3Framwork for Evaluation of Sustainable Land Management:A Case Study of Two Rain-Fed Ceroal-Livestock Farming Systemes in the Black Chemozemic Soil Zone of Southern Allberta. Canada. Can J Soil Sci., 1995,75(4) :429~437
4Smith V.Rerry. Resource Evaluation at the Crossroads. Resources,1988,90:2~6