It has been reported that when LAI was more than 4, there would be no water loss by E. However, in dryland areas, the LAI is generally lower than 3 even when fertilizer is applied ( Gregory et al., 1984 and Hamblin et al., 1987). Since maize, a sparse crop, was used in our experiment, the LAI was lower than 2 for the non-plastic mulched plots and higher than 2 for the plastic mulched plots at late stages with high N rates.