From Agricultural Biowaste to Sustainable Nanofertilizers: A Circular Approach for Nanosilica Production, Nutrient Management and Environmental Conservation

The increasing generation of agricultural residues, declining soil fertility, inefficient fertilizer use, and environmental degradation have created a need for integrated approaches that simultaneously address waste management and sustainable crop production.Agricultural biowastes such as rice husk, maize husk, wheat straw, sugarcane bagasse and other silica-rich residues represent renewable resources for the production of value-added nanomaterials.Among these materials, nanosilica (SiO₂ nanoparticles) has attracted increasing attention because of its high surface area, tunable physicochemical properties, potential plant availability and ability to influence plant growth, nutrient acquisition and tolerance to environmental stresses.Rice husk is particularly important because it contains a substantial proportion of silica and can be transformed into relatively high-purity amorphous silica through thermal, chemical, hydrothermal or combined extraction approaches.Recent literature indicates that pretreatment, calcination temperature, extraction chemistry and particle formation strongly influence silica purity, morphology, surface characteristics and agricultural performance.This review examines the complete conceptual pathway from agricultural biowaste generation to nanosilica-based nanofertilizer development.Particular attention is given to the composition of silica-rich agricultural residues, pretreatment and extraction strategies, formation and characterization of nanosilica, and the role of nanosilica in plant nutrition.The mechanisms through which silicon can improve nutrient acquisition, photosynthesis, antioxidant defense, water relations and tolerance to drought, salinity, heavy-metal toxicity and biotic stresses are discussed.The review further evaluates the potential of nanosilica to improve nutrient-use efficiency and reduce dependence on conventional fertilizer inputs.A comparative perspective on rice husk and maize-derived biomass is included because feedstock composition and silica recovery can substantially influence the final nanomaterial.The environmental significance of converting agricultural residues into functional nanofertilizers is discussed within the framework of circular economy and sustainable agriculture.Finally, challenges related to reproducibility, dose optimization, nanoparticle fate, soil-plant interactions, ecotoxicity, life-cycle assessment, economic feasibility and field-scale validation are identified.The integration of agriculturalwaste valorization with nanosilicon-based nutrient management offers a promising pathway toward circular, resource-efficient and environmentally responsible agricultural systems.