Nanotechnology and Liquid Nitrogen Fertilizers in Millets: A Review on Nano Urea and Urea Ammonium Nitrate (UAN) for Sustainable Pearl Millet Production

Pearl millet (Pennisetum glaucum) is a climate-resilient cereal cultivated widely in semi-arid regions where nitrogen losses from conventional urea limit productivity and nitrogen use efficiency (NUE). This review synthesizes recent advances in nano urea and urea-ammonium nitrate (UAN) as innovative nitrogen sources for sustainable pearl millet production. A systematic analysis of published literature was conducted to evaluate their mechanisms of action, agronomic performance, environmental implications and economic feasibility. Nano Urea enhances foliar nitrogen absorption and reduces soil-based nitrogen losses, while UAN supplies nitrogen in multiple chemical forms, providing both immediate and sustained availability. Evidence suggests that partial substitution strategies improve NUE, reduce environmental risks and maintain yield stability under dryland conditions. However, long-term ecological assessments and millet-specific dosage optimization remain research priorities. Integrated nitrogen management combining soil and foliar approaches appears most promising for sustainable pearl millet systems.