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SOLUTION 3

Dense saltbush plantings

 

3.3  What are the benefits from dense saltbush plantings?

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Production

Dense plantings of saltbush, growing in saline soils with salinity levels of 8-16dS/m (i.e. the recommended range for this saltland solution) do not produce high levels of usable feed per hectare. It is easy to overestimate the available forage supply in saltbush pastures because of the upright habit of the plants and because most of the ‘dry matter’ is the inedible woody stems.

As a general rule, the higher the density of saltbush planting, the smaller the individual saltbush plants will be and the smaller the contribution that under-storey species will make to total edible dry matter. Dense saltbush plantings (>1000 plants per ha) are recommended where the salinity level is too high for productive under-storey species and so the aim is to maximise production of saltbush per hectare.

To estimate dry matter availability of a stand of old man saltbush measure the widest diameter of 15-20 typical plants, provided they have been allowed to fully re-leaf since the last grazing, and all the dry matter within reach of grazing. The estimated edible dry matter per plant (grams per plant) is the average diameter in centimetres, multiplied by 9.5 then minus 340. For edible dry matter per hectare, simply multiply the per plant estimate by the number of plants.

If the average bush diameter is 120cm, there will be 800 g/plant and if there are 1000 plants per hectare, the total available dry matter from saltbush would be 800 kg/ha.

In the SGSL initiative, grazing trials in Western Australia were used to assess the annual production from stands of old man and river saltbush, with edible biomass being leaves and stems less than 3mm in diameter. Averaged over 2 years, the sheep utilised ~400-600kg edible biomass per hectare from old man saltbush at a density of 930 plants per hectare. Each plant therefore produced an average of 430-650g of edible biomass. The river saltbush stands produced ~500-700kg edible biomass/ha at a planting density of ~870 plants/ha - each plant therefore produced an average of 570-800g of edible biomass. Even in these fairly dense saltbush stands there was some volunteer under-storey of annual grasses and herbs that contributed approximately the same amount to the sheep’s diet as the saltbush.

There are also some rules of thumb that can be used to estimate dry matter without the need for measurement. For an established and healthy stand of dense saltbush plantings, it can be assumed that each saltbush will have ~500g of edible biomass per plant, available for grazing. In this type of situation, a sheep will need to be allocated one plant with its under-storey per day. In other words, a 10ha stand of saltbush with 1000 plants per hectare should support 500 sheep for at least 20 days, though it is likely that some additional supplementation with good quality hay or grain will be required to provide adequate nutrition for liveweight maintenance.

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Water use

If saltbush stands can use groundwater, and therefore draw the watertable down (20-30cm) then this has the potential to make a substantial difference to the surface soil conditions and the ability of a site to support a more productive and higher value under-storey.

This drawing down of the watertable can have a double-barrelled impact. Firstly, by lowering the watertable, saltbush will reduce the amount of salt that the groundwater delivers into the root zone of the more shallow-rooted under-storey species, either by soil saturation or capillary action.

Secondly, drying out the soil profile by lowering the watertable creates a buffer zone that enables winter rain to leach salt beyond the root zone. This too makes the site more suitable for productive under-storey species. The buffer zone, once established, has the added benefit of providing some protection for the saltbush against waterlogging or inundation following heavy or persistent rain.

During the late 1990’s, anecdotal evidence from farmer experiences began to emerge in Western Australia that saltbush stands were making the sites more suitable for productive under-storey species. Research has now confirmed that in some situations (e.g. where the watertable is not too deep or too salty), saltbush stands are able to dry out soil profiles and lower watertables to some degree.

Data from the SGSL trials have shown that old man saltbush plants are able to dry out soil profiles to distances of ~6 m from the base of the shrubs over summer and the effects persist through winter provided that the water-tables do not become shallower than ~1.5 m. Dense plantings of saltbush in these trials lowered water-tables by 20-60cm over summer at Meckering, WA.

Paddock scale measurements showing that watertables are lower with saltbush and improved under-storey compared with adjacent areas with annual (volunteer) pastures only have reinforced these results. Even greater drawdown would be expected with denser stands of saltbush.

Water use by saltbush will be affected by grazing management, since removal of the leaves from saltbush limits the ability of the plant to transpire water. The general principles are that water use will be greatest at times of high evaporative demand (high temperatures and low humidity typical of temperate summers) and when the plants are in full leaf. The ability of a stand of saltbush to use water will therefore be affected by the timing of grazing (plants grazed in late autumn will use more water than plants grazed in summer), and by strategic grazing management (plants that are crash-grazed and allowed to recover are likely to use more water than plants that are continually grazed through set-stocking).

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Amenity and environmental

The amenity value of a well managed stand of saltbush is unmistakeable and farmers take pride in this. Most of the evidence supporting environmental benefits from saltland pastures comes from farmer experience.

Revegetation with saltbush can assist in reducing soil erosion, and can enhance flora and fauna diversity by providing habitat to small local birds, lizards and other small animals. There is some evidence of improved microbial activity in soils established to saltbush compared with bare areas. However all of these potential benefits are dependent on how the saltbush is managed, particularly in terms of the grazing pressure, timing and seasonal conditions. For more information, see Sustainable Grazing on Saline Lands Biodiversity Theme.

Some of these benefits are assumed rather than based on well documented research, and the possibility for negative impacts is apparent. For example, establishment of saltland pastures (saltbush based in WA and perennial grass based in NSW) led to an increase in salt export from the sites in the short term, caused by the soil disturbance associated with pasture establishment. For more information, see Draft final report of the Salt and Water Movement and Site Characterisation Theme. However, rates of salt export declined again after several years when the saltland pasture grew and the soil was no longer disturbed.

By far the most consistently reported environmental benefit of establishing saltland pastures is visual amenity. Although not easily measurable, farmers greatly value the improved visual amenity associated with replacing visibly salt-affected areas with productive groundcover.

More so than other saltland pasture options, saltbush (either dense plantings, or spaced rows with under-storey) can provide a substantial windbreak. These windbreaks increase stock shelter, and anecdotal evidence suggests such shelter can improve lambing percentages and reduce mortality in off-shears sheep. In addition, in areas prone to wind erosion, saltbush stands can support heavy stocking to the point where most groundcover is removed, but without significantly increasing the erosion risk.

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Other Benefits

Bioeconomic (MIDAS) modelling at present does not take account of the financial benefits associated with:

  1. Better risk management: Year-in year-out bio-economic modelling does not take account of the benefits that can be derived from saltland pastures in exceptional years. For example, Michael Lloyd estimates that every saltbush on his farm paid for itself during the drought of 2001/02. Without saltbush he would have had to sell his sheep on a falling market and buy them back on a rising market. The saltbush also paid for itself again in the summer of early 2006 when more than 100mm of rain fell in one day in January. The rain destroyed all annual paddock feed but the rapid growth of the saltbush again meant that sheep could be retained on the farm. Tonkins had a similar experience.
     
  2. Future benefits. Some farmers place a high value on the capacity of the plants to decrease future salinisation. Saltbush can use significant amounts of groundwater and lower watertables at least slightly. The benefits of these effects in protecting cropping land from future salinisation are difficult to estimate but are only likely to be significant in flat landscapes with low rainfall.
     
  3. Benefits from salty diets. No quantitative account is currently taken of the benefits associated with the Vitamin E supplementation that saltbush provides in autumn, the increased efficiency of wool growth and improved keeping quality for meat from animals associated with salty diets and/or saltbush.
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How do the $$$s stack up

Farmer experiences and research results show that dense planting of saltbush is usually an expensive operation and rarely competes with other potential on-farm investments on an economic basis. However, farmers report a lot of unexpected benefits such as lowered watertables, more flexibility in livestock operations, less labour intensive supplementary feeding in autumn, and improved amenity value from a dense stand of saltbush compared to bare saline scalds.

The only other options for low rainfall, highly saline land are:

  1. Fence and exclude from grazing
  2. Volunteer pasture
  3. Revegetation with non-grazing species 

Farmer results

Farmers with dense saltbush stands report many benefits (eg. increased production, enhanced amenity, delayed grazing of other pastures after the autumn break, more land for livestock during the cropping season, out-of-season green pick) but the costs and returns are rarely quantified.

An analysis of farmer trials from the SGSL Producer Network in the low rainfall zone of WA showed that profitability for dense saltbush plantings is almost certainly low. As shown in table 3.1, with most assumptions, the payback period for this type of saltland pasture will be greater than 10 years and in many cases, even with modest discount rates, the original investment may never be repaid (ie. a benefit cost ratio of less than 1). The monetary value estimates in Table 3.1 are significantly less than the benefits that farmers report anecdotally, mainly because these benefits that farmers talk about are not included in the economic analysis. The figures in Table 3.1 also include the infrastructure costs associated (things such as fencing and water supply) that further reduce the apparent profitability.

Table 3.1 An analysis from the SGSL initiative showing estimated payback periods for low rainfall sites for a range of production levels (grazing days per ha) and values for a sheep grazing day.

Discount Rate 

Term of analysis 

Grazing days per ha
per yer 

Value of a
sheep grazing
day 

Payback
Period 

Benefit Cost
Ratio
 

5%

10 years

400 

5 cents

>10 yrs

0.21

10 cents 

>10 yrs

0.42 

15 cents 

>10 yrs 

0.63 

800

5 cents

>10 yrs

0.42

10 cents 

>10 yrs 

0.84 

15 cents 

7 years 

1.25 

9%

10 years

400

5 cents

>10 yrs

0.18

10 cents

>10 yrs

0.36

15 cents

>10 yrs

0.54

800

5 cents

>10 yrs

0.36

10 cents

>10 yrs

0.72

15 cents

8 years

1.08


Profitability is most strongly influenced by both the cost of establishment and the subsequent productive performance. With good grazing management, saltbush is very long lived and the ongoing or maintenance costs are usually very low.

In the 7 low rainfall case studies analysed in the SGSL initiative, establishment costs varied from $77 to $787/ha. The establishment costs for dense saltbush plantings were highest when nursery raised seedlings were used and lowest when the saltbush was direct-seeded. However, direct-seeding had a low success rate except in sandy soils, whereas a high success rate was usually associated with the more labour intensive planting out of seedlings.

From across the SGSL farmer sites, the highest risk of failure and lowest estimates of profitability occurred in the low rainfall areas where dense saltbush plantings are one of the recommended options. These farmer case studies demonstrate cost blow-outs are typically the result of poor establishment and high fencing costs.

Research results

There is very little research that directly reports the profitability of dense saltbush plantings. However, as a general rule at least in dry years it is more economical to provide supplements to saltbush than to bring in fodder for livestock. For more information, see Saltland pastures can pay in WA. Furthermore, some of the issues and lessons from the work that has been done with saltbush and under-storey can be applied to dense saltbush plantings.

In order to better capture the whole farm benefits of saltland pasture, the SGSL Economics Theme used bio-economic (MIDAS) modelling to determine the year-in year-out benefits of saltland pastures in the Central Wheatbelt (~350 mm rainfall zone) of WA.The farm modelled had a total area of 2000ha with 200ha of saltland. The saline areas had higher saltland capability than areas where dense saltbush plantings would be recommended. It was suited to a mixed stand of saltbush with a legume/grass annual under-storey.

The modelling showed that for this farm (with 50ha mildly affected, 50ha moderately, 50ha severely and 50ha so salinised/waterlogged as to preclude any saltland pasture), profit was maximised when saltland pasture was grown on 115ha of the total 200ha of salt-affected land. In fact, the greatest increase in profit came from establishing the first 50ha of saltland pasture on the moderately salt affected land, which delivered an increase in whole-farm profit of about $4000 (or $80/ha averaged over the 50ha).

Further increases in the area of pasture beyond the initial 50ha generated little improvement in profit because:

  • some of the saltland pasture expansion was into mildly saline land which has a higher opportunity cost, being still able to grow barley, albeit with reduced yield;
  • some of the saltland pasture expansion was into severely salt affected land (more of the type suited to dense saltbush plantings); and
  • once the autumn feed gap had been filled, the marginal value of extra feed at other times of the year was small.

Over the full 115ha, saltbush with under-storey increased profits by ~$40/ha for a wool-only flock. Profits for a crossbred lamb production flock were about 50% higher.

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