Productivity and water use efficiency of sweet sorghum (Sorghum bicolor (L) Moench) cv ''Keller'' in relation to water regime

Sweet sorghum (Sorghum bicolor (L.) Moench) has been recognized as an alternative crop for energy purposes. In the central area of the Iberian Peninsula, its main growth period coincides with the dry season and irrigation is needed for reasonable sorghum productivity. Knowledge of irrigation-yield relationships is fundamental, since water is a scarce resource there. Our objectives in this work were to study the effect of water regime on the productivity and water use efficiency (WUE) in a sweet sorghum cultivar ''Keller'' grown in lysimeters in Madrid. Experiments were carried out during three crop cycles. Three irrigation regimes: H-1, H-2 and H-3, corresponding to a water supply of 5.7, 11.4 and 17.1 dm(3) m(-2) day(-1) were experimented with during the main growth period. Maximum aerial biomass production was 4.0 10(3)g DM m(-2) in the H-3 regime. WUE was quite similar for every irrigation regime but varied between sorghum seasons. 4.6 g aerial biomass DM dm(-3) was obtained as the average for a crop cycle length of approximately 130 days. The water regime did not clearly affect the sugar content in stalk sections. The mean value of sugar content in whole stalks was 41.4% w/w on a dry-weight basis. The ratio of ethanol production to evapotranspired crop water was estimated at 0.63 g dm(-3) (mean value).