Agriculture Reference
In-Depth Information
(Shipitalo et al. 1990; Propes et al. 1993; Golabi et al. 1995). Ingestion of herbicide-coated residues
by earthworms can also reduce leaching losses (Farenhorst et al., 2000a,b).
Other potential adverse effects of earthworm burrows on water quality and water utilization include
fostering nonuniform distribution of water during furrow irrigation and loss of water through unlined
irrigation ditches. Possible remedies for these concerns include compacting the ditches and removing
vegetation to reduce earthworm burrowing (Kemper et al. 1988) and adding ammonia at low rates to
the irrigation water to repel earthworms (Trout and Johnson 1989). Burrowing by earthworms can
also contribute to leakage of earthen-lined manure storage lagoons by increasing the hydraulic
conductivity of the berms (McCurdy and McSweeney 1993). Presumably, the procedures used to
reduce water movement through unlined irrigation ditches would help alleviate this concern.
Earthworm burrows can also affect the movement of the constituents in animal wastes applied
to soils. Joergensen et al. (1998) noted greater movement of fecal indicator organisms in cattle
slurry applied to grassland than to plowed soil, which they attributed to greater numbers of
L.
terrestris
burrows in the grassland. Similarly, the results of a study by Shipitalo and Gibbs (2000)
suggested that
L. terrestris
burrows, close to subsurface drains, can contribute to rapid movement
of injected animal wastes off-site. In this instance, rapid movement of the tracer to the buried drains
was limited to burrows 0.5 m to either side of the drain. This suggests that disrupting the burrows
in this region prior to slurry application or avoiding application in this region might reduce this
concern.
CONCLUSIONS
Despite the large number of studies that have been conducted on the effects of earthworm activity
on soil structure, a number of important gaps in knowledge remain. Factors contributing to this
problem include a lack of appropriate techniques to assess aggregation and porosity and often-
inappropriate extrapolation of laboratory findings to the field.
In general, earthworm activity improves soil aggregation, but their casting activity initially
destabilizes the soil. Although laboratory studies can elucidate some of the factors affecting the
improvement of aggregation with time, only when the fate of earthworm casts is investigated in
the field or in microcosms that reflect the complexity of natural systems and managed agroecosytems
will a more complete understanding be obtained. One approach that shows promise is to manipulate
earthworm populations in long-term field plots to assess the effects of different population levels
on soil structural dynamics (Bohlen et al. 1995).
Similarly, quantification of earthworm burrow morphology and the effects of earthworm bur-
rows on water movement and water quality are hampered by limitations in methodology. Earthworm
burrows, particularly those formed by anecic species of earthworms, can function as preferential
flow pathways. Although enhanced infiltration is normally desirable, in rare instances it can result
in increased chemical movement through the soil or inappropriate distribution of irrigation water
and liquid animal wastes. Although there are some management options available to reduce this
concern, the dynamics of water movement through earthworm burrows at the field scale are still
poorly understood. Once problems with limited resolution are overcome, x-ray computed tomog-
raphy holds considerable promise for increasing knowledge of the mechanisms affecting water and
solute transport in earthworm burrows.
REFERENCES
Alakukku, L., J. Ahokas, and A. Ristolainen. 2002. Response of clay soil macroporosity to stress caused by
tracked tractors, in M. Pagliai and R. Jones, Eds.,
Sustainable Land Management Ð Environmental
Protection: A Soil Physical Approach
, Advances in GeoEcology 35, Catena Verlag, Reiskichen,
Germany, pp. 319Ï330.
