1 Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark. Electronic address: ktk@plen.ku.dk.
2 DCA - Danish Centre for Food and Agriculture, Aarhus Universiy, Blichers Allé 20, 8830 Tjele, Denmark.
3 Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark.
4 Department of Agroecology - Climate and Water, Aarhus University, Blichers Allé 20, Tjele, Denmark.