EARTHWORM COMMUNITY STRUCTURE AND DIVERSITY IN EXPERIMENTAL AGRICULTURAL WATERSHEDS IN NORTHEASTERN OHIO

Earthworms are known to have an important impact on soil fertility but much remains to be known about the factors that influence earthworm a bundance 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 Exper imental Watershed near Coshocton, Ohio. We sampled earthworm communiti es in seven such watersheds from 1990 to 1992. Six earthworm species w ere 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 lev els ranged from 10 to 350 worms m(-2). Earthworm community structure a nd diversity differed among watersheds and was influenced by cropping patterns, geographic location and tillage. The greatest earthworm dive rsity and highest earthworm population levels occurred in a no-tillage watershed and a watershed that had previously been in ryegrass and lo ng-term no-till. High earthworm populations were also observed in a ch isel-plowed watershed. Watersheds that had been managed identically fo r 50 years had much different earthworm communities, indicating that f actors other than management were important in determining species com position. The three watersheds with the lowest populations and diversi ty 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 earth worm populations and biomass. However, earthworm species differed in t heir response to drought with Lumbricus rubellus appearing to be the m ost drought-sensitive and Aporrectodea spp. the most drought-tolerant.