Coupling evapotranspiration partitioning with root water uptake to identify the water consumption characteristics of winter wheat: A case study in the North China Plain

Quantifying the contribution of transpiration (T) to evapotranspiration (ET) and determining the main water source for crops at different growth stages are two essential steps for developing water-saving agricultural strategies. In this study, an improved S-W (SWH) model and the MixSIAR model were used for ET partitioning and water source prediction in an irrigated cropland in the North China Plain. Our results indicated that the partition results of SWH model are well consistent with those from micro-lysimeter measurements. T/ET ranged from 13.4% to 87.0% with a mean value of 71.4%, which always exceeded 80% during the peak growing season. Based on δD and δ18O in xylem and soil water, we found that winter wheat derived approximately 78.1 ± 8.9% of its water from the 0-50 cm soil stratum. At the sub-daily time scale, root water uptake from 20 to 50 cm depth mainly occurred during the late afternoon (12:00-18:00 LST). Soil water evaporation was approximately 107.8 mm over the season, 55.8% of which was lost during the filling stage. These results are expected to have implications for the sustainability of irrigated agriculture in this area.