Comparative Impact of Nano-Urea and Nano-DAP on Wheat (Triticum aestivum L.) Productivity, Nutrient Use Efficiency, and Environmental Sustainability: A Critical Review

Wheat (Triticum aestivum L.) is a cornerstone of global food security, yet its intensive cultivation depends on conventional nitrogen and phosphorus fertilisers whose use is characterised by substantial nutrient losses, declining efficiency, and mounting environmental burdens. Nano-urea and nano-diammonium phosphate (nano-DAP) have emerged as a new generation of nanofertilisers designed to deliver nitrogen and phosphorus more precisely, potentially reducing input quantities and associated environmental impacts. This critical review synthesises current evidence on the comparative effects of nano-urea and nano-DAP on wheat productivity, nutrient use efficiency, and environmental sustainability, drawing on peer-reviewed literature published between 2000 and 2026. Nano-urea, formulated as nitrogen-enriched nanoparticles for foliar application, has demonstrated increases in grain yield, chlorophyll content, and nitrogen use efficiency in multiple field trials, whilst enabling substantial reductions in conventional urea dosage. Nano-DAP similarly shows enhanced phosphorus availability and improved phosphorus use efficiency, particularly in phosphorus-fixing soils. Both products hold potential for reducing nitrous oxide emissions, nitrate leaching, and phosphorus runoff. Nevertheless, critical gaps persist in the literature, encompassing limited multi-season field data, unresolved questions about nanoparticle fate in soils, ecotoxicological uncertainties, and an absence of rigorous life cycle assessments. The review evaluates the mechanistic basis of observed benefits, identifies inconsistencies across experimental contexts, and highlights priority research directions. The available evidence, whilst encouraging, does not yet support the replacement of conventional fertiliser programmes with nano-formulations without further rigorous and independent validation.