Enhancing ZnO Efficiency: Humic Substances as Natural Carriers and Stabilizers for ZnO Nanoparticles for Sustainable Agriculture

Zinc is an essential micronutrient in agricultural systems, fulfilling vital roles in both plant physiology and modern fertilizer formulations. Despite its importance, zinc deficiency has emerged as one of the most prevalent micronutrient limitations in global agriculture. Humic acids (HA) can serve as effective transporters of trace elements for crops, including in foliar fertilization. Our investigation addressed two key aspects: (1) the synthesis of HA-stabilized ZnO nanoparticles, and (2) the assessment of nanoparticle efficacy as zinc sources for foliar fertilization. ZnO and HA-coated ZnO nanoparticles were synthesized via a chemical deposition method and characterized by FTIR, XRD, DLS, ELS, UV-Vis spectroscopy, and TEM. The penetration ability of the nanoparticles through plant leaves was investigated using wheat sprouts. After 24 h of saturation, the plants were dried, and their leaves and seedlings were dissolved in nitric acid; the solution was analyzed by ICP-AES. HA-coated ZnO nanoparticles showed competitive performance compared to conventional zinc chelates used in agriculture. Wheat leaf studies confirmed that nanoparticle accumulation and uptake are pH-dependent, with acidic conditions favoring HA-coated ZnO nanoparticles. These findings provide valuable insights for developing advanced zinc-containing formulations for foliar crop fertilization. The demonstrated effectiveness of HA-stabilized ZnO nanoparticles suggests they represent a promising alternative to traditional zinc supplements in agriculture.