Due to limited water resources, research on the optimizing irrigation water use an decrease in yield per unit of water used is very important. Thus, a field study was conducted in 2010 at Research Fields of University of Azad (Karaj) to evaluate the effect of IFI and humic acid under deficit irrigation and without drought stress on water use efficiency and some sugar beet traits. The treatment factors were irrigation methods at two levels (Conventional furrow irrigation (CFI) and intermittent furrow irrigation (IFI)), humic acid application at three levels (zero humic acid control, foliar application of humic acid, and humic acid application with irrigation), water stress at two levels of intensity (based on 40 and 70% depletion of available soil moisture). Irrigation methods and water stress treatments were as the main plot s and application of humic was as the subplot. water use efficiency (WUE), Total WUE, root yield (RY), WSY (white sugar yield), total dry matter (TDM), harvest index (HI) were estimated. Results indicated that statistically significant interactions between irrigation methods × humic acid on root yield and irrigation levels × humic acid on root yield (at P ≤ 0.01 and P ≤0.05, respectively). Results also showed that WUE and Total WUE were affected by irrigation methods, so that IFI method could enhance water saving by 35 %. For RY, WSY, the best results were obtained from humic acid with irrigation (76.94 and 7.94 ton ha -1, respectively). Furthermore, WUE, RY and TDM (at P ≤ 0.01) and WSY (at P ≤0.05) were affected by stress levels.
