Micro/Nanofertilizers for Sustainable Agriculture: A Review

Poorly effective traditional fertilizers and resulting environmental pressure have led to the development of micro/nanosized nutrients. Although a growing number of laboratory studies confirm that micro/nanofertilizers (MNFs) can promote plant growth and improve nutrition, they are not yet commercially produced in force. One major barrier is the higher raw material and processing costs compared to those of conventional industrial fertilizers. Additionally, uncertainties regarding their nutrient delivery mechanisms and potential phytotoxicity have triggered public hesitation. This review aims to present the efforts of MNFs in clarifying enhanced-efficiency mechanisms, managing ecological risks, and reducing economic inputs over the past 30 years. A literature analysis reveals that MNFs function through three primary pathways: (1) direct absorption by plants in the form of micro/nanoparticles, (2) controlled release of ionic nutrients via micro/nanostructures in vitro, and (3) solid-state diffusion into the rhizosphere, where they either stimulate beneficial microbial activity or dissociate into bioavailable forms. These mechanisms can enhance the utilization efficiency of corresponding nutrients, where the first in vivo strategy offers a rapid solution but carries a higher risk of nanotoxicity. Therefore, it is increasingly important to evaluate the formulation, dosage, and surface properties of MNFs. To enable green and cost-effective synthesis, a physical top-down fabrication platform with full-element utilization should be prioritized. Larger-sized MNFs (>100 nm) used via in vivo strategies strike a balance between efficacy, economic feasibility, and potential side effects. These MNFs are most likely to reduce the input of chemical fertilizers and minimize environmental leakage while ensuring high crop yields, thereby supporting large-scale sustainability of agriculture.