study the effect of cut of irrigation at different stages of growth on quantity and quality of sugar beet on khoy region

water stress decrease water content and water potential between soil and root. therefore, water potential  of plant declines and plant faces with water stress. water stress in different stages of growth can be useful in different aspects. water stress can be practiced from two point of view, increasing water use efficiency (wue) and improving cultural practices. no irrigation in insensitive stages of growth for water stress helps us to save water  which could be used for other crops. in this research, the effect of irrigation scheduling at different stages of growth on quality and quantity of sugar beet was studied, in khoy agricultural research station in two years (1999 and 2001). the experimental design was a randomized complete block design with three replications and seven irrigation treatments; as i1:full irrigation at all stages of growth, i2: no irrigation at sowing until germination, i3: no irrigation at germination until the beginning of growth; i4: no irrigation at sowing till germination and again no irrigation at growth season, i5: no irrigation at sowing till germination and no irrigation at the end of season, i6: no irrigation at  the germination till constant growth and one irrigation during constant growth, i7: no irrigation at germination till constant growth and no irrigation at the end of season. according to the results, irrigation treatments influenced the root and sugar yield significantly. lack of irrigation in the initial increased stage sugar yield 13.3% and decreased irrigation water amount 16.5% as compared to the control treatment (i1, full irrigation). wue was 1.7 and 1.25 kg/m3 in i2 and i1 treatments, respectively.  omitling irrigation in the initial and in the  last stage of growth decreased the irrigation water amount 21.2%, increased available sugar 11% and improved wue from 1.25 (control treatment) to 1.76. irrigation treatments had significant effect on sugar content and na (impurities) and  no significant effect on other qualitative characers. no irrigation in initial and last stages of growth caused the most highest increase in sugar content of compared to the control treatment. accordingly, sugar content increased from 12.74% to 16.09%.