Nanofertilisers and Agricultural Productivity: A Critical Appraisal of Mechanisms, Field Evidence and Translational Constraints

Abstract

Mineral fertilisers underpin contemporary crop production, yet a large share of applied nitrogen, phosphorus and micronutrients is never recovered by the crop. Nanoscale nutrient carriers, commonly described as nanofertilisers, have been advanced as a means of raising nutrient use efficiency through smaller particle size, higher reactive surface area, controlled dissolution and more targeted delivery. Commercial products have already entered national fertiliser programmes in several countries, and the peer-reviewed literature has expanded far more rapidly than the evidence needed to justify that deployment. This review critically evaluates the state of knowledge on nanoscale nutrient delivery in crop production, with attention to the strength, consistency and methodological quality of the supporting evidence rather than to the accumulation of positive results. Literature was identified through structured searching of open scholarly databases and citation tracking, with appraisal focused on control selection, particle characterisation, experimental scale and duration, and the correspondence between mechanistic claims and agronomic outcomes. Four findings dominate the synthesis. Mechanistic evidence for size-dependent and coating-dependent foliar entry and translocation is substantial and reproducible, but it has rarely been connected to yield formation in the field. Agronomic gains reported for nanoscale products are typically modest and are frequently not benchmarked against equivalent ionic or bulk nutrient sources applied by the same route, so the increment attributable to the nanoscale state remains poorly resolved. Evidence for the most widely deployed macronutrient product, foliar nano urea, is openly contradictory, with multi-location trials and independent field studies reaching opposite conclusions about whether soil nitrogen can be safely reduced. Environmental, soil-biological and food-safety evidence remains dominated by short-term, high-dose exposures that correspond poorly to agronomic use. Confidence is highest for micronutrient delivery and stress amelioration under controlled conditions and lowest for macronutrient substitution at field scale. Priority requirements are multi-season, multi-site trials with ionic and bulk comparators, transparent particle characterisation, and nutrient-balance accounting rather than yield alone.