Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/10/2017
Publication Date: 3/27/2017
Citation: Colaizzi, P.D., OShaughnessy, S.A., Evett, S.R., Mounce, R.B. 2017. Crop evapotranspiration calculation using infrared thermometers aboard center pivots Agricultural Water Management. 187:173-189.
Interpretive Summary: The freshwater resources available for agriculture are diminishing due to reduced supplies and competition for other uses. Freshwater resources can be used more efficiently in agriculture by knowing when to irrigate crops. One method that can quickly tell farmers when to irrigate is measurement of plant leaf temperature. However, measuring plant leaf temperature in entire fields was previously not practical without wireless technology. Scientists at the USDA Agricultural Research Service in Bushland, Texas, developed a wireless sensor system that can measure plant leaf temperature over entire fields. They tested the system aboard moving center pivot irrigation systems. They also showed that crop water use calculated from plant leaf temperature using the sensor system could be a viable alternative to estimating crop water use by soil water measurements. Because over half of the irrigated area in the USA is now by center pivot, estimates of crop water use by sensors aboard center pivots will provide an unprecedented opportunity to conserve water.
Technical Abstract: Irrigation scheduling using remotely sensed surface temperature can result in equal or greater crop yield and crop water use efficiency compared with irrigation scheduling using in-situ soil water profile measurements. Crop evapotranspiration (ETc) is useful for irrigation scheduling, and can be calculated using surface temperature. Recent advances in wireless infrared thermometers (IRTs) have made surface temperature measurement a viable alternative to in-situ soil water profile measurement, and wireless IRTs are practical for deployment aboard moving irrigation systems, such as center pivots. However, ETc calculation has not been tested using IRTs aboard center pivots in conjunction with recent advances in a two-source energy balance (TSEB) model. We compared daily ETc calculated by a TSEB model to daily ETc estimated by a simple soil water balance (SSWB), where the SSWB used volumetric soil water measured by a field calibrated neutron probe to the 2.4-m depth. Crops included two seasons each of corn (Zea mays L.), cotton (Gossypium hirsutum L.), and grain sorghum (Sorghum bicolor L.) at Bushland, Texas, USA. Discrepancies of TSEB vs. SSWB daily ETc were similar for each crop and season, and had root mean squared error from 1.5 to 1.8 mm per day, mean absolute error from 1.1 to 1.5 mm per day, and mean bias error from -0.51 to 0.63 mm per day. A sensitivity analysis was conducted for daily evaporation (E), daily transpiration (T), and ETc calculated by the TSEB model. These were most sensitive to radiometric surface temperature, air temperature, the reference temperature used in time scaling (i.e., to convert instantaneous to daily E, T, and ETc), and incoming solar irradiance. Because over half of the irrigated area in the USA is now by center pivot, ETc calculated using IRTs aboard center pivots will be useful to maintain or increase crop water productivity.