GRAIN-SORGHUM RESPONSE TO SUPPLEMENTARY IRRIGATIONS UNDER POST-RAINY SEASON CONDITIONS

Irrigated sorghum (Sorghum bicolor L.) in the Sudan is grown during th e rainy season with supplementary irrigation (SI). A field study was c onducted for 2 years (1993 and 1994), at the Gezira Research Station, Sudan, to evaluate effects of SI under the post-rainy season condition s on grain and forage yields, yield components, water use and its econ omics using three promising varieties. Addition of one SI in the first year (FY) and two SIs in the second year (SY) resulted in significant grain yield increases as compared with no SI and one SI. Whereas two SIs in the FY produced a non-significant increase, three SIs in the SY tended to decrease grain yields. Grain yield variations were positive ly correlated with the number of seeds m(-2) and 1000-grain weight. Fo r forage, however, varieties differed significantly only in the FY. Ad dition of SI linearly increased forage yields and the differences were significant in the SY. Irrigation production efficiency (IPE) for gra in yield generally decreased with addition of SI. No appreciable diffe rences in grain yield were found between varieties or their interactio ns with SI in both seasons. Economic evaluation revealed the profitabi lity of adding two rather than three SIs, whereby the investment in th e second SI gave a 192-fold benefit.