Asian Journal of Environment & Ecology

Maize has emerged as one of the fastest-growing cereal crops in South Asia, and nitrogen remains the single most influential input governing its productivity. Conventional urea, despite its dominance in Indian nitrogen management, suffers from nitrogen use efficiency that rarely exceeds 40 per cent, and the unrecovered fraction contributes to ammonia volatilisation, nitrate leaching, nitrous oxide emission and rising input costs. Nano urea, a foliar-applied nanoscale nitrogen formulation developed and commercialised in India, has been promoted as a technology capable of substituting a meaningful share of soil-applied urea while sustaining yield. This review synthesises the peer-reviewed evidence on nano urea use in maize, situates the technology within the wider literature on nanofertilisers and nitrogen management in cereals, and examines its relevance to the alluvial and calcareous soils of Bihar, a state with disproportionately low fertiliser consumption yet comparatively high maize productivity. The synthesis draws on multi-location field trials, mechanistic and molecular studies, energy accounting and a critical body of literature that challenges the scientific basis of some efficacy claims. Evidence indicates that two foliar sprays of nano urea, combined with around three-quarters of the recommended nitrogen dose applied as conventional urea, can sustain maize yield, nitrogen uptake and profitability comparable to a full recommended dose, while reducing greenhouse gas emissions and the embodied energy associated with nitrogen supply. Independent scrutiny of the underlying plant and soil science, however, raises legitimate questions about the generalisability, dose-response consistency and mechanistic transparency of several claims outside controlled trial conditions. For Bihar, where diara and calcareous soils support the state's maize basket under comparatively low fertiliser input, nano urea appears best positioned as a complementary rather than a substitute technology, integrated within site-specific nutrient management frameworks. The review concludes that further multi-season, multi-agroecology research and independent verification are required before nano urea can be recommended as a wholesale replacement for conventional nitrogen fertilisation in maize-growing regions of eastern India.