6Wilson J R,Ludlow M M.Time trend of solute accumulation and the influence of potassium fertilizer on osmotic adjustment of water stressed leaves of three tropical grasses[J].Aust J Plant Physical,1983,110:523-527.
7Victor N,Bushamuka,Zobel R W.Differential genotypic and root type penetration of soil layers[J].Crop science,1998,38:776-781.
8Shierlaw J,Alston A M.Effect of soil compaction on root growth and uptake of phosphorous[J].Plant and Soil,1984,77:15-28.
9Materechera S A.Penetration of very strong soil by seeding roots of different species[J].Plant and Soil,1991,135:31-41.
10Weaver J E.Root development of field crops[M].McGraw-Hill,New York,1926.