Evaluation of Canopy Temperature Based Crop Water Stress Index for Deficit Irrigation Management of Sugar Beet in Semi-Arid Climate

Highlights Sugar beet irrigation scheduling was based on daily average crop water stress index between 13:00 and 16:00 hours. Three crop water stress index thresholds, 0.2, 0.35, and 0.55, were evaluated for irrigation scheduling. Season evapotranspiration decreased and soil water extraction increased as crop water stress threshold increased. There was no significant difference in root or sucrose yield between full irrigation and 0.2 crop water stress index, while seasonal irrigation depths were reduced from133 to 185 mm. Abstract. Sugar beet is an economically important crop in the semi-arid Intermountain Western U.S., with seasonal water use ranging from 500 to 900 mm. Sugar beet is a deep-rooted crop (1.5-2 m) in unrestricted soil profiles that can utilize stored soil water to reduce seasonal irrigation requirements. Effective use of stored soil water below 0.6 m requires precise irrigation scheduling and knowledge of soil water availability below 0.6 m, which is usually unknown due to the labor and expense of soil water monitoring at deeper depths and uncertainty in effective rooting depth and soil water holding capacity. Deficit irrigation (DI) management of sugar beet using a thermal-based crop water stress index (CWSI) has the potential to overcome soil water monitoring limitations and facilitate the utilization of stored soil water to reduce seasonal irrigation requirements. The objective of the research summarized in this paper was to implement and evaluate the effect of automated DI scheduling of sugar beet using three daily average CWSI thresholds (0.2, 0.35, and 0.55) on seasonal irrigation requirement, crop evapotranspiration, seasonal soil water depletion, root yield, estimated recoverable sugar (ERS) yield, and water use efficiency compared to full irrigation. There were no significant differences in root and ERS yield between full irrigation and 0.2 CWSI DI treatment, while seasonal ET was significantly decreased, seasonal soil water extraction was significantly increased, and seasonal irrigation depths were reduced from 133 to 185 mm. Root and ERS yield water production functions were curvilinear with a downward concave. Root and ERS yield water use efficiencies were constant or increased slightly for crop evapotranspiration reductions up to 85% of full irrigation evapotranspiration. The results indicate that irrigating when the average daily CWSI sugar beet exceeds 0.2 is an effective means for mild deficit irrigation scheduling to reduce seasonal irrigation requirements with no significant effect on root and ERS yield. Keywords: Crop water stress index, Evapotranspiration, Irrigation, Irrigation scheduling, Root yield, Sucrose yield, Sugar beet.