1. Dep. of Agroecology, Faculty of Science and Technology; Aarhus Univ.; Blichers Allé 20, PO Box 50 DK-8830 Tjele Denmark
2. Sustainable Agricultural Sciences, Rothamsted Research; Harpenden UK
3. Dep. of Civil Engineering; Aalborg Univ.; Thomas Manns Vej 23 DK-9220 Aalborg Ø Denmark