| The actual evapotranspiration (ETA) data of spring wheat during 19931997 (except 1995) observed by the Lysimeter in Dingxi prefecture of Gansu Province are analyzed. The results show that: in the whole growth season, the daily variation of ETA is random in al arge range. In generally, there is a high value aftera heavy rainfall. The annual variation of ETA is also obvious, and the minimum-value is less than half of the maximum value. The ETA is significantly less than the crop water requirements (CWR) in the growth season of spring wheat, the mean difference being about 1.0 mm/d. The amount of ETA and its consonance degree to CWR prominently affect the yield of spring wheat. |