This study was carried out to understand the relationships between yield and irrigation water applied at different growth periods and to determine the most critical period(s) for sunflower. A rainfed (non-irrigated) treatment as the control and 13 different irrigation treatments (H, F, M, HF, HM, FM, HFM, H60FM, H40FM, HF60M, HF40M, HFM60, HFM40) With full (about 360 min) or limited (40 and 60%) irrigation water, were applied to the hybrid Sanbro (Novartis Seed Company) planted on clay soil, at three critical development periods: heading (H), flowering (F), and milking (M). Evapotranspiration (ET) increased as an increasing amount of irrigation water was applied. The highest seasonal ET (an average of 674 mm) was measured in the HFM treatment. Limited irrigation applied at different at-owing periods had different effects on the yield-related characters examined. The highest seed yield (4056 kg ha(-1)) and oil yield (1841 kg ha(-1)) were obtained from the HFM treatment; 85.4 and 88% increases, respectively, compared with the control. The seed yield and oil yield increases for the limited-irrigation treatments were: 78.7 and 77.4% for H60FM; 77.4 and 78.9% for H40FM; 72.2 and 75% for HF60M; 76.4 and 79.2% for HF40M; 72.7 and 73.6% for HFM60; 77.6 and 79.1% for HFM40. Therefore, we confirm that HFM irrigation is the best choice for maximum yield under the local conditions, but these irrigation schemes must be re-considered in areas where water resources are more limited. In case of more restricted irrigation, the limitation of irrigation water at the flowering period should be avoided. (C) 2003 Elsevier B.V. All rights reserved.