|Water demand of a sunflower crop from emergence to physiological maturity shows that the maximum water demand is around flowering, while an equal amount of water is required at bud appearance as at about physiological maturity. Water is important for leaf expansion and there is an established relationship between leaf area and yields. Up to 70% yield reduction can be realized when water stress is experienced during the growth and development of the crop.
The timing of the stress, however, is most important. Water stress up to flowering can reduce yields up to 22% while stress in the early stages of development have no significant effect on yield. In Zambia most crop production is done during the rain season, while seed production is better conducted during dry season. It is very important, therefore, that adequate water is supplied to the crop from bud formation onwards to physiological maturity.
As a general rule, irrigation should maintain soil moisture to at least 50% of field capacity. Soil moisture at 80% of field capacity at flowering stages and 70% of field capacity at other times is considered optimum. Irrigation should continue beyond anthesis. Actual irrigation requirements will be dictated by the soil texture and other factors. The grower is advised to seek expert advise on irrigation scheduling etc.
Water requirements of sunflower are generally higher than most field crops making it an inefficient water user. However, the crop is capable of producing satisfactory yields under prolonged water stress, when other crops would be severely damaged. This characteristic is attributed to the deep root system.
The critical period of water requirements is about 20 days before and after flowering. Drought conditions during flowering has profound effects on seed yield.
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