Effect of Fe Aminochelates and FeSO₄ Fertigation on the Distribution of Fe Chemical Fractions in the Soil Solid Phase and Fe Concentration in Sunflower

Document Type : Research Article

Authors

M. Alipour Babadi ¹

M. Norouzi Masir ¹

A. Moezzi ¹

A. Rahnama Ghahfarokhi ²

M. Taghavi Zahedkolaei ³

¹ Department of Soil Science, Faculty of Agriculture, Shahid Chamran University of Ahvaz, Ahvaz, Iran

² Department of Plant Production and Genetics, Faculty of Agriculture, Shahid Chamran University of Ahvaz, Ahvaz, Iran

³ Department of Chemistry, Faculty of Science, Shahid Chamran University of Ahvaz, Ahvaz, Iran

https://doi.org/10.22067/jsw.2025.94536.1491

Abstract

Introduction
Iron (Fe) is an essential micronutrient that plays a vital role in various plant metabolic processes. However, in calcareous soils with high pH, the availability of Fe is greatly limited due to its precipitation into insoluble forms, resulting in Fe deficiency and reduced crop yields. This limitation highlights the need for alternative strategies to enhance Fe uptake efficiency in plants. Recent studies suggest that Fe aminochelates (complexes of Fe with organic ligands such as amino acids) can significantly improve Fe availability and uptake in alkaline soils. Fe deficiency is especially problematic in arid and semi-arid regions, where calcareous soils dominate and conventional Fe fertilizers, such as FeSO₄, are often ineffective due to rapid oxidation and fixation of Fe³⁺. Insufficient Fe availability disrupts chlorophyll synthesis, enzyme activity, and overall photosynthetic efficiency, which ultimately affects plant growth, biomass accumulation, and nutritional quality. Therefore, improving Fe acquisition through more stable and bioavailable sources is crucial for sustainable crop production. Among various synthetic and natural Fe sources, Fe aminochelates have drawn attention because of their stability, solubility, and ability to resist precipitation in high-pH environments. By forming soluble Fe–amino acid complexes, these chelates enhance Fe translocation within plant tissues and promote physiological functions even under Fe-limiting conditions. Given this potential, the present study was conducted with the following objectives: (i) to evaluate the effect of fertigation application with Fe aminochelates and FeSO₄ on the distribution of Fe chemical fractions in the solid phase of calcareous soil, (ii) to analyze the correlation between soil Fe fractions and Fe content/uptake in sunflower (Helianthus annuus L. cv. Oscar), and (iii) to establish a comparative efficacy framework for Fe sources in calcareous soil-plant systems under fertigation management.
 
Materials and Methods
A field experiment was carried out using a randomized complete block design (RCBD) with three replications. The treatments included: (1) control (without any Fe fertilizer), (2) FeSO₄ at 20 kg ha⁻¹, (3) Fe-glycine [Fe (Gly)₂] aminochelate at 4 L ha⁻¹, and (4) Fe- methionine [Fe(Met)₂] aminochelate at 4 L ha⁻¹. Fertilizers were applied through irrigation (fertigation). At the end of the growing season, soil samples were collected and analyzed for pH, DTPA-extractable Fe, and Fe chemical forms in the solid phase using the modified Tessier sequential extraction method. The measured Fe fractions included exchangeable (EXC-Fe), organically bound (ORG-Fe), carbonate-bound (CAR-Fe), Fe/Mn oxide-bound (OX-Fe), and residual (RES-Fe). Additionally, Fe concentration in sunflower seeds and leaves and also seed Fe uptake were quantified.
 
Results and Discussion
Application of Fe aminochelates significantly affected Fe dynamics in the soil and improved Fe nutrition of plants. Both [Fe(Gly)₂] and [Fe(Met)₂] treatments resulted in a significant decrease in soil pH compared to the control and FeSO₄, which likely enhanced Fe solubility. The DTPA-extractable, relative to the control, Fe content increased by 28.5% and 35.2% in [Fe(Gly)₂] and [Fe(Met)₂] treatments, respectively. These treatments also increased seed Fe concentration by 5.1% and 7.5%, and seed Fe uptake by 66.6% and 86.7%, respectively. The distribution of Fe chemical fractions in the soil followed the order: residual > Fe/Mn oxides > carbonate-bound > organically bound > exchangeable. Fe aminochelates, especially [Fe(Met)₂], significantly enhanced the relative proportion of EXC-Fe and ORG-Fe while decreasing the proportion of CAR-Fe compared to both control and FeSO₄. Furthermore, DTPA-extractable Fe exhibited strong positive correlations with EXC-Fe (r = 0.87**) and ORG-Fe (r = 0.84**) fractions. Among the different forms, EXC-Fe (r = 0.72**) and ORG-Fe (r = 0.69**) showed significant positive correlations with seed Fe concentration, indicating their critical role in Fe bioavailability and plant uptake. These findings support the hypothesis that [Fe(Met)₂], due to its greater stability and chelation strength, improves Fe mobilization and provides a renewable pool of bioavailable Fe in the soil system. Thus, Fe aminochelates can contribute to improved nutrient acquisition and enhanced crop quality under Fe-deficient calcareous conditions.
 
Conclusion
This study confirms the superior efficacy of Fe aminochelates, particularly [Fe(Met)₂], over conventional FeSO₄ in enhancing Fe bioavailability in nutrient-deficient, calcareous soils. The significant shift in Fe fractions towards more labile pools (EXC-Fe and ORG-Fe) and the strong correlations between these pools and plant Fe uptake underscore the potential of aminochelates to create a more plant-available Fe reservoir. Therefore, the use of Fe aminochelates represents a viable and efficient strategy to correct Fe deficiency and improve crop nutritional quality in calcareous soils, contributing to more sustainable micronutrient management practices.
 
Acknowledgements
The authors would like to thank the Research council of Shahid Chamran University of Ahvaz, Ahvaz, Iran for the financial support of this research (grant number: SCU.AS1401.26962).

Keywords

Aminochelates

Available iron

Iron uptake

Sequential extraction

Sunflower

Subjects

• Soil science

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Authors retain the copyright. This is an open access article distributed under Creative Commons Attribution 4.0 International License (CC BY 4.0).

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