Partitioning evapotranspiration of winter wheat based on oxygen isotope approach under different irrigation regimes

Evapotranspiration (ET), which is an elusive component of the hydrological cycle, comprises transpiration from plants (T) and evaporation from soil surface (E). In this regard, it is essential to know how much water is lost by T and E during the irrigation period. The overall aim of this study is to separate the ET components by stable oxygen isotopes of winter wheat at the field scale under different irrigation regimes. For this purpose, the field experiment was conducted under rain-fed, deficit and full irrigation conditions. Soil-water-plant samples were taken for isotopic (O-18/O-16) analyses. According to the research results, a significant positive relationship was found between applied irrigation water and the average T/ET ratio with a correlation coefficient of 0.81. The T/ET ratios were, on average, 70, 75 and 84% for rain-fed, deficit and full irrigation treatments, respectively. During the growing season, 231 and 78 mm of irrigation water were applied for full and deficit irrigation, respectively. This showed that water savings of 66% were achieved, although there was a slight (12%) change in transpiration in deficit irrigation. Also, in the use of the oxygen isotope content results indicated that T was the dominant source of total evapotranspiration.