Partitioning evapotranspiration using water stable isotopes and information from lysimeter experiments

Stable isotope techniques can be used to investigate evapotranspiration and its partitioning into evaporation and transpiration. However, verification is often difficult due to missing information about actual evapotranspiration. Therefore, in this study a methodology tested for laboratory conditions was modified for field applications. Evapotranspiration, which was determined by weighing lysimeters, and isotope techniques were combined with soil water and lysimeter measurements to calculate evaporation and transpiration rates of soybean under natural conditions. The case study was conducted in 2019 in Groß-Enzersdorf, Austria. The results show that the methodology was suited to measure actual variations of evaporation and transpiration ratios, even during dry periods. Weekly evaporation (0.5–2.2 mm d−1) and transpiration (1.3–4.3 mm d−1) rates as well as the respective ratios (transpiration 43–85%) agreed with the results of numerical modelling and values from the literature, confirming the applicability of the modified methodology for portioning evapotranspiration in the field.