Earth Science Frontiers ›› 2008, Vol. 15 ›› Issue (5): 110-125.
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1.Agriculture and AgriFood Canada, Crops and Livestock Research Centre, Charlottetown, P.E.I., C1A 7M8, Canada
2.Department of Land Science and Technology, China University of Geosciences(Beijing), Beijing 100083, China
3.Department of Land Science and Technology, China University of Geosciences(Beijing), Beijing 100083, China