Green Synthesis of Nano-Fertilizers and Their Impact on Soil Physicochemical Properties

Abstract

The overreliance on conventional chemical fertilizers to meet global food demand has resulted in severe environmental consequences, including nutrient leaching, greenhouse gas emissions, soil degradation, and eutrophication of aquatic ecosystems. In response, nanotechnology has emerged as a transformative tool for agriculture, enabling the design of nano‑fertilizers with enhanced nutrient use efficiency. However, the chemical synthesis of nanoparticles often involves toxic reagents and high energy inputs, undermining sustainability goals. This has catalyzed a shift toward green synthesis—an eco‑friendly approach that harnesses plants, microorganisms (bacteria, fungi, microalgae), and macroalgae to produce nanoparticles via reduction and stabilization by natural phytochemicals, enzymes, and polysaccharides. Green‑synthesized nano‑fertilizers encompass macronutrient (N, P, K), micronutrient (Zn, Fe, Cu, Mn), organic‑composite, controlled‑release, and nano‑enhanced biofertilizer formulations. Their application profoundly improves soil physicochemical properties: they buffer soil pH, stabilize electrical conductivity, increase soil organic carbon (5–15%), enhance aggregate stability and porosity, raise water holding capacity (20–40% with nano‑biochar), boost cation exchange capacity (10–25 cmol/kg), and dramatically reduce nutrient leaching (N loss <15% vs. 30–50% for conventional fertilizers). Biologically, green nano‑fertilizers stimulate key soil enzymes (urease, sucrase, dehydrogenase, phosphatase) and promote beneficial microbial communities, including plant‑growth‑promoting rhizobacteria and arbuscular mycorrhizal fungi, while suppressing pathogens through slow‑release antimicrobial effects. Mechanistically, their nanoscale size (10–100 nm) enables direct root penetration via apoplastic and symplastic pathways; controlled release via biodegradable carriers (chitosan, alginate, nano‑zeolites) responds to rhizosphere pH, enzymes, or redox signals, achieving zero‑order or sigmoidal release kinetics over 30–60 days. Consequently, nutrient use efficiency for nitrogen rises from 30–40% to >70–80%, and for phosphorus from 10–20% to 40–60%, allowing 30–50% reduction in fertilizer inputs with 15–40% yield increases. Green nano‑fertilizers thus represent a cornerstone of sustainable agriculture, regenerating soil health while reducing environmental pollution and fossil‑fuel dependence.