Novel multi-disciplinary approaches suggest profitable and sustainable farming systems for valley floors at risk of salinity Ed Barrett-Lennard1,3, Greg Hamilton1,3, Hayley Norman2,3 and David Masters2,3 1: Department of Agriculture of Western Australia, 3 Baron-Hay Court, South Perth WA 6151 2: CSIRO Livestock Industries, Floreat Park WA 6014 3: CRC for Plant-based Management of Dryland Salinity

Abstract

Introduction

This paper addresses the need to develop new farming systems for land at risk of salinity. Although we focus primarily on the south west of Western Australia, our conclusions have relevance to the other southern states of Australia.

Western Australia now has 4.4 million hectares of land at high risk of secondary salinity, and 8.8 million hectares are predicted to be at risk by the Year 2050 (1). Farmers have been alerted to the likely extent of future salinity through the publication of regional-scale maps from the Land and Water Resources Audit, and farm and paddock scale maps from the Land Monitor project (2, 3).

Some farmers maintain that the best means of ameliorating salinity lies in the use of deep open drains to remove excess water from the landscape, lowering water-tables and leaching salt back into the subsoil. About 11,000 km of deep drains have now been dug in WA (4). Three factors appear to be encouraging farmers to adopt deep drains: these are increased political support, increased advocacy by early adopting farmers, and localised examples of drainage success where land at risk continues to grow cereal crops. Notwithstanding this, there are impediments to the adoption of deep drainage. There can be difficulties in disposing of drainage effluent onto neighbouring land and waterways because of problems of high salinity and low pH. Also, the universal adoption of deep drains seems unlikely given (a) the low value of production from most dryland farming systems, (b) the high costs of drainage, and (c) the low hydraulic conductivity of valley floor soils, and therefore the limited area that would be reclaimed from such drainage.

One part of the drainage philosophy that appears increasingly tenable is the assertion that the main focus for treatment of the salinity problem should be on the affected land itself. With local groundwater systems of low slope (hydraulic gradient) such as those that are mainly found in the south-west of WA, hydrologists now recognise that the most significant lateral flow occurs as surface runoff. This accumulates on valley floors where it can remain for some time, recharging valley floor aquifers. George, Bennett and Speed (5) now believe that this local recharge may be a more important cause of salinisation than recharge on hillsides. Amelioration of salinity risk therefore requires combinations of: (a) engineering strategies that decrease runon to valleys and increase runoff from valleys, and (b) plant-based strategies in the valleys that decrease recharge and increase use of the shallow groundwater.

Salt-affected land can be used to support a range of industries and products. For example there are at least 26 plant species capable of producing 13 products or services of value to agriculture in Western Australia (6). However the development of farming systems requires components that are compatible and complementary. The convergence between the use of raised beds combined with improved surface water control, the breeding of salt and waterlogging tolerant cereals, and the use of saltbush pastures provides one such example. This paper outlines the principles behind these three approaches and shows how they could come together to create more resilient valley floor landscapes.

Approach 1 – Raised beds with improved surface water control

The focus of farmers on deep drains may stem partly from a poor understanding of the causes of impaired plant growth on land at risk of salinity. Plant growth in valley floors is constrained by the twin stresses of salinity and waterlogging. Waterlogging (the more poorly understood of these stresses) decreases the ability of plants to exclude salt at the root surface; it therefore causes increased concentrations of salt in the shoots, which adversely affect growth and survival (7). Thus, in land of mild salinity, there can be great benefits from growing plants on raised beds. In beds, the improved soil physical conditions and exclusion of water-tables to depths greater than ~25 cm effectively prevents waterlogging from occurring (8). Of course such beds can only be effective if the drained water is efficiently conducted off-site in catch drains and waterways. Because the forming of beds also loosens the soil and encourages better crop growth there is probably also decreased capillary rise of saline water to the soil surface.

Approach 2 – Breeding of salt and waterlogging tolerant cereals

Attempts to breed cereals for tolerance to salinity commenced in the 1970s (9), but the selected material was not successful probably because the importance of waterlogging tolerance was not appreciated (7). Today, there is a significant chance that truly tolerant cereals will be developed because researchers are transferring genes for both salt and waterlogging tolerance from wild grasses to commercial cereals. In one promising case, an amphiploid of sea barley grass and wheat has been developed which shares the improved tolerance of barley grass to salinity and waterlogging (10).

Approach 3 – Saltbush pastures

Saltbushes (Atriplex species) are the major salt-tolerant fodder species for productive use of saltland in WA. Good animal production requires fodders that contain high concentrations of metabolisable energy, moderate to high concentrations of crude protein and relatively low concentrations of salt. Saltbush fodder has low metabolisable energy concentrations, high crude protein concentrations and high salt concentrations (11, 12). The key to the use of saltbush fodder is to mix it with feeds with complementary characteristics. The potential of this approach is clear from a pen-feeding trial in which sheep were fed diets of 100% low quality hay (dry matter digestibility 57%), 100% wavy leaf saltbush, or a 50:50 mixture of hay and saltbush (13). Sheep fed the saltbush or the hay alone had low feed intakes and lost liveweight. However, when saltbush leaf was mixed with hay, feed intake doubled, and the sheep gained liveweight at about 70 g/day.

There are three major opportunities for saltbush fodder to be used with other fodders under field conditions. These are to:

·         Provide complementary supplements of straw or grain to sheep grazing saltbush pastures.

·         Grow higher value understorey species (like balansa clover) with saltbushes and intensify the grazing so that the sheep eat the palatable and unpalatable components of the feed on offer simultaneously.

·         Use saltbushes with adjacent cereal stubbles.

Synergies: putting the system together

The elements described above could be pulled together into a resilient and profitable farming system based around the growth of salt tolerant cereals on raised beds in alleys bounded by rows of saltbush. The major products and services of the system would be: (a) grain for sale, (b) improved grazing value of the combined saltbush plus stubble fodder resource, and (c) lowered water-tables beneath the saltbushes. In this way, the strips of saltbush would act as ‘biological’ deep drains (cf 14, 15).

Concluding remarks: scale and bio-economic modelling

The strategies required to invent the novel farming systems that we need for sustainable agriculture in valley floors are not obvious and may evolve out of our current farming systems in unexpected ways. Two examples are given below.

1.       Leverage over other fodders. Saltland pastures are probably applicable to about 50% of WA’s current land at risk of salinity (~2 million hectares – cf. 1, 16). Using these figures, we might conclude that the priority to develop better saltbush cultivars is low compared to the development of improved annual pastures (where about 7 million hectares are grown in WA). However, if saltbushes could be used to lever improved grazing value from cereal stubbles (~5 million hectares in WA), the true area of this system could be up to 7 million hectares. When seen in this broader context, there could be substantial economic gain from the development of higher value saltbush cultivars.

2.       Inadequacies of bio-economic modelling. Current bio-economic modelling approaches tend to focus on testing the benefits of slight changes to otherwise ‘typical’ farms. For example, O’Connell and Young (17) examined the value of saltbush pastures on a typical farm in the south west of WA. Farm profits were maximised only if the moderately productive saline land (2.5% of the total) was revegetated and used to fill the autumn feed gap. This kind of scenario and economic gain could be irrelevant to farmers with a far greater salinity problem. For example, how should we model the benefits of saltbush for a farm that is 50% saltland and where the farmer is forced to crop all arable land to maintain income?  This farmer would have an excess of feed in late summer and autumn (from his saltbush and stubbles) and a deficiency of feed in Spring (from his very few hectares of annual pastures); this is the reverse of the situation on the ‘typical’ modelled farm. Clearly if we are to understand the economic forces operating on farmers with large areas of saltland and most to gain from new farming systems, we will need to build radically different conceptual and bio-economic models.

Acknowledgements

We are grateful for the thoughtful input of Richard George, Richard Price and Michael Lloyd. Support for our research into the growth of cereals on raised beds and the nutritive value of saltbushes has been received from the Grains Research and Development Corporation and the Sustainable Grazing on Saline Lands initiative (a component of the Land, Water and Wool Program).

References

(1)     National Land and Water Resources Audit (2001). Australian Dryland Salinity Assessment 2000. Extent, impacts, processes, monitoring and management options. Commonwealth of Australia, Canberra, 129 pp.

(2)     Short, R., and McConnell, C. (2001). Extent and Impacts of Dryland Salinity. Resource Management Technical Report 202, Department of Agriculture, South Perth, 99 pp.

(3)     Land Monitor (2003). Products. www.landmonitor.wa.gov.au/products/index.html.

(4)     ABS (2002). Salinity on Australian Farms, Bulletin 4615.0, Australian Bureau of Statistics, Canberra.

(5)     George, R.J. Bennett, D.L. and Speed, R.J. (2004). Salinity management – the case for focusing on wheatbelt valleys. These proceedings.

(6)     Barrett-Lennard, E.G. (2000). Natural Resource Management, Special Issue (June), pp. 9-13.

(7)     Barrett-Lennard, E.G. (2003). Plant and Soil, 253, 35–54.

(8)     Hamilton, G. and Bakker, D. (2002). In: Proceedings of the 8^th National Conference and Workshop on the Productive Use and Rehabilitation of Saline Lands (PUR$L), Promaco Conventions Pty Ltd, pp. 105–114.

(9)     Epstein, E., Norlyn, J.D., Rush, D.W., Kingsbury, R.W., Kelley, D.B., Cunningham, G.A. and Wrona, A. (1980). Science, 210, 399–404.

(10)   Colmer, T.D., and Islam, A.K.M.R. (2002). In: Proceedings of the 8^th National Conference and Workshop on the Productive Use and Rehabilitation of Saline Lands (PUR$L), Promaco Conventions Pty Ltd, pp. 241–247.

(11)   Norman, H.C., Dynes, R.A. and Masters, D.G. (2002). In: Proceedings of the 8^th National Conference and Workshop on the Productive Use and Rehabilitation of Saline Lands (PUR$L), Promaco Conventions Pty Ltd, pp. 59–69.

(12)   Barrett-Lennard, E.G., Malcolm, C.V. and Bathgate, A. (2003). Saltland Pastures in Australia – a Practical Guide, Second Edition. Sustainable Grazing of Saline Lands (a sub-program of Land, Water and Wool), 176 pp.

(13)   Warren, B.E., Bunny, C.J. and Bryant, E.R. (1990). Proceedings of the Australian Society of Animal Production, 18, 424–427.

(14)   Barrett-Lennard, E.G. and Malcolm, C.V. (1999). Australian Journal of Experimental Agriculture, 39, 949–955.

(15)   Stirzaker, R.J., Cook, F.J. and Knight, J.H. (1997). In: Proceedings of Workshop on Agroforestry for Sustainable Land-use: Fundamental Research and Modelling, Temperate and Mediterranean Applications, Montepellier, 23–29 June, pp. 169–173.

(16)   Barrett-Lennard, E.G., Griffin, T. and Goulding, P. (1999). Assessing areas of saltland suitable for productive use in the wheatbelt of WA: a preliminary assessment for the State Salinity Council, Perth.

(17)   O’Connell, M. and Young, J. (2002). In: Proceedings of the 8^th National PUR$L Conference and Workshop, Promaco Conventions Pty Ltd, pp. 223-232.

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Citation: Barrett-Lennard, E., Hamilton, G., Norman, H. and Masters, D. (2004). Novel multi-disciplinary approaches suggest profitable and sustainable farming systems for valley floors at risk of salinity. In. "Salinity Solutions". Proceedings of the Salinity Solutions Conference " Working with Science and Society" 2 - 5 August 2004, Bendigo, Victoria.
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