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Rehabilitation of Open Cut Coal Mines Using Native Grasses: Management Guidelines

Open Cut » Environment

Published: July 99Project Number: C6004

Get ReportAuthor: Charles Huxtable | Hunter Valley Environment Group, Department of Land and Water Conservation

A two year project was undertaken to develop practical management techniques and guidelines for the use of native grasses in open cut coal mine rehabilitation in the Hunter Valley. The project aimed to enhance and expand on the findings of a preceding three year project which had identified several native grasses with promise for mine rehabilitation.

The most promising yearlong green native grasses included five species of Wallaby Grass and Plains Grass, while the best warm season species included Queensland Bluegrass, Windmill Grass and Couch. A range of other species were also successfully established from sown seed or from the soil seedbank.

Quality of topsoil was found to be a critical factor in the establishment success of native grasses with key factors including the chemical and physical attributes of the soil and the seed bank. Slightly acidic, loamy, non-saline topsoil collected from areas of native pasture and freshly spread on rehabilitation sites resulted in good establishment of a wide range of species from both sown seed and from seed in the soil seedbank.

While having initially very low establishment rates, native grasses sown on raw spoil have survived, proliferated and increased their groundcover by seeding and vegetative growth, which was largely attributable to lack of weed competition. On topsoil areas of comparable age, uncontrolled competition from vigorous grasses and weeds has out-competed the native grasses over a period of four and a half years.

All native grasses tested responded to the addition of conventional fertiliser or biosolids with higher dry matter production, however in some cases germination was reduced. Plant growth in some raw spoil types was improved significantly by fertiliser or biosolids, however was not as high as with topsoil. In a pot trial, crude protein levels were higher in all native grasses than Rhodes Grass of a similar age, but were variable in the field.

A review of native grass seed handling technology showed there are a range of machines available for harvesting, cleaning and sowing which are suited to the special characteristics of native grass seed. The situation is likely to improve in the next 5-10 years as this technology improves.

Recommendations are made for the use of native grasses in mine rehabilitation relating to topsoil selection and stockpiling, sowing into raw spoil, landscape position, recommended species, seed supply and provenance, sowing rates and techniques, multi-phase sowings, fertiliser application, weed control and ongoing management options.

Recommendations for decommissioning criteria relating to native grasses are made, relating to seasonality of species, forage value, species diversity, groundcover and stability over time, suggesting that monitorings of sites is necessary for a minimum period of four years.

The future use of native grasses in open-cut coal mine rehabilitation in the Hunter Valley will depend on the desired final land use of the rehabilitated minesite, the commitment of mining companies to their inclusion in the revegetation program, community perceptions and expectations, the support of relevant government agencies and further research into the management of native grasses

This comprehensive final report details the abovementioned findings.

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