5Gale M R, Grigal D F. Vertical Root Distributions of Northern Tree Species in Relation to Successional Status [ J]. Canadian Journal of Forest Research, 1987, 17 (8) : 829-834.
6Hamza M A, Anderson W K. Soil Compaction in Cropping Systems: A Review of the Nature, Causes and Possible Solutions [J]. Soil and Tillage Research, 2005, 82 (2) : 121-145.
7BENGOUGH A G. Modeling Rooting Depth and Soil Strength in a Drying Soil Profile [ J ]. Journal of Theoretical Biology, 1997, 186 (3) : 327-338.
8Materechera S A, Dexter A R, Alston A M. Penetration of Very Strong Soils by Seedling Roots of Different Plant Species [ J ]. Plant and Soil, 1991, 135 ( 1 ) : 31-34.
9LI Y Y, SHAN M. Change of Soil Physical Properties Under Long Term Natural Vegetation Restoration in the Loess P1 atean of China[J]. Journal of Arid Environments, 2006, 64( 1 ) : 77-96.
10Young I M, Montagu K, Conroy J, et al. Mechanical Impedance of Root Growth Directly Reduces Leaf Elongation Rates of Cereals [J]. New Phytologist, 1997, 135 (4) : 613-619.