¹⁵N-isotope tracing reveals enhanced nitrogen uptake, assimilation and physiological response from Nano urea in maize

Nano fertilizers are gaining attention for enhancing agricultural production by increasing the nutrient use efficiency and reducing environmental pollution. While the previous reports suggesting these are all based on various indirect parameters like physiological and biochemical indicators which may not fully capture the actual nutrient uptake, assimilation and translocation. To address the research gap, an experiment was conducted using stable isotopes of nitrogen(¹⁵N) in maize to trace the uptake, assimilation and translocation of foliar applied nano urea (IFFCO Nano Urea Plus) compared with foliar applied conventional urea. Plant samples (leaf, shoot and root) were collected at different time intervals: Initial, 1st,2nd,6th hours, 1st, 2nd, 7th & 14th days after application of various treatments. The tracing of ¹⁵N was done, using Laser Ablation-Combustion-Gas Chromatography-High Resolution Isotope Ratio Mass Spectrometry (LA-CGC-HR-IRMS), for uptake and translocation, while leaf urease activity was assessed for nitrogen assimilation pattern. Physiological parameters like Chlorophyll content (Soil Plant Analysis Development, SPAD value) and chlorophyll fluorescence (effective quantum yield Y(II) and maximum quantum efficiency Fv/fm) also studied alongside. The results showed that plants treated with nano urea had higher total percent nitrogen derived from foliar fertilization (%Ndff) (0.43 %) than conventional urea (0.36 %) at 14th day. Nano urea had faster absorption of 92.5 % in just 2 days while the conventional urea has 75.9 % at same time. The urease activity peaked at 3.123 μmol NH₄⁺/min/g FW for nano urea, compared to 2.141 for conventional urea and 0.177 for the control. The SPAD and chlorophyll fluorescence values also improved with nano urea on 7th day. This study provides first direct quantifiable, isotopic evidence that foliar-applied nano urea is more efficiently absorbed, assimilated and translocated than equimolar conventional urea, offering a mechanistic understanding of enhanced performance in maize.