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SOLUTION 4

Saltbush & under-storey

 

4.5  Establishment & management of saltbush & under-storey

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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 and under-storey will have little practical control.

The three most important saltbush species used in Australia are old man saltbush, river saltbush and wavy leaf saltbush. Mixtures of species are often sown with direct-seeding to reduce the risk of establishment failure. If nursery-raised seedlings are to be planted, the planting of old man saltbush or a mixture of old man and river saltbushes is recommended.

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 (named ‘Meeberrie’ and ’Rivermor’) and a line of old man saltbush seed - ‘De Kock’ - was also released at about this time.

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.

The under-storey will usually be sown as a shotgun mixture, with different mixtures suited to different regions, so local advice is essential. For lower salinity sites, legumes can be the critical element of the under-storey and the most appropriate species will depend on the salinity levels, with burr medic the most salt-tolerant, and sub-clover the least. Balansa clover (cv. Frontier) has a reputation for soils with low levels of winter soil salinity and waterlogging, however it seems to have a problem with persistence. As the salinity of the site increases, or for the more saline areas within a site, the legumes will decline rapidly in production and persistence, so it is normal practice to include  grasses (such as Italian ryegrass or perennial saltland grasses) in the mix.

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Establishment techniques

In the saltbush and under-storey system, the saltbush provides the perennial component that can use water over summer and improve the site for under-storey species. This makes the successful establishment of the saltbush critical. The under-storey can be established, or re-established relatively cheaply at a later stage.

There are two ways of establishing the saltbush component of the pasture: niche seeding (growing saltbush directly from seed) and the planting of nursery-raised seedlings with a tree planter. As part of the SGSL/CRC Salinity activities, an establishment guide for saltbush was produced. It contains information about both direct-seeding and planting nursery-raised seedlings.

Growing a good stand of saltland is based on the same skills used to other crops and pastures(eg. good site preparation, weed control, insect control, timing and grazing management). On non-saline land, germination and establishment success is routinely challenged by drought, frost, insect attack, and weed competition. The same occurs on saltland, but with additional risks associated with salinity, waterlogging and inundation.

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Direct seeding of saltbush

Direct seeding should only be used on soils with low to moderate salinity and a sandy surface soil. It is usually carried out by a contractor with a niche seeder that 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. Contract rates for the seeding operation can be about $150-$200 per hectare (2006 pricing).

Method

  1. Spring of the year before planting. The site should be no more than moderately saline (with a summer  ECe in the subsoil of less than 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. 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.
     
  3. Grazing. A light grazing of the saltbush is usually available in the first autumn after planting.
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Nursery-raised seedlings

Nursery-raised seedlings are more versatile and can be grown on more saline soils and with a wider range of textures than direct seeding. If the site is suited to either method, then there is a trade-off between cost and reliability. Saltbush seedlings are available from a number of nurseries in WA and the eastern states, and are usually planted with a commercial tree planter.

Method

  1. Spring of the year before planting. The site should be no more than moderately saline (to allow for the under-storey), with  ECe in the subsoil of no more than 8dS/m. 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. Red-legged earth mites 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. A light grazing of the saltbush is usually available 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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Establishing the under-storey

Establishing the sown under-storey between the saltbush rows is the same process as establishing pastures on other parts of the farm.

Optimal establishment practice includes weed control (in the previous season before seed set and at planting), fertiliser application (soil testing is recommended), consideration of insects, and sowing of quality seed. It is critical to include an appropriate rhizobia with the legume seed because it is unlikely that there will be existing rhizobia in the saline soil where there may not have been any legumes for many years.

In general:

  • Weed control with a knockdown spray in spring of the year before sowing (ie the same knockdown spray recommended in Section 4.5c and Section 4 to control the weeds that will compete with the saltbush seedlings) to kill all plants before they set seed.
     
  • Spraying for RLEM (red-legged earth mite), as close as possible to the optimal TIMERITE® spraying date.
     
  • After weeds have germinated following the break of season, apply a knockdown, fertilise and sow.
     
  • Through July and August, check for insects.
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Timing of establishment

The establishment of a saltbush and under-storey pasture is usually a two stage process. As a warm season grower, saltbush needs to be established (sown, or planted) in spring, while the annual under-storey species need to be established in autumn.

Saltbush. The timing of direct seeding is a tactical choice which must be adapted to the prevailing seasonal conditions. Seeding early can be extremely difficult if the site is wet, with most salty sites wet over winter. Even if the soil is dry enough to sow, there is a risk of failure because of waterlogging damage from subsequent spring rainfall. Germination will be slow from early sowing. River saltbush in particular is very slow to emerge if the average daily temperature is less than 10oC.

These challenges subside as spring advances, waterlogging risk declines and temperatures rise. However the emerging saltbush seedlings have a greater risk of not being able to establish sufficiently developed root systems to ensure survival as the soil dries out and becomes more saline over summer.

The best time to direct seed will vary with the location (annual rainfall and temperature), site conditions (soil texture, waterlogging) and the current seasonal conditions.

Under-storey. For the under-storey there are essentially two choices – sowing in the autumn prior to saltbush establishment, or sowing in the autumn following saltbush establishment. While both are possible, we tend to recommend sowing the under-storey in the autumn prior to establishing the saltbush because of the following advantages:

  • Sowing both the under-storey and the saltbush in the same year minimises both the costs and time involved, so when the saltbush is ready for its first grazing in the autumn after it has been established, there is an under-storey already in place;
     
  • There is less chance of bare soil and concentration of salts in the soil surface if there is an under-storey present over the first summer;
     
  • Weed and insect control in the spring prior, and then in the autumn with the sowing of the under-storey will reduce the weed and insect pressure on the saltbush;
     
  • Sowing rates for the under-storey can be low as the site will not be grazed till the following autumn and the pasture will get a chance to bulk up and set seed;
  • Predation (by rabbits and kangaroos) of the saltbush seedlings may be reduced because of the availability of under-storey;
     
  • There is no saltbush to be affected if a knockdown is used prior to sowing the under-storey; and
     
  • Large commercial machinery (eg air seeders) can be used because the saltbush rows are not yet established.

The downside with sowing the under-storey prior to the saltbush is that it can compete strongly with the saltbush seedlings. This can be managed by either a narrow band of knockdown herbicide along the planting rows for the saltbush if it is to be direct seeded, or by physical control if planting seedlings as most seedling planters scalp the under-storey out of the way.

If the under-storey is sown in the autumn following saltbush establishment, most normal practices for sowing the under-storey pasture can be followed. That is, waiting for germination of the annual weeds, spraying with a knockdown herbicide and then sowing. If possible try to avoid spraying the knockdown herbicide directly over the saltbush rows. However if this in not possible, anecdotal evidence suggests that well-established saltbush can tolerate glyphosate at approximately 1 L/ha without permanent ill-effects. As the saltbush will be quite well established to survive the summer it will not be out-competed by the more actively growing under-storey.

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Management needs and tips

Early stages. Newly established saltbush seedlings are quite vulnerable. They are very poor competitors against weeds, and are vulnerable to insect pests and grazing animals (including rabbits and kangaroos). Annual weeds can be controlled by over-spraying well-established saltbush with gyphosate at approximately 1 L/ha. Once firmly established, little further input is required and 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 carefully monitored to ensure stock are removed when there is still significant leaf remaining, and before there is heavy damage to the main branches. This grazing can also reduce the susceptibility of the saltbush plants to herbicide sprays that might be applied if the under-storey is still to be sown.

Fencing. Preventing grazing during establishment is critical. Many farmers can save on a fence at the outset by planting saltland while the rest of the paddock is being cropped. 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.

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 the plants generally recover satisfactorily. Reports of major pest or disease damage are relatively rare, except insect attacks on seedlings (especially by mites, aphids and budworms), which if not controlled, can kill many seedlings.

Fertiliser for sown understory.  If the nutrition requirements of the understory sown pasture is not addressed, the most productive species will disappear.



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Grazing options and grazing management

As with many other aspects of the saltbush and under-storey option, it is the saltbush that requires the more specialised management to ensure its productivity and persistence. Constant heavy grazing will eventually weaken and kill saltbush.

To a large degree, the under-storey species behave the same on saltland as they do on other parts of the farm. They are best not grazed while they germinate and establish, they can be rotationally grazed or set stocked at other times, and those legumes that are aerial seeders (such as balansa clover and medics) require some protection from grazing during seed set.

Saltbush and under-storey pastures, like dense saltbush plantings, have been shown to thrive under a grazing management system that involves an annual crash-grazing where the under-storey is entirely consumed and the saltbush is grazed back to the twigs in autumn when other farm feed sources have been exhausted. The saltbush provides protection from wind erosion needed to allow this hard grazing.

SGSL research showed that there is no advantage in saving saltbush-based pastures for less productive seasons as a living haystack or drought reserve. The research shows that old man saltbush drops a lot of leaves when left ungrazed and there is little advantage in deferred grazing between years. For more information, see Saltbush Biomass in a Saline Grazing System - Use it or lose it! In addition, not grazing the saltbush at least annually increases the risk of the plants exceeding sheep grazing height and then preferentially directing future growth to the non-grazed parts of the plant.

There has been little research comparing different grazing management options for saltbush and under-storey pastures when grazed more than once a year. Research in SGSL compared set stocking with rotational grazing of a saltbush and under-storey pasture at Lake Grace, WA. Some animal production and pasture composition benefits from rotational grazing emerged but it was not clear if the extra effort required to manage the animals in the rotational system was justified in the return.

Before this study almost nothing was known about diet selection of sheep grazing saltbush and under-storey pastures. The balance of saltbush and under-storey species selected by the sheep varied between seasons, depending of the nutritive value of the saltbush compared to the under-storey (Figure 4.17). Interestingly, the sheep never chose 100% saltbush or 100% under-storey. In autumn when the under-storey had its lowest nutritive value, the sheep chose a diet consisting of approximately half saltbush and half dead under-storey, while in spring when the under-storey was highly nutritious, the sheep still included 10% saltbush in their diet. 

        

Figure 4.17. Diet selection by sheep grazing a saltbush and under-storey pasture showing the saltbush component as a proportion of the total diet compared to the digestibility of the legume based under-storey

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Animal nutrition issues

The saltbush component of saltbush and under-storey pastures provides a nutritional challenge to livestock because of the high salt concentration in the leaves. As salt in the feed increases, appetite is suppressed, intake is decreased and digestion is disrupted. Research shows clearly that livestock grazing saltbush alone will not get sufficient nutrients for maintenance. For more information, see Salty Diets - feed.

For grazing animals 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 saltbush is further reduced. In one study, feed intake of sheep on old man saltbush fell by more than half when pure drinking water was replaced by water containing 1% salt (10,000 mg/L sodium chloride). For more information, see Salty Diets 2 - water.

One of the great advantages of this saltbush and under-storey option is that some of the nutritional challenges associated with the saltbush are overcome by the under-storey. As shown in Figure 4.17, when sheep self select a diet from a saltbush and under-storey pasture, they never select more saltbush than their digestive system can manage. Good quality water is important, but less critical than is the case if animals are grazing dense saltbush plantings where there is little understorey to balance their diet and reduce their salt intake.

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