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ARS Home » Plains Area » Fort Collins, Colorado » Center for Agricultural Resources Research » Water Management and Systems Research » Research » Publications at this Location » Publication #333404

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

item HAN, MING - Colorado State University
item Zhang, Huihui
item DeJonge, Kendall
item Comas, Louise
item Gleason, Sean

Submitted to: Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2018
Publication Date: 3/27/2018
Citation: Han, M., Zhang, H., Dejonge, K.C., Comas, L.H., Gleason, S.M. 2017. Comparison of three crop water stress index models with sap flow measurements in maize. Remote Sensing. vol. 203, issue C, 366-375.

Interpretive Summary: Crop water stress index (CWSI) has been recognized as an indicator of plant water status based on canopy temperature. Various models have been developed to calculate CWSI. It is critical to know the accuracy and uncertainties of these different models before applying them for irrigation application. In this research, we evaluated three CWSI models using maize transpiration estimates determined from sap flow measurements. Field experiments in replicated plots were conducted at our deficit irrigation research farm for the 2015 growing season. We measured continuous canopy temperature with infrared thermometers and sap flow from four treatments at different irrigation levels. Results showed that all three models gave reasonable overall estimates of crop water stress, and the theoretical model with seasonal average aerodynamic resistance is recommended for assessing maize water status. These findings are valuable for potentially using continuous canopy temperature measurements by infrared thermometers for managing deficit irrigation.

Technical Abstract: Both empirical and theoretical models have been widely used to calculate crop water stress index (CWSI) – a metric often used to describe annual crop or tree water status. We report here the accuracy, limitations and uncertainty of an empirical model (CWSI-E) and two theoretical models using sap flow measurements 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 both crop coefficient and sap flow measurements, all three models gave reasonable overall estimates of water stress. The averaged root mean square deviation at each growth stage from each model ranged from 0.16 to 0.33. However, CWSI-T1 did not accurately predict water stress between growth stages or between irrigation events. In contrast, CWSI-T2 and the CWSI-E provided relatively accurate prediction of crop stress, both between growth stages and irrigation events. By including climate factors, crop water stress estimated from 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). The intercept of non-water stress baseline was the main source of the uncertainty. Considering both uncertainty and stability, we recommend CWSI-T2 model (i.e., seasonal average aerodynamic resistance) for maize water stress assessment.