Optimal size of Fe3O4 nanoparticles for different crops depends on the unique nanoscale microstructure of plant leaves under rainy conditions

Metal-based nanoparticles (NPs) have garnered attention as a potential micronutrient nano-fertilizer. Most studies have focused on the effects of individual NP size on environmental risks and the uptake, translocation, and biological progress of NPs in plants. However, there is a lack of research on the effects of NPs of different sizes and their interactions with the nanoscale layers of plant leaves (hereafter, nanosheets), which may affect adhesion ability, anti-leaching properties, release rate, and fertilizer efficiency. In this study, various sizes (10, 20, 50, 100 nm, and 10 μm) of Fe₃O₄-NPs (Fe₃O₄-NPs) were applied to peanut (Fe strategy I, dicotyledon) and maize (Fe strategy II, monocotyledon) leaves to quantitatively compare their fertilization efficiency and anti-leaching effects. The optimal size for different crop leaves differed due to the distinct microstructures of the nanosheets on the leaf surface. In peanut, the optimal size was 50 nm, resulting in superior dry weight (1.32 g per plant), leaf iron concentration (483 μg g⁻¹ DW), and adhesion amount (0.039 mg per plant). For maize, the optimal size was found to be 100 nm, leading to increased dry weight (1.98 g per plant), leaf iron concentration (258 μg g⁻¹ DW), and adhesion amount (0.061 mg per plant). A model was developed to simulate the force and work exerted by Fe₃O₄-NPs of different sizes on leaf nanosheets, resulting in the optimal size consistent with the experimental findings. These findings will guide the selection of the optimized NP size for different leaves, thereby enhancing the efficiency of nano-fertilizer utilization and facilitating the development of new types of nano-fertilizers.