Establishing saltbush and understorey for dryland salinity management in Western Australia

Give the plants a chance to survive

Minimise environmental stresses, such as salinity, waterlogging, seed burial, moisture deficiencies, weed competition and insect attack. These can all reduce survival of young saltbush and understorey.

Reduce waterlogging and prevent inundation before planting

We recommend controlling surface water on the saline site and upslope, as part of a whole-farm water management plan. These expenses would be recommended in a farm plan regardless of saltland revegetation.

On-site management

Use shallow relief drains to decrease waterlogging and increase water movement off the low-lying (saline) land. Plant seed or seedlings onto mounds on waterlogged sites. Align mounds and furrows to drain into the shallow relief drains.

Upslope management

Upslope, use surface water structures (such as grade banks and grassed waterways) to decrease surface water flowing onto the low-lying (saline) land. Water from upslope can be harvested into dams, or diverted around and downstream of the saltbush plantings.

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Establishing a saltbush plus under-storey system

Timing of establishment

Establishing saltbush and under-storey pasture is a two-stage process. Saltbush needs to be established (seed or seedlings) in later winter (from July to early September), while the annual under-storey species need to be established in autumn at the break of season.

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

Good practice for establishing saltbush plus understorey is:

• control weeds in the previous season before weed seed set, and again at planting
• apply fertiliser based on soil test results
• control insects and other pests (all the way from red legged earth mite to kangaroos!)
• sow seed with a proven germination rate, or use healthy seedlings

Use an appropriate rhizobia with legume seed, because it is unlikely that there will be existing rhizobia in the saline soil where there have not been legumes for many years.

In general:

• Control weeds with a knockdown spray in spring of the year before sowing as saltbush establishment.
• Spray for red-legged earth mite as close as possible to the optimal Timerite® spraying date and again before germination of the seed.
• After weeds have germinated following the break of season, apply a knockdown herbicide, fertilise and sow.
• Through July and August, check for insects.
• Planting an understorey before the saltbush allows the use of large seeding machinery. If you plan to sow an understorey after saltbush, match the alley width to the width of your seeding and spraying equipment.

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Establishing saltbush with seedlings or cuttings

We recommend using nursery raised seedling or cuttings in preference to direct seeding in most cases.

Seedlings can be grown on more-saline soils and with a wider range of soil textures.

The costs of seedlings is higher than for direct seeding, but success is more reliable.

Nursery raised seedlings (or cuttings such as Anameka^TM) are the easiest and least risky way to establish saltbush. Prepare the site by controlling weeds and (if appropriate) sow an understorey. Seedlings are typically planted from early July to late August. Use a tree planter that mounds or scalps the soil to suit the site conditions. 
Saltbush seedlings are available from tree nurseries.

For large areas, we recommend planting with a commercial seedling planter – these are often available for hire through the local shire, Landcare Group or tree nursery. Seedling planters, such as the Chatfield’s tree planter, scalp the soil surface (to remove weed seed), rip through the subsurface compaction, oxygenate the soil (with disks), plant the seedling and push the soil back around the seedling roots to remove air spaces. You can plant 5000–10 000 trees a day, depending on the reflexes and tolerance of the person on the planter!

For small areas, you can using a Pottiputki style hand planter. To prepare for hand planting, rip the site and control weeds first. With hand planting, it is very important to press soil around the seedling, to remove air pockets that prevent root growth.

Method

• Measure subsoil salinity in the spring of the year before planting: ECe should be in the range 400–800mS/m, or down to 200mS/m where rainfall is too low for salt tolerant perennials. Where direct measurement is not possible, check the indicator species and visual signs.
• Deep-rip to break up hardpans.
• On waterlogged sites, mound in spring of the year before or autumn of the year of planting. Allow time for the mound to settle. The instructions for raised beds can be adapted for mounding sites. Only plant river saltbush on waterlogging sites.
• On mounded sites, after rains and before planting, make sure the mounds do not hold back surface water, and the furrows empty into the shallow relief drains. Correct any mistakes if possible.
• Control red-legged earth mites (RLEM) in the spring of the preparation year by spraying as close as possible to the optimal Timerite spraying date. Germinating seeds are much more susceptible to insect attack than seedlings. Control other insect pests as needed: RLEM and Rutherglen bug can kill seedlings during the establishment year.
• In the year of planting, wait until the risk from waterlogging has abated (August to October depending on location and climate), and the soil is still moist.
  • Apply a knockdown herbicide.
  • Cultivate non-mounded sites.
  • Plant the seedlings: Plant seedlings as deep as you can. The first summer after planting is the most challenging time and you want the roots as far from the soil surface as possible. It does not matter if you bury the bulk of the leaves – as long as a couple of leaves are above the soil surface.
• Monitor for red-legged earth mite and spray promptly as needed.
• If you have an unusually dry spring and summer after establishment, consider getting the fire unit out and watering the first-year plants: it does not take long and may save you from having to replant.

Layout

This is largely a personal decision and is very site specific. Ask yourself:

• How much rainfall do you expect? Mature saltbushes will compete for rainfall so you can get the same amount of leaves from half the number of shrubs. In dry areas (250–450mm annual rainfall), 600 plants/ha could be plenty.
• Do you have a shallow water table? Saltbushes will utilise the groundwater if it is not too saline or acidic. If you have fresh to moderately saline water under the plantation, you could increase shrub numbers.
• How are you going to monitor and move stock? Moving sheep through dense saltbush plantations can be challenging. Leaving gaps can assist in stock management. Do you want to see the sheep while driving past the paddock?
• Do you need shelter for lambs and sheep off-shears? Double rows or blocks may provide better shelter than single rows. Where do the coldest prevailing winds come from?
• What is the longest straight run to minimise the time spent planting?

Shrub density

If you have a reasonably fresh watertable within 3m of the soil surface, the site will support more than 600 plants/ha. However, nursery raised seedlings are expensive, and competition with undertsorey will increase with higher saltbush densities.

For vehicle and livestock access, we suggest alley widths of about 10m, and saltbush at about 600 plants/ha.

Tables 1 and 2 provide spacings to achieve a range of saltbush planting densities.

Costs

To calculate total costs, include:

• cost per seedling delivered to the farm
• seedling density per hectare
• area planted, in hectares
• mounding and additional surface water management (do not include standard surface water management costs)
• insect and weed control
• planting costs (including spraying and cultivation)
• stock water systems and any other additional infrastructure.

We do not recommend including all the fencing costs against the saltland pasture activity – fencing saltland is a whole-farm capital expense, considered in the same manner as fencing other pasture or cropping paddocks.

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Establishing saltbush with direct seeding

Direct seeding has a lower cost, but success is less reliable than for seedlings.

Conditions for successful direct seeding

Soils

Use direct-seeding of saltbush only on soils with low to moderate salinity and a sandy surface soil. Areas with more summer rainfall will have greater success than areas with little or no summer rainfall.

Seasonal conditions

Match your direct seeding to to the prevailing seasonal conditions. Saltbush seeds are tiny (<1mm) and not tolerant of salt, weed competition or any bugs. There are high salt concentrations in the soil solution with the first rains, so wait for some flushing rains. Seeding in winter can be extremely difficult if the site is wet. Even if the soil is dry enough to sow, there is a risk of failure from subsequent spring waterlogging.

Cold conditions with early direct seeding will slow down germination. River saltbush in particular is very slow to emerge if the average daily temperature is less than 10°C.

Conditions for germination improve during spring: waterlogging declines and temperatures rise. However, the germinating saltbush has to develop a sufficient root system to survive, while the soil dries out and becomes more saline over summer.

Seeding technology

Viable saltbush seed is only found in bracts from female flowers that have been fertilised by male pollen. Many saltbushes are have separate male and female plants (dioecious plants). You will find most viable seed in bracts from female plants that have male plants nearby. Check the bracts for seed by carefully prising open the bract – seeds are very small.

Use a niche seeder to place the seeds mixed with vermiculite at 2–3m intervals along the top of a raised M-shaped mound (Figure 1). Raising the mound reduces waterlogging, and vermiculite acts as a mulch, reducing the movement of salt to the soil surface by capillarity.

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.

Check the germination rate of your saltbush seed before use.

Figure 1Mound, mulch and black paint spray left by niche seeder

Method for successful direct seeding

• Measure subsoil salinity in the spring of the year before planting: ECe should be in the range 4–8dS/m or less. Where direct measurement is not possible, check the indicator species and visual signs.
• Only direct seed into sandy-surfaced soil. Do not direct seed into clay soils.
• In the year before planting, spray-top with a knockdown herbicide to prevent seed-set by annual grasses.
• Plan the niche seeding lines so that the mounds will not hold back surface water, and the furrows will empty into the shallow relief drains.
• Control red-legged earth mites in the spring of the preparation year by spraying as close as possible to the optimal Timerite spraying date. Germinating seeds are much more susceptible to insect attack than seedlings. Control other insect pests as needed: Rutherglen bug can kill seedlings during the establishment year.
• In the year of seeding, wait until the soil has warmed and the risk of waterlogging has abated (August-September, depending on location and winter rainfall).
  • Apply two knockdown herbicide sprays – glyphosate 4 weeks before seeding, and SpraySeed 2 days before seeding.
  • Cultivate just before niche seeding.
  • Seed with specialist niche seeder, seeding at 300–400g/km, with about 1.5m between seed spots.
  • Monitor every week for 10 to 15 weeks, and control damaging insects:  red-legged earth mites, aphids or native budworm.

Costs of direct seeding

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/ha.

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Establishing the under-storey

We recommend sowing the under-storey in the autumn prior to a spring planting of saltbush.

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, sowing the under-storey in the autumn prior to establishing the saltbush has several advantages:

• Sowing both the under-storey and the saltbush in the same year minimises both the costs and time involved.
• 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 if an under-storey or cover crop is present.
• There is no saltbush to be affected if a knockdown is used prior to sowing the under-storey.
• Large commercial machinery (e.g. air seeders) can be used because the saltbush rows are not yet established.

With the recommended understorey establishment, manage competition of the understorey with the young saltbush by using either a narrow band of knockdown herbicide along the saltbush planting rows (direct seeding), scalping with a seedling planter.

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 with fertiliser. If possible try to avoid spraying the knockdown herbicide directly over the saltbush rows. Saltbush that is well established will not be out-competed by the more actively growing under-storey.

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). Seek specialist advice for herbicide and pesticide use over saltbush plants. Once firmly established, little further input is required.

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 more than 30% leaf remaining, and before there is heavy damage to the main branches. If you can pull the shrubs out of the ground, so can livestock.

This grazing can reduce susceptibility of saltbush plants to herbicide spray drift when sowing late under-storey.

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 red legged earth mites, Rutherglen bugs, aphids and budworms), which if not controlled, can kill many seedlings.