[1] Northwest A&F Univ, Coll Econ & Management, Yangling 712100, Shaanxi, Peoples R China
[2] Peking Univ, Coll Environm Sci & Engn, Beijing 100871, Peoples R China
[3] Tech Univ Munich, Chair Agr Prod & Recourse Econ, D-85354 Freising Weihenstephan, Germany
[4] Univ Stavanger, UiS Business Sch, Dept Econ & Finance, N-4036 Stavanger, Norway