Short-term effects of ploughing on the abundance and dynamics of two endogeic earthworm species in organic cropping systems in northern France
Résumé
An understanding of the effects of ploughing on earthworm dynamics is required for the design of organic cropping systems maximising the beneficial effects of earthworms. Earthworms are often reported to be disturbed by ploughing, which is frequently used for weed control in organic farming. In this preliminary study, we investigated the effect of ploughing on the dynamics of two common endogeic species: Aporrectodea caliginosa and Aporrectodea rosea, to test the assumption that the sensivity to ploughing is species dependant. Two field trials were set up in October 2009 and November 2010, at two locations on a haplic luvisol, located in northern France. For comparison, part of each field was left unploughed, with the rest being ploughed. Earthworms were sampled at ten dates between October 2009 and July 2010 at Vi and six dates between November 2010 and March 2011 at Fa. Seven species were found in these two fields, with more than 88% of the earthworms belonging to two endogeic species, A. caliginosa and A. rosea. Ploughing had contrasting effects on the two species. A. caliginosa was more sensitive than A. rosea to tillage. In the unploughed part of the field, in 2009, the population remained small (less than 100 individuals m(-2)) and it was assumed that the two species were in competition for food. In 2010, the carrying capacity was higher, and A. caliginosa abundance reached 300 individuals m(-2), whereas the abundance of A. rosea remained below 90 individuals m(-2). In 2009, the effect of ploughing on A. caliginosa was immediate and persisted throughout the experiment, from October 2009 to June 2010, with an 80% decrease in abundance in June 2010. In 2010, the effect was delayed, but populations decreased during the winter following ploughing, with a 60% decrease in January 2011. Concerning A. rosea, the differences between the ploughed and the unploughed treatments were lower than for A. caliginosa. Our results confirm that endogeics earthworms may adapt themselves to the disturbance caused by tillage. Our observations suggest that A. caliginosa is more sensitive to ploughing than previously reported. These preliminary findings were obtained under favourable climatic conditions. They may help to define the optimal scheduling of tillage for earthworm conservation. (C) 2012 Elsevier B.V. All rights reserved.