Agriculture Reference
In-Depth Information
In field cages in S.A. and Victoria, the addition of 4 t lime ha
had no influence on the
−
1
establishment of
A. longa
after 5 months in a range of soil types (initial pH 4.3 to 5.2) but reduced
sp. at some sites (Baker et al. 1999c; Baker unpublished data). Garnsey
(1994a) reported that the addition of lime (5 t ha
the survival of
Spenceriella
) increased populations of
A. trapezoides
,
L.
−
1
rubellus,
in one Tasmanian pasture after 1 or 2 years (initial pH 5.9) but had no
influence on earthworms in another pasture (initial pH 6.0). Garnsey attributed the earthworm
responses he collected to an indirect effect that was mediated through increased clover production
and hence improved residue food quality for the earthworms.
In other studies, at several lime trial field sites in pastures in southern N.S.W., Baker and Chan
(unpublished data) failed to detect a response to liming by the population and biomass of earthworms
(Megascolecidae and Lumbricidae). The numerical responses of earthworms to liming seem likely
to vary according to the soil type, earthworm species present, and the range of pH involved.
Barley (1959a) showed that population and biomass of earthworms (probably mostly
and
A. longa
A. rosea
and
) increased after the addition of superphosphate to a pasture in S.A. Barley argued
this was because of an increase in plant productivity and hence available residue food (as decom-
posing plant material). Similarly, Fraser et al. (1994) reported that earthworm populations (mostly
A. trapezoides
A. caliginosa
) increased with superphosphate use and plant productivity in a New
Zealand pasture. However, such relationships are not always evident. Baker et al. (1993a,b, 1998a)
were unable to demonstrate any changes in earthworm populations after superphosphate applica-
tions to pastures in Victoria and S.A. Food supply was possibly not limiting for earthworms in
these last situations.
Lee (1985) indicated that some fertilizers can acidify soils and hence reduce earthworm
abundance. The additions of nitrogenous fertilizers and moderate amounts of manures and slurries
usually increase earthworm populations (Gerard and Hay 1979; Edwards and Lofty 1982b; Curry
1994). However, excessive amounts of slurries may reduce earthworm populations.
Disposal of human sewage sludge by environmentally acceptable means poses a major
challenge worldwide. However, safe and profitable disposal of such sludge as biosolids has been
achieved in Europe and North America through its addition to pastures (Smith 1996). The disposal
of biosolids has also been considered in N.S.W. (Joshua et al. 1998). An experiment that began
near Goulburn in 1992 to assess the benefits and risks associated with the application of dewatered
biosolids (DWB) to pastures grazed by sheep was surveyed 7 years later to measure impacts of
the sludge on the abundance and diversity of earthworms (Baker et al. 2002b). Application of
and
L. rubellus
DWB increased local earthworm populations (
Figure 14.5
). Earthworm species composition
varied with the amount of DWB applied. Introductions of earthworms (
A. longa
and
A. caligi-
nosa
), which were not present naturally at the site, were successful (in the short term) and
unaffected by the DWB applications.
The water repellency of sandy soils is a serious agricultural problem across southern Australia,
leading to significant land degradation and losses in productivity (Bond 1969). One potential way
of offsetting the effects of these nonwetting sands is to add a dispersible clay to assist in water
infiltration and holding capacity (MaÔshum et al. 1989). A field trial in the southeast of S.A. (Baker
et al. 1998a) in which different amounts of clay were added to a nonwetting sandy soil beneath a
pasture demonstrated that populations and biomass of
A. trapezoides
increased after the addition
of clay (
Figure 14.6
)
.
Trampling by agricultural animal stock can squash earthworms that live near the soil surface,
compact the soil, and return organic matter and nutrients to the soil in a different form (dung
and urine) and spatial distribution than occurs with senescent plants. Thus, animal stock therefore
can influence earthworm populations. However, surprisingly few data have been published on
interactions between animal stocking rates and earthworm abundance. Lobry de Bruyn (1993)
excluded dairy cattle from pastures in Tasmania and demonstrated that trampling reduced pop-
ulations of both
(25%). As well as the differences in
earthworm populations because of the trampling, pasture growth was reduced in the untrampled
A. caliginosa
(19%) and
L. rubellus
