Critical external inputs : off-farm compost, off-farm manure and biochar / $hGerman Environment Agency ; authors: Prof. Dr. Andreas Gattinger, Dr. Wiebke Niether (Justus-Liebig-Universität Giessen), Dr. Ana Frelih-Larsen, Antonia Riedel, Rachael Oluwatoyin Akinyede (Ecologic Institute)