EFFECT OF WATER AVAILABILITY PATTERN ON YIELD OF PEARL-MILLET IN SEMIARID TROPICAL ENVIRONMENTS

Throughout much of the semi-arid tropics, fluctuations in grain yield can largely be attributed to differences in timing and intensity of dr ought stress. Since seasonal rainfall in these environments is often p oorly related to grain yield, the aim of this paper was to establish a relationship between water availability and grain yield for pearl mil let (Pennisetum glaucum (L.) R. Br.), grown across 24 semi-arid tropic al environments in India. We used a simple soil water budget to calcul ate a water satisfaction index (WSI) throughout the season. The cumula tive WSI at maturity explained 76% of the variance in grain yield. Thi s was three times as much as explained by actual rainfall, because WSI accounted for differences in water losses and pan evaporation. A clas sification of environments into four groups of water availability patt erns explained 75% of the environmental sum of squares for grain yield . For a subset of 13 environments, environmental differences in grain number could also be explained by water availability patterns, whereas differences in grain mass were related to both water availability and temperature. Our results indicate that cumulative WSI, which is an in tegrated measure of plant-available water, can provide an adequate est imation of the environmental potential for yield in environments where grain yield is mainly limited by variable availability of water.