Water Regime Effect on Growth Indices and Quantitative and Qualitative Yields Characteristics of Sugar Beet

This study was conducted to determine the appropriate irrigation interval on the basis of cumulative water evaporation from Standard Evaporation Pan (Class A) and to find out the effects of irrigation regimes on growth indices and on qualitative and quantitative yields of sugar beet. The experiment was conducted in 2005 at the Lavark Agricultural Experiment Station Fields, Isfahan University of Technology located near Nejaf-abad using a randomized complete block design with four replications. The study included four irrigation regimes of: I1, I2, I3, and I4, namely, irrigation after 70, 85, 100 and 115 mm of cumulative pan evoporation up to September while afterwards, irrigation at 85, 100, 115 and 130 mm of cumulative pan evaporation, as the main plots along with two monogerm cultivars (Zarghan and Shirin) as subplots. Total dry weight decreased by about 45% as water regime was held from I1 to I4 treatment, while the effect of cultivar on total dry weight being non significant. The effect of irrigation treatments on leaf area index (LAI) was significant in all the samplings, being reduced with hold in water. The effect of cultivar on LAI was non significant in some samplings, but LAI in Zarghan was higher than that in Shirin cultivar. Crop growth rate decreased as irrigation was held from I1 to I4. However, moisture stress further than I2 negligibly affected net assimilation and relative growth rate. The effect of water regime was significant on root yield. Maximum root yield (77.5 t ha-1) was obtained from I1 treatment while the minimum (54.37 t ha-1) obtained from I4. Cultivars did not significantly differ for root yield. Maximum (17.19%) and minimum (15.02%) sugar content was obtained from I3 and I2 irrigation treatments, respectively. The highest and the lowest sodium, potassium as well as harmful nitrogen contents were found in I1 and I4 irrigation treatments respectively. The highest extractable sugar content (13.47%) was obtained from I3 irrigation treatment. The highest (8.45 t ha-1) and the lowest (6.99 t ha-1) white sugar yield were obtained from I3 and I4 irrigation treatments, respectively. From the obtained results, it can be concluded that to economize in irrigation water and at the same time to obtain optimum yield, irrigation of the crop (at the beginning of the growing season, namely months of April an May) must be on the basis of I3 while later on the irrigation should be based upon I1 treatment.