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The re-use of agricultural land after open-cut coal mining

M.J. Russel and B.R. Roberts

School of Applied Science, D.D.I.A.E., c/- Post Office, Darling Heights, Toowoomba, 4350

Open-cut coal mining in sedimentary basins of eastern Australia is starting to produce appreciable areas of spoil which require revegetating as part of a sound land-use programme. The sediments, laid down since the Upper Permian, are generally argillaceous with high total soluble salts (often exceeding 1.0 mS per cm) which usually include high levels of sodium chloride, a high pH (sometimes exceeding 9.0) and rather low levels of phosphate and nitrate available to plants.

The Amax Iron Ore Corp. (Coal Division) has an exploratory box-cut at its Commodore No. 1 site near Millmerran. This has a heap of spoil derived from Walloon coal measures, covering 1 ha in area. An experiment to investigate revegetation of this spoil was planted on 18 December, 1977. Three test grass species were selected, partly on the basis of a review of pasture agronomy in the area. These were Rhodes grass, green panic and buffel. The legumes siratro and lucerne were sown in all plots. -superphosphate and ammonium sulphate were each applied at 0, 100 and 400 kg ha-1. Experimental design was 33 factorial with three replicates. Plot size was 4 m x 4 m.

A count of emerged seedlings was made 14 weeks after sowing, and plant cover was assessed twelve months after sowing (Table l). Four 50 cm square quadrats were sampled in each plot.

TABLE l. The effects of two fertilizers on mean densities and mean percentages of cover of three grasses on two sampling occasions on spoil at Millmerran.

The apparent lack of response of Rhodes grass and buffel seedling numbers to application of nitrogenous fertiliser is masked by likely competitive effects from siratro and lucerne seedlings. By the second summer all three grasses had responded to the nitrogen as indicated.

The apparent lack of response of buffel grass to superphosphate persisted into the second summer. This lack of response is unusual, and currently unexplained.

However, this experiment suggests that Rhodes grass and green panic will give a cover on the spoil type investigated provided adequate amendments of nitrogenous and phosphatic fertilisers are used. This cover is roughly equivalent to that obtained in the first season of establishment on spoils in the Bowen Basin where increases to 60% occur in three years from sowing with the same species (Russell, in press).

Russell, M.J. (in press) Pr.Int.Cong. Energy and the Ecosystem, North Dakota, 1978.

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