultivate just before niche seeding. After seeding, look carefully for damaging insects as saltbush seedlings are very vulnerable to attack from these insects. Spray immediately if red-legged earth mites, aphids or native budworm are present. Check at weekly intervals for 10-15 weeks. More than one spray may be required.

    Researchers at Kings Park Botanic Garden in WA have found that priming river saltbush seed with smoked water significantly increases germination rates by breaking seed dormancy. This technique has been used to stimulate germination of many native flora seed, but has not delivered similar results for old man saltbush or for wavy leaf saltbush. Further research is exploring other practical options. Researchers at Kings Park have also made progress developing seed coatings that inhibit the mass removal of seed by ants.
     
  3. Grazing. For dense saltbush stands with no under-storey, light grazing can commence in the first autumn after planting.

The cost of establishment from niche seeding will depend mainly on the cost of seed and vermiculite and the costs associated with preparing the site, hiring a seeding machine and providing infrastructure (such as surface drains, fences, sources of stock water).

In some regions, contractors are available to do niche seeding. Contract rates can be about $150 - $200 per hectare.

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Timing of establishment

In most areas the timing of saltbush establishment is a balance between going early (late winter, very early spring) or going late (spring). The general issues apply to both nursery-raised seedlings and direct-seeding, but timing is far more critical for direct-seeding as the following example shows.

The timing of direct-seeding must be adapted to the seasonal conditions prevailing at the time. The advantage of early seeding or early planting (late winter or early spring) is that the small plants have an opportunity to establish sufficiently to survive the likely high temperatures and low rainfall of the first summer. However, seeding early can be extremely difficult if the site is wet, and most salty sites are very wet at that time of year. Moreover, if seeding occurs too early there is a risk of failure because of waterlogging damage from subsequent rainfall. River saltbush in particular is likely to germinate very slowly at average daily temperatures less than 10oC.

However, if seeding is delayed into the spring then establishment can be significantly better as low temperature and waterlogging shocks are much less likely. If sown too late, the small establishing plants are unlikely have root systems that are sufficiently developed to allow the plants to survive as the soil dries out and becomes more saline over summer.

The decision on when to sow or plant will depend very much on the year. Salt-affected sites can become untrafficable. On the other hand, an early finish to the season can leave the site highly saline and with little or no rainfall for several months. Added to these issues are the usual seasonal demands of the farm.

“Planting in July-August fits in well with our other farming operations. As with most crops, it helps to have rain just before and after planting, but we have had no real failures with establishment except on the severely waterlogged sites. The planter creates a weed-free corridor, but annual grass weeds soon move in and need to be controlled by over-spraying with 1 to 1.2 l/ha of glyphosate when the saltbush are well established.”

Ted Bear and Martin Wilkinson, ‘Maro Creek’, Snowtown, SA

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Management needs and tips

Early stages

When first established, saltbush seedlings are quite vulnerable. Saltbush seedlings are very poor competitors and they must be protected from weeds, insect pests and grazing animals (including rabbits and kangaroos) during their early development. Annual weeds can be controlled by over-spraying well established saltbush with gyphosate at approximately 1 L/ha. Once firmly established, little further input (apart from grazing management) is required. Individual plants of old man saltbush are very long lived.

First grazing

Most saltbush planted in early spring will be large and robust enough to graze during the following autumn. This first grazing should be lighter than subsequent grazings, and should be carefully monitored to ensure the stock are removed when there is still significant leaf remaining on the bushes, and before any damage to the main branches.

Fencing.

Grazing control during establishment is critical. Many farmers can save on a fence at the outset by planting saltland while the rest of the paddock is in crop. Then the investment in fencing only needs to be made once the level of establishment – and the likely value of the pasture – can be seen.

Fertiliser

While it is likely that saltbush would respond to fertiliser, it is rarely applied in practice. Little is known about the availability of soil nutrients in saline sites, and because the edible yield from dense saltbush plantings in saline soils is quite low (usually less than 1000kg of edible material per ha), applying fertiliser is not usual practice.

Pests and diseases

Many saltbushes (not wavy leaf) are native to Australia and therefore have a range of local insects and diseases that eat or attack them. Mostly, pest and disease attacks are episodic and plants generally recover satisfactorily. Reports of major pest or disease damage are relatively rare. The exception is insect attacks on seedlings (especially by mites, aphids and budworms), which if not controlled, can kill many seedlings. Locusts can do significant damage in a short time. In the face of clear evidence of an advancing locust swarm it can be prudent to crash-graze the saltbush so as to make use of the green matter while it is still there.

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Grazing options and management

There is little research comparing different grazing management options for dense saltbush plantings, but there is considerable farmer experience from both saline land, and from the native saltbush areas in the rangelands. The different species of saltbush vary to some degree in palatability and ability to recover from grazing (see Table 3.2).

Once established, saltbush can withstand very hard grazing and the most common practice with dense saltbush plantings on saltland is for annual crash-grazing where the bushes are effectively grazed back to the twigs each autumn. Saltbush recovers well as long as it is allowed sufficient time. Constant heavy grazing will eventually weaken and kill most saltbush.

Some farmers do not graze their saltbush each season, preferring to save the feed for less productive seasons. However, research in Western Australia has shown that heavy grazing of mature old man saltbush in autumn has little detrimental impact on the amount of edible dry matter that is available at the start of the following autumn, compared to an ungrazed control. The research showed that old man saltbush drops a lot of leaves when left ungrazed, so that there is little advantage in deferred grazing between years.

Table 3.2 – Some characteristics of different saltbush species

Common Name

Species Name

Tolerance to:

Palatability

Grazing 
Recovery 

Suitability for direct seeding

 

Salinity

Waterlogging

Old man saltbush

Atriplex nummularia

xxxx

xx

xx 

xxxx 

xx 

River saltbush 

A amnicola

xxxx 

xxx 

xxxx 

xxxx

xx 

Wavy leaf saltbush 

A undulata

xxxx 

xxx 

xxx 

xx 

xxxx 

Quail saltbush

A lentiformis

xxxx 

xxx 

xxxx 

xxx 

xxx 

Key xxxx (high), xxx (moderate), xx (low)

Regular (at least annual) grazing of saltbush is essential or the individual bushes quickly exceed sheep grazing height if growth conditions are good. Once this occurs, future growth will be preferentially directed to the area where grazing is no longer possible and the value of the saltbush stand may be reduced. Some form of pruning may be needed, though grazing with cattle can assist in reducing the top growth, and anecdotal evidence suggests that sheep get very good at dragging the saltbush down to graze. Mechanical pruning is expensive, but if undertaken, cutting the bushes back to about 60cm in height is an effective way to restore the stand to full productivity. It is important not to overemphasise this as annual grazing will mostly keep saltbush within sheep grazing height. In addition, some leaf left above sheep height and not grazed will allow the saltbush to keep using water even when heavily grazed.

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Integration into farming systems

The economics of dense saltbush plantings has been discussed in Section 3.3e. The conclusion is that dense saltbush plantings are seldom a good investment if the only benefit will be feed production. However, farmers claim a range of other benefits when saltbush is considered as part of their overall farming system. Indeed, farmer experience (now backed up to some extent by economic modelling) suggests that about half the value from saltland pastures comes from the direct feed input, and the other half comes from the range of other benefits to the whole farm system.

The major production benefits of dense saltbush plantings flow primarily from their ability to provide green feed at times when it is otherwise not available (usually late summer and autumn in southern Australia) and the fact that they are using land of very little other value. Dense saltbush plantings can significantly decrease the requirement for hand feeding, especially in summer and autumn.

Dense saltbush plantings are an ideal holding area (or sacrifice paddock) during periods of intensive supplementary feeding and/or after the autumn break to allow other pastures (especially annual pastures or pasture components that have to germinate and establish) to get away elsewhere on the farm.

Shelter for lambing ewes can be a further benefit, but a possible downside is that it can become more difficult to monitor lambing in dense stands of saltbush. Saltbush can offer emergency shelter for off-shears sheep, but there is the risk of saline sites becoming very wet when shelter is needed.

The growth of saltbush can increase the resilience of farm businesses to drought and flood and these benefits are widely ignored in the bio-economic modelling.

“Saltbush is important because it helps fill the feed gap in autumn. I allow sheep to access it ad lib from stubble paddocks at this critical time. This arrangement means that I don't have to provide separate water for small saltbush paddocks.

“I allow most of my ewes to lamb in the saltbush, which provides excellent shelter whilst they still have access to an adjoining pasture paddock. Gradually I am pushing my lambing back later in the year to match feed demand more closely to feed supply.

“Mustering out of the saltbush takes some practice. The rotation of stock has to be carefully planned to allow the saltbush and the inter-row pasture to recover from grazing.” 

Bradley Hicks, ‘Lowandale’ , Arthurton, Yorke Peninsula, SA

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Animal nutrition issues

Research shows that livestock grazing saltbush alone will not get sufficient nutrients for maintenance, but with appropriate supplementation, saltbush can be used for both sheep and cattle. The critical issue is the high salt concentration in the saltbush leaves and stems – as much as 30% in extreme cases. If grazing sheep the use of these shrubs as the sole feed supply presents a major nutritional challenge. As salt in the feed increases, appetite is suppressed, intake decreased and digestion disrupted. Sheep cope well with less than 10% of the diet as salt or with a total salt intake of less than 100grams per day. At salt intakes between 150 and 250g/d (which might represent as little as 500g of saltbush dry matter) sheep will reach an upper limit in their ability to process and excrete salt. For more information, see Salty Diets.

Energy

Saltbush has relatively low metabolisable energy (less than that required for a maintenance diet for sheep or cattle). The energy value of saltbush can be over-estimated (by up to 30%) if standard laboratory measurements are not corrected for the high salt content which is soluble and so appears to be digested. Saltbush leaves are reasonably digestible but small stems make up much of the edible portion of saltbush.

When eating feeds with an energy level similar to saltbush, animals would normally attempt to increase their intake. A 50kg sheep would need to eat in excess of 1kg per day of a straight saltbush diet to maintain condition. This is impossible with saltbush because the high salt concentration in the feed limits intake to about 800grams depending on the level of salt in the soil and in the plant’s leaves.

Protein

Saltbush appears to have a very high crude protein content (typically 12-20%). This is a very valuable feature, especially in summer and autumn when green feed (and therefore protein) can be very limited on farms. Crude protein is calculated from the nitrogen concentration in the leaves because in normal pasture plants most of the nitrogen is contained in protein molecules. However, about half of the crude protein in saltbush is not protein at all, but is nitrogen contained in a range of other compounds, primarily those that are used to assist the plant cells manage the high salt loads. This non-protein nitrogen can be converted into microbial protein in the rumen if there is a good supply of energy available. This is unlikely to be the case for livestock grazing dense saltbush plantings with little or no under-storey without a significant energy supplement.

Salt

Sheep will select a diet that balances the need for high nutrient intake against the cost of managing a salt load. Salt, protein and energy content of a feed all interact to drive diet selection. Feeding value of a high salt diet can be improved by offering low salt alternatives and sheep will actively select quantities of high and low salt feeds that improve the feeding value of their diet.

Water

For sheep to cope with high levels of salt in the diet they must have access to a large supply of high quality drinking water. If the drinking water also contains salt, then the ability of livestock to eat large amounts of saltbush is further reduced. In one study, feed intake of sheep on old man saltbush fell by more than half when the drinking water was replaced by water containing 1% salt. Though it varies considerably with temperature, wind exposure and distance walked to water, sheep typically drink 3-4 litres of water per day when eating a non-salty, dry feed. By contrast, sheep need to drink about 4l of extra water for every 100 grams of salt (or approximately 350g of saltbush) that they consume.

Vitamin E

Dried annual pastures can be highly deficient in vitamin E, which can cause a muscle wasting disease in sheep. Research in Western Australia has shown that old man saltbush is an excellent source of vitamin E, containing about 250mg vitamin E per kilogram of green leaf. Vitamin E is also associated with improved meat quality.

Increased salt and wool growth

Salty diets can increase the efficiency of wool growth by up to 20%. It has been hypothesised that these benefits come from the increased salt in the diet causing increased passage through the gut which prevents the rapid destruction of protein in the rumen. It seems likely that saltbush in the diet would have a similar effect. These effects have not been taken into account in the MIDAS modelling.

For more information, see Old man saltbush in agriculture: feeding value for livestock production systems.

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