Engineered zinc oxide nanoparticles: an alternative to conventional zinc sulphate in neutral and alkaline soils for sustainable wheat production.

Zinc oxide nanoparticles (ZnONP) were synthesized and characterized using SEM, EDAX, DLS and UV-Vis spectra. Its use as a nanofertilizer as an alternative to conventional zinc sulphate (ZnSO4.7H2O) was evaluated in five Zn-deficient soils with a variable pH range (7.2-8.7). For this, the carbon of the soil microbial biomass (SMBC), the bacterial population, the nutrient dynamics and the biometric parameters of the wheat crop were assessed. The varying dosages (0, 100, 200 and 500 mg/L), sizes (30-100 nm), and the spherical shape of ZnONPs were evaluated in comparison to ZnSO4.7H2O levels. Results showed the maximum SMBC and bacterial population at 100 mg/L of ZnONPs but a sharp decline at higher concentrations. In addition, soil application of ZnONPs at 5 mg/kg produced a higher root elongation (4.3-8.8%), shoot elongation (3.5-4.0%), total chlorophyll (4.9-5.6%), grain yield (1.7-2.3%) and grain Zn-content (1.6-2.1%) in comparison to the conventional ZnSO4.7H2O at 10 mg/L. ZnONPs at 100 mg/L produced a higher soil microbial biomass carbon (3.9-4.6%), bacterial population (7.2-9.0%), germination (22%) and grain Zn-content (17.9-20%) as compared to the conventional ZnSO4.7H2O at 0.5%. The higher grain Zn-contents could be attributed to the small size and high surface area of ZnONPs resulting in easy entry into the plant system either through root or foliar by penetrating the pores present in the cell membranes. Conversely, the conventional ZnSO4.7H2O, due to its larger size and higher solubility as compared to ZnONPs, has low retention in plant systems, high surface run-off and low fertilizer efficiency. Thus, the authors concluded to apply spherically synthesized ZnONPs (average size-36.7 nm) at 5 mg/kg in the soil application and 100 mg/L in the foliar application for maintaining SMBC and bacterial population, improving total chlorophyll, and grain Zn-contents and overall sustaining wheat production in Zn-deficient neutral and alkaline soils. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13205-021-02861-1. © King Abdulaziz City for Science and Technology 2021.