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From moonscape to magic

By | February 4, 2013 at 9:39 am | No comments | Provisioning

In February 2004 Redland Shire Council (now Redland City Council), in South East Queensland, transformed an area of salt-affected parkland to a lush carpet of green. A 0.2 ha demonstration area of parkland was planted with seashore paspalum (Paspalum vaginatum) at Birkdale. Since then, the council has invested significant funds in successfully turfing other similarly ‘impossible’ park areas with seashore paspalum.

Urban salinity can arise for different reasons in different places. In inland areas such as southern New South Wales and the Western Australia wheatbelt, the usual cause is rising groundwater bringing salt to the surface. In coastal sites, salt spray or periodic tidal inundation can cause problems.

In Redland Shire´s case, the issue was compacted marine sediments (mainly mud) dug up and dumped to create foreshore parkland in the course of artificial canal developments. At Birkdale, this had created a site that was both strongly acid (pH 3.3-4.7 surface, 2.9-4.4 subsoil) and saline (as measured by electrical conductivity: ECe 2.8-41.1 decisiemen/metre (dS/m) surface, 4.2-46.7 dS/m subsoil. For comparative purposes, seawater is 54 dS/m).

Not surprisingly, bare saline scalds were interspersed by areas of unthrifty grass. The dilemma was, how could this be grassed to give an aesthetically pleasing and useful space for locals and visitors?

Researching the problem

The Horticulture Australia Ltd research project Amenity Grasses for Salt Affected Parks in Coastal Australia provided the answer. The research was conducted by the then Department of Primary Industries and Fisheries (now DEEDI) turf research team from nearby Redlands Research Station, with financial support from Horticulture Australia Ltd and Redland Shire Council.

Trial plots of a range of turfgrasses were planted on similar salt-affected parkland at Raby Bay. These studies identified Paspalum vaginatum (seashore paspalum) as the most salt-tolerant of the commercially available turfgrasses.

Armed with this information, Redland Shire Council then set about grassing large park areas at Birkdale, and later Raby Bay, with seashore paspalum. Separate glasshouse trials looked at the salt tolerance of various turfgrass cultivars. Finding a salt-tolerant grass is no ‘silver bullet’ or easy solution to salinity problems, but it does buy time to implement sustainable long-term management practices.

The selection of a salt-tolerant grass was just the first step in the integrated process of site preparation, establishment and management required to successfully revegetate saline areas.

These various practices included annual slicing or coring in conjunction with gypsum/dolomite amendment and light topdressing with sandy loam soil (to about 1 cm depth), adequate maintenance fertiliser, and irrigation scheduling to maximise infiltration and minimise run off.

Prior to rolling out full sod, the ground was sliced to relieve compaction, gypsum applied to improve soil structure and calcium status, and sandy loam (up to 5 cm deep) laid under the turf. Regular leaching irrigation was applied to flush salts below the root zone.

The council´s maintenance program on these revegetated parks now includes annual solid tyne aeration, soil amendment and topdressing, plus regular fertiliser applications.

Using appropriate management strategies, coupled with the proper choice of turfgrass based on scientific research, stable, complete grass cover has now been established on various salt-affected reclaimed foreshore sites in the new Redland City.

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