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SOLUTION 4

Saltbush & under-storey

 

4.3  What are the benefits from saltbush & under-storey

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Production

Saltbush does not produce high levels of utilisable feed per hectare, whether growing in dense plantings, or as part of a ‘saltbush and under-storey’ system. It is easy to overestimate the available forage from saltbush because of the upright habit of the plants and because most of the standing dry matter is made up of low nutritive value twigs (which may be eaten but the animals get no net benefit because of the low digestibility), and the inedible woody stems.

Estimating the dry matter that is available for grazing from a stand of old man saltbush is relatively easy and involves measuring the widest diameter (D1), the diameter at right angles to D1 (D2) and the height (H) of 15-20 typical plants. If the shoot volume is calculated as D1 x D2 x H then the plants will contain approximately 0.2 kg of dry leaf per cubic metre of volume.

An easier rule of thumb is to simply allow half a kilogram of edible material (0.5 kg drymatter) per saltbush plant that is well leafed and where the growth is not above sheep height. For edible dry matter per hectare, simply multiply the per plant estimate by the number of plants per hectare.

In the SGSL initiative, grazing trials in Western Australia assessed the annual production from stands of old man and river saltbush. Averaged over 2 years, the sheep utilised ~400 to 600 kg of  dry biomass per hectare from old man saltbush at a planting density of 930 plants per hectare. Each plant therefore produced an average of 430 - 650 g of edible dry biomass. Each river saltbush plant produced 570 - 800 g of edible dry biomass. Even in these dense saltbush stands the volunteer under-storey of annual grasses and herbs contributed about the same amount of edible dry biomass as the saltbush.

However, when wider alleys are left between the saltbush rows to give more opportunity to the under-storey, dry matter production results can be significantly boosted. In such situations, the saltbush will typically contribute only 10 to 30% of the total edible dry matter.

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Water use

During the late 1990s, anecdotal evidence from farmer experiences began to emerge in Western Australia that saltbush stands were using sufficient water to draw down the watertable. This drawing down of the watertable can have a double barrelled impact. Firstly, by lowering the watertable, saltbush can reduce the amount of salt entering into the root zone of the more shallow-rooted under-storey species. Secondly, drying out the soil profile by lowering the watertable creates a buffer zone that enables winter rain to leach salt out of the surface soil. This makes the site more suitable for productive under-storey species that are less salt tolerant than saltbush.

The extensive research undertaken in the SGSL initiative has provided some support for the farmer experiences. It showed that saltbush can lower the water table, but was not able to show significant improvements in the soil conditions for under-storey. However, we know from first principles that lowering watertables in summer will decrease the rise of salts into the root zone, and increase the potential for rainfall to leach salts down out of the root zone. It is likely that several years would be needed for this effect to have a measurable impact in the low rainfall zones where saltbush and under-storey is an option.

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Amenity and environmental

The amenity value of a well managed stand of saltbush and under-storey, particularly when compared with bare and untreated saltland, is unmistakeable. Most of the evidence supporting amenity benefits from saltland pastures, including saltbush and under-storey, also comes from farmer experience.

Revegetation with saltbush and under-storey 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 also dependent on how the saltland pasture is managed, particularly in terms of the grazing pressure and timing, and on seasonal conditions. For more information, see Sustainable Grazing on Saline Lands Biodiversity Theme.

Some of these benefits are assumed, or based upon intuition rather than on well documented research, and the possibility for negative impacts cannot be ignored. 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 first couple of years, 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 or Perennial pastures on saline land can change salt and water balances. However, rates of salt export declined to below the untreated control after the saltbush pasture had been properly established and the soil was no longer disturbed.

By far the most consistently reported environmental benefit from establishing saltland pastures (including dense saltbush plantings) is visual amenity. Though not easily measurable, farmers greatly value the improved visual amenity associated with replacing visibly salt affected areas with productive groundcover. For more information, see Case studies on how farmers are successfully managing saltland for profit and sustainability.

More so than other saltland pasture options, saltbush (either dense plantings, or spaced rows with under-storey) can provide a substantial windbreak. These windbreaks can give increased stock shelter, and there is widespread anecdotal evidence to suggest that 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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How do the $$$s stack up?

Farmer results

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

An analysis of farmer trials (many of which were based on saltbush and under-storey systems) from the SGSL Producer Network in WA  showed that profitability in 2006 with a sheep grazing day valued at 10 cents varies greatly (see Table 4.1) though 16 of the 21 sites reached break even within 10 years. The monetary value estimates in Table 4.1 are significantly less than the benefits that farmers report anecdotally, mainly because the non financial benefits are not included in the economic analysis. Whole farm economic modelling supports the farmers’ contention, suggesting that the whole farm benefits are about double the easily identifiable cash benefits.

Table 4.1. An analysis of 21 of the WA grower network sites from the SGSL initiative, showing project cost and estimated benefits. For more information, see SGSL- Economics WA Producer Network .

Result 

Excluding cost of infrastructure

 

Average 

Range 

Establishment cost per ha

$324/ha

 $77/ha to $787/ha

Payback period* 

16 out of 21 sites payback inside 10 years

 2 yrs to >20 yrs

Benefit Cost Ratio (BCR)*

1.64

 0.22 to 6.19

Internal Rate of Return (IRR)**

8% (19 sites only)

 < -10% to 37%

Net Present Value (NPV)**

+$6,177

 -$6,214 to +$54,761

Project Area

26 ha 

 4 ha to 49 ha

There are also research results on the economic value of saltbush and under-storey that are discussed below.

From the economic analyses of the on-farm trials in SGSL, we can conclude that the profitability of saltbush and under-storey pastures in general is determined by:

  • Infrastructure costs. If the site requires significant expenditure on site preparation (raised beds, surface water management), fencing or water supply then profitability will be more difficult.
     
  • Establishment costs. These are a primary determinant of profitability and in the SGSL data (see Table 4.1) they varied from $77 to $787/ha. In general, the cost of establishing a saltland pasture are similar to those of a non-saline pasture if sown from seed, but costs will be substantially higher if the pasture is established with nursery-raised saltbush seedlings.
     
  • Risk of failure. This is significantly higher than for non-saline pastures because of the salinity and waterlogging. There is also a risk with the under-storey because for the improved species the present levels of tolerance to salinity and waterlogging are not high. With the saltbush, the risk associated with establishing the plants can be significantly reduced by using nursery-raised seedlings, but this increases the establishment costs.
     
  • Pasture productivity. In general terms, the lower the rainfall and the saltier the site, the lower the pasture and animal production that can be expected. Given that saltbush and under-storey systems are most suited to the low rainfall zone, the production potential will be lower than for higher rainfall sites and therefore profitability will be dependent on keeping the establishment costs down.
     
  • Nutritive value. As saltbush accumulates salt, animals cannot usually eat enough of it to meet their nutritional needs. This is more of a problem in dense saltbush plantings than for saltbush and under-storey. The main nutritional challenge for saltbush and under-storey is that in autumn, the most common time for grazing saltbush-based pastures, the under-storey is dead and has lower nutritive value. The presence of legumes in the under-storey will help maintain nutritive value to some degree;
     
  • Product prices. The cost of ongoing inputs and the prices paid for meat and wool products will always impact on the economics of any pasture establishment expenditure and saltbush and under-storey systems are no exception.

In summary, from across the SGSL farmer sites, the highest risk of failure and lowest estimates of profitability occurred in the low rainfall areas where saltbush and under-storey are one of the recommended options  Economics SGSL WA Producer Network Report. However, balancing this is the fact that such land has little opportunity cost and any green feed in autumn has a particularly high value.

Research results

In order to better capture the whole farm benefits of saltland pasture, the The SGSL Economics Theme Report 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 2000 ha with 200 ha of saltland. The saline areas were suited to a mixed stand of saltbush with a legume/grass annual under-storey.

The modelling showed that for this farm (with 50 ha mildly affected, 50 ha moderately affected, 50 ha severely affected and 50 ha so salinised/waterlogged as to preclude any saltland pasture), profit was maximised when saltland pasture was grown on 115 ha of the total 200 ha of salt-affected land. In fact, the greatest increase in profit came from establishing the first 50 ha 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 50 ha). Further increases in the area of pasture beyond the initial 50 ha generated little improvement in profit because:

  • some of the saltland pasture expansion was into mildly affected land which had a higher opportunity cost, being still able to grow barley, albeit with reduced yield;
     
  • some of the saltland pasture expansion was into severely affected land (more of the type suited to dense saltbush plantings rather than saltbush and under-storey); 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 115 ha, saltbush and under-storey increased profits by ~$40/ha for a wool only flock. Profits for a crossbred lamb production flock were about 50% higher.

Such 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 the saltbush he would have had to sell his sheep on a falling market and buy them back on a rising market. He claims the saltbush also paid for itself again in the summer of early 2006 when more than 100 mm of rain fell in one day in January. The rain destroyed all his annual paddock feed, but the rapid growth of the saltbush again meant that sheep could be retained on the farm.     

In conclusion, the economic case for establishing saltbush and under-storey on sites with low to moderate salinity in the low rainfall zone is quite strong provided due attention is paid to the risks and challenges discussed in Section 4.4. Farmer experience suggests that the additional benefits significantly add to the value of saltbush and under-storey as part of their farming systems.

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