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The effect of nitrogen on growth and quality of sugarbeet (Beta vulgaris L.) has been extensively studied, but its interaction with irrigation levels is not yet well understood. Experiments were conducted in two years
(1996-97) and two stations in Fars province (Badjgah and Kooshkak) with four levels of nitrogen (0, 90, 120, and 150 kg/ha) at three times of application and three levels of irrigation frequency (7, 10, and 14 days). The experimental
results indicated that although the effect of irrigation frequencies were different in different stations, however, longer irrigation intervals decreased
root yield per hectare, but percent sugar did not change. The longer irrigation intervals increased water use efficiency. Increasing nitrogen increased root yield per hectare, but times of nitrogen application did not show a predictable effect on yield. The combined analysis of experiments showed that 150 kg
N/ha is the optimum rate. However, high nitrogen decreased percent sugar content in experiments carried out in Kooshkak station. The sugar percent
was higher when the whole fertilizer was applied once, as compared to partitioning the same amount of fertilizer. The interaction of irrigation and fertilizer levels was not significant, but, the interaction of nitrogen levels and year was significant. Sugar percent showed a negative correlation with root yield as well as percent purity.