Multi-site field validation of improved morpho-physiological responses and yield in Allium hirtifolium with zinc oxide nanoparticle treatments in semi-arid soils

Zinc oxide nanoparticles (ZnONPs) offer a superior alternative to conventional Zn fertilizers for improved crop production, particularly under semi-arid regions where nutrient efficiency and stress tolerance are critical. Using two semi-arid locations, an annual field trial was conducted to evaluate improved performance of ZnONPs in shallot ( Allium hirtifolium) upon bulb priming and foliar treatments. Cellular, morpho-physiological, biochemical, and yield-related endpoints were measured. Transmission electron microscopy revealed ZnONP-treated plants had markedly improved subcellular integrity promoting drought stress. At both locations, ZnONPs at 450 mg Zn/L significantly enhanced relative water content, photosynthetic apparatus (chlorophylls), and carotenoids compared to ionic Zn 2+ treatment and control, indicating improved photosynthetic efficiency and water status. These physiological improvements translated directly into agronomic benefits: ZnONP-treated plants exhibited greater plant height, leaf biomass, bulb number, and bulb size. More importantly, ZnONPs at 450 mg Zn/L led to higher bulb yield by 57–61% compared to control and by 18–27% compared to ionic Zn 2+ treatment. Moreover, ZnONPs substantially increased antioxidant capacity, phenolic and flavonoid content, and Zn fortification in bulbs. Collectively, our multi-site findings establish ZnONPs as a superior Zn fertilizer that couples improved Zn biofortification with cellular protection, thereby enabling increased productivity and nutritional quality in semi-arid soil-grown shallot.