Environmental Engineering Reference
In-Depth Information
litter decomposition in the restored system that may be related to a biotic
dysfunction in litter decomposition.
Soil fertility and management
Soil development is the improvement that occurs in physical, chemical and
biological properties, as the soil reorganises and acquires fertility with increas-
ing restoration period. As with recently restored soils elsewhere, those of post-
mining environments are incipient at best and are therefore likely to be poor
in the stocks of nutrient elements available, at least initially (Odum
1969
).
Continuing soil development is, therefore, necessary to conserve ecosystem
nutrient balances and is thus essential for self-sustainability.
The restored soils at most bauxite mines are developing on are permeable
pisolitic, gravel-rich and highly weathered soil materials (Spain et al.
2006
).
Physical aspect of pedogenic activity seems to progress surprisingly rapidly
and parameters such as soil hydraulic conductance can develop at a remarkable
pace (Fourie & Tibbett
2007
). Chemical and biological fertility, however, seem to
develop more slowly and these aspects may need intervention to allow ecosystem
restoration to succeed in human time scales.
Chemical fertilisation is common to all Australian bauxite mines as studies
have shown that natural fertility after soil movement is too low to secure
significant seedling establishment and vigour, important in the initial stabil-
isation of soils (Bradshaw & Chadwick
1980
; Hinz
1992
; Ward
2000
; Standish
et al.
2008
). Recently, detailed studies have been undertaken to establish the
effect of fertiliser application (particularly phosphorus) and soil management
on soil fertility in the long term and short term (George et al.
2006
; Standish
et al.
2008
). These have found significantly enhanced concentration of soil
phosphorus (up to five times that of unfertilised soil and natural forest soils)
18 months after fertilisation (George et al.
2006
) and significant residuals that
remain after 13 years (Standish et al.
2008
). This may be particularly important
in forests where low nutrient status is considered to have contributed to the
high floristic diversity (Myers et al.
2000
; Hopper & Gioia
2004
). The manage-
ment of soil and placement of fertiliser also seems to be important in deter-
mining the availability of soil phosphorus in what are typically P-fixing soils
(
Fig. 15.11
)
(George et al.
2006
). Management strategies such as soil scarification
and deep ripping (and the generation of ridges and furrows) and the timing of
fertiliser application can have a profound effect (again of up to five times the
difference) on phosphorus availability and determine the position of the avail-
able phosphorus in the soil profile
(
Fig. 15.11
)
.
Biological fertility is more difficult to measure, predict and manage. A wide
range of functional groups of organisms must be considered here such as
invertebrates, heterotrophic bacteria and fungi, mycorrhizal fungi, pathogens,
rhizobia, frankia and blue-green algae ( Jasper
2007
; Majer et al.
2007
). Certain
