Effects of Nano Zinc Oxide (n-ZnO) on Soil Physicochemical Properties, Micronutrient Dynamics, and the Growth Performance of Ficus benjamina

Abstract

Background: Despite its agronomic promise, the ecological effects of n-ZnO in soil remain underexplored. Soils are complex and dynamic systems, and nanoparticle interactions can influence nutrient cycling, microbial communities, and micronutrient availability, potentially causing imbalances or toxicity. Aims: The study aims to investigate the impacts of nano zinc oxide (n-ZnO) on soil physicochemical properties, micronutrient dynamics, and the growth performance of Ficus benjamina. Materials and Method: The study employed a completely randomized design (CRD). Screen house experiment was set up in Institute of Ecology and Environmental Studies, Obafemi Awolowo University, Ile Ife, Nigeria.  Ten concentrations of n-ZnO (0, 10, 25, 50, 75, 100, 150, 200, 250, and 300 ppm) were applied to sandy loam soils and allowed to equilibrate for two weeks. Three-week-old Ficus benjamina seedlings were then transplanted into the amended soils, and growth parameters were monitored biweekly over twelve weeks. Post-harvest soil samples were analyzed for pH, electrical conductivity (EC), total nitrogen (TN), organic carbon (OC), available phosphorus (P), moisture content, cation exchange capacity (CEC), and micronutrients (Fe, Mn, Cu, Zn) using standard methods. Results: Results showed significant dose-dependent effects of n-ZnO on soil chemistry and plant performance. Soil pH declined from 6.5 (control) to 5.3 at 300 ppm, indicating progressive acidification. EC increased from 0.20 dS/m to 1.12 dS/m at the highest dose, suggesting ionic enrichment. TN and OC slightly increased at 10–50 ppm but declined markedly at ≥150 ppm, indicating microbial suppression. Available P peaked at 50 ppm (35 mg/kg) before falling to 7.3 mg/kg at 300 ppm. Moisture retention improved at moderate levels but declined at higher concentrations. CEC and exchangeable bases decreased at high n-ZnO doses, likely due to cation displacement. Micronutrient trends were inconsistent, with elevated Zn causing nutrient imbalances. Ficus benjamina showed improved growth at 10–50 ppm but experienced phytotoxicity and biomass reduction at ≥150 ppm, culminating in plant mortality at 250 ppm. Conclusion: The study concludes that while moderate n-ZnO levels enhance soil fertility and plant growth, higher concentrations adversely affect soil health, nutrient dynamics and plant performance. The study recommends regulation and threshold-specific application of n-ZnO to avoid ecological toxicity.