Irrigation Control System Based on Hanging-Gutter-Scale Evapotranspiration Measurement for Tomato (Solanum lycopersicum L.) Cultivation in Greenhouse Hydroponics

Abstract

Purpose Water scarcity and environmental pollution have highlighted the need for efficient water use and drainage in greenhouse hydroponic systems. Evapotranspiration, an indicator of crop water demand, can be measured using the water balance method, based on changes in substrate weight and drainage volume. However, irrigation based on evapotranspiration measurements has not yet been widely adopted in greenhouses. Moreover, single-substrate measurements cannot capture the spatial variations in plant growth and microclimatic conditions across hanging-gutter systems. This study aimed to (1) develop an hourly gutter scale evapotranspiration-based irrigation system for greenhouse tomatoes cultivated in South Korea and (2) evaluate its feasibility and resource-saving effect compared with cumulative solar radiation-based irrigation. Methods An evapotranspiration measurement system comprising three load cells and an ultrasonic level sensor was constructed to measure hourly evapotranspiration using the water balance method. After testing substrate weight and drainage measurements through a preliminary experiment, a cultivation experiment was conducted across two cropping cycles. In the first cycle, the evapotranspiration measurement system was validated under varying environmental and crop growth conditions. In the second cycle, irrigation was performed using 1 an automated system relying on the evapotranspiration measurements from the first cycle. Results During the first cultivation cycle, the measured daily evapotranspiration at the same growth stage varied from 13.13 to 26.27 kg/day, depending on environmental conditions. Additionally, evapotranspiration increased as crop growth progressed. During the second cycle, the evapotranspiration rate-based irrigation method reduced nutrient solution use by 23.9% compared with cumulative solar radiation-based irrigation. T-tests on plant height, leaf area index, and stem diameter showed no significant differences (p > 0.05) between the treatments. Conclusions The results demonstrate that the proposed system can measure hourly gutter scale evapotranspiration effectively, improving water and nutrient use efficiency while maintaining crop growth in hanging-gutter greenhouses.