University of Tehran Press Iranian Journal of Soil and Water Research 2008-479X 56 8 2025 10 23 Evaluation of Water Stress Indicators in Spinach Plants under Greenhouse Conditions Evaluation of Water Stress Indicators in Spinach Plants under Greenhouse Conditions 2163 2177 104845 10.22059/ijswr.2025.396628.669956 FA Mohammad Kargar Department of Horticultural Sciences, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran. 0009-0000-2169-9648 Mojtaba Delshad Department of Horticultural Science, Faculty of Agriculture, College of Agriculture& Natural Resources, University of Tehran, Karaj, Iran. 0000-0003-2685-0348 Hadisseh RahimiKhoob Department of Irrigation and Reclamation Engineering, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran. 0000-0002-3848-7470 Journal Article 2025 06 03 Water scarcity is one of the most significant challenges facing agricultural production. Accurate monitoring of plant water status is essential for optimizing irrigation management. This study was conducted to evaluate two physiological indicators—Relative Water Content (RWC) and Crop Water Stress Index (CWSI)—during the growth period of spinach to simulate relative dry biomass under greenhouse conditions and various irrigation treatments. The experiment was arranged in a completely randomized design with four irrigation levels (40%, 60%, 80%, and 100% of field capacity) and three replications, conducted over two cropping seasons (autumn and winter 2023) in the research greenhouse of the College of Agriculture and Natural Resources, University of Tehran. The upper and lower baselines required for calculating CWSI were determined based on the method proposed by Idso, using leaf temperature data and climatic parameters inside the greenhouse. The results indicated that both indices were effective tools for assessing drought stress in spinach under greenhouse conditions. A direct relationship was observed between irrigation level and the RWC index, while an inverse relationship was found with CWSI. Moreover, both indices were significantly correlated with relative dry biomass. As RWC increased and CWSI decreased, relative biomass also increased. Although RWC showed higher accuracy in predicting relative yield, its destructive and time-consuming measurement process limits its practical application. In contrast, CWSI, as a non-destructive method, offers a more practical approach for facilitating irrigation management. Water scarcity is one of the most significant challenges facing agricultural production. Accurate monitoring of plant water status is essential for optimizing irrigation management. This study was conducted to evaluate two physiological indicators—Relative Water Content (RWC) and Crop Water Stress Index (CWSI)—during the growth period of spinach to simulate relative dry biomass under greenhouse conditions and various irrigation treatments. The experiment was arranged in a completely randomized design with four irrigation levels (40%, 60%, 80%, and 100% of field capacity) and three replications, conducted over two cropping seasons (autumn and winter 2023) in the research greenhouse of the College of Agriculture and Natural Resources, University of Tehran. The upper and lower baselines required for calculating CWSI were determined based on the method proposed by Idso, using leaf temperature data and climatic parameters inside the greenhouse. The results indicated that both indices were effective tools for assessing drought stress in spinach under greenhouse conditions. A direct relationship was observed between irrigation level and the RWC index, while an inverse relationship was found with CWSI. Moreover, both indices were significantly correlated with relative dry biomass. As RWC increased and CWSI decreased, relative biomass also increased. Although RWC showed higher accuracy in predicting relative yield, its destructive and time-consuming measurement process limits its practical application. In contrast, CWSI, as a non-destructive method, offers a more practical approach for facilitating irrigation management. https://ijswr.ut.ac.ir/article_104845_93e626eea8a4c287be6b0672d432eb75.pdf