5Jordan D, Kremer R J, Bergfield W A, et al.Evaluation of microbial methods as potential indicators of soil quality in historical agricuhur- al fields[J] ,Biology and Fertility of Soils, 1995,19(4) :297-302.
6Morrison I K,Foster N W. Fifteen-year change in forest floor or- ganic and element content and cycling at the Turkey lakes water- shed [J]. Ecosvstems. 2001.4 ( 6 ) : 545- 554.
