Agriculture Reference
In-Depth Information
numbers of dead earthworms (
) were inoculated into a red-brown earth soil. Straw
yields (grams) responded to the dead earthworms (at six or more earthworms per pot), but the grain
did not. The N content of both the straw and grain also increased significantly above that in the
controls in response to six or more dead earthworms per pot. Of course, different responses may
well occur for different plant species in different soil types based on the initial nutrient status. In
a similar experiment in a yellow clay soil, ryegrass did not respond in terms of shoot growth when
2 to 10 dead
A. trapezoides
A. trapezoides
were added per pot. Some of the pasture yield increases illustrated in
Figure 14.2
(particularly at the highest inoculation density) may be explained by a fertilizing effect
of earthworms that did not survive the experiment, but at the lower earthworm inoculation densities,
survival was sufficient to discount this explanation reasonably.
Some Australian experiments have explored interactions between earthworms and pasture roots
(Hirth et al. 1997, 1998), with those reported from similar studies in New Zealand (e.g., Springett
and Gray 1997). Hirth et al. (1997) could find no evidence that ryegrass roots elongated in the
direction of soil pores filled with earthworm casts. On the other hand, Hirth et al. (1998) reported
that
was attracted to ryegrass roots. Springett and Gray (1997) argued that interactions
between roots and earthworms were two way.
As in many other countries, soil acidity is a major environmental problem in high-rainfall
regions of Australia (Coventry 1985; Chartres et al. 1992). The use of ammonium-based nitrogenous
fertilizers and nitrogen-fixing legumes has contributed significantly to soil acidification. Lime is
applied commonly to the surface of the soil to offset acidity but is generally slow to be incorporated
into the root zone where it is needed (Helyar 1991). It is often too costly or inappropriate to
incorporate lime mechanically using tillage (e.g., in permanent pastures on steep slopes). Research
in New Zealand (Stockdill and Cossens 1966; Springett 1983, 1985) has shown that some species
of earthworms have the potential to bury lime and increase the soil pH. Similar experiments have
recently been done in southeastern and southwestern Australia to determine the earthworm species
most likely to be useful in reducing soil acidity in this way (Baker 1998a; Baker et al. 1993e,
1998b, 1999a; Chan and Baker unpublished data). The results suggested that the endogeic species
A. rosea
A. trapezoides
can be effective in burying surface-applied lime into the top few
centimeters of soil, but the anecic species
and
A. caliginosa
is much more effective in burying lime deeper
into the profile (e.g., to a depth of 15 cm within a few months with high earthworm populations)
A. longa
(
Figure 14.4
)
. Some other earthworm species (e.g.,
A. rosea
) are ineffective in lime transport. Baker
et al. (1993e, 1999a) explained such differences between earthworm species in terms of their relative
surface activities and depth of their burrows.
greatly disturbs the soil surface
during its feeding and creates surface-venting pores down which lime particles can be washed by
rainwater. Similar transport of other surface-applied materials (e.g., gypsum, fertilizers) is likely
but has not been tested. Chan and Baker (unpublished data) have demonstrated that the activities
of mixes of endogeic and anecic earthworm species can be complementary in terms of moving
lime throughout the soil profile.
Large amounts of cattle and sheep dung accumulate on the surface of Australian pastures
(Waterhouse 1974). As well as fouling pasture growth and increasing fly populations, this dung
represents an inefficient return of plant nutrients to the soil. Many species of exotic dung beetles
have been introduced to Australia to encourage the burial of cattle dung (Tyndale-Biscoe 1990),
but the role of earthworms in this process has been largely ignored (Ferrar 1975). Holter (1979)
showed that
Aporrectodea longa
, working in concert with dung beetles, was particularly effective in burying
cattle dung in a Danish pasture, and Martin and Charles (1979) demonstrated that
A. longa
A. caliginosa
and
buried large amounts of both cattle and sheep dung in New Zealand pastures. The
influence of earthworms on the burial of sheep dung has been measured in southern Australia on
a few occasions in cage experiments (Baker 1998a).
L. rubellus
is clearly very efficient
at burying such dung, more so than several other earthworm species, especially some native species.
However, the influence of earthworms on cattle dung burial and on any dung type at a field scale
in Australian pastures remains unclear.
Aporrectodea longa
