Agriculture Reference
In-Depth Information
positively with earthworm population density and biomass.
Aporrectodea caliginosa
and
A. trap-
ezoides
, possibly because of
greater exploitation of available resources by larger populations of the two smaller species. A few
studies have shown that induced increases in pasture production are additive among earthworm
species (Baker 1998b), that is, species (functional) diversity within earthworm communities matters.
However, much more work is needed to substantiate this conclusion fully.
The influence of native earthworms (Megascolecidae) on pasture production has been relatively
poorly studied. In general, native earthworm species have failed to influence plant growth signifi-
cantly (Baker et al. 1996; Baker 1998a and Baker unpublished data), but in one study (Baker et
al. 2004a),
increased pasture production per unit of biomass more than
A. longa
did increase ryegrass growth slightly in a glasshouse experiment.
However, a much larger native earthworm species,
Spenceriella macleayi
Spenceriella hamiltoni
, had no effect on ryegrass
growth in the same experiment.
The majority of research on the effects of earthworms on pasture production in Australia either
has not discriminated among pasture grass species or has focused on ryegrass. Research on grain
crops in Australia (e.g., Baker et al. 2004a) and overseas (Brown et al. 1999) has demonstrated
that the effects of earthworms vary among crop types. In the main, legumes are less responsive to
earthworm activities than are cereals. The abilities of legumes to fix their own nitrogen may obviate
the ÑneedÒ for earthworms to some extent. Some studies have demonstrated how plant growth
responses to earthworms can vary among sites and soil types, ranging from responses that are
mostly positive, through neutral, to occasional negative ones (Doube et al. 1997; Baker et al. 1999b).
Reasons for this variability in responses are not at all clear.
Most studies of the abilities of earthworms to enhance the transfer of nutrients from fertilizers
and organic residues to agricultural plants in Australia have been confined to grain crops (Stephens
et al. 1994a; Baker, unpublished data; Baker and Amato 2001; Baker et al. 1997b, 2004a). The
mechanisms are poorly understood, but some earthworm species (e.g.,
A. trapezoides
) are known
to release more N from decomposing organic matter into the soil than others (e.g.,
). Whalen
et al. (1999) showed that N from dead earthworms can be transferred rapidly to plants, and they
argued for care in interpreting data on the effects of earthworms on plant growth in experiments
in which earthworms die. Figure 14.3 illustrates responses in growth of wheat when different
A. rosea
12
12
Straw
Grain
Earthworms
B
B
B
10
10
AB
A
A
8
8
6
6
4
4
2
2
0
0
0 2 4 6 8 10
Dead Earthworms/Pot
FIGURE 14.3
Average grain and straw yields of wheat when grown in a red-brown earth soil in flower pots
(3 kg soil per pot) in the presence of varying numbers of dead worms (
, killed in
boiling water). Grain and straw yield are dry weights; worm biomass is fresh weight. Different letters at the
tops of histograms indicate significant differences.
Aporrectodea trapezoides
