Comparison of evapotranspiration measurements between eddy covariance and lysimeters in paddy fields under alternate wetting and drying irrigation.

Evapotranspiration from paddy fields under alternate wetting and drying (AWD) irrigation was measured using lysimeters (ET_L) and eddy covariance (ET_ec) during the late 2016 and early 2017 rice seasons. Four energy balance closing methods were explored, and discrepancy of ET_L and ET_ec (with or without adjustment) in different growth stages and wet/dry conditions were examined. The results indicated that both energy balance non-closure and wet/dry conditions of the field affect the discrepancy of ET_L and ET_ec. Energy balance was suggested to be closed each half hour by 'residual-LE closure' method only at daytime, and nighttime flux stayed unchanged, while a careful data control and interpolation should be noted for nighttime flux. In the meantime, wet-to-dry patterns of AWD irrigation can affect the discrepancy between ET_ec and ET_L. In wet periods, ET_ec with suitable adjustment method was well matched with the ET_L. However, ET_L was underestimated in dry periods due to lower water content in the lysimeter. Finally, net radiation (R_n), vapor pressure deficit (VPD), air temperature (T_a), soil and water temperature (T_s and T_w), and wind speed (u) were selected to conduct path analysis on ET_L and ET_ec (with adjustment) for both wet and dry conditions. The direct dependencies of each meteorological factor on ET_L and ET_ec were similar under wet conditions; however, under dry conditions, VPD and R_n are the respective main controls for ET_L and ET_ec. Moreover, ET_L is more sensitive to T_a and T_w under wet conditions. [ABSTRACT FROM AUTHOR]