College of Mathematics and Informatics South China Agricultural University Guangzhou 510642 P.R.China;
Department of Agricultural Economics and Management School of Public Affairs China Academy for Rural Development (CARD) Zhejiang University Hangzhou 310000 P.R.China;
Environmental Policy Group Wageningen University Hollandseweg 16706 KN Wageningen;
China Agricultural Science and Technology Press Chinese Academy of Agricultural Sciences Beijing 100081 P.R.China;
Agricultural Information Institute Chinese Academy of Agricultural Sciences Beijing 100081 P.R.China;