Effects of Nano-iron Foliar Spray on Tea Leaf Chlorophyll Content and Leaf Absorption

Nanomaterials offer promising strategies for improving nutrient use efficiency in agriculture. In this study, foliar-applied nano-iron was evaluated as a potential fertilizer for tea plants. The nano-iron exhibited a high specific surface area (130.93 m2/g), a mesoporous structure (∼14 nm), and a mixed-valence surface layer containing both Fe 2+ and Fe 3+ , all of which are favorable for leaf-surface attachment, dispersion, and gradual iron release. Chlorophyll content was monitored over 25 days, revealing a pronounced time-lag effect: no significant difference from the control was observed during the first 12 days, whereas a clear increase emerged after day 20. By day 25, the optimal treatment (750 mL/L) increased chlorophyll content by 13.6% (P<0.01), while further increasing the concentration provided no additional benefit. Surface and bulk analyses showed that nano-iron remained largely dispersed on the leaf surface, with only a small fraction undergoing near-surface internalization. During this process, the iron species evolved toward a low-crystallinity and low-magnetism state, and residual aggregates were rare. The presence of surface Fe 2+ may further facilitate direct biological utilization. Overall, the results establish a process chain involving surface attachment and dispersion, partial uptake, and delayed chlorophyll enhancement. This work identifies an effective concentration threshold and application window, providing both mechanistic and practical guidance for the precise use of nano-iron fertilizers in tea production.