Measuring short-crop reference evapotranspiration in a humid region using electronic atmometers

Authors: STRAATMANN, ZACHARY - Monsanto Corporation; STEVEN, GENE - University Of Missouri; Vories, Earl; GUINAN, PAT - University Of Missouri; TRAVLOS, JOHN - University Of Missouri; RHINE, MATT - University Of Missouri

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/10/2017
Publication Date: 10/20/2017
Citation: Straatmann, Z., Steven, G., Vories, E.D., Guinan, P., Travlos, J., Rhine, M. 2017. Measuring short-crop reference evapotranspiration in a humid region using electronic atmometers. Agricultural Water Management. 195(1):180-186.

Interpretive Summary: The Crop Water Use phone app is a weather based program developed by the Missouri Extension Service and linked to the Missouri state agricultural weather station network to help farmers with irrigation scheduling. For farmers outside Missouri who might be interested using this app, the cost of installing and maintaining weather stations would be expensive and a less costly option would be to install atmometers. University and ARS scientists at Portageville, Missouri, compared evapotranspiration (ET) data from atmometers to values calculated by electronic weather stations with traditional sensors. Results showed a close relationship between the two; however, values from atmometers were consistently lower than values calculated by the weather stations. Additional studies will be needed to determine if regional or localized calibration is required before using ET data from atmometers in irrigation scheduling apps. If atmometers can be shown to provide reliable estimates of ET, then these findings can be used by farmers throughout the world to irrigate their crops more efficiently.

Technical Abstract: The Crop Water Use phone app is a weather-based program developed by the Missouri Extension Service to help farmers with irrigation scheduling. A limitation of the program is that it only works on Missouri fields. The app is linked to the state agricultural weather station network, which supplies daily, standardized, short-crop evapotranspiration (ETo). For farmers outside the network, the cost of installing and maintaining appropriately equipped weather stations is cost prohibitive. A less costly option would be to install atmometers within the fields of interest. The objective of this study was to compare ETo data from atmometers to electronic weather stations with traditional sensors. In 2015 and 2016, electronic atmometers were installed at three locations in Missouri. Atmometers were placed near electronic weather stations programmed to calculate daily ETo. Each atmometer ceramic cup was fitted with a disposable paper wafer and #30 diffusion canvas cover and wired to an event data logger to record daily ETo measurements. Regression analysis showed a close relationship between ETo measured with atmometers and weather station across locations and years (R2=0.74). However, ETo from atmometers averaged 15% lower than weather stations, the accepted standard. Regional or localized calibration equations may be required before using ETo from atmometers in irrigation scheduling apps, but additional research is needed to determine if the observed differences impact recommended irrigation intervals.