Seasonal variations in vineyard ET partitioning and dual crop coefficients correlate with canopy development and surface soil moisture

The challenge of partitioning evapotranspiration (ET) components and figuring out the main factors controlling ET partitioning was addressed over four seasons in a furrow-irrigated vineyard located in northeast China. Based on the directly measured vineyard ET and its components (soil evaporation E and plant transpiration T) using eddy covariance, microlysimeters and sap flow sensors, respectively, dynamics and controlling factors of ET partitioning and dual crop coefficients were studied. The seasonal cumulative ET was 399, 398 and 392 mm, where E was 185, 245 and 224 mm, T was 173, 167 and 158 mm, and E + T was 358, 412 and 382 mm, in 2013, 2014 and 2015, respectively. Seasonal average E represented about 52-59% of E + T and T about 41-48% of E + T. Seasonal ET partitioning was mainly controlled by surface soil water content (SWC) and leaf area index (LAI). Previous studies have found T/ET was correlated to LAI using regression functions. In this study a more biophysically robust model to estimate ET partitioning from LAI and SWC is proposed, based on dual crop coefficient theory. The evaluation of the proposed model indicated that 46% of the vineyard ET partitioning was explained. Soil evaporation coefficients (Ke) were closely correlated to SWC and peaked after rain and irrigation (even exceeding 1.0), and basal crop coefficients (Kcb) were mainly correlated to LAI. The average Kcb was 0.12, 0.31, 0.40, 0.42, 0.31 and 0.18 from May to October, respectively.