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Comparison of three crop water stress index models with sap flow measurements in maize

Han, Ming, Zhang, Huihui, DeJonge, Kendall C., Comas, Louise H., Gleason, Sean
Agricultural water management 2018 v.203 pp. 366-375
climatic factors, corn, crop coefficient, developmental stages, irrigation, models, prediction, sap flow, uncertainty, vapor pressure, water stress
Both empirical and theoretical models have been widely used to calculate a crop water stress index (CWSI) − a metric often used to describe crop water status. The purpose of this study was to determine the accuracy, limitation, and uncertainty of an empirical (CWSI-E) and two theoretical models compared with sap flow measurement in maize. One theoretical model used a calculated aerodynamic resistance (CWSI-T1), and the other theoretical model used seasonal average aerodynamic resistance (CWSI-T2). Considering the uncertainty of crop coefficient and sap flow measurement, CWSI-T2 and CWSI-E models gave reasonable overall estimates of water stress. The average root mean square deviation at each growth stage from each model ranged from 0.16 to 0.33. CWSI-T2 and the CWSI-E provided relatively accurate prediction of crop stress, both between growth stages and irrigation events. However, CWSI-T1 did not accurately predict water stress between growth stages or between irrigation events. By including climate factors, crop water stress estimated by CWSI-T2 showed less variation and uncertainty than CWSI-E. The uncertainty of both CWSI-T2 and CWSI-E decreased with increasing vapor pressure deficit (VPD), and CWSI-E show larger crop water stress prediction uncertainty. The intercept of non-water stress baseline was the main source of the uncertainty for CWSI-E and CWSI-T2. Considering both uncertainty and stability, we recommend CWSI-T2 model (i.e., seasonal average aerodynamic resistance) for maize water stress assessment.