Nitrogen Assimilation Mechanisms of Liquid Nano-urea Fertilizer and Its Impact on Key Enzymes and Downstream Nitrogen Metabolites

A significant knowledge gap exists in the characterization of Nano-Urea plus (a commercially available liquid nano-urea fertilizer) and its N-assimilation mechanisms. These data are vital for scientific consensus and advancing nanofertilizers. Dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA) showed that Nano-Urea plus had an optimal count rate and particles per frame, and a higher particle concentration (1.58 × 10 11 particles/mL), with 95% of particles ≤58.7 nm ± 3.10 nm. A real-time spatiotemporal study demonstrated that 4 h postfoliar application, Nano-Urea plus has steadily mobilized 1.9 mM NO 3 – /h along the root–shoot–leaf axis and elevated NR-GS activity. Low free amino acids (FAA) and H + accumulation, higher total soluble protein (TSP), higher total chlorophyll, and higher C–N content signified the impact of Nano-Urea plus over a foliar urea solution. Compared to urea solution, Nano-Urea plus showed a lower contact angle (63 ± 1.9°), higher retention (44 ± 2.2 mg/cm 2 ), and fewer foliar residues, indicating improved absorption. The study found that Nano-Urea plus, despite having 11.5-fold less N than 2% urea solution, consistently influenced NO 3 – mobilization and N assimilation through feed-forward regulation. Despite the underlying improvements, the modest impact of Nano-Urea plus on the C/N ratio suggested that optimizing the N content in liquid nanofertilizer could improve the carbon–nitrogen (C–N) balance.