1. Research Institute of Organic Agriculture, Ackerstrasse, CH-5070 Frick, Switzerland
2. Agroscope Reckenholz-Tänikon Research Station ART, Reckenholzstrasse 191, CH-8046 Zürich, Switzerland
3. Institute of Terrestrial Ecosystems, ETH Zürich, Universitätstrasse 16, CH-8092 Zürich, Switzerland