This field study was conducted in order to investigate the yield and quality of sugar beet cv zargan in relation to different irrigation regimes during 2005 at Ardabil conditions. The experimental design was a randomized complete block design with four replicates. In this experiment irrigation regimes were I₁ = Irrigation at 13.3 F.C (30% F.C), I_2b= Irrigation at 15.5 F.C (50% F.C), I₃ = Irrigation at 17.7 F.C (70% F.C) and I₄ = Irrigation at 19.9 F.C (90% F.C). Parameters such as root yield (t/ha), leaf yield (t/ha), sugar content (%), Molasses (%), pure sugar content (%), white sugar yield (t/ha), Na (mmol/100 g root), K (mmol/100 g root) were evaluated. Irrigation treatments had a significant effect on sugar yield and its quality. Potassium concentration was not significantly affected by irrigation treatments. Results of irrigation treatments showed that the optimum soil water content for root yield is 70% of field capacity with 78.5 t/ha. The minimum root yield (52.5 t/ha) was observed at 90% of field capacity. Irrigation at 30, 50 and 70% of field capacity (I_1, I₂ and I₃) had same effect on sugar content while sugar content decreased at 90% field capacity (I₄). When the available soil water content was at 70% of field capacity, maximum root yield and quality was observed.

Key word: Beta vulgaris, irrigation, root yield, sugar quality.