EFFECTS OF ZINC OXIDE NANOPARTICLES ON PLANT GROWTH RESPONSE AND MICROBIAL COMMUNITY OF LOAM SOIL

This study explores the effects of zinc oxide nanoparticles (ZnO NPs) on the growth response of Abelmoschus esculentus (okra) and the microbial community in loam soil. Different concentrations of ZnO NPs (0 mg/kg, 500 mg/kg, and 1000 mg/kg) were applied to the soil to observe their effects on seed germination, plant development, and soil microorganisms. The germination rate of Abelmoschus esculentus plant in control loam soil was a 49.95 ± 15.76 %, compared to 55.5 ± 19.65 % and 58.25 ± 27.5 % for the 500 and 1000 mg of ZnO kg⁻¹ treatments. The germination rate for the control was 1.11 and 1.05 times lower than the 500 and 1000 mg of ZnO kg⁻¹ treatments, respectively. The shoot length Albemoschus esculentus for the control ranged from 3.72 ± 0.12 cm compared to 11.5 ± 1 cm compared to 3.34 ± 0.25 cm to 9.78 ± 0.17 cm in 500 mg ZnO kg⁻¹ of soil. The shoot length of the 500 mg ZnO kg⁻¹ treatment on week 4 was 1.23 times lower than the shoot length of the control. For the 1000 ZnO mg kg-1, shoot length ranged from 3.21 ± 0.16 cm to 7.95 ± 1.15 cm denoting 1.12 to 1.45 times longer shoots of the Albemoschus esculentus in the control loam than the ZnO nanoparticle amended soil. The mean wet weight of the roots harvested from the control in the loam soil was 1.01 ± 0.17 g, which was higher than the 500 and 1000 mg ZnO kg⁻¹ treatments, which weighed 0.62 ± 0.15 g and 0.45 ± 0.22 g, respectively. The plant roots wet weight for the control was 1.62 and 2.24 times greater than for the 500 and 1000 mg ZnO kg⁻¹ treatments, respectively. The counts of total heterotrophic bacteria (THBC) in the control were 7.75 ± 1.43 Log10 cfu g⁻¹ compared to 7.83 ± 0.69 Log10CFU g⁻¹ and 7.88 ± 0.15 Log10 cfu g⁻¹ in the 500 and 1000 mg ZnO kg⁻¹ treatments, respectively. This indicated that the THB counts in the control were 1.01 and 1.02 times lower, respectively, than in the soils treated with 500 and 1000 mg ZnO kg⁻¹.The counts of total heterotrophic fungi (THFC) in the control soil were higher at 6.42 ± 2.42 Log10 cfu g⁻¹ compared to the 1000 mg ZnO kg⁻¹ treatment with 5.55 ± 2.07 Log10 cfu g⁻¹. However, the 500 mg ZnO kg⁻¹ treatment with 6.53 ± 0.67 Log10 cfu g⁻¹ THF was 1.13 times higher than control. The total coliform counts (TCC) in the control soil were higher at 4.4 ± 1.32 Log10 cfu g⁻¹ compared to 33.66 ± 0.66 Log10 cfu g⁻¹ in the 1000 mg ZnO/kg treatments. The fecal coliform count (FCC) in the control was measured at 33.24 ± 1.95 Log10 cfu g⁻¹, while it decreased to 2.1 ± 0.58 Log10 cfu g⁻¹ in the presence of 1000 mg of ZnO/kg, with no recorded growth for the 500 mg/kg. Changes in soil physicochemical properties, such as nitrogen levels which was 19.01 mg/kg in the control soil and decreased to 14.15 mg/kg in 500 mg ZnO/kg and slightly increased to 15.22 mg/kg in 1000 mg ZnO/kg. Also, the pH in the control which was measured as 7.27, decreased to 7.26 and 7.06 in the soil amended with 500 mg ZnO/kg and 1000 mg ZnO/kg respectively raises questions about the long-term sustainability of nanoparticle use in farming. These results suggest that while ZnO NPs have potential benefits, their application must be carefully managed to avoid unintended consequence.