Sugar Beet Yield and Quality Response to Irrigation Management.

Sugarbeet requires a considerable amount of water (250-450 mm). Over irrigation not only negatively affect root yield and sucrose content/purity but also increases water waste and nutrient leaching, and boost disease infestation. In the sprinkler-equipped field, excessive irrigation also increases fuel/electricity cost for irrigation. A field experiment was conducted in eastern Montana in a split-plot arrangement based on RCBD to evaluate the effect of irrigation on sugarbeet. Main plots were irrigation cutoff time (last irrigation 15 vs. 30 days before harvest). Subplots were irrigation levels (irrigation based on 100%, 66%, and 33% crop evapotranspiration [ET]). Crop evapotranspiration was calculated on a daily basis according to the modified FAO Penman-Monteith method. Consequently, 33 and 66% less irrigation water were used in ET66 and ET33 treatments, respectively, which can be translated into 33 and 66% less energy (diesel or electricity). The results showed that time of irrigation cutoff and irrigation level had a significant effect on sucrose percent and IWUE. It was notable that reducing irrigation water to 66 and 33% of the crop ET did not affect plant growth, root yield, and sucrose yield. Whereas irrigation water depth had no significant effect on root yield, sucrose percent followed an increasing trend (from 18.3% to 18.8%) in response to lowering irrigation water depth. Although the impurity value and SLM showed a slight increase in response to lowering irrigation water depth, the difference between irrigation treatments in this regard was not statistically significant. Extractable sucrose yield showed a positive response to lowering the irrigation depth. The positive response of root and sucrose yield to lower irrigation depth caused a significant improvement in IWUE. We also noted that one more irrigation during September (15 days before harvest) had a positive effect on plant aboveground biomass, root yield, and extractable sucrose yield. It should be noted that this experiment took place in a field with water table as shallow as 1.2m. Therefore, a partial contribution of the high water table to the soil moisture within the root zone is possible, which was not quantified in this experiment. These results show the high potential for water, energy, and money savings in sugarbeet production through optimization of irrigation management. Specifically, optimum irrigation management is likely to be even more important in near future considering the scenarios of climate change.