The POSEIDON project (2009-2013) was funded by the Nordic Joint Committee for Agricultural and Food Research (NKJ). It included researchers from Denmark, Sweden, Norway and Finland: Per Schjønning, Feto E. Berisso, Mathieu Lamandé, Bo V. Iversen, Lis W. de Jonge (Denmark), Thomas Keller, Nick Jarvis, Johan Arvidsson, Ararso Etana, Mats Larsbo, Mona Mossadeghi-Bjørklund (Sweden), Laura Alakukku, Asko Simojoki, Kristiina Regina (Finland), and Trond Börresen, Peter Dörsch, Hanne Silvennoinen (Norway). The research was organized in a matrix structure of four national coordinators and two topic coordinators. The national coordinators were all strongly involved with soil compaction studies, while the two topic coordinators contributed with their deeper knowledge of the specific processes in each their field. The research group can be reached by contact to Per Schjønning (project leader), Department of Agroecology, Aarhus University.