[1] Swiss Fed Inst Technol, Agr Econ & Policy Grp, CH-8092 Zurich, Switzerland
[2] Michigan State Univ, Dept Agr Food & Resource Econ, E Lansing, MI 48824 USA
[3] Agroscope, Res Div Competitiveness & Syst Evaluat, CH-8356 Ettenhausen, Switzerland
[4] Swiss Fed Inst Technol, Crop Sci Grp, CH-8092 Zurich, Switzerland