Comparison of water stress coefficient using three alternative canopy temperature-based indices

Abstract: In this study three crop canopy temperature-based water stress indices, standard deviation of the distribution of canopy temperature (CTSD), the ratio of canopy temperature of non-stressed to stressed canopy (Tc –ratio ) and Degrees Above Non-Stressed (DANS), were tested as the substitute of water stress coefficient (Ks) for maize crop water use estimation. Thermal imagery was taken from maize under various levels of deficit irrigation at different crop growth stages in 2015 and 2016 growing seasons. The Expectation-Maximization algorithm was used to estimate the canopy temperature distribution from thermal imagery under a range of crop coverage and water stress conditions. CTSD, Tc –ratio and DANS were calculated from the extract canopy temperature and converted to water stress coefficient denoted as Ks –CTSD , Tc –ratio , and Ks –DANS . Crop transpiration estimated using three water stress coefficients were compared with sap flow measurements in 2015. The results further confirmed that CTSD responded well to irrigation events (timing and depth) on crops with water stress and was significantly correlated to leaf water potential and soil water deficit, especially when stress level was above moderate. Ks –CTSD was more sensitive to soil water deficit than Tc –ratio and Ks –DANS . Crop transpiration estimated using Ks –CTSD preformed the best among all methods when compared with sap flow measurements ( R 2 _ adj =0.58, relative absolute error =0.63, and root mean square error =0.87 mm day -1 ). Nash-Sutcliffe coefficient of 0.61 indicates the performance of the prediction model is sufficient and satisfactory. The canopy temperature-based index, CTSD, is easy to acquire from high resolution thermal imagery from remote sensing platforms, such as ground and unmanned aerial vehicles. It has a strong application potential to improve crop water stress detection and crop water use estimation for irrigation scheduling. Keywords: canopy temperature, CTSD, maize, water stress, thermal, soil water deficit DOI:  10.33440/j.ijpaa.20200302.78  Citation: Zhang H, Zhang L Y, Niu Y X, Han M, Yemoto K.  Comparison of water stress coefficient using three alternative canopy temperature-based indices.  Int J Precis Agric Aviat, 2020; 3(2): 28–34.