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UNIT 4

Plant and animal performance

 

4.4  Weed risk

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Naturally occurring saltland often supports a unique floral community and most state governments have laws to protect these areas and their plants. Such naturally occurring saltland is called ‘primary dryland salinity’ and this makes up the vast bulk of saltland in Australia. There are perhaps 30 million hectares of primary salinity along the coastline, in the farming zone, and in the arid interior. It is only land that has become salinised as a result of human activity such as irrigation or land clearing (termed secondary salinity and making up perhaps 2 million hectares), or natural saltland that has been overrun by introduced species, that should be considered for a return to productivity.

Perennial vegetation plays a key role in tackling dryland salinity, but we must make sure that in solving one environmental problem we don't cause another. Environmental weeds invading bushland and watercourses are a major threat to biodiversity, displacing native flora and degrading habitats for native fauna. If those environments are salt-affected, it is even more likely that a salt-tolerant weed will thrive in the absence of significant competition.

Tall wheatgrass has been identified as a particular threat in some regions, such as the higher rainfall areas of  Victoria and is considered to be of such a risk that it is no longer recommended in Victoria. In South Australia escapes have been largely confined to roadsides and management techniques have been devised to minimise the spread.

Salt-tolerant plants introduced to saltland grazing systems can pose a weed risk to adjacent wetlands and areas of native vegetation, especially if the adjacent areas are also saline. On the other hand, such salt tolerant plants generally do not pose a significant weed risk to agricultural crops and pastures growing in adjacent, non-saline areas. Salt-tolerant plants tend to uncompetitive (ie non-weedy) with agricultural plants in the absence of salinity.

Some Melilotus species contain secondary compounds (coumarins) that can be toxic to stock or taint contaminated grain crops. Melilotus albus, the low coumarin species likely to be of interest to graziers when it is commercially released, has shown very little potential to become a weed.

The Future Farm Industries CRC is researching salt-tolerant wheat. If this crop becomes an option on salt-affected land, then it is highly likely that the saltland plants, described as ‘non-weedy’ above could be highly competitive with salt-tolerant wheat.

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