School of Economics and Management, Beijing University of Agriculture, Beijing 102206, P.R.China;
Institute of Rural Economy and Agricultural Regional Planning, Tianjin Academy of Agricultural Sciences, Tianjin 300192, P.R.China;
Institute of Agricultural Economics and Development, Chinese Academy of Agricultural Sciences, Beijing 100081, P.R.China;
Department of Economics, University of Waikato, Hamilton 3240, New Zealand;
Col ege of Economics and Management, Henan Agricultural University, Zhengzhou 450002, P.R.China;