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SOLUTION 10

Legumes for saltland

 

10.3 What are the benefits from saltland legume

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Production

The contribution of legumes to the productivity of pastures is well known and documented – they have higher protein content and digestibility than grasses, and they increase soil nitrogen levels for the benefit of grasses. Similar benefits could be expected from legumes in saltland pastures.

The challenge is to find and manage legumes that can cope with an environment to which they are typically unsuited. It is difficult to make general claims about the production benefits of most plants growing on saltland, and even more so with the legumes that are relatively sensitive to these conditions. In practice, there are few saline pastures across southern Australia where legumes make the sort of contribution that would be expected on non-saline sites. 

Tall wheatgrass (in higher rainfall zones) and saltbush (in lower rainfall zones) have some ability to locally lower the saline watertable in catchments with local groundwater flow systems and therefore provide a more hospitable environment for companion legumes. It has certainly been shown that when effectively managed, tall wheatgrass pastures sown with companion legumes are capable of increasing stocking rates quite dramatically. 

SGSL research at Mt Charles in the Upper South East of South Australia has quantified the benefits of integrating balansa clover with well managed puccinellia pasture. The addition of balansa clover into the pasture resulted in a further 24% increase in per hectare animal performance.

The dry matter production and nutritive value of saltbush is generally not sufficient by itself to cover establishment costs, but introducing higher quality pasture plants in the inter-row, such as burr medics and balansa clover, can dramatically tip the balance. The role of the saltbush is then partly to provide a more hospitable site for the legumes which are relatively salt-sensitive. For more information, see Saltland Solution 4 – saltbush and under-storey.

Research in WA by the CRC Salinity has shown that burr medics persist and produce more feed over 3 or more years than balansa and Persian clovers on low rainfall (<400 mm), moderately saline land with little or no waterlogging Similar results were also found in the summer-dominant rainfall regions of northern NSW on sites not subject to waterlogging.

In northern NSW research by the CRC Salinity found that lucerne out-performed strawberry clover and other prospective perennial legumes in terms of both herbage production and persistence on saltland over four years from establishment. However, it should be noted that this research was carried out during an unusually dry period for the region, with a lower incidence of waterlogging than normal.

In southern regions with winter dominant rainfall the performance of commercially available perennial legumes on saltland subject to waterlogging is not encouraging. Limited production and poor persistence, particularly over long hot summers, to some extent mirrors the situation for non-saline land – but more so.

Overall, a mix of grasses, legumes, shrubs and forbs is likely to maximise the feeding value of saltland pasture, allowing grazing animals to select specific plants for a balanced diet. The legumes also help improve the growing conditions and dry matter production of the other pasture plants.

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Water use

Annual legumes are generally shallow-rooted and do not contribute significantly to water use on discharge sites. In fact it is the role of complementary perennial grasses and shrubs that are often sown with these legumes that help relieve sites of waterlogging.

The ability of tall wheatgrass and saltbush to use water throughout summer means that the soil needs more water to become saturated following the autumn the break. This delays the onset of winter waterlogging under tall wheatgrass pastures which may include other species such as balansa clover, or in saltbush pastures that may contain a mixture of under-storey grasses and legumes. Monitoring of a site in the Great Southern Region of WA showed that winter waterlogging occurred a month later on tall wheatgrass-balansa pasture compared to balansa-only pasture. The duration of waterlogging on tall wheatgrass-balansa pastures was also reduced to a third of the time that the balansa-only pasture was waterlogged during a growing season (May - October).

Lucerne is renowned for its ability to intercept recharge and can perform this role on some discharge sites, provided the site is free from the risk of waterlogging. In summer rainfall situations lucerne can be productive at salinities of up to ECe ~8 dS/m, in the process reducing recharge. In southern Australia the opportunities to use lucerne in this way are limited. However, farmers in South Australia have demonstrated very good results where the risk of waterlogging has been reduced with well planned drainage and dryer than average years. 

David Liddicoat (Ungarra, Eyre Peninsula, SA) ‘rescued’ a 42 ha paddock that was rapidly going out to salt by excavating blockages from a nearby creek, so reducing the risk of flooding, and establishing lucerne. ECe measurements on the site have shown that soil salinity has gradually decreased as salts are slowly flushed from the soil.

Leith Cooper (Jamestown, Mid North, SA) established a 200 m wide buffer of lucerne around approximately 100 ha of saline discharge, but only after run-off from the town, which used to flood the saline flats, was diverted into Baderloo Creek. Having managed the watertable and the flooding risk in this way he has been able to grow 130 ha of lucerne for seed production. “In total, on all farms in the valley, there would now be in excess of 1000 ha of lucerne where 20 years ago there might have been 100 ha.”

The conclusion from this investigation of water use is that the legumes can be expected to contribute very little to water use on saline sites, but can benefit substantially if other species use a lot of water and reduce the waterlogging incidence. Lucerne has a major ability to use water on or around saline sites, provided the water is non or mildly saline and there is little or no waterlogging.

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Amenity and environmental

Improved visual amenity is a strong motivator for most farmers who are actively involved in revegetating saltland. Under suitable conditions (low to moderate salinity and waterlogging), saltland pastures can transform a salt-affected site otherwise supporting only sparse sea barleygrass, and sometimes, legumes can be a significant contributor to such a pasture.

The spontaneous comment of Tim Heffernan: "The farmer showed me his salt problem, but all I could see was a paddock covered in waist high green feed in the middle of summer!" expresses the sentiment of many farmers who have to look every day at a salt affected paddock. 

Geoff Kroemer of Tumby Bay (SA) spoke of his experience: “Five years ago I would never have dreamed that we could turn such apparently useless land into something so good. I just wish we had started this 20 years ago, but I am pleased to be doing it now for the next generation.”

It is also worth noting that increased urbanisation increases the demand for using land and water resources in many ways – including improving the quality of water supply, improving the health of riverine habitats, and landscape amenity. Indeed, research in the United States has shown that landscape amenity is the best predictor of rural area population change – a trend that is likely to be replicated in Australia.

In terms of biodiversity value, SGSL research showed that mixed species pastures are intermediate between bare salt scalds and remnant native vegetation as measured by Landscape Functional Analysis and therefore represent a ‘win:win’ situation, with better production and environmental outcomes compared to untreated saline areas.

However, the above conclusions are about saltland pastures in general, and not about legumes in particular. It would be rare for legumes to be included in a saltland pasture mixture for their contribution to amenity or environmental values. The pasture might be primarily established for that purpose, but the inclusion of a legume will be primarily to increase pasture production and animal nutrition. The exception might be that if legumes disappear from a pasture because of salinity, waterlogging or poor pasture management, it is reasonable to expect that their place will be taken by weeds or bare ground.

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How do the $$$s stack up?

Farmer experiences

The profitability of legumes on saltland is generally not separated out from the profitability of complementary grasses or shrubs in the pasture - rarely will a legume be sown as a single species in saline conditions.

Given that legumes are considerably less tolerant of salinity and/or waterlogging than grasses and shrubs, they really only represent an economic opportunity on higher capability land.

Two case studies illustrate the potential for profitable use of legumes in mixed pastures on salt-affected land.

  1. Sheep grazier Michael Blake (Hamilton, Victoria – 690 mm annual average rainfall) sowed 90ha of salt affected land to Dundas at 7 kg/ha through an air seeder along with balansa and strawberry clover.

    The benefits of a tall wheatgrass pasture with balansa were modelled with an annualised stocking rate of 15.5 dse/ha with a provision for supplementary feeding on alternative pastures in winter. The investment in pasture establishment was analysed on a gross margin basis for a self-replacing merino wool flock and accounting for the extra costs of grazing management labour and fertiliser to maintain the pastures. This modelling showed that gains in carrying capacity resulted in annual increases in gross margin per hectare, up to $162/ha by year 3.

    The Blakes’ tall wheatgrass/balansa pastures were analysed over 10 and 20 years to determine the net present value (NPV) and internal rate of return on investment (IRR) in pasture establishment. The results indicate that the tall wheatgrass and clover pasture may well be a highly profitable investment for unproductive saline areas, even if the pasture is only maintained for 10 years.
     
  2. David Liddicoat farms at Ungarra on Eyre Peninsula (SA). As part of a SGSL project he sowed puccinellia and balansa clover as unde-rstorey between rows of saltbush previously established on 18 ha of land that had been dominated by samphire. Following the excavation of drains, the soils of the creek flat grazing areas improved dramatically, allowing volunteer pastures of ryegrass, sub-clovers and burr medic.

    The grazing of improved saltland pastures integrates well with the rest of the farming operation. Saltbush stands with dried under-storey of puccinellia, volunteer ryegrass and medics are lightly grazed over April to May when feed on the rest of the farm is low. When the rains come the sheep are grazed on winter-active lucerne, volunteer clovers, medics and ryegrass on other parts of the once salt-affected creek flats. Given time to recover, the saltbush and now green understorey pastures also provide valuable winter-spring grazing. In summer the sheep are turned onto the crop stubbles.

    The increased productivity from the grazing land has reduced the requirement for hay production (for supplementary feed) from 30 ha to 15 ha on good cropping land. The same number of sheep can be run but hay production costs are reduced, while regaining 15 ha for grain or canola.

    Assuming a gross margin of $30/dse and David’s stocking rate of 9dse/ha is maintained over the 20 year life of the pasture, the total future profit arising from pasture development, in today’s dollars (assuming a discounting rate of 10%) would be $370/ha. To start returning a profit the pasture needs to last at least 10 years. If the saltland pasture (with these establishment costs) can only support 7-8dse/ha, then the investment will only return a profit if high sheep gross margins can be obtained, and the pasture lasts longer than 12 - 13 years.

    This analysis does not include gains in cropping production achieved through reduced requirements for hay production (supplementary feed). However, it does include large costs associated with fencing and drainage that may not be applicable to other development scenarios.

    The estimated pasture life in this analysis (20 years) is conservative. Some producers report saltbush and puccinellia pastures lasting at least 25 years. David estimates that his increased production outcomes have paid for the establishment of his saltbush system within 5 years. This is likely to be due to a combination of increased stocking rates, gains in cropping production and reduced expenses on supplementary feed and weed control.

Research results

In one of the few studies to directly investigate the inclusion of a legume in saltland pastures, Sustainable Grazing on Saline Lands (SGSL) research has assessed the relative profitability of puccinellia and puccinellia-balansa clover based pastures on moderately saline, waterlogging prone areas of the upper south-east of South Australia.

When the research results are combined with local knowledge and run through a whole-farm computer simulation model (MIDAS) for the region, it is possible to investigate the profitability of various production scenarios. Accordingly, a model 2000 ha farm was established for the Upper South East of South Australia, of which 40% (800 ha) was saline. In the model, lucerne was grown on the sandy dune country, tall wheatgrass-dominant pastures on the transition soils and either barley grass-dominant, puccinellia-dominant (P) or puccinellia with balansa clover (P&B) pastures on the saline soils. A self-replacing merino flock was chosen as typical of the area and run as the sole farm enterprise.


  

  

Figure 10.17. Effect on profit per hectare of saltland of (a) achieving less than the 100% pasture production assumed for the model and (b) a reduction in the digestibility (%DMD) of saltland pastures. The blue line is puccinellia plus balansa clover, while the red line is puccinellia alone.

Maximum profitability for this model farm was dependant on achieving high levels of pasture production of highly digestible feed (see Figure 10.12), but at all levels of production and at different pasture quality levels, the inclusion of balansa clover significantly increased the estimated profit. These results indicate the importance of pasture improvement and good pasture management on saline soils, and highlight the value that a legume can add. Unfortunately, keeping the legume in the pasture is more difficult in the field than in a computer model.

The SGSL initiative showed that across southern Australia, saltland pastures could provide a profitable investment. The final report from the SGSL Economics Theme stated “Introducing improved pasture species to salt-affected land to increase the feed value for livestock is profitable across a broad range of environments, production conditions and commodity price assumptions, according to the results of this study.”

However, the profitability of saltland pastures is complex because up to half the benefits typically come from saltland pastures providing ‘support’ for the cropping and grazing on the rest of the farm. This may be out-of-season feed allowing a higher stocking rate across the rest of the farm; the additional grazing resource allowing more cropping while maintaining stock numbers; shelter (at least with saltbush) for lambs or off-shears sheep when they are most vulnerable to the elements; and perhaps also increased value of their real estate asset when the salinity problem is seen to be manageable.

Notwithstanding these benefits, the SGSL program clearly identified several factors that can undermine the profitability from saltland pastures, and we can apply some of these general conclusions specifically to the addition of legumes to the pasture mix:

  • Establishment costs are a primary determinant of profitability. If the legume is incorporated in the species mix of a new pasture, the additional cost is only that of seed (at least partly offset by reduction in the amount of grass seed) and possibly inoculant and specific pest control. If the legume is used to renovate an existing pasture (such as with balansa sown into a puccinellia or tall wheatgrass pasture), labour, weed control, fertiliser, fencing and loss of grazing opportunity might all have to be included.
     
  • Risk of  failure is significantly higher than for non-saline pastures, and perhaps even more so for legumes if seasonal conditions lead to excessively high salinity levels or waterlogging at critical times, or if the management and timing compromises are made in favour of the other, more reliable species in the sowing mix.
     
  • Pasture productivity – in general terms, the saltier the site, the lower the pasture and animal production that can be expected. Seeding rates are no lower for saline than for non-saline sites, so the return on investment can be expected to be less. Higher capability sites can benefit from elevated watertables that maintain production from perennial legumes well into summer.
     
  • Nutritive value of the pasture – many saltland species either accumulate salt, or have unusual compounds in the leaves that help them survive the inhospitable saline environment, but that can be detrimental to grazing animals. Most legumes do not have any of these limitations, so nutritionally we can expect them to be similar to their non-salt-tolerant relatives. A potential concern with Melilotus albus, however, is its relatively high coumarin levels, which could lead to a haemorrhagic condition in livestock under some conditions.
     
  • Product prices – the cost of ongoing inputs such as fertiliser or supplements and the prices paid for meat and wool products will always impact on the ‘bottom line’ of any pasture system whether legumes are included or not.
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