Current agronomic evidence on nano-urea in the nitrogen transition of cropping systems. A mini-review.

Nitrogen fertilisation remains a major challenge in the transition towards more sustainable cropping systems. Despite decades of research, nitrogen use efficiency (NUE) is still low in many agricultural contexts, while reactive nitrogen losses continue to affect air quality, water quality and climate targets. Within this broader search for innovation, nano-urea has emerged as one of the most visible cases of nano-enabled agriculture, although its agronomic value remains debated. This mini-review examines the current evidence on nano-urea in conventional cropping systems and places it within a broader regulatory and strategic context. A PRISMA-informed literature search was conducted in the Scopus and Web of Science databases for the period 2015–2026, complemented by bibliometric mapping. After screening and de-duplication, 194 relevant records were retained. The literature is recent, strongly India-centred, and increasingly dominated by field-oriented studies. The agronomic evidence shows a consistent pattern: first-generation nano-urea does not replace soil-applied urea, but it can support moderate reductions in soil N input, generally around 20–25%, when combined with adequate basal fertilisation and correctly timed foliar sprays. Attempts to replace 50% or more of conventional urea usually led to yield penalties or weaker N uptake. Reported gains in NUE and emission-related indicators are modest and appear to depend more on lower N rates and improved management than on a distinctly nano effect. Overall, nano-urea is best regarded not as a breakthrough substitute for conventional urea, but as an early test case within the wider nitrogen transition in agriculture.