Hansen, Sissel; A. Bleken, Marina; Løes, Anne-Kristin; Govasmark, Espen; Falk Øgaard, Anne and Breland, Tor Arvid    (2007) Sustainable nutrient supply of organic farming challenged by specialisation.   In: Lund, Mogens and Larsen, Torben Ulf (Eds.)  NJF Report: NJF 23rd Congress 2007 - Trends and Perspectives in Agriculture, Nordic Association of Agricultural Scientists, 3 (2), NJF Report, no. 3 (2), pp. 193-194.