Earthworm populations in two low-input cereal farming systems

Summary

Earthworm populations in low-input integrated crop management (ICM: no application of insecticides, fungicides and growth regulators) and organic farming systems were compared. The study was performed as a 3-year field survey using a paired-farm approach in six different locations in northwestern Switzerland. Earthworms were extracted from soils sampled from 24 winter cereal fields using a combined method of extraction by mustard flour solution and handsorting.
Earthworm communities differed between these farming systems. Over all sites, the mean biomass, abundance and species richness of earthworms found in the low-input ICM fields were significantly lower than in the organic fields. Adult earthworms in organic fields were 114% more abundant than in ICM fields, but the frequencies of most species within the respective systems were similar in both farming systems. The numbers of earthworm species and juveniles were higher in organic fields. Five species – Lumbricus terrestris (L.), Nicodrilus longus (Ude), Nicodrilus nocturnus (Evans), Nicodrilus caliginosus (Sav.) and Allolobophora rosea (Sav.) – were significantly more numerous in the organic fields than in the ICM fields.
Multivariate analysis showed that the farming system explained most of the variance and was found to be the key factor in altering the earthworm fauna. Late ploughing in autumn was found to have a major negative effect on earthworm abundance, irrespective of the farming system. Farming practices that differ between these farming systems and may considerably influence earthworm populations and diversity are discussed.
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