Synthesis, characterisation, and agronomic assessment of ZnO/SiO₂/frass nanofertiliser for sustainable tomato production

Sustainability in agricultural production has driven the development and use of nanofertilisers as eco-friendly alternatives to chemical fertilisers amid rising food insecurity. Developing an alternative, sustainable fertiliser that is affordable, multifunctional and made from locally available inorganic and bio-based resources remains limited. In this study, nanofertilisers (ZnO/SiO₂/frass) were formulated at different mixing ratios and tested for sustainable tomato cultivation. The proportions of ZnO nanoparticles, kaolin-derived SiO₂ and frass were set at 1:1:1, 1:1:2, 1:2:1 and 2:1:1, and the formulations were characterised by XRD, HRSEM/EDS, elemental mapping and BET analysis. The effect of the nanofertiliser on soil properties, tomato ( Solanum lycopersicum ) growth, chlorophyll content, yield and fruit quality was evaluated. The ZnO/SiO₂/frass fertiliser exhibited composition-dependent crystallite size, crystallite morphology and mesoporosity. The ZnO/SiO₂/frass nanofertiliser formulated at a 1:1:1 mixing ratio had the highest surface area of 136.42 m² g⁻¹ , the highest pore volume of 0.412 cm³ g⁻¹ , and performed best for the agronomic properties of tomato growth. It produced the tallest plants, with an average of 74.37 cm, followed by the highest number of leaves under 19, but not as high as 21 with chemical fertiliser, and the highest fruit yield of 357.61 g plant⁻¹ , close to 380.19 g plant⁻¹ with chemical fertiliser. Formulation-related performance, potential nutrient imbalance, industrial scale-up, and long-term environmental assessment are among the challenges. Further research is needed to optimise nutrient-release kinetics, to assess the fate of soil nanoparticles, and to validate performance under different field conditions. In conclusion, the balanced formulation of ZnO/SiO₂/frass is highly promising as a sustainable, circular-economy approach to enhance tomato productivity and nutrient-use efficiency.