SORGHUM YIELD, WATER-USE AND CANOPY TEMPERATURES UNDER DIFFERENT LEVELS OF IRRIGATION

This research was initiated to examine water use of differentially irr igated sorghum (Sorghum bicolor (L.) Moench) and to evaluate the plant water stress using canopy temperature measurements. Field experiments were conducted for 3 years characterised by different weather conditi ons at Montpellier, France. The crop was subjected to 14 differentiall y irrigated treatments which included, each year, a full irrigated and a dry treatment. Plant and soil measurements monitored during the cro p cycle included soil water content, leaf water potential, and canopy temperature. Mid-day measurement of crop canopy temperature (Tc)/air t emperature (Ta) difference reached a maximum of 7 degrees C in the dry treatment and was maintained close to 0 degrees C in full irrigated t reatment. The relationships between (Tc-Ta) and vapour pressure defici t (VPD) commonly referred to as 'baseline' in the determination of cro p water stress indicator (CWSI) were examined on function of wind spee d and global solar radiation. Three approaches of estimating CWSI were compared. Summations of stress-degree-day (SDD) and temperature-stres s-day (TSD) were well related to both relative evapotranspiration and yield (r(2) > 0.70).