Agriculture Reference
In-Depth Information
products, and greater awareness of soil structural decline encouraged farmers to adopt reduced
cultivation techniques. Under such practices, populations abundance of earthworms are enhanced
(Rovira et al. 1987), and their presence in optimal numbers is needed to replace some of the benefits
previously achieved by the plough. In addition, the increasing costs of inorganic fertilizers, as well
as the pollution problems they cause (e.g., through leaching and erosion into waterways), has
stimulated thought on more efficient and safer means of transfer of nutrients from natural sources
to plants. Studies in other countries that have shown the potential for earthworms to help offset
soil degradation, such as improved lime burial and reductions in soil acidity, improved water
infiltration, and increased rates of breakdown of surface litter, leading to reduced surface runoff of
phosphorus and nitrogen (Sharpley et al. 1979; Springett 1983), also heightened interest in intro-
ducing such benefits to Australia.
During the late 1980s and through the 1990s, research on earthworms in southern Australia
was aimed primarily at determining the distribution and abundance of earthworms in agricultural
soils, measuring the effects of the most common species on soil properties and plant productivity,
and identifying means by which the beneficial role of earthworms can be enhanced (e.g., optimal
farm management practices, introduction of new taxa of earthworms) (Baker 1998a). This chapter
considers briefly the progress that has been made on these topics and identifies gaps in knowledge
that could, if filled, lead to benefits for the grazing industries, because the focus here is on pastures.
There is also substantial literature available on earthworm ecology and activities in grain cropping
systems in southern Australia (e.g., Buckerfield 1992; Baker et al. 1993c, 1997b, 2004a; Doube et
al. 1994a, 1997; Stephens et al. 1994a, 1995). Such information is referred to here only if it is
particularly relevant. The majority of earthworm research that has been done in Australia has been
in the southern temperate and mediterranean climatic regions. Knowledge of the biology, role, and
management of earthworms in tropical grazing systems in Australia is more or less uncharted
territory. Parallels may be sought in the extensive studies of Lavelle and colleagues in Africa and
Central and South America (Lavelle et al. 1999).
THE EARTHWORM FAUNA IN AUSTRALIA
Extensive surveys have demonstrated that populations and species diversity of earthworms are
generally low in soils used for pastures in southern Australia (Kingston and Temple-Smith
1989; Mele 1991; Baker et al. 1992b, 1994; Garnsey 1994b; Lobry de Bruyn and Kingston
1997; Baker 1998a; Mele and Carter 1999b). Populations of more than 1200 earthworms m
Ï2
have been recorded occasionally, but most pastures have fewer than 200 earthworms m
.
Although up to six species have been recorded per field, more commonly only two to three
species are found.
The earthworm fauna is dominated by exotic species, most notably Lumbricidae (e.g.,
Ï2
Apor-
rectodea caliginosa
), which have been introduced
accidentally from Europe. The dominant species vary regionally and among habitat types. For
example,
,
Aporrectodea trapezoides
,
Aporrectodea rosea
is dominant in permanent pastures in South Australia (S.A.) and southern
New South Wales (N.S.W.), but
A. trapezoides
is more abundant in similar pastures in western
Victoria. In pasture-cereal rotations in the same regions,
A. caliginosa
is the dominant species. Indige-
nous, native species (Megascolecidae), which are common in undisturbed, native habitats, are
generally much more rare in agricultural soils than are exotic species. Reasons for this relative
rarity of native species in managed soils are poorly understood, but tillage and changes in shelter,
food type, and soil fertility have been suggested as possibly important factors. Interestingly, native
species are more common in pasture soils in Victoria and southern N.S.W. (e.g., 42% here are
A. rosea
native) than they are in S.A. and southwestern West Australia (W.A.) (
Figure 14.1
)
.
Reasons for this cline in species richness are not clear, but possibly it is correlated with
differences in summer aridity. Summers in S.A. and southwestern W.A. are hot and dry, with most
