Evaluating the influence of magnetic iron as an eco-friendly soil amendment applications on agronomic and fruit quality parameters of ‘Fremont’ mandarin

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 'Control (0 g MI)', '250 g MI', '500 g MI', and '750 g MI /tree' respectively (where MI denotes Magnetic Iron). Results revealed that canopy volume significantly increased with magnetic iron application, with the most pronounced effects observed at the 750 g MI/tree rate (213.6% and 209.2% increase over control in 2023 and 2024, respectively). Leaf macronutrient contents, including total nitrogen (N), phosphorus (P), and potassium (K), were markedly elevated across all treated trees, with increases reaching 38.7%, 42.3%, and 35.8% respectively under the highest application rate. Tree yield increased by up to 71.6% compared to control in the 750 g MI/tree treatment. 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 MI g/tree proved to be an effective agronomic input for improving nutrient status, physiological performance, and fruit yield and quality of 'Fremont' mandarin trees.