Land Degradation

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Land degradation has been associated with the Murray-Darling Basin throughout its human occupancy. The Aboriginal Australians certainly left their mark, though nothing like as rapidly as did the European settlers (see Land and its Changing Use). There is evidence to indicate that, in many parts of the Basin, problems emerged within no more than 20 to 30 years of the arrival of the first white settlers. For example, in the early 1870s, the British writer and traveller, Anthony Trollope, commented on the decline and disappearance of saltbush with sheep grazing in the Riverina (Edwards & Joyce 1967, 329). In 1899, a New South Wales politician, Ernest Millen, wrote of the devastation of the western plains by rabbits and over-grazing:

The roots of trees spread out like cobwebs, exposed by the denudations of the wind. Where the butts of salt and other bushes remained, they served to keep a little soil around them, but between the wind had cut down to the underlying cement-like clay (quoted in Bonyhady 1995).

Other writers made similar observations (see Powell 1993). In 1901, a Royal Commission was set up to investigate the problems of tenants in the Western Division of New South Wales.

Land degradation can be defined in many ways (Table 1). In brief, it is any change in the land that reduces its condition or quality and hence its productivity or productive potential. It occurs whenever the natural balances in the landscape are changed by human activity, through misuse or overuse (Williams 1991; Cocks 1992). Put another way, it is the result of using land and other resources beyond their capability. There are obviously many causes and land degradation takes many forms. One of the most serious, land salinisation, is considered in Water and Land Salinity. In turn, most forms of land degradation contribute to the impairment of the Basin's water resources (see Water Quality ).

At the present time, comprehensive data on the full areal extent and severity of the Basin's land degradation problems are not available. However, leaving aside such areas as national parks, it is unlikely that any part of the Murray-Darling Basin is free of one or more problems. Whilst it is impossible to give a complete overall picture, various indications of the extent and severity of the problems have been provided. One such study was undertaken in New South Wales in 1987-88, though, as it states, it has to be used with caution (Graham et al. 1989). The same comment applies to data collected by the Australian Bureau of Statistics in its annual Census of Agriculture, under the category of 'Land not available for grazing/crops due to degradation', with such data being a significant under-estimation of the overall problem.

No form of land degradation can be regarded as unimportant (ABS 1996). A number now regarded as very serious were barely recognised only a few years ago. Nonetheless, at the present time, some clearly stand out. This page is concerned with problems other than those caused by salinity.

Land degradation at its most spectacular

Of particular concern is the fact that many of the degradation problems stem from an inadequate or totally absent vegetation cover. Nowhere is this more evident than with soil erosion by wind and water, which provides some of the most visible examples of land degradation, though some of the more obvious forms, such as gullies and landslides, are not necessarily the most serious. Far more significant, especially in terms of the impact on land productivity, is the stripping of topsoil by wind and rain. There are times when such losses can be barely visible, but the biggest ones occur in severe events, the occasional torrential rains and severe wind storms.

Wind erosion

Wind erosion is a major problem throughout the Basin, especially as it involves the loss of the finer soil particles. This also has the effect of reducing the soil's nutrient levels and its ability to retain moisture for plant growth (Graham et al. 1989, 10). It is a particular feature of the drier parts of the Basin, especially those areas with sandy soils, and where repeated disturbance of the soil surface, by cultivation or stock, breaks down the soil particles into sizes that are more susceptible to wind erosion. In such areas, whenever the soil is not protected by plant cover, because of over-grazing, frequent cultivations or leaving the land fallow, there is the danger of wind erosion.

The drier parts of the Basin include many of the grain growing areas, the wheat-sheep belt, such as the light sandy and loamy soils on the Central and South-Western Slopes of New South Wales, the Mallee lands in western Victoria and adjoining areas of South Australia and New South Wales, as well as the arid and semi-arid rangelands of western New South Wales and Queensland.

In Victoria, an estimated 2.6 million ha (2.5 per cent of the Basin) of cropland is potentially subject to wind erosion, while in NSW, grazing lands are mainly affected with the total area at risk being 21.3 million ha (20 per cent of the Basin) (MDBMC 1987, 43).

It is not only the areas from which soil and nutrients are removed that are affected. When the material is dropped, crops can be buried, roads and fences covered, and drains and culverts filled.

With wind erosion, storm events take on particular significance and some places are frequently affected by them. For example, between 1960 and 1984, 75 dust storms were recorded at Wilcannia and 74 at Mildura. However, perhaps the most publicised dust storm of recent years was the one that carried huge quantities of topsoil from the Mallee lands of Western Victoria that enveloped Melbourne in February 1983.

Water-induced erosion

Water-induced soil erosion takes many forms. Gully erosion occurs in the uplands on the margins of the Basin, in both arable and pastoral farming areas. Sheet and rill erosion is found on the Western Slopes of NSW and other areas where arable farming is undertaken, especially for cereals. There are particular problems in the arable farming areas of the Darling Downs.

Water erosion from cropland in Victoria is estimated to affect 1 million ha, most of it in the Basin. Another 4.8 million ha (about.5 per cent) of grazing land is affected and most of this is also within the Basin. In NSW, 15 million ha of cultivation land and 16.3 million ha of grazing land (14 per cent and 15 per cent respectively) are subject to water and wind erosion. The actual area affected in any one year, however, would be significantly less than the area at risk (MDBMC 1987, 45). ). Thirty percent of the Murray-Darling Basin has moderate or high density (i.e. > 1 km/km²) of gully erosion, most of which are not actively forming but remain significant suppliers of sediments to rivers (http://audit.deh.gov.au/ANRA/agriculture/docs/national/Agriculture_Soil_Erosion.html).

The quantities of soil lost through water erosion can be considerable. Soil loss rates from erosion typically average several tonnes per hectare per year, various studies indicating 2 tonnes per ha in Wagga area, 4-8 tonnes in Gunnedah, and over 20 tonnes per hectare in the degraded rangelands. It also has to be remembered that most of the soil nutrients are stored in the top few centimetres of the soil profile, that is, the part of the profile from which the soil is lost.

One measure to reduce erosion is strip-cropping, introduced to Queensland's Darling Downs in 1956 by a Pittsworth farmer, Hector Todd, and now a characteristic feature of arable farming on the Downs. As with wind erosion, the maintenance of a vegetative cover is of critical importance, including such practices as leaving stubble on the surface, thus avoiding leaving the ground bare and prone to erosion from heavy rainfalls. However, specially modified techniques and equipment have had to be devised to cultivate and sow crops through stubble. For example, a small group of farmers in the Glengallan district near Warwick, also on the Darling Downs, has developed machines to plant seed into stubble without ploughing.

Both wind and water contribute to some forms of soil erosion, especially scalding. Scalds are bare unproductive areas from which the topsoil has been removed; they can cover areas of a few square metres to hundreds of hectares (Graham et al. 1989, 16-17). The main affected areas are on the Riverine Plain, along the Bogan River around and north of Nyngan, and in the Darling-Culgoa River areas north of Bourke.

Land degradation that is often unseen

Some forms of land degradation are not so spectacular as many forms of wind and water-induced erosion. They can often remain unseen except by the specialist and those suffering their consequences. Yet it is becoming increasingly clear that they are probably the most costly and serious of the land degradation problems in the Murray-Darling Basin and many other parts of Australia. They are having a particular impact on soil chemistry and result in lowered soil fertility (Williams 1991; Hamblin & Kyneur 1993). Surface and subsoil acidity exists in all Australian States. It has an estimated total area of eight to nine times that affected by dryland salinity. The largest areas of acid soils are in New South Wales, Western Australia, Victoria and Queensland (http://audit.deh.gov.au/anra/agriculture/docs/national/Agriculture_Soil_Deg.html).

Acid soils, or those suffering ‘induced acidity’, have a pH of less than 5.6*. The yields of most plants begin to decline when the pH is 5.0 or less and subsoil acidification can occur. Australia-wide, some 50% of agricultural land (approximately 50 million hectares) have surface pH values less than or equal to 5.5. A further 12 to 24 million hectares are extremely to highly acidic with pH values less than or equal to 4.8 (below optimum for the acid-sensitive agricultural plants). The geographical distribution of the affected areas is not accurately known, but acid soils are a particular problem in the higher rainfall areas on the eastern and southern margins of the Basin (Figure 1 and Table 2).

Figure 1 Aspects of land degradation in the MDB (source: Land Assessment and Policy Unit, CRCSLM; Spencer et al. 1996; Noble 1997)

Induced soil acidity is a problem that has only emerged since the mid-1970s, but it is now seen as one of the most serious of all problems and one of the most neglected (AACM International 1995). (http://audit.deh.gov.au/anra/agriculture/docs/national/Agriculture_Soil_Deg.html).

High acidity levels generally result from repeated applications of ammonia-based fertilisers without liming, and the growing of pastures based on legumes such as subterranean clover. Such pastures tend to die off in summer, and with nothing to use the nitrogen, it leaches through the soil, increasing soil acidity instead of being used for plant growth. However, soil acidity is not confined to areas under annual pastures or crops. As acidity increases, certain elements that are important to plant nutrition become less available, while aluminium and manganese, which are toxic at high levels, become more readily available. Because it often takes twenty to fifty years for plant yields to decline, it is only relatively recently that farmers have realised that their management practices are resulting in acid soils.

Since the Second World War, there has been extensive growing of improved pastures over wide areas of agricultural land in Australia. The so-called ' super-sub' revolution, whereby native pastures were replaced by sub-clover dominant pastures fertilised with superphosphate, has been an important contributor to acidity (Dalziell & Poulter 1992 http://audit.deh.gov.au/anra/agriculture/docs/national/Agriculture_Soil_Deg.html).

In other words, "The whole chemistry of the soil is being changed by the farming system that has been imposed" (Williams 1991).

Even though soil acidity is reducing crop yields (Table 3), it is not perceived as a priority issue by many farmers, except for those with high value agricultural systems. At the same time, many cannot afford the required remedial measures. Lime is required in large amounts (1–5 t/ha) and it may have to be transported a long way from where it is mined and hence is expensive. Further, profitability in some farming sectors is declining (e.g. in Queensland low sugar prices have dramatically reduced lime use in recent years); and surface applications of lime to correct subsoil acidity may take many years before improvements are realised. Even where soil acidity and the benefits of lime applications are recognised by farmers, liming may not be tenable because massive applications of lime are required to reduce prevailing acidity levels.

High value industries (e.g. horticulture), where fertiliser is a small proportion of the total operating cost, are more likely to use lime compared to broadacre dryland farming industries. Broadacre industries are often located a long way from where the lime is mined and have lower profit margins, increasing the relative costs of lime use. At the same time, their farming practices induce acidification over larger areas of land. Including cartage and spreading costs, an application of 2.5 t/ha, costs will vary from $145 to $200 per hectare in Queensland to $52 to $110 per hectare in Western Australia and $45 to $100 per hectare in South Australia (NLWA 2001).

There is increasing evidence that cultivation is resulting in depletion of organic matter and nutrients. Among other things, this is contributing to declining protein levels in wheat, while "gains in productivity through improved agronomy and plant breeding are barely keeping up with the deteriorating soil fertility" (Williams 1991). There is also depletion of the biological properties of soils due to cultivation and the build-up of pesticides, herbicides and other chemicals.

Another problem often associated with cultivation and grazing is the deterioration of soil structure, shown by compaction, surface crusting and sealing, loss of porosity, and loss of organic matter and biological activity (Graham et al. 1989, 20-21; Williams 1991). The frequent use of heavy machinery can cause compaction, as with the deep clay soils in some of the cotton growing areas. Frequent cultivation can produce a plough pan at the base of the cultivation layer, limiting the penetration of plant roots and affecting water infiltration patterns. Not surprisingly, such problems are found throughout the main arable farming areas of the Basin. They all contribute to lower crop yields (Hamblin & Kyneur 1993; https://www.epa.qld.gov.au/register/p01258bb.pdf).

Problems such as soil acidity and soil structural decline are reversible. Where farmers take the required remedial action, they are main beneficiaries. However, farmers need the necessary resources in order to undertake the remedial action, and they have to be able to see the benefits of such investment in the medium to longer term. For many farmers, this may not be possible.

What has been outlined above presents a complex mix of situations, with many of the measures that have been taken to improve agricultural activity now creating serious problems.

* pH is a measure of the acidity or alkalinity of a substance, such as soil or water. On a scale of 1 to 14, neutral substances have a pH of 7; for acidic substances, the pH ranges from 1 to 6, for alkaline substances, from 8 to 14.

Land degradation that is often overlooked

There are forms of land degradation that are often overlooked, except by those who are directly affected, even though they are frequently very visible. Some are now receiving greater attention.

As indicated in the introduction to this page, in little more than 100 years, much damage has been done by grazing in the rangeland areas of the western parts of the Basin. It is now a major problem. For example, over-grazing has resulted in the loss of valuable edible perennial bush, especially species of saltbush and bluebush, in areas extending west from the Riverine Plain. Much of the decline in productivity is due to the loss of the bladder saltbush (Atriplex vesicaria) and old man saltbush (Atriplex nummularia) and their replacement by less productive species (Jacobs 1988; Graham et al. 1989). The mallee lands are also suffering from similar problems of overgrazing. Confirmation that such problems can be reversed is being provided by successes being achieved, even in drought conditions, by some sheep graziers in the western and north-western parts of the Basin who are planting and carefully managing saltbush and other native species (Francis 1995). There has been a renewed interest in saltbush in recent years for a variety of reasons. These include use as a drought fodder, to reduce water tables, erosion control, and seed and seedling production. Because saltbush can survive long periods of drought it is being seen as a possible source of drought reserve fodder. Saltbush has received a lot of attention from Victorian Landcare groups as a plant to help in rehabilitation projects. Because of saltbush’s deep root system and salt tolerance it is ideally suited to planting on saline affected areas and to aid in erosion control (DPI, 2000).

Rural tree decline is becoming one of the most serious problems in many parts of the Basin, for both agriculture, biodiversity decline, and the environment (Glanznig et al. 1995; http://www.clw.csiro.au/heartlands/publications/general/040729final.pdf). The individual and small groups of trees that remain are remnants of earlier ecosystems and they are not regenerating (LWRRDC 1995, 32-34; Anon. 1996, 6; Francis 1997). This is reflective of loss of forest communities across Australia, with the most recent NCAS assessment showing deforestation in 2004 to be around 400,000 hectares across Australia. While this represents a very small proportion of Australia’s total native vegetation cover, the concentration of this loss of vegetation in particular areas suggests regional and local impacts on terrestrial biodiversity may have been significant ( http://www.environment.gov.au/erin/nvis/publications/pubs/major-veg-summary.pdf).

There are many causes of eucalypt dieback and other native tree decline. Remnant vegetation cannot cope with the consequences of the intensification of land use, such as arable farming and grazing activities, salinisation, weeds, disease and insects. In the absence of any or inadequate understorey, young trees cannot become established to replace the older ones. "In terms of biotic erosion, the loss of these remnants is far more critical than indicated by their small areas" (Graetz et al. 1995, 83).

Another major problem for graziers is woody weed infestation (Figure 1), over much of the arid and semi-arid Western Division of New South Wales and areas to the north in Queensland, especially the Warrego and Paroo catchments, but also as far east as the Waggamba Shire, the mulga lands (Barson et al. 1993, 17-19). In 1982 it was estimated that in New South Wales alone, 20 million hectares were affected or liable to invasion (Hassalls and Associates, 1982). Woody weeds are native species, growing up to 3 metres high, that have increased because of reduced fire frequency and their unpalatability to livestock. Some species are inedible. Woody weeds compete with and exclude other plants. Combined with overstocking, this can result in soil erosion. Control of woody weeds is difficult and costly.

Other weeds are taking their toll on agriculture in other parts of the Basin. They include serrated tussock (Nassella trichotoma), a native of South America, now a particular problem in south-eastern New South Wales, St John’s wort (Hypericum perforatum), and Scotch thistle (Onopordum acanthium). Like other weeds, they are difficult and costly to control and eliminate.

Feral plants are now affecting many of the Basin's ecosystems and, in the process, eliminating many native flora and fauna species (ANCA 1995). For example, prickly acacia (Acacia nilotica), a native of Africa and India, is taking over large areas of the Mitchell grasslands, rendering the land almost impenetrable and useless.

The costs of land degradation

In the absence of comprehensive data on the extent and severity of the various forms of land degradation, it is obviously impossible to provide an accurate indication of their costs. A variety of indicators are available, compiled on different bases and by different sources. Whilst there may be no precise agreement, they all indicate that the costs of land degradation are enormous and that they are increasing . One of the first compilations of figures is given in Table 4. In 1993, the annual cost of lost agricultural production due to land degradation was put at over $1.4 billion per annum, approximately 6 per cent of the gross value of Australian agricultural production (see Agriculture) (Table 5) (LMTF 1995, 27; Karssies & East 1997). Another study put losses due to soil structure decline in the MDB at $144 million per year. A recent NSW study, covering areas of the state primarily within the Basin, put some of the costs as follows (1987-88 dollars): acidity on the tablelands, $64 million; gully erosion in the wheat-sheep zone, $405 million; and woody shrub infestation in the western zone, $289 million (CALM 1995). An encouraging outcome from this study was that the benefit-cost ratios of treatment for these problems were all positive, being 1.1, 1.9 and 1.7 respectively.

The costs of land degradation cannot be considered simply in terms of losses of agricultural and other production. There are other costs, including reduced land values, detrimental aesthetic impacts, detrimental impacts on natural ecosystems and native flora and fauna, and costs of remedial action where these are feasible.

Combating the problems of land degradation

Much work to combat land degradation continues to be undertaken by many individual farmers and the various state government agencies. Some measures have been in operation for many years, such as those to combat soil erosion. Others are more recent.

At the Australia-wide level, the National Landcare Program, established in 1989 and since 1997 one of the activities of the Natural Heritage Trust (NHT) (Anon. 1997; http://www.daffa.gov.au/natural-resources/landcare/national-landcare-programme), is involving large numbers of farmers and other people, working as community groups to tackle local problems and to bring about improvements to land and water resources. All kinds of issues are being addressed, including soil erosion, soil acidity, streambank erosion, declining water quality, remnant vegetation, urban issues, and habitat loss. Another NHT program is Bushcare, through which community groups, land users, government and industry are working together to protect native bushland, increase and improve tree-planting activities, and promote the use o f native vegetation into farming systems.

At both government and community levels, considerable work is now being undertaken through the Integrated Catchment Management Policy of the Murray-Darling Basin Ministerial Council. Some of the work is Basin-wide, such as studies of land management to reduce nutrient movement from catchments, the improved management of soils, and the establishment of basin-wide vegetation and land-use data sets. Other projects are more regional in their focus, such as sustainable land management in the Murray Mallee, Chowilla Floodplain resource management, and pesticide use in the cotton industry. At the local level, large numbers of community-based projects are being undertaken, many of them in the context of integrated catchment management. Examples include local action plans for natural resource management in the South Australian Murray Valley, catchment planning for sustainable land use in the Bremer catchment, greening the Wimmera catchment and Numeralla River catchment restoration. Especially with the local and regional programs, the emphasis is on integrated catchment management in all parts of the Murray-Darling Basin.

Conclusion

As yet, the problems of land degradation outlined in this page have not received the same attention as land salinisation, nor have they received comparable levels of public funding. This is in spite of the fact that there are indications that some of these are actually or potentially as severe or worse (LWRRDC 1995). At different times and in different places, land degradation problems are exacerbated by drought, as in the northern parts of the Basin and the Monaro in the mid-1990s.

There is no doubt about the serious nature of land degradation throughout the Murray-Darling Basin. As has been indicated, two issues alone, namely soil acidification and dryland salinisation, pose serious threats to agriculture within the Basin, as well as much of the rest of Australia. Soil acidification in particular also highlights the danger of solving one problem and, sooner or later, creating another.

References

ABS (1996): Australians and the Environment. Catalogue No. 4601.0. Australian Bureau of Statistics, Canberra.

AACM International (1995): Social and Economic Feasibility of Ameliorating Soil Acidification: a national review. Land and Water Resources Research and Development Corporation, Canberra.

ANCA (1995): Environmental Weeds in Australia. Australian Nature Conservation Agency, Canberra.

Anon. (1996): Managing Australia’s Vegetation: a community perspective. Greening Australia, Canberra.

Anon. (1997): Natural Heritage Trust: a better environment for Australia in the 21^st Century. Environment Australia, Canberra.

Barson, M. et al. (1993): Opportunities for Regional Rural Adjustment. Bureau of Resource Sciences, Canberra.

Bonyhady, T. (1995): "Cracks in the canvas". Sydney Morning Herald, September 23.

CALM (1995): Conservation or Degradation of Land: what is the cost? Department of Conservation and Land Management, Sydney.

Cocks, D. (1992): Use With Care: managing Australia's natural resources in the twenty first century. New South Wales University Press, Sydney.

Dalziell, I. & Poulter, D. (1992): The economics of land degradation: the case of acid soils. 36th Conference of the Australian Economics Society, ANU, Canberra.

DPI (2000): Agriculture Notes – Saltbush. Farm Diversification Information Service, Victorian Department of Primary Industries, Bendigo. ISSN 1329-8062.

Edwards, P.D. & Joyce, R.B. (Editors)(1967): Anthony Trollope's Australia. University of Queensland Press, St. Lucia. First published 1873 in Australia and New Zealand by Chapman & Hall, London.

Francis, J. (1997): "Understorey helps to halt dieback". Australian Farm Journal Sustainable Agriculture, September, 14-15.

Francis, P. (1995): "Grazing strategy combines profit and sustainability". Australian Farm Journal Wool, November, 19-21.

Glanznig, A. et al. (1995): Native Vegetation Clearance, Habitat Loss and Biodiversity Decline. Biodiversity Series Paper No. 6. Department of Environment, Sport and Territories, Canberra.

Graetz, R.D. et al. (1995): Landcover Disturbance over the Australian Continent: a contemporary assessment. Biodiversity Series Paper No. 7. Department of Environment, Sport and Territories, Canberra.

Graham, O.P. et al. (1989): Land Degradation Survey, New South Wales 1987-1988. Soil Conservation Service of New South Wales, Sydney.

Hamblin, A. & Kyneur, G. (1993): Trends in Wheat Yields and Soil Fertility in Australia. Bureau of Resource Sciences / Australian Government Publishing Service, Canberra.

Hassalls and Associates (1982): An Economic Study of the Western Division of New South Wales, Report commissioned by the NSW Western Lands Division, Sydney.

Jacobs, S. (1988): A Graziers Guide to the Saltbush Plains Country of Western New South Wales. Soil Conservation Service of NSW, Sydney.

Karssies, L. & East, J. (1997): "Australia’s cereal producing lands: the state of the resource base". Agricultural Science, 10(2), 33-39.

LWRRDC (1995): Data Sheets on Natural Resource Issues. Occasional Paper No. 06/95. Land and Water Resources Research and Development Corporation, Canberra,

LMTF (1995): Managing for the Future: report of the Land Management Task Force. Rural Division, Commonwealth Department of Primary Industries and Energy, Canberra.

MDBMC (1987): Murray-Darling Basin Environmental Resources Study. Murray-Darling Basin Ministerial Council, Canberra.

Noble, J.C. (1997): The Delicate and Noxious Scrub: CSIRO studies on native tree and shrub proliferation in the semi-arid woodlands of Eastern Australia. CSIRO Division of Wildlife and Ecology, Canberra.

Powell, J.M. (1993): The Emergence of Bioregionalism in the Murray-Darling Basin. Murray-Darling Basin Commission, Canberra.

Spouncer, L.R. et al. (1996): Allocation of Acidity Profile Classes to Atlas of Australian Soils Mapping Units. CSIRO Division of Soils Technical Report 20/1996. Land Assessment and Policy Unit, CRC for Soil and Land Management, Adelaide.

Williams, J. (1991): "Search for sustainability: agriculture and its place in the natural ecosystem". Agricultural Science, 4(2), 32-39.

Table 1 Major land degradation problems in the Murray-Darling Basin

Source: MDBMC 1987.

Table 2 National and State areas (million hectares) of surface soil (0 - 10 cm) pH (measured in calcium chloride) based on information from Australian Soil Resources Information System (first number) and commercial laboratories (second number) (source: http://audit.deh.gov.au/anra/agriculture/docs/national/Agriculture_Soil_Deg.html). 

^aInclusive
^bNumbers rounded to 0.0 vary from 0.01-0.03.
^cTotal Values may be slightly different to adding up the values in the table because of rounding errors.

Table 3 Effect of soil pH on plant yields in Wagga Wagga, NSW¹ 

¹ Based on moderately responsive soil
Source: quoted in Dalziell & Poulter 1992.

Table 4 Costs of land degradation, c.1987: estimated value of annual yield losses

Source: MDBMC 1987, 54.

Table 5 Estimated annual value of lost agricultural production due to land degradation

Source: LMTF 1995, 27