<i>Evaluation of the Surface Renewal Method for Measuring Crop Evapotranspiration in a Humid Environment</i>

Abstract

Abstract. Water is a limiting factor in the growth of plants such as fiber producing cotton. Due to its importance, an effort has been undertaken to measure water use through an array of methodologies measuring evapotranspiration (ET). One holding promise as an affordable method is the surface renewal (SR) method. The objective of this study was to take the SR method and compare its ET measurements to other methods such as weighing lysimeters and the eddy covariance (EC) method. Measurements were taken over cotton in a temperate, fully humid, hot summer environment using two in-field weighing lysimeters and two energy budget towers. The energy budget towers measured sensible heat using the EC method and the SR method at 1.5 m and 1.6 m, with ET estimated as a residual for both methods. The 1.5 m SR measurement showed the strongest agreement with both EC ET values (R2 >= 0.99) and 1 lysimeter (R2 = 0.75). Application of the Castellvi method improved the agreement of the 1.6 m ET measurement with both EC ET estimates (R2 before = 0.93, 0.94; Castellvi R2 = 0.98, 0.99) and the lysimeter sited nearest a tower used for Castellvi measurements (R2 before = 0.61; Castellvi R2 = 0.73). Fetch could have played a factor at both sites, though was not able to be analyzed due to a diurnal pattern in lysimeter readings. The diurnal pattern suggests condensation or temperature effects on lysimeter load cells. We recommend that SR‘s ability to measure condensation be further analyzed.