Drought Sensitivity at Various Growth Stages of Barley in Relation to Relative Evapotranspiration and Water Stress1

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Abstract
Previous investigations into the influence of drought on yield of barley (Hordeum distichurn L.) have been related to either the intensity of water stress or the duration of drought periods. Little attention has been given to the combination of intensity and duration of water stress. In this investigation drought sensitivity (F), calculated as relative grain yield reduction (1 — u/U) of barley at various growth stages, was related to the number of stress days (SD). The number of stress days was calculated as the product of relative evapotranspiration deficit (1 — Ea/Er) and the duration of drought periods (days). Barley (‘Zita’), grown in loamy sand (mixed mesic Typic Udipsamment) in lysimeters, was exposed to drought at different development stages. The lysimeters were automatically protected from rain by a mobile glass roof. Each drought treatment consisted of a single period without irrigation. Watering resumed when all available soil water was used. The first drought occurred during jointing and the final one during ripening. Relative evapotranspiration (Ea/Er) was found to be a more sensitive expression for crop water stress than leaf water potential. Relative evapotranspiration began to decrease when two‐thirds of available soil water had been used. The length of drought periods is defined from that time until irrigation was resumed. Drought sensitivity per stress day (F/SD) was decreased from 0.14 during jointing to 0.08 during booting. For drought after heading F/SD was 0.038 corresponding to a 3.8% grain yield reduction per stress day. This means that one stress day corresponds to one day without grain growth.

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