Introduction of earthworms into an organic arable farming system

Earthworms were inoculated into an experimental field on a reclaimed polder soil in 1988, using a sod transplantation method. The donor field was a clover grass ley in an organic farm with a comparable sandy clay loam soil. The receptor field received different manurial treatments (farmyard manure, deep pit chicken manure or no manure) in replicate plots, and earthworms were introduced into one half of each plot. Five introduced species became established in manured plots, with dispersal rates of about 2 m per year in the first 4 years, increasing to about 11 m per year in the following 4 years and reaching a maximum population density of 776 earthworms per m(2) to a depth of 30 cm. Differences between effects of manurial treatments were not significant, whereas crop and cultivation direction significantly influenced earthworm distribution. The species composition did not differ with manure treatment, but the Shannon-Weaver diversity index was highest in the chicken manure-treated plots and lowest in the unmanured plots (C) 1998 Elsevier Science B.V.