Utilizing infrared radiometry thermometer and two source energy balance model for irrigation scheduling of dry edible beans in western Nebraska: Part 2. Modeling

Having an accurate yet simple estimation of crop evapotranspiration (ET) is a vital component of reliable irrigation scheduling. The Two-source energy balance model (TSEB) has been proposed to estimate ET, where sensible and latent heat flux for both soil and canopy sources can be calculated separately using a single measurement of composite surface temperature (TR), meteorological variables (air temperature, wind speed, solar radiation, relative humidity), and vegetation information (crop height, canopy cover percentage, leaf area index). Ability of partition TR into canopy temperature (TC) and soil temperature (TS) is key, yet the most challenging component of using TSEB model to estimate crop ET. In this study, we proposed a new method to separate Tc and Ts during full crop growing cycle, by using RGB canopy cover picture and an in-house developed canopy cover detection software. The results indicated that IRT and calibrated TSEB-PM model provide reasonable estimation of evapotranspiration of dry edible beans in western Nebraska, which is in close agreement with ET calculated by FAO56 method (R² ranged from 0.85 to 0.93). This new approach allows us to calculate crop ET and water stress indexes from IRT and the TSEB model during the full crop growing cycle.