Earthworms are known to have an important impact on soil fertility but much remains to be known about the factors that influence earthworm abundance and species diversity in agicultural soils and the impact of earthworm diversity on soil processes in those soils. We have studied factors that influence earthworm community structure and biodiversity in experimental agricultural watersheds at the North Appalachian Experimental Watershed near Coshocton, Ohio. We sampled earthworm communities in seven such watersheds from 1990 to 1992. Six earthworm species were present: Aporrectodea caliginosa, A. trapezoides, A. tuberculata, Lumbricus rubellus, Lumbricus terrestris and Octolasion tyrtaeum. The total earthworm biomass ranged from 2 to 32 g m(-2) and population levels ranged from 10 to 350 worms m(-2). Earthworm community structure and diversity differed among watersheds and was influenced by cropping patterns, geographic location and tillage. The greatest earthworm diversity and highest earthworm population levels occurred in a no-tillage watershed and a watershed that had previously been in ryegrass and long-term no-till. High earthworm populations were also observed in a chisel-plowed watershed. Watersheds that had been managed identically for 50 years had much different earthworm communities, indicating that factors other than management were important in determining species composition. The three watersheds with the lowest populations and diversity were adjacent to one another at one end of the station, indicating that at this site geographic location had the predominant influence on earthworm communities. A severe drought in 1991 greatly reduced earthworm populations and biomass. However, earthworm species differed in their response to drought with Lumbricus rubellus appearing to be the most drought-sensitive and Aporrectodea spp. the most drought-tolerant.
