Thermal crop water stress index base line temperatures for sugarbeet in arid western U.S.

Authors: King, Bradley - Brad; Tarkalson, David; SHARMA, V - University Of Wyoming; Bjorneberg, David - Dave

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2020
Publication Date: 8/26/2020
Citation: King, B.A., Tarkalson, D.D., Sharma, V., Bjorneberg, D.L. 2020. Thermal crop water stress index base line temperatures for sugarbeet in arid western U.S. Agricultural Water Management. 243. https://doi.org/10.1016/j.agwat.2020.106459.
DOI: https://doi.org/10.1016/j.agwat.2020.106459

Interpretive Summary: Sugarbeet is a deep-rooted crop in unrestricted soil profiles that can readily utilize stored soil water to reduce seasonal irrigation requirements. Utilization of soil water below 0.6 m is not commonly considered for irrigation scheduling due to the labor and expense of soil water monitoring at deeper depths and uncertainty in site-specific effective rooting depth and soil water holding capacity. A canopy temperature based crop water stress index (CWSI) has the potential to overcome soil water monitoring limitations and facilitate utilization of stored soil water to reduce seasonal irrigation requirements while maintaining sugar yield. Canopy temperature of irrigated sugarbeet under full irrigation (FIT) and 25%FIT in 2014, 2015, 2017 and 2018 in southcentral Idaho and FIT and 60%FIT in 2018 in northwestern Wyoming was monitored from full cover through harvest along with meteorological conditions and soil water content. The collected data were used to develop data driven models for estimating baseline canopy temperatures needed to compute sugarbeet CWSI. A daily CWSI value calculated as the average 15-min CWSI calculated between 13:00 and 16:00 MDT was well correlated with irrigation amounts and timing. The daily CWSI value provided a more responsive indication of crop water stress than soil water monitoring in deficit irrigation treatments. The methodology used to calculate a daily CWSI could be automated for use in irrigation scheduling to utilize soil water storage without knowledge of soil depth, crop rooting depth, or deep (> 0.6 m) soil water monitoring.

Technical Abstract: Sugarbeet is a deep-rooted crop in unrestricted soil profiles that can readily utilize stored soil water to reduce seasonal irrigation requirements. Utilization of soil water below 0.6 m is not commonly considered for irrigation scheduling due to the labor and expense of soil water monitoring at deeper depths and uncertainty in effective rooting depth and soil water holding capacity. Thermal-based crop water stress index (CWSI) irrigation scheduling for sugarbeet has the potential to overcome soil water monitoring limitations and facilitate utilization of stored soil water. The traditional canopy temperature based CWSI for monitoring plant water status has not been widely used for irrigated crops partly because of the need to know well-watered and non-transpiring canopy temperatures under identical environmental conditions. In this study, canopy temperature of irrigated sugarbeet under full irrigation (FIT) and 25%FIT in 2014, 2015, 2017 and 2018 in southcentral Idaho and FIT and 60%FIT in 2018 in northwestern Wyoming USA was monitored from full cover through harvest along with meteorological conditions and soil water content. Data driven models, multiple linear regression (MLR) and neural network (NN), were used to predict well-watered canopy temperature based on 15-min average values for solar radiation, air temperature, relative humidity, and wind speed collected within 2 hours of solar noon (13:00 – 16:00 MDT). The NN model had significantly less (p < 0.01) prediction error variance than MLR. A linear regression driven physical model for estimating the difference between a non-transpiring canopy and air temperature resulted in a value of 13.7 degrees C for the average meteorological conditions of the study. A daily CWSI value calculated as the average 15-min CWSI calculated between 13:00 and 16:00 MDT was well correlated with irrigation amounts and timing. The daily CWSI value provided a more responsive indication of crop water stress than soil water monitoring in deficit irrigation treatments. The methodology used to calculate a daily CWSI could be automated for use in irrigation scheduling to utilize soil water storage without knowledge of soil depth, crop rooting depth, or deep (> 0.6 m) soil water monitoring.