Canopy temperature to assess daily evapotranspiration and management of high frequency drip irrigation systems

Abstract

The infrared thermometer (IRT) can be an important tool for detection of crop water stress symptoms for it measures the canopy temperature. This enables the system operator to translate it into a crop water stress index (CWSI). IRT has not yet been used to manage irrigation by using it to estimate the daily transpiration rate. The goal of this study was to test the applicability of IRT to control precise irrigation by: (1) comparing crop water stress index (CWSI) with standard pressure chamber, and (2) comparing IRT-estimated transpiration of tomato and cotton with other, more standard, methods. A model for using IRT as a tool for evaluating daily transpiration is presented. This was tested in Israel and California. The IRT was found to measure adequately differences in canopy temperature and its derivatives only when water treatments differ largely from one another. Good agreement was obtained under optimal water regime when daily lysimeter measurements were compared to IRT measured transpirations. An acceptable correlation was obtained when CWSI was related to ψ L (leaf water potential). The resolution of IRT was insufficient to detect small differences between well irrigated treatments; nor was it able to assess transpiration on a short-time scale. It is concluded that at its present status implementation of the IRT using both CWSI and transpiration estimation could not improve efficiency of high frequency irrigation.