Evaluation of humic acid application on morpho-physiological indices of corn (Zea mays) under salinity stress

Subject Areas : Morphophysiological

Ebrahim Fani ¹ , Mohammad Ali Jalalpoori ²

1 - Department of Biology, Faculty of Basic Sciences, Khatam Al-Anbiya University of Technology, Behbahan, Khuzestan, Iran
2 - 2Department of Agriculture, Behbahan Branch,Behbahan Islamic Azad University, Behbahan, Iran

Received: 2024-10-26 Accepted : 2025-02-09 Published : 2025-09-23

Keywords: Anthocyanin, Chlorophyll a, Soluble sugar, Stem height, Total chlorophyll.,

Abstract :

Salinity stress is a significant factor that diminishes plant yield globally. Humic acid, as an organic acid, plays a crucial role in enhancing plant yield under salt-stress conditions. To investigate the effects of salinity stress and humic acid fertilization on corn plants, a pot study was conducted with three replications using a factorial experimental design in a completely randomized layout. Treatments included salinity stress at two levels (no stress and 100 mM stress) and humic acid fertilization at three levels (no fertilization, 100 mg/L fertilization, and 200 mg/L fertilization). This study aimed to investigate the effects of humic acid fertilization on the morphological and physiological traits of corn plants under salt stress conditions and to evaluate the role of humic acid in improving the mentioned traits and reducing the harmful effects of salt stress in corn plants, as an important plant in terms of human food supply. The results indicated that salinity stress significantly reduced stem height and total chlorophyll levels in corn plants, while treatment with humic acid effectively mitigated the detrimental effects of salinity. At 100 mM salinity, the application of 100 mg/L humic acid fertilizer increased stem height by 26.6% compared to no application. Also, under 100 mM salinity stress, the total chlorophyll content increased more than twice when fertilizing with 200 mg/L humic acid compared to no fertilization. Based on the findings of this study, humic acid is recommended to promote the vegetative growth of corn plants under salt stress conditions.

 

Extended Abstract

Introduction

Maize (Zea mays L.) is one of the most important cereal crops worldwide, with an annual production exceeding one billion tons, and plays a key role in human nutrition, animal feed, and industrial applications. Environmental stresses disrupt normal physiological processes in plants, leading to growth reduction and yield losses. Among abiotic stresses, salinity is one of the most serious constraints to agricultural production, particularly in arid and semi-arid regions. More than six percent of the world’s land area and a considerable proportion of irrigated agricultural lands are affected by salinity, and this trend is continuously increasing.
Salinity stress induces morphological, physiological, and biochemical alterations in plants, including reduced root and shoot growth, decreased photosynthetic pigments, impaired photosynthesis, and changes in osmotic regulation. Previous studies have reported a reduction in plant height, chlorophyll content, and biomass in maize under salinity stress, while increases in soluble sugars and anthocyanins have also been observed as adaptive responses.
Humic acid, as an organic soil amendment, has gained attention for its ability to improve soil physical and chemical properties, enhance nutrient availability, and modulate plant physiological responses under stress conditions. Therefore, the present study aimed to investigate the effects of humic acid application on selected morphological and physiological traits of maize plants under salinity stress.

Materials and Methods

This experiment was conducted as a pot trial during autumn 2023 under open-field conditions in Behbahan, Khuzestan Province, Iran. The experiment was arranged as a factorial based on a completely randomized design with three replications. Treatments consisted of two salinity levels (0 and 100 mM NaCl) and three humic acid concentrations (0, 100, and 200 mg L⁻¹).
Maize hybrid cultivar ‘Ajeeb’ was used in this study. Salinity stress was applied two weeks after seedling establishment, while humic acid treatments began one day before stress imposition and were repeated every three days. To prevent salt accumulation, pots were leached with tap water after every two saline irrigations.
Morphological traits (plant height and root volume) and physiological parameters including photosynthetic performance index (PI), SPAD chlorophyll index, chlorophyll a, b and total chlorophyll, carotenoids, soluble sugars, and anthocyanin content were measured 30 days after treatment application. Data were statistically analyzed using two-way analysis of variance (ANOVA), and mean comparisons were performed using Duncan’s multiple range test at the 5% probability level.

Results and Discussion

Salinity stress significantly reduced several morphological and physiological traits of maize plants. A marked decline in photosynthetic performance index (PI), SPAD value, and chlorophyll a content was observed under salinity, indicating impairment of the photosynthetic apparatus.
Application of humic acid mitigated the adverse effects of salinity. Under salinity stress, application of 100 mg L⁻¹ humic acid increased plant height compared to the non-treated control, while 200 mg L⁻¹ humic acid significantly enhanced root volume. The interaction between salinity and humic acid had a significant effect on total chlorophyll content, such that under salinity stress, application of 200 mg L⁻¹ humic acid more than doubled total chlorophyll compared to the untreated plants.
Carotenoid content increased with humic acid application, suggesting a protective role against oxidative damage caused by salinity. Although the effects of salinity and humic acid on soluble sugar and anthocyanin contents were not statistically significant, both parameters showed increasing trends in humic acid-treated plants. This response may be associated with improved osmotic adjustment and enhanced antioxidant capacity under stress conditions.
Overall, the results indicate that humic acid improves nutrient uptake, stabilizes chloroplast structure, enhances photosynthetic pigments, and promotes root growth, thereby increasing maize tolerance to salinity stress.

Conclusion

Salinity stress negatively affected growth and photosynthetic efficiency of maize plants. However, humic acid application effectively alleviated the detrimental effects of salinity by improving morphological and physiological characteristics. Among the tested treatments, application of 200 mg L⁻¹ humic acid was the most effective in enhancing root volume and photosynthetic pigment content under salinity stress. Therefore, humic acid can be recommended as a practical and environmentally friendly strategy to improve maize growth and stress tolerance in saline soils.

 

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