Agriculture Reference
In-Depth Information
aged or composted can have temporary adverse effects on earthworm populations when applied to
soils as slurries because of their ammonia and salt contents, but these effects are usually short term.
Many inorganic fertilizers also contribute indirectly to the buildup of earthworm populations
because of increased crop yields and hence increased amounts of crop residues added to the soil.
However, earthworms are very sensitive to ammonia, and ammonia-based fertilizers often have
adverse effects on earthworm populations, especially when these fertilizers are applied annually
over several seasons (Edwards and Lofty 1982b).
, which include insecticides, herbicides, fungicides, and nematicides, are used exten-
sively on agricultural land in developed countries. It is often assumed that many pesticides are
Pesticides
toxic to earthworms or have harmful effects on them. However, most herbicides have few direct
effects on earthworms, although the triazine herbicides are slightly toxic. However, herbicides have
drastic indirect effects on earthworms through their influence on the availability of organic matter
(Edwards and Thompson 1973). Most fungicides have few effects on earthworms, with the exception
of the carbamate-based fungicides, such as benomyl, which are very toxic. Of the insecticides in
current use, only the organophosphate, phorate, and most carbamate-based compounds such as
carbaryl, carbofuran, and methiocarb, and the avermectins are toxic to earthworms (Edwards 1984a,
b). Of more than 200 pesticides reviewed by Edwards and Bohlen (1992), fewer than 20 were
seriously toxic to earthworms (see
Chapters 16
and
17
, this volume).
have been progressively decreasing in industrialized agriculture. There has
been relatively little work on the effects of crop rotations on earthworm problems. In general, the
inclusion of crops such as cereals that leave considerable organic residues encourage the buildup
of earthworm populations more than do legumes, which decompose quite rapidly. Root crops, for
which most of the crop is removed, discourage the buildup of earthworm populations (Edwards
and Bohlen 1996).
Crop rotations
EARTHWORMS AS INDICATORS OF SOIL QUALITY AND HEALTH
There has been considerable interest in the concept of maintaining soil quality and health. There has
been considerable discussion on defining these terms and on identifying appropriate physical, chemical,
and biological indicators of soil quality. One definition is Ñthe ability of a soil to sustain biological
productivity, maintain environmental quality and promote plant, animal and human healthÒ (Doran and
Parkin 1996). Soil is a heterogeneous mixture of abiotic and living components, including a very
complex range of soil-inhabiting organisms. The basic functions of soils depend on their structural and
functional integrity and the impacts of disturbances on management on these functions.
A wide range of indicators of soil quality and health criteria has been suggested, but it is
becoming increasingly clear that it is essential that the indicators must include biological compo-
nents because soil is a dynamic entity (Blair et al. 1996). It is difficult to use microbial indicators
of soil quality and health as much as desired because of a lack of simple methodologics that can
be used in the field by relatively untrained workers.
Soil microinvertebrates have been suggested as possible indicators of quality and health (Linden
et al. 1994), but sampling microarthropod or nematode populations is difficult, so their identification
and utility as suitable indicators is a complex problem. There is a consensus among soil ecologists and
most farmers that earthworms may be one of the best indicators available of soil quality (Doube and
Schmidt 1997). They are easy to sample and identify and, as the discussions in this topic illustrate, are
important indicators of both soil health and soil quality (see
Chapters 2
and
6
, this volume).
EARTHWORMS AND SOIL POLLUTION
There has been increasing interest in the use of earthworms as organisms to assess the environmental
effects of soil pollution. Three Conferences on Earthworm Ecotoxicology (1991, U.K.; 1997, the
