Water shortage sensing through infrared canopy temperature: timely detection is imperative

Three versions of the crop water stress index (CWSI) have been tested: the theoretical approach reported by Jackson et al. (1981), its modification proposed by Clawson et al. (1989) and an original development which takes into account the actual value of the canopy resistance of a well-watered crop. All three have been considered in order to evaluate their suitability to field detection of water stress of sweet pepper plants. Water shortage detection was not fully satisfying in any case; CWSI values were strongly influenced by the rapid adaptation of plants to water shortage.