Evaluation of two temperature stress indices to estimate grain sorghum yield and evapotranspiration

This study was performed to examine the relationship between canopy temperature (T(c))-based stress indices and grain yield and evapotranspiration (ET) of sorghum [Sorghum bicolor (L.) Moench]. The crop was subjected to 14 differentially irrigated treatments of which two were controls maintained at well-watered and dry conditions during three consecutive years. Soil water content and T(c) were measured, and relationships between T(c)-based stress indices [stress degree day (SDD), temperature stress day (TSD), and crop water stressed index (CWSI)] and yield as well as ET were examined. The T(c)-air temperature (T(a)) difference varied from -2 to +8 degrees C in the stressed treatments and maintained a negative value for most of the time in the well-watered treatment. The relationship between T(c) - T(a) and vapor pressure deficit, commonly referred to as baseline in the determination of CWSI, was examined on function of wind speed and global solar radiation. Although observations showed that T(c) can be influenced by climatic condition, this study confirmed that it can serve as a useful indicator of water stress in the case of sorghum. High correlation found between T(c)-based stress indices TSD, SDD, and CWSI and ET as well as grain yield suggest the possibility of using these relationships for predictive purposes.