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

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 maintained weather stations is cost prohibitive. A less costly option would be to install atmometers within the field 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. 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.