Agriculture Reference
In-Depth Information
rate corresponded with maximum grass primary productivity. On the other hand, Baker et al.
(1993a,b) and Baker and Chan (unpublished data) could show no consistent patterns between
earthworm populations and the stocking rates of sheep (range 5 to 23 ha
−1
) in several pastures in
western Victoria, N.S.W., and S.A. Pizl (1992), Sochtig and Larink (1992), and Hansen and
Engelstad (1999) demonstrated significant declines in earthworm populations after compaction
from machinery traffic in orchards, cereal fields, and dairy pastures in the Czech Republic, Germany,
and Norway, respectively. The only comparable Australian study is that of T. Ellis in S.A. (personal
communication 1992), who demonstrated a reduction in earthworm populations beneath wheel
tracks in a controlled-traffic cereal production trial.
Lee (1985), Edwards and Bohlen (1992, 1996), and Curry (1994) provided detailed discussions
of the effects of various pesticides on earthworm populations. It is generally accepted that most
herbicides are not directly toxic to earthworms, but they may influence populations indirectly by
changing plant productivity, food supply, and soil microclimate. Interestingly, Mele and Carter
(1999a) found that heavy (c.f. recommended) application rates of post-emergent herbicides
increased earthworm populations, but this may have been caused by increased weed residues. Some
fungicides, such as benomyl, can be very toxic to earthworms and influence them indirectly by
altering their food supply. Buckerfield (1993a) showed that the use of fungicides can alter the
species composition of earthworm populations in S.A. pastures. Fumigants such as methyl bromide
and many insecticides (e.g., organochlorines and carbamates) also kill earthworms. However, very
few studies have been made along these lines in Australia. Choo and Baker (1998) assessed the
influence of several commonly used pesticides, including endosulfan (insecticide) and fenamiphos
(nematicide), on
A. trapezoides
in both the field and the laboratory and showed that its growth and
reproduction were affected at recommended application rates (Figure 14.7).
A worrying trend in southern S.A. has been the increased use of molluscicides to control
introduced helicid and hygromiid snails, which are pests of grain crops and pastures (Baker 1989,
2002). These snails are particularly numerous where tillage is reduced and organic matter is retained,
just the situation where earthworm populations are likely to increase. Some authors have argued
20
100
Number of
Cocoons
% Clitellate
Adults
0.22
18
90
0.14
16
80
0.13
14
70
12
60
10
50
8
40
0.03
6
30
4
20
- 0.03
2
10
0
0
Control
Fenamiphos Endosulfan
Methiocarb
Ridomil
FIGURE 14.7
Average numbers of cocoons/pot
−1
and percentage of
Aporrectodea trapezoides
that were
clitellate after 5 weeks of culture in the laboratory in a brown loam soil to which fenamiphos (nematicide),
endosulfan (insecticide), methiocarb (molluscicide), and ridomil (fungicide) were applied at recommended
rates. Numbers at the tops of the histograms indicate average weight change (g) earthworm
−1
during a similar
experiment in the same soil in the field. (Data redrawn from Choo and Baker 1998.)
