1. Department of Agroecology; Aarhus University; Blichers Allé 20 P.O. Box 50 DK-8830 Tjele Denmark
2. Department of Engineering; Aarhus University; Hangovej 2 P.O. Box 239 DK-8200 Aarhus Denmark
3. Joanneum Research Forschungsgesellschaft mbH; Elisabethstraße 18/II 8010 Graz Austria
4. EcoSys Research Unit; AgroParisTech, INRA; F-78850 Thiverval-Grignon France