Submitted to: Encyclopedia of Soil Science
Publication Type: Book / Chapter
Publication Acceptance Date: June 8, 2001
Publication Date: N/A
Technical Abstract: Earthworms ingest large amounts of soil and plant residue in the process of obtaining food and constructing their burrows. In temperate region soils, earthworms ingest as much as 100 Mg of soil per hectare per year. Thus, they can have profound effects on soil aggregation and porosity. The ingest soil is excreted on the soil surface or below ground depending on the species and soil bulk density. Freshly excreted soil is initially less water stable than the uningested soil due to the peristaltic action of the earthworm gut, but it is intimately mixed with the organic matter ingested as food. If it is allowed to age or dry before being subjected to disruption its stability will exceed that of the uningested soil, thereby enhancing formation of a desirable, water-stable, granular soil structure. Earthworm burrowing activity creates preferential flow paths that under some soil, tillage and rainfall conditions can reduce surface runoff, thereby decreasing losses of soil and agricultural chemicals in overland flow. If heavy rainfall occurs shortly after surface application of fertilizers or pesticides, however, these flow paths can accelerate movement of these materials through the soil. The potential for this to occur is minimized with the passage of time or if light rainstorms precede the first major leaching event. By selecting appropriate agronomic practices the beneficial effects of earthworms on soil structure can be maximized and the potential for undesirable consequences can be reduced.