Abstract: Afield experiment with five spring wheat (Triticum aestivum) varieties 8275(A),79157(B),8832(C),8624(D) and DX24(E) which have different drought resistance shows that the average root density in 0～120 cm soil layer is 66 μg·cm^-3 for A,104 μg·cm^-3 for B,137 μg·cm^-3 for C,102 μg·cm^-3 for Dand 99 μg·cm^-3 E, and their total root weight is 78.7,124.3,164.3,121.8 and 118.7 g·m^-2 ,respectively.The grain yield of these five varieties are respectively 201,207,141,218 and 190 g·m^-2 .When water is a primary limiting factor, the drought resistance of wheat is worse for those with large root systems,and an intense competition for water is existed among individuals;but is better for those with small ones, and no competition for water is existed.

Key words: Competitive selection, Drought resistant variety, Root system, Semi arid region, Spring wheat, soil microbial community diversity., land consolidation, soil organic carbon