Carbon nanofertilizers in agriculture: A critical review of soil ecosystem impacts and phytotoxicity

The rapid growth in global population has placed immense pressure on food production systems. As a result, the overuse of chemical fertilizers and pesticides in modern farming has severely reduced soil fertility and disrupted critical ecosystem functions and equilibria. There have been significant leaching and runoff losses of key mineral elements in the environment due to synthetic fertilizer application, resulting in a substantial reduction in nutrient use efficiency (NUE) in different cropping systems. Nanofertilizers (NFs) have been considered more effective and economical than synthetic fertilizers because their nanostructure regulates the delivery of nutrients and enhances plant absorption due to a high surface area to volume ratio. Different types of carbon-based nanoparticles (CNPs), such as carbon nanotubes (CNTs), carbon nanodots (CDs), and carbon nanofibers (CNFs), have been synthesized from various biological sources acting as carbon nanofertilizers (CNFs). These CNPs stimulate soil microbial and enzymatic activities, promote organic matter decomposition, enhance carbon sequestration, and improve water retention, mainly through enhanced nutrient accessibility, aggregation with soil organic matter, and a high-surface-area matrix for microbial habitat and proliferation. Although CNFs exhibit considerable potential, several critical challenges remain, including high production costs, limited knowledge of their long-term environmental behavior, and the requirement for well-defined concentration thresholds tailored to specific soil–crop systems. This review outlines the benefits, potential drawbacks, and key challenges of CNFs for plants and soil health that must be addressed to harness their full potential as plant growth stimulants and soil quality boosters. • A critical review of carbon nanofertilizers' soil ecosystem impacts. • CNFs enhance soil health, microbial activity, and carbon sequestration. • Synthesis methods and structure-activity relationships are thoroughly discussed. • Dose-dependent phytotoxicity and soil microbial risks are key concerns. • Identifies knowledge gaps and future research priorities for safe use.