The Gezira Scheme is Sudan's oldest and largest gravity irrigation system. The scheme has played an important role in the economic development of the country, and is a major source of foreign exchange. The farming system of the Gezira Scheme is dominated by crop production. The main crops grown are sorghum, wheat, groundnut and the oilseed crop sesame. Sunflower (Helianthus annuus L.) is an important oil crop in the world and a new edible oil crop in Sudan. Knowledge of the effects of irrigation scheduling on sunflower production and water productivity under water stress conditions is becoming increasingly important. Irrigation scheduling is particularly important since many field crops are more sensitive to water deficit at specific phonological stages. Sunflower has several growth stages: emergence, vegetative, reproductive, flowering, seed formation and maturity. Water stress in each stage results in reduction in seed yield and oil content. The treatments in the test plots, which were conducted to study the effect of water stress at different growth stages, showed that sunflower was significantly affected by water stress that occurred in the sensitive flowering and seed formation stages. Highest seed yield was obtained when water stress was avoided during these stages. The AquaCrop model was used to simulate the seed yield and water productivity. The model was able to precisely simulate seed yield, but overestimated water productivity under different irrigation treatments.

The Gezira Scheme is Sudan's oldest and largest gravity irrigation system. The scheme has played an important role in the economic development of the country, and is a major source of foreign exchange. The farming system of the Gezira Scheme is dominated by crop production. The main crops grown are sorghum, wheat, groundnut and the oilseed crop sesame. Sunflower (Helianthus annuus L.) is an important oil crop in the world and a new edible oil crop in Sudan. Knowledge of the effects of irrigation scheduling on sunflower production and water productivity under water stress conditions is becoming increasingly important. Irrigation scheduling is particularly important since many field crops are more sensitive to water deficit at specific phonological stages. Sunflower has several growth stages: emergence, vegetative, reproductive, flowering, seed formation and maturity. Water stress in each stage results in reduction in seed yield and oil content. The treatments in the test plots, which were conducted to study the effect of water stress at different growth stages, showed that sunflower was significantly affected by water stress that occurred in the sensitive flowering and seed formation stages. Highest seed yield was obtained when water stress was avoided during these stages. The AquaCrop model was used to simulate the seed yield and water productivity. The model was able to precisely simulate seed yield, but overestimated water productivity under different irrigation treatments.