Using Eddy Covariance, Soil Water Balance, and Photosynthetically Active Radiation Methods for Corn Evapotranspiration Measurements in the Red River Valley

Abstract

Abstract. Evapotranspiration (ET) is an important component for determining water balance and water transfer. Water management practices (WMP) that utilize soil water balance algorithms to determine the best irrigation schedules tend to rely heavily on measured or estimated ET values. However, ET values can be difficult and expensive to obtain. In this study, three different methods were used to estimate ET: eddy covariance (EC), soil water balance (SWB), and photosynthetically active radiation (PAR). The EC method is considered as one of the most accurate methods, but the EC system is relatively expensive and requires trained personnel to conduct the calculations. The real-time ET estimates using the PAR method and wireless data access have provided simple and cheap ways to estimate ET. The SWB method has been traditionally used to estimate ET, but when a shallow water table is present and upward flux is not considered, its accuracy is questionable. In 2012, these three methods were used to estimate ET for two corn varieties in four production fields located in Clay County, Minnesota. The four adjacent fields each had a different water management system; undrained (UD), subsurface drained (SD), controlled drained (CD), and CD plus subirrigated (CD + SI). At the CD + SI site, EC, SWB, and PAR were used to measure ET, while for the other three fields, only one method, either SWB or PAR, was used. It was found that PAR ET agreed relatively well with ET by EC method with a coefficient of determination (R 2 ) of 0.94 and root mean square error of 0.02 mm/30 min. However, the SWB estimates were highly variable and showed little to no correlation with EC ET data. This paper will present comparisons across the three ET methods, four water management practices, and two corn varieties.