The flux of evaporation, transpiration and deep percolation play an important role in agricultural water management. In this study, oxygen-18 was used to determine the three fluxes in the summer corn and winter wheat field under existing irrigation pattern in Shanxi Province, China. Precipitation, irrigation water, soil water, groundwater and stem water were sampled for oxygen-18 analyses, and supported by hydrological observations. By the method of soil water balance and isotope mass balance, combined with eddy correlation method, the following results are reached. After the irrigation on August 11th, 2008 for summer corn (flowering stage, 90mm, flood irrigation), transpiration of corn accounts for 71.3% of total evapotranspiration, and the irrigation water use efficiency is 38.0%. And after the irrigation on March 15th, 2009 for winter wheat (re-green stage, 110mm, sprinkler irrigation), transpiration of winter wheat accounts for 61.7% of evapotranspiration, and the irrigation water use efficiency is 42.3%. Compared to flood irrigation, the deep percolation loss of irrigation water under sprinkler irrigation is lower, especially in the first day after irrigation. Overall, the existing irrigation efficiency is low in study area, and measures should be taken to reduce the deep percolation after irrigation.
