[1]Institute of Agricuhural hfformation and Economics, Beijing Academy of Agriculture and Forestry Sciences, Beijing 100097, China;
[2]Infomlation Center of Zhangjiakou Agricultural Bureau, Zhanjiiakou 075000, China;
[1]Institute of Agricuhural hfformation and Economics, Beijing Academy of Agriculture and Forestry Sciences, Beijing 100097, China;
[2]Infomlation Center of Zhangjiakou Agricultural Bureau, Zhanjiiakou 075000, China;