Effects of Tensiometer-Based Automated Irrigation on Growth and Fruit Quality of ‘Fuji’/M9 Apples in an Open-Field Orchard

Climate change has increased the demand for precise water management in open-field orchards, and soil moisture tension-based management is gaining attention.This study investigated an optimal irrigation strategy for high-quality apple production using a tensiometer-based automated irrigation system over two years (2022)(2023) in a 'Fuji'/M9 apple (Malus domestica) orchard in Andong, Korea.Five irrigation treatments, including three soil moisture tension thresholds (-30, -45, and -60 kPa), a growth stage-based recommended threshold, and a rainfall-based conventional irrigation treatment were compared.The automated irrigation system operated appropriately at each threshold and maintained stable soil moisture, whereas the conventional treatment, particularly in the high-rainfall year 2023, failed to irrigate when apple trees needed, resulting in excessively negative soil moisture tension.Vegetative growth showed no irrigation treatment effects; interannual variation was attributed to rainfall and solar radiation.Fruit quality traits were generally better in 2023 than in 2022.The -30 kPa treatment produced the largest fruit, while the -45 kPa treatment achieved the highest sugar contents.The effects of irrigation treatment differed by year, affected by cumulative water management over two years and high rainfall in 2023.The conventional treatment produced the smallest fruit in 2023, because irrigation was not applied at the time when the trees needed water, despite abundant rainfall.Cumulative irrigation indicated that the -45 kPa treatment used about 8% less water than the -30 kPa treatment while maintaining fruit size and enhancing sugar contents and acidity, identifying -45 kPa as an efficient irrigation threshold for apple orchards.These results indicate that the tensiometer-based automated irrigation system can effectively produce high-quality apples and improve water-use efficiency in open fields.