Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: October 8, 2003
Publication Date: March 1, 2004
Citation: Shipitalo, M.J., Le Bayon, R. 2004. Quantifying the effects of earthworms on soil aggregation and porosity. In: Edwards C.A. (Ed.). Earthworm Ecology, 2nd Edition, CRC Press LLC. p. 183-200.
The potential for earthworms to improve soil aggregation and porosity and the subsequent effects of these changes in soil structure on plant growth and soil hydrology were first recognized by Gilbert White and Charles Darwin. Despite the large number of scientific studies that have been conducted since these pioneering naturalists made their observations, there are still a number of important gaps in our knowledge on the affects of earthworm activity on soil structure. Factors contributing factors to this problem include a lack of appropriate techniques to assess aggregation and porosity and inappropriate extrapolation of laboratory findings to the field. In general, earthworms improve soil aggregation, but their casting activity initially destabilizes the soil. While 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 will a more complete understanding be obtained. Earthworm burrows, particularly those formed by deep burrowing earthworms, can function as preferential flow paths. 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 wastes. While there are some management options available to reduce this concern, the dynamics of water movement in earthworm burrows at the field scale are still poorly understood. Once problems with limited resolution are overcome, x-ray computed tomography holds considerable promise for increasing our knowledge of the mechanisms affecting water and solute transport in earthworm burrows.