Evaluation of Water Stress Indicators in Spinach Plants under Greenhouse Conditions

Document Type : Research Paper

Authors

1 Department of Horticultural Sciences, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran.

2 Department of Horticultural Science, Faculty of Agriculture, College of Agriculture& Natural Resources, University of Tehran, Karaj, Iran.

3 Department of Irrigation and Reclamation Engineering, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran.

Abstract

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.

Keywords

Main Subjects

Introduction

The water resource crisis is one of the major challenges to sustainable development, and the agricultural sector, as the largest consumer of water, requires strategies to improve water use efficiency. Greenhouse cultivation, due to its ability to control climatic conditions, is considered an effective method for conserving water and enhancing economic productivity, particularly for water-intensive crops such as spinach. Spinach is highly sensitive to water deficiency and requires precise irrigation management during its growth period. Among the key indicators for monitoring plant water status are the Relative Water Content (RWC) of the leaves and the Crop Water Stress Index (CWSI). The Crop Water Stress Index, by comparing plant and ambient temperatures, provides a more accurate assessment of the plant's water status.

Objective(s)

This study was conducted to evaluate two key indicators—Relative Water Content (RWC) and the Crop Water Stress Index (CWSI)—throughout the growth period of spinach under greenhouse conditions with varying irrigation treatments.

Material and Methods

This study was conducted using a completely randomized design, incorporating four irrigation treatments (40%, 60%, 80%, and 100% of field capacity) and three replications over two successive cultivation periods. The Relative Water Content (RWC) of the leaves and the Crop Water Stress Index (CWSI) were measured throughout the growth cycle. At the end of each cultivation period, the dry biomass of the plants was recorded. To assess the predictive accuracy of the evaluated methods, statistical indicators including coefficient of determination (R²), index of agreement (d), relative root mean square error (RRMSE), and mean bias error (MBE) were applied.

Results

In this study, the upper and lower baseline curves of the Crop Water Stress Index (CWSI) for baby spinach (cv. Racoon) were determined over two cultivation periods. According to the results, as the vapor pressure deficit increased, the temperature difference between the plant canopy and the ambient air also increased. With higher irrigation levels, the Relative Water Content (RWC) of the leaves increased, while the CWSI decreased. Additionally, the relationships between RWC and CWSI with relative dry biomass were analyzed. Ultimately, the RWC index demonstrated higher accuracy in predicting relative dry biomass, although it is a destructive and time-consuming measurement process. In contrast, the CWSI, as a non-destructive indicator, provided reasonably acceptable accuracy.

Conclusions

Generally, increasing the irrigation level led to a higher Relative Water Content (RWC) and a lower Crop Water Stress Index (CWSI). Both indices showed significant correlations with the plant’s relative dry biomass. Although the RWC index exhibited greater accuracy in predicting relative yield, its destructive and time-consuming measurement process limits its widespread use in practical applications. In contrast, the CWSI, as a non-destructive method, provides reasonably acceptable accuracy and can serve as a practical and efficient tool for improved irrigation management under greenhouse conditions.

Author Contributions

All authors contributed equally to the conceptualization of the article and writing of the original and subsequent drafts.

Data Availability Statement

Data is available on reasonable request from the corresponding author.

Acknowledgements

The authors would like to thank all participants of the present study.

Ethical considerations

The authors avoided data fabrication, falsification, plagiarism, and misconduct.

Conflict of interest

The author declares no conflict of interest.

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Iranian Journal of Soil and Water Research
Volume 56, Issue 8
November 2025
Pages 2163-2177

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