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

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.