1. Department of Agroecology; Aarhus University; Research Centre Foulum; P.O. Box 50 DK-8830 Tjele Denmark
2. Faculty of Agriculture; Payame Noor University (PNU); P.O. Box 19395-3697 Tehran Iran
3. Dep. of Agroecology; Aarhus University; Research Centre Foulum; P.O. Box 50 DK-8830 Tjele Denmark
4. Dep. of Soil and Environment; Swedish University of Agricultural Sciences; Almas Alle 8 750 07 Uppsala Sweden