Eco-Friendly Controlled-Release Nano-Biofertilizer Combining Silver Nanoparticles and Azospirillum Enhances Tomato Growth and Nitrogen Use Efficiency

Abstract

Over-reliance on chemical N fertilizers has significantly increased crop production but has also led to extremely low nitrogen use efficiency (NUE) and serious environmental issues. In this investigation, a biodegradable nanobiofertilizer, PS+[AZO+G-AgNPs] was prepared using green-synthesized silver nanoparticles (AgNPs) from Allium sativum leaf extract, incorporating Azospirillum spp., immobilized in a porous starch (PS) matrix and hydrogel bead system. Physicochemical characterization confirmed the synthesis of stable, crystalline AgNPs (~100 nm) with good colloidal stability, as well as successful microbial conjugation. An experimental station was conducted on tomatoes under 100%, 50%, and 25% of the recommended nitrogen dose (RDN). Two-way ANOVA showed that treatments, nitrogen gradients, and the interaction between treatments and nitrogen all had significant effects on biomass accumulation, nutrient absorption, yields, and fruit quality. The nitrogen uptake efficiency, dry matter accumulation, total yield, and fruit weight were significantly increased by PS+[Azo+AgNPs], especially at 50–100% RDN. Increases in vitamin C, firmness, and total soluble solids are associated with enhanced carbon–nitrogen metabolism and antioxidant capacity. The results show that the proposed nanobiointegrated platform synchronizes nutrient inputs, reduces nitrogen dependence, and increases yield and fruit quality. This biodegradable system provides an environmentally friendly approach to improve NUE and reduce the environmental pollution associated with traditional fertilization.