Nano-biofertilizer as next generation input for sustainable agriculture: Synthesis strategies, mechanisms, and application

Nano fertiliser integrates nanoscale nutrient carriers with biogenic components to improve nutrient use efficiency, soil biological function, and stress resilience while lowering fertiliser losses. They have garnered significant scientific attention as a next-generation solution capable of addressing these challenges while supporting global food security objectives. This review systematically examines synthesis pathways, mechanistic interactions, and agronomic applications of nano-biofertiliser. Nanoparticle synthesis strategies are evaluated within two principal frameworks: top-down and bottom-up approaches, with particular emphasis on green synthesis pathways mediated by bacteria, fungi, algae, and plant extracts, which offer environmentally benign, cost-effective, and scalable alternatives to conventional methods. The review critically assesses the dual role of nanoparticles in the soil ecosystem, demonstrating beneficial enhancement of microbial diversity, enzymatic activity, and nutrient availability at optimised concentrations, while acknowledging documented toxicological risks at elevated doses. Crop-targeted delivery through elemental nanoparticles is discussed across multiple application modalities, including seed priming, foliar spray, soil incorporation, and a hydrogel-based delivery system. Physicochemical characterisation methodologies, such as Scanning and Transmission electron microscopy, X-ray diffraction, dynamic light scattering, zeta potential, and Fourier transform infrared spectroscopy analysis, are systematically reviewed in relation to nanoparticles' performance. The literature indicates the transformative potential of nano-fertiliser in revolutionising precision agriculture, improving crop productivity, and minimising environmental footprint, while highlighting critical research gaps – an undercharacterised framework, and the need for mechanistic studies and standardised evaluation protocol to fully harness their potential in sustainable agriculture. Critically evaluates dose-dependent toxicity thresholds, long-term soil accumulation risks, trophic to consumers, and the absence of a globally harmonised regulatory framework.