Effect of Irrigation on Water Use Efficiency on the Loess Plateau

Water use efficiency of Pinus tabulaeformis, Platycladus orientalis and Robinia pseudoacacia were studied by irrigating. The results showed that the irrigation improved the soil water state, especially the discrepancy of the soil water content between arid year and normal year decreased with increase of irrigation level .The water use efficiency of P. tabulaeformis, P. orientalis and R. pseudoacacia increased by 35.3%,32.2%,26.9% than that of control in normal year in irrigation of 1.0 times precipitation, while that of the trees was positively correlated with the irrigation level in arid year.