This study was conducted to determine an appropriate sub-irrigation frequency for producing grafted tomato transplants in a plant factory with artificial lighting. Three irrigation frequencies were evaluated: twice per day, once per day, and once every two days. Daily water absorption did not differ among treatments during the early growth stage (0－3 days after treatment), but once-per-day irrigation showed the highest values during days 4－9, after which its levels became similar to those of twice-per-day irrigation. In contrast, once-every-two-days irrigation consistently resulted in the lowest daily water absorption throughout the experiment. Accumulated water absorption exhibited similar trends, with twice-per-day and once-per-day irrigation showing comparable increases, whereas once-every-two-days irrigation remained substantially lower. Growth analysis revealed that once-every-two-days irrigation led to reduced plant height, leaf number, fresh weight, and dry weight, indicating growth suppression caused by repeated root-zone water deficits. Although twice-per-day irrigation produced the most vigorous growth, it required the largest amount of water and nutrient solution, reducing resource-use efficiency. In contrast, once-per-day irrigation-maintained growth parameters comparable to those under twice-per-day irrigation while markedly reducing total water use, thereby achieving a favorable balance between growth stability and resource efficiency. Excessively frequent irrigation during the early post-grafting stage was also found to disrupt the air–water balance within the substrate, potentially hindering root establishment. Overall, these findings indicate that once-per-day sub-irrigation is an appropriate basic irrigation strategy for efficient and stable production of grafted tomato transplants in plant factories with artificial lighting and may serve as a foundation for future research on automated irrigation control and transplant production systems across various cultivars and tray specifications.

Abstract
서 론
재료 및 방법
결과 및 고찰
    1. 수분흡수 특성
    2. 생육 분석
적 요
Literature Cited

• 박선우(농협대학교 협동조합디지털경영과 교수) | Seon Woo Park (Professor, Department of Digital Cooperative Management, Agricultural Cooperative University, Goyang 10292, Korea) Corresponding author