Evapotranspiration of crops widely grown in greenhouses using the energy balance method

In this study, it was aimed to estimate the evapotranspiration (ET) of tomato, eggplant, pepper and cucumber plants that have the highest production and commercial potential in low-tech polyethylene (PE) greenhouses in the Mediterranean Region by energy balance method. For this purpose, aerodynamic resistance value, which is the most important parameter of the energy balance equation, was calculated by different methods proposed in the literature and estimated by the new model developed based wind speed, plant height, and on the difference of crop canopy-air temperature. The ET values estimated by using aerodynamic resistance values determined by different methods in the energy balance equation were compared with the ET values measured directly from the lysimeters. The obtained results showed that the ET values predicted by using the aerodynamic resistance equations suggested in the literature are not compatible with the values measured in low-tech Mediterranean type PE greenhouses. When the ET values obtained by using the approach related to aerodynamic resistance developed in this study were compared with the actual ET values, in tomato plant R2, 0.96; RMSE, 12.11; RE, 0.15; MBE, -3.19; dw, 0.99; in eggplant plant R2, 0.95; RMSE, 12.09; RE, 0.19; MBE, 5.04; dw, 0.98; in pepper plant R2, 0.93; RMSE, 10.90; RE, 0.20; MBE, -4.95; dw, 0.97 and in cucumber plant R2, 0.94; RMSE, 13.25; RE, 0.20; MBE, -4.95; dw, 0.97 performance criteria were obtained and very strong relationship was determined. In order to facilitate the application of the obtained method under farmer conditions, ET values were determined based on various scenarios including estimating and neglecting net radiation (Rn) and soil heat flux (G) parameters of energy balance equation and compared with measured values. The results obtained in this study conducted in Mediterranean greenhouse conditions can be used in the optimization of plant water use in greenhouse, irrigation automation, and related computer software, as well as the basis for future studies.