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| An idealised vision of Millers Point looking north-westward up the Harbour in 1823. The little bays and headlands were later obliterated, but the Barangaroo development will recreate the feel of the original..
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Recreating Barangaroo soils
The NSW Government’s plans to redevelop the disused container terminal at Darling Harbour into the Barangaroo site include the creation of a 6 ha park at the northern end. Instead of taking the easy option and throwing some soil and trees at the site, the Barangaroo Delivery Authority is showing foresight and sensitivity to Sydney Harbour by planning to recreate the landscape that existed at Millers Point in 1788.
The Headland Park will be landscaped with sandstone and local native plants to complement and blend with the surviving natural headlands, including Mrs Macquarie’s Point, Balls Head, Goat Island and Ballast Point.
SESL has been involved in the plans to recreate the landscape from the beginning of the project.
Remaking the original
Sandstone quarried on site for the development of Barangaroo South will be used to recreate the tidal foreshore. Some of the sandstone will be crushed to create facsimile soils.
Local native species will be planted. While the nutrient requirements, particularly phosphorus (P), of most of the species have not been researched, many of the species to be used may show adverse reactions to P and iron (Fe) interactions in common commercial soil mixes (Handreck 1991, 1997). So the native soils need to be recreated.
DIY soil
Very little is known about how to create facsimile sandstone soils. SESL has begun trials to test different formulations. To guide the trials, SESL sampled soils from Mangrove Mountain and Somersby. These soils were acidic, with low P and calcium (Ca) contents. Analysis of the biomass (living plants and leaf litter) confirmed the low P and Ca.
The first trial, now finished, used soil made from equal parts crushed sandstone and washed sand with either 10% or 30% compost made from municipal garden waste (from the green-waste bins that most of us have). Species included silver banksia (Banksia marginata), hill banksia (Banksia spinulosa var. collina), sweet-scented wattle (Acacia suaveolens), scribbly gum (Eucalyptus haemastoma) and forest red gum (Eucalyptus tereticornis); all are common in the Sydney area. Apart from extra nitrogen supplied as urea, the compost supplied all the nutrients.
Surprisingly, all plants grew better with 10% compost. Some of these still showed P toxicity and Fe deficiency, due to a high pH.
A second trial is now being conducted using 5% and 10% compost and acidification with iron sulphate to fine-tune the formulation.
Further reading
Handreck KA. 1991. Interactions between iron and phosphorus in the nutrition of Banksia ericifolia L. f. var. ericifolia (Proteaceae) in soil-less potting media. Aust J Bot 39: 373–384.
Handreck KA. 1997. Phosphorous requirements of Australian native plants. Aust J Soil Res 35: 241–289.
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