1. Grassland Science, Department of Crop Sciences, Georg-August-University Göttingen , D-37075 Göttingen , Germany
2. Centre of Biodiversity & Sustainable Land Use , D-37077 Göttingen , Germany
3. Geo-Lab, University of Vechta , D-49377 Vechta , Germany
4. Department of Livestock Sciences, FiBL , CH-5070 Frick , Switzerland