DOC Trial: effects of the farming systems on the earthworms

The DOC long-term trial in Therwil has been comparing two organic farming systems, with one another since 1978: two conventional systems and one unfertilized control system. Earthworm surveys from 2001 to 2005 revealed no statistically significant differences between the farming systems D2, O2 and K2, which were fertilized with solid and liquid manure, either in terms of biomass or number of earthworms. Generally speaking, values were relatively high for arable soils. Since the use of plant-protection products, which are toxic to earthworms, was dispensed as from 1992, earthworm populations have been better protected and regenerated than in earlier investigations, even in conventional farming systems. The conventional farming system (M2) using mineral fertilizers exclusively had an earthworm biomass that was 13 % lower than that of the main systems, which is explained by the lack of organic fertilizers. The lowest values were found in the unfertilized treatment N (minus 25 %). In both the organic and conventional farming systems, earthworm populations in the fertilized treatment were influenced most strongly by the tillage system (ploughing). The cultivation of clover-grass appreciably boosted earthworm numbers. A total of eleven different earthworm species were found in seven investigations.