WATER EFFICIENCY AND STRESS ON GRAIN-SORGHUM AT DIFFERENT REPRODUCTIVE STAGES

The effects of water stress occurring at various growth stages during the reproductive cycle of grain sorghum were evaluated in open field c onditions under a Mediterranean climate. This research was carried out under the same conditions in two steps: (1) assessing the degree of w ater stress; (2) evaluating the water use efficiency (WUE) and the sen sitivity of phenological stages submitted to identical water stress, T he first step consists in field calibration of the water stress criter ion, During three soil drying cycles it was observed that: (1) the hig hest stomatal conductance occurred in correspondence with leaf water p otential (Psi) values higher than - 1.5 MPa; (2) stomata tended to clo se when Psi becomes lower than -1.8 MPa. These values were retained in the second step for monitoring plant water status in four different p lots: one never stressed and three stressed at different phenological stages (early flowering, seed-setting and ripening). An evaluation of the sensitivity of phenological stages submitted to identical water st ress was obtained by comparing four yield components (above ground bio mass, grain yield, 1000 grain weight and seed number) and WUE to those of the well-irrigated crop, The sensitivity was greatest at the early flowering stage. For water saving purposes, these conclusions could b e useful for scheduling grain sorghum irrigation.