Evaluating the Influence of Magnetic Iron Applications on Agronomic and Fruit Quality Parameters of 'Fremont' Mandarin

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Al-Saif, Hosny F. Abdel-Aziz, Abd El-Wahed N. Abd El-Wahed, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8741488/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 12 You are reading this latest preprint version Abstract Fremont mandarin is highly valued for its early ripening, deep orange peel coloration, and elevated juice content, making it an appealing cultivar for both local markets and international trade. This study was conducted to evaluate the effects of magnetic iron soil applications on canopy volume, leaf nutrient status, physiological leaf traits, yield, and fruit quality of Fremont mandarin trees. Magnetic iron was applied at rates of 0 (control), 250, 500, and 750 g/tree. Results revealed that canopy volume significantly increased with magnetic iron application, with the most pronounced effects observed at the 750 g/tree rate. Leaf macro nutrient contents, including total nitrogen (N), phosphorus (P), and potassium (K), were markedly elevated across all treated trees, with the highest concentrations recorded under the highest application rate. Additionally, iron (Fe) content in leaves increased proportionally with the magnetic iron levels, indicating enhanced nutrient uptake efficiency. Magnetic iron also influenced key physiological and biochemical traits. Total chlorophyll content in leaves was significantly improved, reflecting enhanced photosynthetic activity. Meanwhile, leaf proline levels a stress indicator were significantly reduced in treated trees, suggesting alleviated environmental stress. Relative water content (RWC) of leaves increased, indicating improved plant water status. Conversely, sodium (Na⁺) and chloride (Cl⁻) ion accumulation, often associated with salinity stress, was substantially decreased in response to magnetic iron, especially at higher doses. These physiological improvements were mirrored in yield and fruit quality. Trees treated with magnetic iron produced heavier fruits with higher juice volume, better firmness, elevated vitamin C content, increased total soluble solids (TSS), and an improved TSS/acid ratio. In conclusion, magnetic iron particularly at 750 g/tree proved to be an effective agronomic input for improving nutrient status, physiological performance, and fruit yield and quality of Fremont mandarin trees. Biological sciences/Physiology Biological sciences/Plant sciences canopy volume magnetic amendment antioxidant activity juice quality Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction Citrus fruits represent a significant segment of global horticultural production, with mandarins ( Citrus reticulata Blanco) ranking among the most economically important citrus species due to their favorable flavor, nutritional content, and consumer preference (Kato-Noguchi and Kato 2025 ). Among mandarin cultivars, Fremont’ is valued for its early maturity, deep orange peel color, and high juice content, making it a preferred choice in both domestic and export markets. Enhancing the growth performance and fruit quality of Fremont mandarin trees under diverse agroecological conditions is, therefore, a priority for sustainable citrus production (Camilla et al. 2016 ). Soil fertility management plays a crucial role in citrus yield and fruit quality (Wijana et al. 2025 ). In recent years, increasing attention has been given to the use of mineral based soil amendments such as magnetic iron (Fe₃O₄), a naturally occurring form of iron oxide known for its paramagnetic properties and ability to enhance soil physicochemical characteristics (Eldeeb et al. 2023 ). Magnetic iron has been reported to improve soil aeration, nutrient availability, and microbial activity (Tang et al. 2024a ), thereby promoting better root development and nutrient uptake in various fruit trees. Iron, as a micronutrient, is essential for chlorophyll biosynthesis, photosynthetic efficiency, and enzymatic activities in plants (Aras et al. 2022 ). In citrus, iron deficiency is commonly manifested as interveinal chlorosis, reduced vegetative growth, and impaired fruit development, especially in calcareous or alkaline soils (Zang et al. 2023 ). The application of iron sources, particularly in forms that improve soil structure and cation exchange capacity, can mitigate such deficiencies and lead to improved plant health and productivity (Mahmoud et al. 2022 ). Magnetic iron has gained interest not only as a direct source of iron but also for its indirect role in modifying soil physical and biological properties (Malhas et al. 2023 ). Several studies have indicated that soil amendments with magnetic iron can enhance root elongation, increase leaf chlorophyll content, and improve the bioavailability of essential nutrients such as nitrogen, phosphorus, and potassium (Das and Yogalakshmi 2022 ). Furthermore, its influence on soil microbial activity may contribute to a more balanced rhizosphere environment, which in turn supports plant vigor and fruiting capacity (He et al. 2016 ). Despite these promising attributes, the effects of magnetic iron on citrus trees particularly on Fremont mandarins have not been extensively studied. While existing literature provides preliminary evidence of improved performance in other fruit trees such as olives, grapes, and guavas, empirical data on its impact on mandarin growth dynamics, fruit yield, and quality parameters such as (total soluble solids, acidity, vitamin C, and fruit size) remain limited and fragmented. Given the growing emphasis on eco-friendly and sustainable horticultural practices, exploring the potential of magnetic iron as a soil amendment in citrus cultivation holds considerable promise. Therefore, this study aims to evaluate the effects of different levels of magnetic iron soil application on the vegetative growth, yield components, and fruit quality attributes of Fremont mandarin trees grown under field conditions. The findings are expected to contribute to a better understanding of how magnetic iron can be utilized to improve citrus productivity while maintaining soil health and sustainability. 2. Materials and Methods 2.1. Experimental Site and Plant Material The present study was conducted during the 2023 and 2024 growing season at private orchard located at Wadi Elmollak, Abu-Hammad, Al-Sharqia Governorate (altitude 30˚25’53N, longitude 31˚46’08E). The study was conducted with the clear permission of the orchard owner. The soil in the orchard is predominantly sandy, comprising 94.72% sand with a pH of 8.15 and electrical conductivity (EC) of 4.3 dS m⁻¹. The experiment was carried out on ‘Fremont’ mandarin trees ( Citrus reticulata Blanco), which were grafted onto Volkamer lemon ( Citrus volkameriana Ten. & Pasq.) rootstock and planted in 2015. Trees were spaced at 2 × 4 meters, resulting in a planting density of approximately 525 trees per feddan. Drip irrigation was employed using two irrigation lines per tree, each equipped with four adjustable emitters (8 emitters/tree, delivering 8 liters/hour). Irrigation lines were positioned 50 cm away from the trunk on each side. All trees received a uniform fertilization regime in line with the recommendations of the Egyptian Ministry of Agriculture. The annual fertilization program included 1000 g nitrogen, 1500 g phosphorus (as P₂O₅), and 500 g potassium (as K₂O) per tree. In addition, micronutrients were supplied as chelated forms of Fe, Mn, Zn, Cu (at 300, 150, 100, and 50 mg, respectively), and B (as 50 mg boric acid) in three split applications during March, May, and August. 2.2. Experimental Design and Treatments The experiment was arranged in a randomized complete block design comprising four soil applied magnetics iron treatments at rates of 0, 250, 500, and 750 g per tree. Each treatment was replicated four times, with three trees per replicate, resulting in a total of 12 trees per treatment. The treatments were defined as follows: Control: No magnetic iron application (untreated), T₁: Magnetic iron applied at 250 g per tree., T₂: Magnetic iron applied at 500 g per tree. And T₃: Magnetic iron applied at 750 g per tree. Magnetic iron (Fe₃O₄) was applied once per season, in mid-January, by incorporating it into the soil at a depth of 20 cm beneath the irrigation lines on both sides of each tree. Magnetic iron is a naturally occurring raw rock characterized by its high iron content and distinctive black coloration. It possesses a hardness of approximately 6 on the Mohs hardness scale. The composition of this material includes 48.8% Fe₃O₄, 17.3% FeO, 26.7% Fe₂O₃, 2.6% MgO, 4.3% SiO₂, and 0.3% CaO. The magnetic iron used in this study was sourced from El-Ahram Company for Mining and Natural Fertilizers, located in Giza, Egypt. 2.3. Data Collection The following parameters were measured to evaluate the effects of the treatments: 2.3.1. Vegetative Growth Tree canopy volume (m³) was used as an indicator of vegetative growth to assess the response of ‘Fremont’ mandarin trees to different magnetic iron treatments. Canopy volume, representing overall tree size, was calculated according to the formula described by (Zekri 2000 ): Tree canopy volume (m 3 ) = 0.52 × tree height × (diameter 2 ). Tree height and canopy diameter were measured for each tree, and the resulting values were used to compute the canopy volume in cubic meters. 2.3.2. Leaf Chemical Contents Total Chlorophyll Leaf total chlorophyll content was measured in September using a nondestructive method with a Minolta SPAD-502 chlorophyll meter, following the procedure described by (Wood et al. 1993). Leaf Proline Content Proline, the most abundant amino acid in citrus leaves, was quantified following the method of (Bates et al. 1973 ) and modified by (Claussen 2005 ). Relative Water Content (RWC) Relative water content (RWC) of leaves was assessed according to the method of (Claussen 2005 ). RWC was calculated using the following formula: $$\:RWC\left(\text{%}\right)=\frac{Fresh\:weight-Dry\:weight}{Saturation\:weight-Dry\:weight}\times\:100$$ 1 Total Phenolic Content Total phenolic content of ‘Fremont’ mandarin leaves was determined following the method described by (Casquete et al., 2005), with modifications based on (Singleton et al. 1999 ). TPC was expressed in mg gallic acid equivalents (mg g⁻¹ FW). Leaf Nutrient Contents To assess nutrient status, ten mature leaves per tree (specifically the fifth fully expanded leaf from labeled shoots) were collected in September of both seasons. The collected leaves were analyzed for the following macro- and micronutrients: Nitrogen (N): Determined by the micro-Kjeldahl method, as described by (Adams and Laughlin 1981 ), and expressed as total nitrogen (% dry weight), Phosphorus (P): Measured calorimetrically using the method of(Murphy et al. 1981 ), Potassium (K): Analyzed using a flame photometer, following the protocol by (Thomas et al. 1967 ), and Micronutrients (Fe, Na, Cl): Quantified using atomic absorption spectrophotometry, as outlined by(Cheng and Bray 1951 ). Tree Yield The harvest was completed within the normal commercial harvesting season on Sep. 21st at the maturity stage for each season (109 d from full bloom, according to (Abdel-Sattar et al., 2024 ). The tree yield was recorded per kg. Increasing yield percentage was compared to the control according to the calculation of (Abd El-Naby et al. 2019 ) as the following: $$\:Yield\:increasing\left(\text{%}\right)=\frac{Yield\left(treatment\right)-Yield\left(control\right)}{Yield\left(control\right)}\times\:100$$ 2.3.3. Physical Characteristics of Fruits At harvest, ten representative fruits were randomly collected from each tree. Each treatment was replicated three times. The samples were immediately transferred to the Chemical Analysis Laboratory, Department of Horticulture, Faculty of Agriculture, Cairo, Al-Azhar University, for evaluation of the following physical parameters: Fruit weight (g), Fruit volume (cm³), Juice volume (cm 3 ), Fruit Pulp Firmness. Fruit pulp firmness, expressed in (lb/in²), was measured using a digital force gauge pressure tester (Model IGV-O.SA to FGV-100A, Shimpo Instruments). 2.3.4. Chemical Characteristics of Fruits The following chemical parameters were analyzed from freshly extracted juice: Total Soluble Solids (TSS), Total Acidity, and TSS/Acid Ratio TSS (%) was measured using a digital refractometer. According to the methods of (Latimer 2023 ) Total acidity (%) was determined by titration against 0.1 N NaOH and expressed as citric acid equivalent, following the standard method of the Association of Official Analytical Chemists (Latimer 2023 ) TSS/Acid ratio was calculated by dividing TSS (%) by total acidity (%), serving as an indicator of fruit flavor balance. Ascorbic Acid Content Ascorbic acid (vitamin C) content was determined by titration using 2,6-dichlorophenol-indophenol dye, as outlined in (Latimer 2023 ), and expressed in mg ascorbic acid per 100 mL of juice. Statistical Analysis All collected data were subjected to analysis of variance (ANOVA) using Co-stat software. Means were compared using the Least Significant Difference (LSD) test at a significance level of 0.05. 3. Results and discussion 3.1. Tree Canopy Volume of Fremont Mandarin Magnetic iron soil application had a pronounced impact on the canopy volume of Fremont mandarin trees across both the two studied seasons (Fig. 1 A and B). The untreated control trees consistently exhibited the lowest volume of canopy in both years. However, the application of magnetic iron at increasing rates led to substantial enhancements in canopy development. In 2023, the application of 250 g/tree (T1) increased canopy volume by approximately 154.6% compared to the control, while 500 g/tree (T2) and 750 g/tree (T3) treatments showed even greater increases of 179.5% and 213.6%, respectively. A similar trend was observed in 2024, with T1, T2, and T3 treatments increasing canopy volume by 148.6%, 179.9%, and 209.2%, respectively, relative to the control. These findings clearly indicate a positive, dose-dependent relationship between magnetic iron application and canopy expansion, suggesting improved vegetative growth and vigor under enhanced nutritional conditions. The results indicate a clear, positive relationship between the application rate of magnetic iron and canopy expansion. The marked increase in canopy volume under T3 (750 g/tree) reflects vigorous vegetative growth, likely driven by improved iron availability that enhances chlorophyll formation, enzymatic activity, and cellular respiration processes vital for shoot elongation and leaf development (Alharbi et al. 2022 ). The year over year increase from 2024 to 2025, even in the control group, suggests a natural effect of tree maturity. However, the substantially greater expansion in treated trees indicates a cumulative and sustained benefit from magnetic iron application. A larger canopy increases photosynthetic capacity, offers more fruiting surface, and ultimately contributes to improved yield and fruit quality. These observations align with previous studies highlighting the role of magnetite in enhancing root soil interactions and nutrient translocation, thereby improving canopy development and overall tree performance (Zheng et al., 2023 ; Yang et al., 2024 ) 3.2. Leaf macro and micronutrients Content 3.2.1. Leaf Macronutrients Content (N, P, K) The results in Fig. 2 (A-C) revealed that magnetic iron soil application significantly improved the nutritional status of Fremont mandarin leaves, as reflected in the increased concentrations of nitrogen (N), phosphorus (P), and potassium (K) across both the two seasons. The response of all three macro nutrients was positively correlated with the applied rates of magnetic iron. Compared to the control, all treated trees exhibited higher N, P, and K contents, with the magnitude of increase becoming more evident as the application rate increased. The lowest dose (250 g/tree) resulted in a clear enhancement in nutrient content over the untreated trees, indicating that even modest levels of magnetic iron are effective. Further improvements were recorded with the medium (500 g/tree) and high (750 g/tree) rates, with the highest treatment consistently yielding the greatest leaf concentrations of all three macro nutrients. In both seasons, nitrogen content showed the most pronounced increase, particularly under the two higher application rates, suggesting that magnetic iron may play a direct or indirect role in facilitating nitrogen assimilation or root uptake efficiency. Similarly, phosphorus content increased significantly, with a steady and consistent trend from the lowest to the highest application level, indicating improved phosphorus solubility and availability in the rhizosphere. Potassium content followed a comparable pattern, with clear and significant increases corresponding to the application rate, reflecting enhanced nutrient transport and retention in the plant soil system. The concurrent rise in N, P, and K concentrations suggests a synergistic improvement in overall nutrient uptake efficiency driven by magnetic iron, likely through its influence on soil physicochemical properties, microbial activity, and root absorption capacity (Joseph et al. 2015 ). These findings provide strong evidence that magnetic iron, when applied at suitable rates, enhances macro nutrients acquisition in citrus trees and could be an effective strategy to support balanced nutritional management in commercial orchards. The current study demonstrates that soil application of magnetic iron substantially improved the physiological and nutritional status of Fremont mandarin trees, with effects that intensified with increasing application rates and persisted consistently over two successive seasons. The enhancement in macro nutrients (N, P, K) content in response to magnetic iron application is likely attributed to improved soil physicochemical properties and nutrient availability. Iron, particularly in its magnetic form, may enhance nutrient solubility and uptake efficiency by improving root zone aeration and microbial activity (Shirsat and Suthindhiran 2024 ). The observed increases in N, P, and K concentrations, especially at 500 and 750 g/tree rates, underline the role of magnetic iron in facilitating macro nutrients acquisition under field conditions. 3.2.2. Leaf Micronutrient Content 3.2.2.1. Leaf Total Iron Content The application of magnetic iron had a notable and consistent impact on the total iron content of Fremont mandarin leaves across both growing seasons (Fig. 2 C). A gradual and statistically significant increase in leaf iron concentration was observed in response to the rising application rates of magnetic iron, confirming its role in improving iron nutrition in citrus foliage. Untreated control trees recorded the lowest levels of iron leaf content in both years. The application of magnetic iron at the lowest rate (250 g/tree) resulted in a modest yet measurable increase in iron content relative to the control, indicating an initial positive response to supplementation. As the application rate increased to 500 g/tree, leaf iron concentration improved further, with an even more pronounced enhancement recorded at the highest rate (750 g/tree). This dose dependent trend was consistent across both seasons, with leaf iron content progressively increasing with each incremental rise in magnetic iron application. The data suggest that higher levels not only improved immediate iron availability but also had a cumulative effect over time. This is likely due to improved iron solubility in the rhizosphere and enhanced root absorption efficiency. Our findings demonstrate that magnetic iron application is effective in improving the iron nutritional status of Fremont mandarin trees. Enhanced foliar iron levels are critical for chlorophyll synthesis, enzymatic activity, and overall metabolic function, which in turn can support better vegetative growth and fruiting potential in citrus under field conditions. Leaf iron content followed a similar trend, with significant increases correlating with application rate. Iron is critical for chlorophyll biosynthesis and numerous redox reactions in plants (Foyer and Hanke 2022 ). The parallel increase in total chlorophyll content confirms this relationship, as chlorophyll levels rose markedly in trees receiving magnetic iron, reaching peak values at the 750 g/tree dose. This enhancement in chlorophyll suggests an improvement in photosynthetic capacity and overall plant vigor (Huang et al. 2021 ). 3.2.2.2. Leaf Sodium and Chloride Content The results in (Fig. 2 E and F) demonstrate that magnetic iron application significantly reduced sodium (Na%) and chloride (Cl%) accumulation in the leaves of Fremont mandarin trees. A clear inverse relationship was observed between the rate of magnetic iron and the levels of both ions, indicating that magnetic iron plays a role in mitigating salt accumulation in plant tissues. Control trees exhibited the highest concentrations of both sodium and chloride, confirming the plant’s exposure to potential salt stress under untreated conditions. The lowest concentration of magnetic iron (250 g/tree) led to a moderate but statistically significant reduction in both Na and Cl content. As the application rate increased to 500 and 750 g/tree, further reductions were observed, with the 750 g/tree treatment producing the lowest Na and Cl levels in both seasons. These findings suggest that magnetic iron may enhance salt tolerance mechanisms by limiting the uptake or translocation of toxic ions such as sodium and chloride. This could be attributed to improved soil structure, cation exchange capacity, or changes in root membrane selectivity. By reducing ionic stress, magnetic iron application likely contributes to the overall physiological resilience of citrus trees grown under marginal or saline soil conditions (Rahim et al. 2025 ). The suppression of Na and Cl uptake indicates that magnetic iron may play a protective role against salt stress, possibly by modulating ion selectivity in the roots or enhancing the plant’s ability to compartmentalize and exclude these ions (Weng et al. 2025 ). This finding is critical in citrus cultivation, where salt sensitivity can limit productivity in semi-arid and marginal soils. Collectively, the results indicate that magnetic iron application improves the nutritional status, stress tolerance, and physiological performance of Fremont mandarin trees. The level dependent nature of these improvements suggests that 750 g/tree is the most effective rate for enhancing both macro- and micronutrient levels, boosting chlorophyll content, and mitigating stress-related parameters such as proline accumulation and ionic toxicity. These findings align with previous reports on the benefits of magnetic iron in other fruit crops and reinforce its utility as a soil amendment under suboptimal growing conditions (Lakhani et al. 2025 ). 3.3. Leaf chemical composition of Fremont mandarin 3.3.1. Relative Water Content (R.W.C.) Magnetic iron soil application significantly enhanced the relative water content (R.W.C.) of Fremont mandarin leaves throughout both seasons (Fig. 3 A). The increase in R.W.C. was positively associated with the increasing rates of magnetic iron, indicating improved water status and hydration in treated trees. Control trees recorded the lowest R.W.C. values in both seasons. Application of magnetic iron at 250 g/tree resulted in a noticeable improvement in leaf water content, with further significant increases observed at 500 and 750 g/tree. The highest R.W.C. values were consistently recorded in trees treated with 750 g/tree, highlighting the beneficial role of magnetic iron in enhancing the water retention capacity of leaf tissues. This trend suggests that magnetic iron plays an important role in improving plant water relations, likely through enhanced root efficiency, nutrient balance, and osmotic regulation. Improved hydration status under higher application rates may contribute to better physiological performance, particularly under environmental conditions where water availability is a limiting factor (Sarraf et al. 2020 ). 3.3.2. Total Leaf Chlorophyll Content Magnetic iron application significantly enhanced total chlorophyll content in Fremont mandarin leaves across the two seasons. A clear dose-dependent trend was observed, with higher application rates leading to progressively greater increases in chlorophyll concentration (Fig. 3 B). The control group recorded the lowest chlorophyll levels in both years. Application of magnetic iron at 250 g/tree resulted in a marked improvement over the control, indicating the positive effect of even low doses on chlorophyll synthesis. Substantially higher chlorophyll content was observed at 500 g/tree, while the maximum values were consistently recorded in trees treated with the highest dose (750 g/tree). These enhancements in chlorophyll concentration may be attributed to improved iron availability, which is essential for chlorophyll biosynthesis and the maintenance of photosynthetic activity (Dos Santos et al. 2021 ). 3.3.3. Leaf Proline Content The data in (Fig. 3 c) clearly indicate that magnetic iron soil application significantly reduced proline accumulation in the leaves of Fremont mandarin trees over both the 2023 and 2024 seasons. Proline levels decreased progressively with increasing magnetic iron rates, suggesting a dose-dependent alleviation of stress conditions. The highest proline content was consistently recorded in the untreated control trees, while trees treated with the lowest magnetic iron dose (250 g/tree) exhibited a moderate but statistically significant reduction. Further decreases were observed at the 500 g/tree application rate, with the lowest proline concentrations found in trees treated with 750 g/tree. The marked decline in proline levels with increased magnetic iron suggests that this treatment may help mitigate oxidative or environmental stress, as proline accumulation is often associated with drought, salinity, or nutrient deficiencies. The results imply that magnetic iron enhances plant metabolic balance and reduces stress related metabolite buildup, contributing to improved physiological status under orchard conditions (Tang et al. 2024b ). A particularly important observation was the decline in proline content with higher magnetic iron application. Proline serves as a stress indicator, commonly accumulating in response to abiotic stress such as drought or salinity. The reduction in proline, especially in T3 treated trees, suggests that magnetic iron alleviated stress conditions, possibly by improving plant water balance and reducing oxidative pressure. 3.3.4. Total Phenolic Content The total phenolic content in leaves was significantly influenced by the application rates of the treatment across both seasons (Fig. 3 d). The highest levels of phenolic compounds were recorded in the control and T1 (250 g/tree) treatments, with no significant differences between them. In contrast, T2 (500 g/tree) and T3 (750 g/tree) treatments resulted in a marked and statistically significant reduction in total phenolic content. In 2023, the total phenolic content reached its peak in the T1 treatment, followed by the control. This trend was replicated in the 2024 season, with both T1 and control again producing the highest levels of phenolics. However, increasing the application rate to 500 g/tree (T2) significantly lowered phenolic concentrations compared to the control, and the most pronounced reduction was observed in the T3 treatment (750 g/tree), which recorded the lowest phenolic levels across both seasons. These results suggest a dose-dependent suppression of phenolic synthesis in response to higher application rates. It could be concluded that, magnetic iron soil application utilizes a multifaceted influence on the physiological and biochemical characteristics of ‘Fremont’ mandarin leaves. Enhanced relative water content and chlorophyll levels reflect improved plant hydration and photosynthetic capacity, both essential for vegetative vigor and yield. Simultaneously, reduced proline and phenolic content under higher application rates point to a lowered stress environment and a shift in metabolic priorities toward growth and productivity rather than defense. These findings align with previous studies highlighting the role of magnetic iron in modifying soil structure, promoting nutrient uptake, and mitigating ionic and osmotic stress in citrus and other fruit species (Mahmoud et al. 2022 ). The level dependent nature of these responses underscores the importance of optimizing magnetic iron rates for maximum agronomic benefit while minimizing potential tradeoffs in fruit phytochemical composition (Rahman et al. 2023 ). 3.5. Yield of Fremont Mandarin Trees Magnetic iron soil application significantly enhanced the yield of Fremont mandarin trees across both seasons. The control group (no magnetic iron) consistently recorded the lowest yields. In contrast, yield improvements were observed with each increase in magnetic iron application rate. In 2023, yields rose by approximately 32.2%, 58.7%, and 70.4% under T1 (250 g/tree), T2 (500 g/tree), and T3 (750 g/tree), respectively, compared to the control (Fig. 4 a and b). A similar pattern was evident in 2024, with respective increases of 34.2%, 59.3%, and 71.6%. These results highlight a clear dose dependent relationship, with the T3 treatment consistently delivering the highest yield. This suggests that magnetic iron contributes to improved soil fertility and nutrient uptake, ultimately enhancing physiological activity and fruit production in Fremont mandarin trees. This study demonstrated that soil application of magnetic iron significantly enhanced the yield and fruit quality of Fremont mandarin trees under semi-arid conditions. The consistent positive response across two seasons supports the view that magnetic iron functions as an effective soil amendment, improving soil fertility, plant nutrition, and physiological performance. Especially, yield increases under T2 (500 g/tree) and especially T3 (750 g/tree) align with earlier findings that magnetic iron enhances nutrient uptake and stimulates metabolic activities and increase citrus tree yielding (El-Gioushy et al. 2021 ); (Hu et al. 2017b ). The observed yield improvement is likely linked to enhanced root function and increased micronutrient availability particularly iron, which is essential for chlorophyll biosynthesis, enzyme activation, and photosynthesis (Hu et al. 2017a ). 3.6. Physical attributes of Fremont mandarin fruits Throughout both seasons, a clear pattern emerged in how the physical traits of Fremont mandarin fruits responded to magnetic iron application. As the application rate increased, consequently the volume, weight, and firmness of the fruits show a consistent and meaningful trend across the board (Fig. 5 a, b and c). Fruits from untreated trees were generally the smallest and lightest, especially in the second season. However, magnetic iron was introduced, even at the lowest rate (250 g/tree), fruit size and weight began to improve. The effect became more pronounced with the 500 g/tree treatment and peaked with the highest dose (750 g/tree), which consistently produced the largest and heaviest fruits. This suggests that magnetic iron may have supported better nutrient absorption and more efficient fruit development. Firmness followed a similar trend. Fruits from the control group were noticeably softer compared to those from treated trees. The difference was especially striking in the first season, where the highest magnetic iron dose resulted in fruits that were nearly three times firmer than those from the untreated trees. Even in the second season, firmness remained highest in fruits from the 750 g/tree treatment, pointing to stronger cell structure and potentially longer shelf life. Specific gravity the fruit was a bit more variable. In general, it tended to improve slightly with higher iron rates, especially in the second season, but the changes weren’t as dramatic as those seen in the other traits. This may reflect subtle differences in internal fruit composition, like juice concentration or sugar content, which can vary from year to year. The trend was clear: the more magnetic iron applied to the soil, the better the fruits performed physically. Trees receiving the highest dose produced larger, firmer fruits with improved market quality, highlighting the value of magnetic iron as a practical tool for enhancing citrus fruit development under field conditions. Magnetic iron application also significantly improved fruit physical characteristics, including weight, volume, and firmness. The enhancement under T3 is particularly noteworthy and corresponds with findings by (Abd El-Rhman 2019 ) who reported that magnetic treatments promoted fruit growth via enhanced cell division and expansion. Increased firmness may reflect improved calcium uptake and peel structure, contributing to fruit durability and postharvest longevity. While specific gravity was occasionally higher in control fruits (Fig. 5 d), the greater volume in treated fruits suggests more extensive expansion relative to weight, potentially due to increased water and sugar content a dilution effect also observed by (Okba et al. 2022 ). These findings underscore the agronomic value of magnetic iron, especially at 500–750 g/tree, in improving fruit set, marketable yield, and overall quality, offering a sustainable strategy for citrus production in nutrient-limited soils. Across two seasons, magnetic iron application consistently enhanced both yield and fruit quality. These results are consistent with earlier reports supporting the use of magnetic materials for improving soil fertility, nutrient uptake, and plant performance (Tang et al. 2025 ). The notable yield increases under T3 (750 g/tree) may stem from improved root activity and better absorption of essential nutrients, particularly iron, which plays a pivotal role in chlorophyll production and energy metabolism (El-Dengawy et al. 2019 ). The yield gain exceeding 70% compared to control indicates the potential of magnetic iron to alleviate micronutrient deficiencies in calcareous and sandy soils. Improvements in fruit physical attributes, including weight, volume, and firmness, followed a level dependent pattern. These changes likely reflect enhanced cell expansion and more efficient internal water and nutrient transport, as also reported by (Strano 2024 ). Increased firmness in treated fruits suggests stronger cell walls, contributing to better postharvest performance. Interestingly, specific gravity did not increase linearly with application rate. T1 showed the highest values, while T2 and T3 showed slightly lower readings, possibly due to volume increases exceeding weight gains an expected physiological outcome in rapidly expanding fruits (Abd El-Shafik et al. 2019 ). These results confirm the efficacy of magnetic iron, particularly at 750 g/tree, in improving yield and fruit quality under semi-arid conditions. The findings also suggest magnetic iron acts not only as a nutrient source but also as a soil conditioner enhancing overall plant vigor. Further studies are warranted to assess its interactions with other micronutrients and its long-term impact on soil health and fruit nutrition. The results demonstrated a clear and consistent improvement in both pulp weight and juice volume of Fremont mandarin fruits as the rate of magnetic iron application increased across the two consecutive growing seasons (Fig. 5 E and F). In terms of pulp weight, fruits from untreated trees (control) recorded the lowest values in both years, with a slight increase observed in 2024 compared to 2023. However, a significant enhancement in pulp weight was evident in all magnetic iron treatments. The application of 250 g/tree led to a noticeable increase, while 500 g/tree provided further improvement. The highest pulp weight was consistently observed in fruits from trees treated with 750 g/tree, which showed a statistically significant difference from all other treatments in both seasons. This indicates a dose-dependent effect of magnetic iron in promoting fruit flesh development, likely due to enhanced nutrient uptake and translocation. A similar trend was observed in juice volume. The control treatment produced fruits with the lowest juice content, especially in 2024. With the application of magnetic iron, juice volume increased progressively. The 250 g/tree treatment led to a moderate rise, while 500 g/tree and 750 g/tree resulted in significantly higher juice volumes. The highest juice content was recorded in the 750 g/tree treatment during the 2024 season, highlighting the cumulative benefit of repeated application over time. Overall, the data suggest that increasing rates of magnetic iron soil application can significantly enhance the internal edible and juiciness quality of Fremont mandarins. These improvements are important both from a consumer perspective and for juice yield in processing industries, demonstrating the practical value of magnetic iron in citrus orchard management. These effects support prior evidence highlighting the role of magnetic minerals in enhancing plant metabolism and fruit development (Alharbi et al. 2022 ). The increase in pulp weight under T3 can be attributed to enhanced nutrient uptake, particularly iron, which is essential for photosynthesis and carbohydrate metabolism (Hamed 2017 ). Improved assimilate partitioning likely contributed to greater pulp development, an important commercial trait. Peel weight and thickness also increased with higher application rates. While thicker peel may be less desirable to some consumers, moderate thickening can improve fruit resistance to mechanical damage and extend shelf life. The enhancement may be associated with better calcium uptake facilitated by magnetic iron (Sun et al. 2023 ). A notable improvement was observed in juice volume, especially under T3, which reached 45 cm³ and 57.33 cm³ in 2023 and 2024, respectively. This increase reflects both enhanced pulp mass and likely improved solute and water transport into fruit tissues, consistent with findings by (Samarah et al. 2021 ). Overall, magnetic iron was shown to enhance not only external traits but also internal fruit characteristics critical for consumer preference, processing, and postharvest quality. 3.7. Chemical composition of Fremont mandarin fruits The chemical composition of Fremont mandarin juice was influenced by the application of magnetic iron, with variable trends observed across total soluble solids (TSS), total acidity, TSS/acid ratio, and vitamin C content over both growing seasons (Fig. 6 A, B, C and D). The TSS (%), which reflects the concentration of sugars and soluble compounds, showed a slight increase across all treatments compared to the control, particularly in the first season. The highest TSS values were observed in the 250 g/tree treatment (13.2% and 13.3% in 2023 and 2024, respectively), indicating a slight enhancement in sugar accumulation at moderate magnetic iron levels. However, the TSS in fruits from higher application rates (500 and 750 g/tree) remained relatively close to the control, suggesting that beyond a certain threshold, magnetic iron does not strongly affect sugar concentration. In contrast, total acidity (%) showed a more noticeable response to magnetic iron treatments. Fruits from treated trees recorded lower acidity values than the control, especially at 250 and 500 g/tree rates, which may contribute to improved taste quality. The lowest acidity in 2023 was found in the 250 g/tree treatment (1.49%), while in 2024, the 500 g/tree treatment showed the lowest acidity (1.493%). These values reflect a reduction in organic acid accumulation possibly due to improved fruit maturity and respiration processes. The TSS/acid ratio, a key indicator of flavor balance, improved across all magnetic iron treatments relative to the control. The 500 g/tree application consistently provided the highest ratio in 2024 (8.692), indicating better sweetness-to-acidity balance an essential trait for consumer acceptance and market value. This enhancement may reflect the cumulative influence of iron in modulating carbohydrate and acid metabolism. The chemical composition of the fruit also improved under magnetic iron treatments. The increase in TSS under T1 and T2 suggests enhanced carbohydrate accumulation driven by improved photosynthesis and assimilate translocation (Putti et al. 2024 ). Although total acidity remained largely stable, its slight decline under T1 improved the TSS/acid ratio, a key indicator of palatability and market acceptance. The significant increase in vitamin C content under T2 and T3 is particularly important from a nutritional standpoint. Iron may play a role in stimulating biosynthetic pathways responsible for ascorbic acid production (Alós et al. 2021 ). Thus, magnetic iron not only improves sensory attributes but also enhances the nutritional value of fruit. In conclusion, magnetic iron application at optimal rates (500–750 g/tree) substantially improves canopy growth, yield, and both external and internal fruit quality in Fremont mandarin trees, making it a valuable agronomic tool in nutrient-deficient, semi-arid environments. Regarding vitamin C (ascorbic acid) content, a notable improvement was observed with increasing magnetic iron rates. While the control fruits contained the lowest levels of vitamin C in both seasons (30.0 and 32.0 mg/100 ml), fruits from the 500 and 750 g/tree treatments exhibited significantly higher contents. The highest values were recorded under the 750 g/tree treatment, with 42.0 mg/100 ml in both seasons. This increase in vitamin C might be attributed to improved leaf nutrition and photosynthetic activity, promoting better antioxidant accumulation in the fruit. Taken together, the results suggest that magnetic iron application positively influences the chemical quality of Fremont mandarin fruits, particularly by enhancing their flavor profile and nutritional value. Moderate to high doses (500–750 g/tree) were most effective in improving the TSS/acid balance and vitamin C concentration without excessively increasing total sugar levels. 4. Conclusion The results of this study clearly demonstrate that soil application of magnetic iron significantly enhances the vegetative growth, yield, and fruit quality of Fremont mandarin trees. Across both the two seasons, the application of magnetic iron at increasing rates (250, 500, and 750 g/tree) led to progressive improvements in canopy volume, and yield per tree, with the most pronounced effects observed under the highest application rate (750 g/tree). Particularly, trees treated with magnetic iron showed increased fruit weight, juice content, vitamin C concentration, and improved TSS/acid ratios compared to the untreated control. Enhanced pulp weight, firmer texture, and larger canopy volumes under magnetite treatments suggest improved physiological and nutritional status of the trees. These effects are attributed to the role of magnetic iron in improving soil properties, nutrient availability, and plant metabolic activity. The findings suggest that magnetic iron, particularly at 750 g/tree, is an effective agronomic tool for boosting productivity and fruit quality in Fremont mandarin orchards under semi-arid conditions. Continued application over consecutive seasons appears to compound its benefits. Further studies are recommended to evaluate long-term impacts, economic feasibility, and optimal integration with other fertilization strategies. Declarations Ethics approval and consent to participate The authors confirmed that the institutional committee and licensing committee approved the experiments, including all relevant details and that all experiments have been performed in accordance with specified named guidelines and regulations. Consent for publication : The article contains no such material that may be unlawful, defamatory, or which would, if published, in any way whatsoever, violate the terms and conditions as laid down in the agreement. Competing interests: The authors declare that they have no conflict of interest in the publication. Funding: This research was funded by Ongoing Research Funding Program (ORF-2026-334), King Saud University, Riyadh, Saudi Arabia. Author Contribution Authors' contributions: Conceptualization, Ashraf E. Hamdy (A.E.H.); methodology, Abd El-wahed N. Abd El-wahed (A.N.A.), Hosny F. Abdel-Aziz (H.F.A.), Ibrahim A. Elnaggar (I.A.E.) and A.E.H.; software, A.N.A., H.F.A., I.A.E., and A.E.H.; validation, A.N.A., H.F.A., I.A.E. and A.E.H.; formal analysis, A.N.A., H.F.A., I.A.E., Rasha F. El-Flaah (R.F.E.) and A.E.H., resources, A.N.A., H.F.A., I.A.E., R.F.E., and A.E.H. data curation, A.N.A., H.F.A., I.A.E., and A.E.H. writing—original draft preparation, A.N.A., H.F.A., I.A.E. and A.E.H. writing—review and editing, A.N.A., H.F.A., I.A.E., R.F.E., Mohamed H. Farouk (M.H.F), and A.E.H., visualization, A.N.A., H.F.A., and A.E.H.; Funding, Adel M. Al-Saif (A.M.A.), supervision, A.M.A. and A.E.H. All authors have read and agreed to the published version of the manuscript. Acknowledgement The authors extend their appreciation to Ongoing Research Funding Program (ORF-2026-334), King Saud University, Riyadh, Saudi Arabia. Data Availability The data generated and/or analysed during the current study are available per request to the corresponding author. 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Means within each column followed by the same letter are not significantly different at the 5% level according to Duncan’s multiple range test.\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8741488/v1/e4c7147c1b9dacf782ab852c.jpeg"},{"id":102415528,"identity":"0f923191-26cf-4871-b436-f80ded08de6e","added_by":"auto","created_at":"2026-02-11 12:44:01","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":901221,"visible":true,"origin":"","legend":"\u003cp\u003eThe effect of magnetic iron soil application on the leaf nutrient content of Fremont mandarin trees over the 2023 and 2024 growing seasons: (A) nitrogen (N), (B) phosphorus (P), (C) potassium (K), (D) iron (Fe), (E) sodium (Na), and (F) chloride (Cl). Within each season, means followed by the same letter are not significantly different (P \u0026gt; 0.05) according to Duncan’s multiple range test.\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8741488/v1/b07681be1391e7b1878cc592.jpeg"},{"id":102415536,"identity":"691d5ba6-9e3d-489e-91d7-fb49c85d7732","added_by":"auto","created_at":"2026-02-11 12:44:05","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":646046,"visible":true,"origin":"","legend":"\u003cp\u003eThe effect of magnetic iron soil application on the leaf physiology and biochemistry of Fremont mandarin trees over the 2023 and 2024 growing seasons: (A) relative water content, (B) total chlorophyll, (C) proline content, and (D) total phenolic content. Means followed by the same letter within a season are not significantly different (\u003cem\u003eP\u003c/em\u003e \u0026gt; 0.05) according to Duncan’s multiple range test.\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8741488/v1/a6e980474a69c4e4df078bd2.jpeg"},{"id":102415530,"identity":"0f1bf89d-f968-4fd1-bc63-40438f532633","added_by":"auto","created_at":"2026-02-11 12:44:01","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":304249,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of magnetic iron soil application on yield (kg/tree) and yield increasing (%) over control in Fremont mandarin trees during the 2024 and 2025 seasons. Means within each season followed by the same letter are not significantly different at the 5% level according to Duncan’s multiple range test.\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8741488/v1/e86dbbc2d14f0438eda7b7a7.jpeg"},{"id":102415529,"identity":"8abbe64c-edeb-4d74-8c0e-6b1210e0efe3","added_by":"auto","created_at":"2026-02-11 12:44:01","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":938360,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of magnetic iron soil application on fruit weight, fruit volume, specific gravity pulp weight, fruit firmness and juice volume of Fremont mandarin during the 2023 and 2024 seasons. Means within each season followed by the same letter are not significantly different at the 5% level according to Duncan’s multiple range test.\u003c/p\u003e","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8741488/v1/7d1a8618aa9a9d704da6ce55.jpeg"},{"id":102415531,"identity":"bc654c95-04c0-433b-a551-2b1863962b8b","added_by":"auto","created_at":"2026-02-11 12:44:01","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":587173,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of magnetic iron soil application on fruit chemical composition, TSS, acidity, TSS/acid ratio, and vitamin C content of Fremont mandarin juice during 2024 and 2025 seasons. Means in each season followed by the same letter are not significantly different at the 5% level according to Duncan’s multiple range test.\u003c/p\u003e","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8741488/v1/207963eb766ce962d9c913c8.jpeg"},{"id":102415543,"identity":"cba49508-420d-4019-9309-c6a4e269d278","added_by":"auto","created_at":"2026-02-11 12:44:13","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4798765,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8741488/v1/897e4678-24a2-4e98-8a05-cafbda7470a4.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Evaluating the Influence of Magnetic Iron Applications on Agronomic and Fruit Quality Parameters of 'Fremont' Mandarin","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eCitrus fruits represent a significant segment of global horticultural production, with mandarins (\u003cem\u003eCitrus reticulata\u003c/em\u003e Blanco) ranking among the most economically important citrus species due to their favorable flavor, nutritional content, and consumer preference (Kato-Noguchi and Kato \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Among mandarin cultivars, Fremont\u0026rsquo; is valued for its early maturity, deep orange peel color, and high juice content, making it a preferred choice in both domestic and export markets. Enhancing the growth performance and fruit quality of Fremont mandarin trees under diverse agroecological conditions is, therefore, a priority for sustainable citrus production (Camilla et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Soil fertility management plays a crucial role in citrus yield and fruit quality (Wijana et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). In recent years, increasing attention has been given to the use of mineral based soil amendments such as magnetic iron (Fe₃O₄), a naturally occurring form of iron oxide known for its paramagnetic properties and ability to enhance soil physicochemical characteristics (Eldeeb et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Magnetic iron has been reported to improve soil aeration, nutrient availability, and microbial activity (Tang et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2024a\u003c/span\u003e), thereby promoting better root development and nutrient uptake in various fruit trees.\u003c/p\u003e \u003cp\u003eIron, as a micronutrient, is essential for chlorophyll biosynthesis, photosynthetic efficiency, and enzymatic activities in plants (Aras et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In citrus, iron deficiency is commonly manifested as interveinal chlorosis, reduced vegetative growth, and impaired fruit development, especially in calcareous or alkaline soils (Zang et al. \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The application of iron sources, particularly in forms that improve soil structure and cation exchange capacity, can mitigate such deficiencies and lead to improved plant health and productivity (Mahmoud et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eMagnetic iron has gained interest not only as a direct source of iron but also for its indirect role in modifying soil physical and biological properties (Malhas et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Several studies have indicated that soil amendments with magnetic iron can enhance root elongation, increase leaf chlorophyll content, and improve the bioavailability of essential nutrients such as nitrogen, phosphorus, and potassium (Das and Yogalakshmi \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Furthermore, its influence on soil microbial activity may contribute to a more balanced rhizosphere environment, which in turn supports plant vigor and fruiting capacity (He et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Despite these promising attributes, the effects of magnetic iron on citrus trees particularly on Fremont mandarins have not been extensively studied. While existing literature provides preliminary evidence of improved performance in other fruit trees such as olives, grapes, and guavas, empirical data on its impact on mandarin growth dynamics, fruit yield, and quality parameters such as (total soluble solids, acidity, vitamin C, and fruit size) remain limited and fragmented. Given the growing emphasis on eco-friendly and sustainable horticultural practices, exploring the potential of magnetic iron as a soil amendment in citrus cultivation holds considerable promise. Therefore, this study aims to evaluate the effects of different levels of magnetic iron soil application on the vegetative growth, yield components, and fruit quality attributes of Fremont mandarin trees grown under field conditions. The findings are expected to contribute to a better understanding of how magnetic iron can be utilized to improve citrus productivity while maintaining soil health and sustainability.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Experimental Site and Plant Material\u003c/h2\u003e \u003cp\u003eThe present study was conducted during the 2023 and 2024 growing season at private orchard located at Wadi Elmollak, Abu-Hammad, Al-Sharqia Governorate (altitude 30˚25\u0026rsquo;53N, longitude 31˚46\u0026rsquo;08E). The study was conducted with the clear permission of the orchard owner. The soil in the orchard is predominantly sandy, comprising 94.72% sand with a pH of 8.15 and electrical conductivity (EC) of 4.3 dS m⁻\u0026sup1;.\u003c/p\u003e \u003cp\u003eThe experiment was carried out on \u0026lsquo;Fremont\u0026rsquo; mandarin trees (\u003cem\u003eCitrus reticulata\u003c/em\u003e Blanco), which were grafted onto Volkamer lemon (\u003cem\u003eCitrus volkameriana\u003c/em\u003e Ten. \u0026amp; Pasq.) rootstock and planted in 2015. Trees were spaced at 2 \u0026times; 4 meters, resulting in a planting density of approximately 525 trees per feddan. Drip irrigation was employed using two irrigation lines per tree, each equipped with four adjustable emitters (8 emitters/tree, delivering 8 liters/hour). Irrigation lines were positioned 50 cm away from the trunk on each side. All trees received a uniform fertilization regime in line with the recommendations of the Egyptian Ministry of Agriculture. The annual fertilization program included 1000 g nitrogen, 1500 g phosphorus (as P₂O₅), and 500 g potassium (as K₂O) per tree. In addition, micronutrients were supplied as chelated forms of Fe, Mn, Zn, Cu (at 300, 150, 100, and 50 mg, respectively), and B (as 50 mg boric acid) in three split applications during March, May, and August.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Experimental Design and Treatments\u003c/h2\u003e \u003cp\u003eThe experiment was arranged in a randomized complete block design comprising four soil applied magnetics iron treatments at rates of 0, 250, 500, and 750 g per tree. Each treatment was replicated four times, with three trees per replicate, resulting in a total of 12 trees per treatment. The treatments were defined as follows: Control: No magnetic iron application (untreated), T₁: Magnetic iron applied at 250 g per tree., T₂: Magnetic iron applied at 500 g per tree. And T₃: Magnetic iron applied at 750 g per tree.\u003c/p\u003e \u003cp\u003eMagnetic iron (Fe₃O₄) was applied once per season, in mid-January, by incorporating it into the soil at a depth of 20 cm beneath the irrigation lines on both sides of each tree. Magnetic iron is a naturally occurring raw rock characterized by its high iron content and distinctive black coloration. It possesses a hardness of approximately 6 on the Mohs hardness scale. The composition of this material includes 48.8% Fe₃O₄, 17.3% FeO, 26.7% Fe₂O₃, 2.6% MgO, 4.3% SiO₂, and 0.3% CaO. The magnetic iron used in this study was sourced from El-Ahram Company for Mining and Natural Fertilizers, located in Giza, Egypt.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Data Collection\u003c/h2\u003e \u003cp\u003eThe following parameters were measured to evaluate the effects of the treatments:\u003c/p\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.3.1. Vegetative Growth\u003c/h2\u003e \u003cp\u003eTree canopy volume (m\u0026sup3;) was used as an indicator of vegetative growth to assess the response of \u0026lsquo;Fremont\u0026rsquo; mandarin trees to different magnetic iron treatments. Canopy volume, representing overall tree size, was calculated according to the formula described by (Zekri \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2000\u003c/span\u003e):\u003c/p\u003e \u003cp\u003eTree canopy volume (m\u003csup\u003e3\u003c/sup\u003e)\u0026thinsp;=\u0026thinsp;0.52 \u0026times; tree height \u0026times; (diameter\u003csup\u003e2\u003c/sup\u003e).\u003c/p\u003e \u003cp\u003eTree height and canopy diameter were measured for each tree, and the resulting values were used to compute the canopy volume in cubic meters.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.3.2. Leaf Chemical Contents\u003c/h2\u003e \u003cp\u003eTotal Chlorophyll\u003c/p\u003e \u003cp\u003eLeaf total chlorophyll content was measured in September using a nondestructive method with a Minolta SPAD-502 chlorophyll meter, following the procedure described by (Wood et al. 1993).\u003c/p\u003e \u003cp\u003eLeaf Proline Content\u003c/p\u003e \u003cp\u003eProline, the most abundant amino acid in citrus leaves, was quantified following the method of (Bates et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e1973\u003c/span\u003e) and modified by (Claussen \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2005\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eRelative Water Content (RWC)\u003c/p\u003e \u003cp\u003eRelative water content (RWC) of leaves was assessed according to the method of (Claussen \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). RWC was calculated using the following formula:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:RWC\\left(\\text{%}\\right)=\\frac{Fresh\\:weight-Dry\\:weight}{Saturation\\:weight-Dry\\:weight}\\times\\:100$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003cb\u003eTotal Phenolic Content\u003c/b\u003e \u003c/p\u003e \u003cp\u003eTotal phenolic content of \u0026lsquo;Fremont\u0026rsquo; mandarin leaves was determined following the method described by (Casquete et al., 2005), with modifications based on (Singleton et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). TPC was expressed in mg gallic acid equivalents (mg g⁻\u0026sup1; FW).\u003c/p\u003e \u003cp\u003e \u003cb\u003eLeaf Nutrient Contents\u003c/b\u003e \u003c/p\u003e \u003cp\u003eTo assess nutrient status, ten mature leaves per tree (specifically the fifth fully expanded leaf from labeled shoots) were collected in September of both seasons. The collected leaves were analyzed for the following macro- and micronutrients: Nitrogen (N): Determined by the micro-Kjeldahl method, as described by (Adams and Laughlin \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e1981\u003c/span\u003e), and expressed as total nitrogen (% dry weight), Phosphorus (P): Measured calorimetrically using the method of(Murphy et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1981\u003c/span\u003e), Potassium (K): Analyzed using a flame photometer, following the protocol by (Thomas et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e1967\u003c/span\u003e), and Micronutrients (Fe, Na, Cl): Quantified using atomic absorption spectrophotometry, as outlined by(Cheng and Bray \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1951\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cb\u003eTree Yield\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe harvest was completed within the normal commercial harvesting season on Sep. 21st at the maturity stage for each season (109 d from full bloom, according to (Abdel-Sattar et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). The tree yield was recorded per kg. Increasing yield percentage was compared to the control according to the calculation of (Abd El-Naby et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) as the following:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:Yield\\:increasing\\left(\\text{%}\\right)=\\frac{Yield\\left(treatment\\right)-Yield\\left(control\\right)}{Yield\\left(control\\right)}\\times\\:100$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e2.3.3. Physical Characteristics of Fruits\u003c/h2\u003e \u003cp\u003eAt harvest, ten representative fruits were randomly collected from each tree. Each treatment was replicated three times. The samples were immediately transferred to the Chemical Analysis Laboratory, Department of Horticulture, Faculty of Agriculture, Cairo, Al-Azhar University, for evaluation of the following physical parameters: Fruit weight (g), Fruit volume (cm\u0026sup3;), Juice volume (cm\u003csup\u003e3\u003c/sup\u003e), Fruit Pulp Firmness. Fruit pulp firmness, expressed in (lb/in\u0026sup2;), was measured using a digital force gauge pressure tester (Model IGV-O.SA to FGV-100A, Shimpo Instruments).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e2.3.4. Chemical Characteristics of Fruits\u003c/h2\u003e \u003cp\u003eThe following chemical parameters were analyzed from freshly extracted juice:\u003c/p\u003e \u003cp\u003e \u003cb\u003eTotal Soluble Solids (TSS), Total Acidity, and TSS/Acid Ratio\u003c/b\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eTSS (%)\u003c/b\u003e was measured using a digital refractometer. According to the methods of (Latimer \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2023\u003c/span\u003e)\u003c/p\u003e \u003cp\u003e \u003cb\u003eTotal acidity (%)\u003c/b\u003e was determined by titration against 0.1 N NaOH and expressed as citric acid equivalent, following the standard method of the Association of Official Analytical Chemists (Latimer \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2023\u003c/span\u003e)\u003c/p\u003e \u003cp\u003e \u003cb\u003eTSS/Acid ratio was calculated by dividing TSS (%) by total acidity (%), serving as an indicator of fruit flavor balance.\u003c/b\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eAscorbic Acid Content\u003c/b\u003e \u003c/p\u003e \u003cp\u003eAscorbic acid (vitamin C) content was determined by titration using 2,6-dichlorophenol-indophenol dye, as outlined in (Latimer \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), and expressed in mg ascorbic acid per 100 mL of juice.\u003c/p\u003e \u003cp\u003e \u003cb\u003eStatistical Analysis\u003c/b\u003e \u003c/p\u003e \u003cp\u003eAll collected data were subjected to analysis of variance (ANOVA) using Co-stat software. Means were compared using the Least Significant Difference (LSD) test at a significance level of 0.05.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Tree Canopy Volume of Fremont Mandarin\u003c/h2\u003e \u003cp\u003eMagnetic iron soil application had a pronounced impact on the canopy volume of Fremont mandarin trees across both the two studied seasons (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA and B). The untreated control trees consistently exhibited the lowest volume of canopy in both years. However, the application of magnetic iron at increasing rates led to substantial enhancements in canopy development. In 2023, the application of 250 g/tree (T1) increased canopy volume by approximately 154.6% compared to the control, while 500 g/tree (T2) and 750 g/tree (T3) treatments showed even greater increases of 179.5% and 213.6%, respectively. A similar trend was observed in 2024, with T1, T2, and T3 treatments increasing canopy volume by 148.6%, 179.9%, and 209.2%, respectively, relative to the control. These findings clearly indicate a positive, dose-dependent relationship between magnetic iron application and canopy expansion, suggesting improved vegetative growth and vigor under enhanced nutritional conditions. The results indicate a clear, positive relationship between the application rate of magnetic iron and canopy expansion. The marked increase in canopy volume under T3 (750 g/tree) reflects vigorous vegetative growth, likely driven by improved iron availability that enhances chlorophyll formation, enzymatic activity, and cellular respiration processes vital for shoot elongation and leaf development (Alharbi et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The year over year increase from 2024 to 2025, even in the control group, suggests a natural effect of tree maturity. However, the substantially greater expansion in treated trees indicates a cumulative and sustained benefit from magnetic iron application. A larger canopy increases photosynthetic capacity, offers more fruiting surface, and ultimately contributes to improved yield and fruit quality. These observations align with previous studies highlighting the role of magnetite in enhancing root soil interactions and nutrient translocation, thereby improving canopy development and overall tree performance (Zheng et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Yang et al., \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2024\u003c/span\u003e)\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Leaf macro and micronutrients Content\u003c/h2\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e3.2.1. Leaf Macronutrients Content (N, P, K)\u003c/h2\u003e \u003cp\u003eThe results in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e (A-C) revealed that magnetic iron soil application significantly improved the nutritional status of Fremont mandarin leaves, as reflected in the increased concentrations of nitrogen (N), phosphorus (P), and potassium (K) across both the two seasons. The response of all three macro nutrients was positively correlated with the applied rates of magnetic iron. Compared to the control, all treated trees exhibited higher N, P, and K contents, with the magnitude of increase becoming more evident as the application rate increased. The lowest dose (250 g/tree) resulted in a clear enhancement in nutrient content over the untreated trees, indicating that even modest levels of magnetic iron are effective. Further improvements were recorded with the medium (500 g/tree) and high (750 g/tree) rates, with the highest treatment consistently yielding the greatest leaf concentrations of all three macro nutrients. In both seasons, nitrogen content showed the most pronounced increase, particularly under the two higher application rates, suggesting that magnetic iron may play a direct or indirect role in facilitating nitrogen assimilation or root uptake efficiency. Similarly, phosphorus content increased significantly, with a steady and consistent trend from the lowest to the highest application level, indicating improved phosphorus solubility and availability in the rhizosphere. Potassium content followed a comparable pattern, with clear and significant increases corresponding to the application rate, reflecting enhanced nutrient transport and retention in the plant soil system. The concurrent rise in N, P, and K concentrations suggests a synergistic improvement in overall nutrient uptake efficiency driven by magnetic iron, likely through its influence on soil physicochemical properties, microbial activity, and root absorption capacity (Joseph et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). These findings provide strong evidence that magnetic iron, when applied at suitable rates, enhances macro nutrients acquisition in citrus trees and could be an effective strategy to support balanced nutritional management in commercial orchards. The current study demonstrates that soil application of magnetic iron substantially improved the physiological and nutritional status of Fremont mandarin trees, with effects that intensified with increasing application rates and persisted consistently over two successive seasons. The enhancement in macro nutrients (N, P, K) content in response to magnetic iron application is likely attributed to improved soil physicochemical properties and nutrient availability. Iron, particularly in its magnetic form, may enhance nutrient solubility and uptake efficiency by improving root zone aeration and microbial activity (Shirsat and Suthindhiran \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). The observed increases in N, P, and K concentrations, especially at 500 and 750 g/tree rates, underline the role of magnetic iron in facilitating macro nutrients acquisition under field conditions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003e3.2.2. Leaf Micronutrient Content\u003c/h2\u003e \u003cdiv id=\"Sec15\" class=\"Section4\"\u003e \u003ch2\u003e3.2.2.1. Leaf Total Iron Content\u003c/h2\u003e \u003cp\u003eThe application of magnetic iron had a notable and consistent impact on the total iron content of Fremont mandarin leaves across both growing seasons (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eC). A gradual and statistically significant increase in leaf iron concentration was observed in response to the rising application rates of magnetic iron, confirming its role in improving iron nutrition in citrus foliage. Untreated control trees recorded the lowest levels of iron leaf content in both years. The application of magnetic iron at the lowest rate (250 g/tree) resulted in a modest yet measurable increase in iron content relative to the control, indicating an initial positive response to supplementation. As the application rate increased to 500 g/tree, leaf iron concentration improved further, with an even more pronounced enhancement recorded at the highest rate (750 g/tree). This dose dependent trend was consistent across both seasons, with leaf iron content progressively increasing with each incremental rise in magnetic iron application. The data suggest that higher levels not only improved immediate iron availability but also had a cumulative effect over time. This is likely due to improved iron solubility in the rhizosphere and enhanced root absorption efficiency. Our findings demonstrate that magnetic iron application is effective in improving the iron nutritional status of Fremont mandarin trees. Enhanced foliar iron levels are critical for chlorophyll synthesis, enzymatic activity, and overall metabolic function, which in turn can support better vegetative growth and fruiting potential in citrus under field conditions. Leaf iron content followed a similar trend, with significant increases correlating with application rate. Iron is critical for chlorophyll biosynthesis and numerous redox reactions in plants (Foyer and Hanke \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The parallel increase in total chlorophyll content confirms this relationship, as chlorophyll levels rose markedly in trees receiving magnetic iron, reaching peak values at the 750 g/tree dose. This enhancement in chlorophyll suggests an improvement in photosynthetic capacity and overall plant vigor (Huang et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section4\"\u003e \u003ch2\u003e3.2.2.2. Leaf Sodium and Chloride Content\u003c/h2\u003e \u003cp\u003eThe results in (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eE and F) demonstrate that magnetic iron application significantly reduced sodium (Na%) and chloride (Cl%) accumulation in the leaves of Fremont mandarin trees. A clear inverse relationship was observed between the rate of magnetic iron and the levels of both ions, indicating that magnetic iron plays a role in mitigating salt accumulation in plant tissues. Control trees exhibited the highest concentrations of both sodium and chloride, confirming the plant\u0026rsquo;s exposure to potential salt stress under untreated conditions. The lowest concentration of magnetic iron (250 g/tree) led to a moderate but statistically significant reduction in both Na and Cl content. As the application rate increased to 500 and 750 g/tree, further reductions were observed, with the 750 g/tree treatment producing the lowest Na and Cl levels in both seasons. These findings suggest that magnetic iron may enhance salt tolerance mechanisms by limiting the uptake or translocation of toxic ions such as sodium and chloride. This could be attributed to improved soil structure, cation exchange capacity, or changes in root membrane selectivity. By reducing ionic stress, magnetic iron application likely contributes to the overall physiological resilience of citrus trees grown under marginal or saline soil conditions (Rahim et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). The suppression of Na and Cl uptake indicates that magnetic iron may play a protective role against salt stress, possibly by modulating ion selectivity in the roots or enhancing the plant\u0026rsquo;s ability to compartmentalize and exclude these ions (Weng et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). This finding is critical in citrus cultivation, where salt sensitivity can limit productivity in semi-arid and marginal soils. Collectively, the results indicate that magnetic iron application improves the nutritional status, stress tolerance, and physiological performance of Fremont mandarin trees. The level dependent nature of these improvements suggests that 750 g/tree is the most effective rate for enhancing both macro- and micronutrient levels, boosting chlorophyll content, and mitigating stress-related parameters such as proline accumulation and ionic toxicity. These findings align with previous reports on the benefits of magnetic iron in other fruit crops and reinforce its utility as a soil amendment under suboptimal growing conditions (Lakhani et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2025\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003e3.3. Leaf chemical composition of Fremont mandarin\u003c/b\u003e\u003c/h2\u003e \u003cdiv id=\"Sec18\" class=\"Section3\"\u003e \u003ch2\u003e3.3.1. Relative Water Content (R.W.C.)\u003c/h2\u003e \u003cp\u003eMagnetic iron soil application significantly enhanced the relative water content (R.W.C.) of Fremont mandarin leaves throughout both seasons (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA). The increase in R.W.C. was positively associated with the increasing rates of magnetic iron, indicating improved water status and hydration in treated trees. Control trees recorded the lowest R.W.C. values in both seasons. Application of magnetic iron at 250 g/tree resulted in a noticeable improvement in leaf water content, with further significant increases observed at 500 and 750 g/tree. The highest R.W.C. values were consistently recorded in trees treated with 750 g/tree, highlighting the beneficial role of magnetic iron in enhancing the water retention capacity of leaf tissues. This trend suggests that magnetic iron plays an important role in improving plant water relations, likely through enhanced root efficiency, nutrient balance, and osmotic regulation. Improved hydration status under higher application rates may contribute to better physiological performance, particularly under environmental conditions where water availability is a limiting factor (Sarraf et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section3\"\u003e \u003ch2\u003e3.3.2. Total Leaf Chlorophyll Content\u003c/h2\u003e \u003cp\u003eMagnetic iron application significantly enhanced total chlorophyll content in Fremont mandarin leaves across the two seasons. A clear dose-dependent trend was observed, with higher application rates leading to progressively greater increases in chlorophyll concentration (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB). The control group recorded the lowest chlorophyll levels in both years. Application of magnetic iron at 250 g/tree resulted in a marked improvement over the control, indicating the positive effect of even low doses on chlorophyll synthesis. Substantially higher chlorophyll content was observed at 500 g/tree, while the maximum values were consistently recorded in trees treated with the highest dose (750 g/tree). These enhancements in chlorophyll concentration may be attributed to improved iron availability, which is essential for chlorophyll biosynthesis and the maintenance of photosynthetic activity (Dos Santos et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section3\"\u003e \u003ch2\u003e3.3.3. Leaf Proline Content\u003c/h2\u003e \u003cp\u003eThe data in (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec) clearly indicate that magnetic iron soil application significantly reduced proline accumulation in the leaves of Fremont mandarin trees over both the 2023 and 2024 seasons. Proline levels decreased progressively with increasing magnetic iron rates, suggesting a dose-dependent alleviation of stress conditions. The highest proline content was consistently recorded in the untreated control trees, while trees treated with the lowest magnetic iron dose (250 g/tree) exhibited a moderate but statistically significant reduction. Further decreases were observed at the 500 g/tree application rate, with the lowest proline concentrations found in trees treated with 750 g/tree. The marked decline in proline levels with increased magnetic iron suggests that this treatment may help mitigate oxidative or environmental stress, as proline accumulation is often associated with drought, salinity, or nutrient deficiencies. The results imply that magnetic iron enhances plant metabolic balance and reduces stress related metabolite buildup, contributing to improved physiological status under orchard conditions (Tang et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2024b\u003c/span\u003e). A particularly important observation was the decline in proline content with higher magnetic iron application. Proline serves as a stress indicator, commonly accumulating in response to abiotic stress such as drought or salinity. The reduction in proline, especially in T3 treated trees, suggests that magnetic iron alleviated stress conditions, possibly by improving plant water balance and reducing oxidative pressure.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section3\"\u003e \u003ch2\u003e3.3.4. Total Phenolic Content\u003c/h2\u003e \u003cp\u003eThe total phenolic content in leaves was significantly influenced by the application rates of the treatment across both seasons (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). The highest levels of phenolic compounds were recorded in the control and T1 (250 g/tree) treatments, with no significant differences between them. In contrast, T2 (500 g/tree) and T3 (750 g/tree) treatments resulted in a marked and statistically significant reduction in total phenolic content. In 2023, the total phenolic content reached its peak in the T1 treatment, followed by the control. This trend was replicated in the 2024 season, with both T1 and control again producing the highest levels of phenolics. However, increasing the application rate to 500 g/tree (T2) significantly lowered phenolic concentrations compared to the control, and the most pronounced reduction was observed in the T3 treatment (750 g/tree), which recorded the lowest phenolic levels across both seasons. These results suggest a dose-dependent suppression of phenolic synthesis in response to higher application rates. It could be concluded that, magnetic iron soil application utilizes a multifaceted influence on the physiological and biochemical characteristics of \u0026lsquo;Fremont\u0026rsquo; mandarin leaves. Enhanced relative water content and chlorophyll levels reflect improved plant hydration and photosynthetic capacity, both essential for vegetative vigor and yield. Simultaneously, reduced proline and phenolic content under higher application rates point to a lowered stress environment and a shift in metabolic priorities toward growth and productivity rather than defense. These findings align with previous studies highlighting the role of magnetic iron in modifying soil structure, promoting nutrient uptake, and mitigating ionic and osmotic stress in citrus and other fruit species (Mahmoud et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The level dependent nature of these responses underscores the importance of optimizing magnetic iron rates for maximum agronomic benefit while minimizing potential tradeoffs in fruit phytochemical composition (Rahman et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003e3.5. Yield of Fremont Mandarin Trees\u003c/h2\u003e \u003cp\u003eMagnetic iron soil application significantly enhanced the yield of Fremont mandarin trees across both seasons. The control group (no magnetic iron) consistently recorded the lowest yields. In contrast, yield improvements were observed with each increase in magnetic iron application rate. In 2023, yields rose by approximately 32.2%, 58.7%, and 70.4% under T1 (250 g/tree), T2 (500 g/tree), and T3 (750 g/tree), respectively, compared to the control (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea and b). A similar pattern was evident in 2024, with respective increases of 34.2%, 59.3%, and 71.6%. These results highlight a clear dose dependent relationship, with the T3 treatment consistently delivering the highest yield. This suggests that magnetic iron contributes to improved soil fertility and nutrient uptake, ultimately enhancing physiological activity and fruit production in \u003cem\u003eFremont\u003c/em\u003e mandarin trees. This study demonstrated that soil application of magnetic iron significantly enhanced the yield and fruit quality of Fremont mandarin trees under semi-arid conditions. The consistent positive response across two seasons supports the view that magnetic iron functions as an effective soil amendment, improving soil fertility, plant nutrition, and physiological performance. Especially, yield increases under T2 (500 g/tree) and especially T3 (750 g/tree) align with earlier findings that magnetic iron enhances nutrient uptake and stimulates metabolic activities and increase citrus tree yielding (El-Gioushy et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2021\u003c/span\u003e); (Hu et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2017b\u003c/span\u003e). The observed yield improvement is likely linked to enhanced root function and increased micronutrient availability particularly iron, which is essential for chlorophyll biosynthesis, enzyme activation, and photosynthesis (Hu et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2017a\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec23\" class=\"Section2\"\u003e \u003ch2\u003e3.6. Physical attributes of Fremont mandarin fruits\u003c/h2\u003e \u003cp\u003eThroughout both seasons, a clear pattern emerged in how the physical traits of Fremont mandarin fruits responded to magnetic iron application. As the application rate increased, consequently the volume, weight, and firmness of the fruits show a consistent and meaningful trend across the board (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea, b and c). Fruits from untreated trees were generally the smallest and lightest, especially in the second season. However, magnetic iron was introduced, even at the lowest rate (250 g/tree), fruit size and weight began to improve. The effect became more pronounced with the 500 g/tree treatment and peaked with the highest dose (750 g/tree), which consistently produced the largest and heaviest fruits. This suggests that magnetic iron may have supported better nutrient absorption and more efficient fruit development. Firmness followed a similar trend. Fruits from the control group were noticeably softer compared to those from treated trees. The difference was especially striking in the first season, where the highest magnetic iron dose resulted in fruits that were nearly three times firmer than those from the untreated trees. Even in the second season, firmness remained highest in fruits from the 750 g/tree treatment, pointing to stronger cell structure and potentially longer shelf life. Specific gravity the fruit was a bit more variable. In general, it tended to improve slightly with higher iron rates, especially in the second season, but the changes weren\u0026rsquo;t as dramatic as those seen in the other traits. This may reflect subtle differences in internal fruit composition, like juice concentration or sugar content, which can vary from year to year. The trend was clear: the more magnetic iron applied to the soil, the better the fruits performed physically. Trees receiving the highest dose produced larger, firmer fruits with improved market quality, highlighting the value of magnetic iron as a practical tool for enhancing citrus fruit development under field conditions.\u003c/p\u003e \u003cp\u003eMagnetic iron application also significantly improved fruit physical characteristics, including weight, volume, and firmness. The enhancement under T3 is particularly noteworthy and corresponds with findings by (Abd El-Rhman \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) who reported that magnetic treatments promoted fruit growth via enhanced cell division and expansion. Increased firmness may reflect improved calcium uptake and peel structure, contributing to fruit durability and postharvest longevity. While specific gravity was occasionally higher in control fruits (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed), the greater volume in treated fruits suggests more extensive expansion relative to weight, potentially due to increased water and sugar content a dilution effect also observed by (Okba et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). These findings underscore the agronomic value of magnetic iron, especially at 500\u0026ndash;750 g/tree, in improving fruit set, marketable yield, and overall quality, offering a sustainable strategy for citrus production in nutrient-limited soils.\u003c/p\u003e \u003cp\u003eAcross two seasons, magnetic iron application consistently enhanced both yield and fruit quality. These results are consistent with earlier reports supporting the use of magnetic materials for improving soil fertility, nutrient uptake, and plant performance (Tang et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). The notable yield increases under T3 (750 g/tree) may stem from improved root activity and better absorption of essential nutrients, particularly iron, which plays a pivotal role in chlorophyll production and energy metabolism (El-Dengawy et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). The yield gain exceeding 70% compared to control indicates the potential of magnetic iron to alleviate micronutrient deficiencies in calcareous and sandy soils.\u003c/p\u003e \u003cp\u003eImprovements in fruit physical attributes, including weight, volume, and firmness, followed a level dependent pattern. These changes likely reflect enhanced cell expansion and more efficient internal water and nutrient transport, as also reported by (Strano \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Increased firmness in treated fruits suggests stronger cell walls, contributing to better postharvest performance. Interestingly, specific gravity did not increase linearly with application rate. T1 showed the highest values, while T2 and T3 showed slightly lower readings, possibly due to volume increases exceeding weight gains an expected physiological outcome in rapidly expanding fruits (Abd El-Shafik et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). These results confirm the efficacy of magnetic iron, particularly at 750 g/tree, in improving yield and fruit quality under semi-arid conditions. The findings also suggest magnetic iron acts not only as a nutrient source but also as a soil conditioner enhancing overall plant vigor. Further studies are warranted to assess its interactions with other micronutrients and its long-term impact on soil health and fruit nutrition.\u003c/p\u003e \u003cp\u003eThe results demonstrated a clear and consistent improvement in both pulp weight and juice volume of Fremont mandarin fruits as the rate of magnetic iron application increased across the two consecutive growing seasons (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eE and F). In terms of pulp weight, fruits from untreated trees (control) recorded the lowest values in both years, with a slight increase observed in 2024 compared to 2023. However, a significant enhancement in pulp weight was evident in all magnetic iron treatments. The application of 250 g/tree led to a noticeable increase, while 500 g/tree provided further improvement. The highest pulp weight was consistently observed in fruits from trees treated with 750 g/tree, which showed a statistically significant difference from all other treatments in both seasons. This indicates a dose-dependent effect of magnetic iron in promoting fruit flesh development, likely due to enhanced nutrient uptake and translocation. A similar trend was observed in juice volume. The control treatment produced fruits with the lowest juice content, especially in 2024. With the application of magnetic iron, juice volume increased progressively. The 250 g/tree treatment led to a moderate rise, while 500 g/tree and 750 g/tree resulted in significantly higher juice volumes. The highest juice content was recorded in the 750 g/tree treatment during the 2024 season, highlighting the cumulative benefit of repeated application over time. Overall, the data suggest that increasing rates of magnetic iron soil application can significantly enhance the internal edible and juiciness quality of \u003cem\u003eFremont\u003c/em\u003e mandarins. These improvements are important both from a consumer perspective and for juice yield in processing industries, demonstrating the practical value of magnetic iron in citrus orchard management. These effects support prior evidence highlighting the role of magnetic minerals in enhancing plant metabolism and fruit development (Alharbi et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The increase in pulp weight under T3 can be attributed to enhanced nutrient uptake, particularly iron, which is essential for photosynthesis and carbohydrate metabolism (Hamed \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Improved assimilate partitioning likely contributed to greater pulp development, an important commercial trait. Peel weight and thickness also increased with higher application rates. While thicker peel may be less desirable to some consumers, moderate thickening can improve fruit resistance to mechanical damage and extend shelf life. The enhancement may be associated with better calcium uptake facilitated by magnetic iron (Sun et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). A notable improvement was observed in juice volume, especially under T3, which reached 45 cm\u0026sup3; and 57.33 cm\u0026sup3; in 2023 and 2024, respectively. This increase reflects both enhanced pulp mass and likely improved solute and water transport into fruit tissues, consistent with findings by (Samarah et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Overall, magnetic iron was shown to enhance not only external traits but also internal fruit characteristics critical for consumer preference, processing, and postharvest quality.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec24\" class=\"Section2\"\u003e \u003ch2\u003e3.7. Chemical composition of Fremont mandarin fruits\u003c/h2\u003e \u003cp\u003eThe chemical composition of Fremont mandarin juice was influenced by the application of magnetic iron, with variable trends observed across total soluble solids (TSS), total acidity, TSS/acid ratio, and vitamin C content over both growing seasons (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eA, B, C and D). The TSS (%), which reflects the concentration of sugars and soluble compounds, showed a slight increase across all treatments compared to the control, particularly in the first season. The highest TSS values were observed in the 250 g/tree treatment (13.2% and 13.3% in 2023 and 2024, respectively), indicating a slight enhancement in sugar accumulation at moderate magnetic iron levels. However, the TSS in fruits from higher application rates (500 and 750 g/tree) remained relatively close to the control, suggesting that beyond a certain threshold, magnetic iron does not strongly affect sugar concentration. In contrast, total acidity (%) showed a more noticeable response to magnetic iron treatments. Fruits from treated trees recorded lower acidity values than the control, especially at 250 and 500 g/tree rates, which may contribute to improved taste quality. The lowest acidity in 2023 was found in the 250 g/tree treatment (1.49%), while in 2024, the 500 g/tree treatment showed the lowest acidity (1.493%). These values reflect a reduction in organic acid accumulation possibly due to improved fruit maturity and respiration processes. The TSS/acid ratio, a key indicator of flavor balance, improved across all magnetic iron treatments relative to the control. The 500 g/tree application consistently provided the highest ratio in 2024 (8.692), indicating better sweetness-to-acidity balance an essential trait for consumer acceptance and market value. This enhancement may reflect the cumulative influence of iron in modulating carbohydrate and acid metabolism. The chemical composition of the fruit also improved under magnetic iron treatments. The increase in TSS under T1 and T2 suggests enhanced carbohydrate accumulation driven by improved photosynthesis and assimilate translocation (Putti et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Although total acidity remained largely stable, its slight decline under T1 improved the TSS/acid ratio, a key indicator of palatability and market acceptance. The significant increase in vitamin C content under T2 and T3 is particularly important from a nutritional standpoint. Iron may play a role in stimulating biosynthetic pathways responsible for ascorbic acid production (Al\u0026oacute;s et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Thus, magnetic iron not only improves sensory attributes but also enhances the nutritional value of fruit. In conclusion, magnetic iron application at optimal rates (500\u0026ndash;750 g/tree) substantially improves canopy growth, yield, and both external and internal fruit quality in Fremont mandarin trees, making it a valuable agronomic tool in nutrient-deficient, semi-arid environments.\u003c/p\u003e \u003cp\u003eRegarding vitamin C (ascorbic acid) content, a notable improvement was observed with increasing magnetic iron rates. While the control fruits contained the lowest levels of vitamin C in both seasons (30.0 and 32.0 mg/100 ml), fruits from the 500 and 750 g/tree treatments exhibited significantly higher contents. The highest values were recorded under the 750 g/tree treatment, with 42.0 mg/100 ml in both seasons. This increase in vitamin C might be attributed to improved leaf nutrition and photosynthetic activity, promoting better antioxidant accumulation in the fruit. Taken together, the results suggest that magnetic iron application positively influences the chemical quality of Fremont mandarin fruits, particularly by enhancing their flavor profile and nutritional value. Moderate to high doses (500\u0026ndash;750 g/tree) were most effective in improving the TSS/acid balance and vitamin C concentration without excessively increasing total sugar levels.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThe results of this study clearly demonstrate that soil application of magnetic iron significantly enhances the vegetative growth, yield, and fruit quality of Fremont mandarin trees. Across both the two seasons, the application of magnetic iron at increasing rates (250, 500, and 750 g/tree) led to progressive improvements in canopy volume, and yield per tree, with the most pronounced effects observed under the highest application rate (750 g/tree). Particularly, trees treated with magnetic iron showed increased fruit weight, juice content, vitamin C concentration, and improved TSS/acid ratios compared to the untreated control. Enhanced pulp weight, firmer texture, and larger canopy volumes under magnetite treatments suggest improved physiological and nutritional status of the trees. These effects are attributed to the role of magnetic iron in improving soil properties, nutrient availability, and plant metabolic activity. The findings suggest that magnetic iron, particularly at 750 g/tree, is an effective agronomic tool for boosting productivity and fruit quality in Fremont mandarin orchards under semi-arid conditions. Continued application over consecutive seasons appears to compound its benefits. Further studies are recommended to evaluate long-term impacts, economic feasibility, and optimal integration with other fertilization strategies.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e \u003cp\u003eThe authors confirmed that the institutional committee and licensing committee approved the experiments, including all relevant details and that all experiments have been performed in accordance with specified named guidelines and regulations.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003e \u003cb\u003eConsent for publication\u003c/b\u003e:\u003c/strong\u003e \u003cp\u003eThe article contains no such material that may be unlawful, defamatory, or which would, if published, in any way whatsoever, violate the terms and conditions as laid down in the agreement.\u003c/p\u003e \u003c/p\u003e\u003cp\u003e \u003ch2\u003eCompeting interests:\u003c/h2\u003e \u003cp\u003eThe authors declare that they have no conflict of interest in the publication.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding:\u003c/h2\u003e \u003cp\u003eThis research was funded by Ongoing Research Funding Program (ORF-2026-334), King Saud University, Riyadh, Saudi Arabia.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAuthors' contributions: Conceptualization, Ashraf E. Hamdy (A.E.H.); methodology, Abd El-wahed N. Abd El-wahed (A.N.A.), Hosny F. Abdel-Aziz (H.F.A.), Ibrahim A. Elnaggar (I.A.E.) and A.E.H.; software, A.N.A., H.F.A., I.A.E., and A.E.H.; validation, A.N.A., H.F.A., I.A.E. and A.E.H.; formal analysis, A.N.A., H.F.A., I.A.E., Rasha F. El-Flaah (R.F.E.) and A.E.H., resources, A.N.A., H.F.A., I.A.E., R.F.E., and A.E.H. data curation, A.N.A., H.F.A., I.A.E., and A.E.H. writing\u0026mdash;original draft preparation, A.N.A., H.F.A., I.A.E. and A.E.H. writing\u0026mdash;review and editing, A.N.A., H.F.A., I.A.E., R.F.E., Mohamed H. Farouk (M.H.F), and A.E.H., visualization, A.N.A., H.F.A., and A.E.H.; Funding, Adel M. Al-Saif (A.M.A.), supervision, A.M.A. and A.E.H. All authors have read and agreed to the published version of the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors extend their appreciation to Ongoing Research Funding Program (ORF-2026-334), King Saud University, Riyadh, Saudi Arabia.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe data generated and/or analysed during the current study are available per request to the corresponding author. [https://figshare.com/s/be335623788c4c3336d7](https:/figshare.com/s/be335623788c4c3336d7)\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAbd El-Naby, Z. M., Hafez, W. A. E. K. \u0026amp; Hashem, H. A. Remediation of salt-affected soil by natural and chemical amendments to improve berseem clover yield and nutritive quality. \u003cem\u003eAfr. J. 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Total Environ.\u003c/em\u003e \u003cb\u003e904\u003c/b\u003e, 166643. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.scitotenv.2023.166643\u003c/span\u003e\u003cspan address=\"10.1016/j.scitotenv.2023.166643\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2023).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"canopy volume, magnetic amendment, antioxidant activity, juice quality","lastPublishedDoi":"10.21203/rs.3.rs-8741488/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8741488/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eFremont mandarin is highly valued for its early ripening, deep orange peel coloration, and elevated juice content, making it an appealing cultivar for both local markets and international trade. This study was conducted to evaluate the effects of magnetic iron soil applications on canopy volume, leaf nutrient status, physiological leaf traits, yield, and fruit quality of Fremont mandarin trees. Magnetic iron was applied at rates of 0 (control), 250, 500, and 750 g/tree. Results revealed that canopy volume significantly increased with magnetic iron application, with the most pronounced effects observed at the 750 g/tree rate. Leaf macro nutrient contents, including total nitrogen (N), phosphorus (P), and potassium (K), were markedly elevated across all treated trees, with the highest concentrations recorded under the highest application rate. Additionally, iron (Fe) content in leaves increased proportionally with the magnetic iron levels, indicating enhanced nutrient uptake efficiency. Magnetic iron also influenced key physiological and biochemical traits. Total chlorophyll content in leaves was significantly improved, reflecting enhanced photosynthetic activity. Meanwhile, leaf proline levels a stress indicator were significantly reduced in treated trees, suggesting alleviated environmental stress. Relative water content (RWC) of leaves increased, indicating improved plant water status. Conversely, sodium (Na⁺) and chloride (Cl⁻) ion accumulation, often associated with salinity stress, was substantially decreased in response to magnetic iron, especially at higher doses. These physiological improvements were mirrored in yield and fruit quality. Trees treated with magnetic iron produced heavier fruits with higher juice volume, better firmness, elevated vitamin C content, increased total soluble solids (TSS), and an improved TSS/acid ratio. In conclusion, magnetic iron particularly at 750 g/tree proved to be an effective agronomic input for improving nutrient status, physiological performance, and fruit yield and quality of Fremont mandarin trees.\u003c/p\u003e","manuscriptTitle":"Evaluating the Influence of Magnetic Iron Applications on Agronomic and Fruit Quality Parameters of 'Fremont' Mandarin","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-11 12:43:46","doi":"10.21203/rs.3.rs-8741488/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-03-16T04:48:00+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-15T03:03:49+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"210652280259870136179662445148428421609","date":"2026-03-11T08:46:50+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-04T15:04:16+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"29260518746327243358106184465368620530","date":"2026-03-03T07:33:38+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-23T10:15:45+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"11311166635936900240985807666464661211","date":"2026-02-20T01:30:45+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"24494636505698587184039448525014038788","date":"2026-02-19T11:53:18+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-02-09T08:28:44+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-02-09T07:07:08+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-02-04T13:59:39+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2026-02-04T13:47:53+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"c75315cd-450b-4bc2-aa44-8d8b2dd14c31","owner":[],"postedDate":"February 11th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":62561874,"name":"Biological sciences/Physiology"},{"id":62561875,"name":"Biological sciences/Plant sciences"}],"tags":[],"updatedAt":"2026-04-24T15:08:48+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-11 12:43:46","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8741488","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8741488","identity":"rs-8741488","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}