Gd. Schwenke et al., Soil stripping and replacement for the rehabilitation of bauxite-mined land at Weipa. I. Initial changes to soil organic matter and related parameters, AUST J SOIL, 38(2), 2000, pp. 345-369
At Weipa, in Queensland, Australia, sown tree and shrub species sometimes f
ail to establish on bauxite-mined land, possibly because surface-soil organ
ic matter declines during soil stripping and replacement. We devised 2 fiel
d experiments to investigate the links between soil rehabilitation operatio
ns, organic matter decline, and revegetation failure.
Experiment 1 compared two routinely practiced operations, dual-strip (DS) a
nd stockpile soil, with double-pass (DP), an alternative method, and subsoi
l only, an occasional result of the DS operation. Other treatments included
variations in stripping-time, ripping-time, fertiliser rate, and cultivati
on. Dilution of topsoil with subsoil, low-grade bauxite, and ironstone acco
unted for the 46% decline of surface-soil (0-10 cm) organic C in DS compare
d with pre-strip soil. In contrast, organic C in the surface-soil (0-10 cm)
of DP plots (25.0 t/ha) closely resembled the pre-strip area (28.6 t/ha).
However, profile (0-60 cm) organic C did not differ between DS (91.5 t/ha),
DP (107 t/ha), and pre-strip soil (89.9 t/ha). Eighteen months after plots
were sown with native vegetation, surface-soil (0-10 cm) organic C had dec
lined by an average of 9% across all plots.
In Experiment 2, we measured the potential for post-rehabilitation decline
of organic matter in hand-stripped and replaced soil columns that simulated
the DS operation. Soils were incubated in situ without organic inputs. Aft
er 1 year's incubation, organic C had declined by up to 26% and microbial b
iomass C by up to 61%.
The difference in organic C decline between vegetated replaced soils (Expt
1) and bare replaced soils (Expt 2) showed that organic inputs affect level
s of organic matter more than soil disturbance. Where topsoil was replaced
at the top of the profile (DP) and not ploughed, inputs from volunteer nati
ve grasses balanced oxidation losses and organic C levels did not decline.