Studies on effect of different zinc fertilizers on antioxidant enzymes activity in rice (Oryza Sativa L.) crop

Nano formulation of fertilizers involves the use of nanotechnology to create nutrient-delivery systems in general and zinc nutrient in particular to enhance efficiency and to improve uptake by rice crop. The present study evaluated the impact of zinc (Zn) fertilizers towards conventional and nano-formulations, on physiological, biochemical, and grain yield parameter in rice (Oryza sativa). Treatments included absolute control, soil-applied Zn, foliar sprays of conventional Zn (ZnSO₄ and Zn-EDTA), and nano zinc (Zn) applied in different concentrations. The investigation demonstrated significant enhancement in photosynthetic pigments, antioxidant enzyme activities, phenolic content, phenylalanine ammonia-lyase (PAL) activity and grain yield with nano Zn applications. Foliar application of nano Zn at 9.375 g Zn/ha (T6) significantly improved chlorophyll a, b, total chlorophyll, and carotenoid contents by 72%, 83%, 78%, and 38%, respectively, compared to control. This was accompanied by substantial increases in total phenolic content (~2-fold) and enzymatic antioxidants including superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX), and glutathione reductase (GR), reflecting a robust oxidative stress defense system. Phenylalanine ammonia-lyase (PAL) activity, a key indicator of phenylpropanoid metabolism, also showed a near 98% increase under nano Zn treatment, suggesting elevated secondary metabolite synthesis. Grain yield was markedly enhanced in nano zinc treated rice cultivar (≈70 q/ha), nearly doubling compared to absolute control (35.12 q/ha), and correlating strongly with total chlorophyll content (R=0.865). Consequently, nano zinc fertilizer not only improved nutrient efficiency and physiological resilience but also contributed significantly enhanced yield. The study supports nano Zn as a sustainable, low-dose alternative for boosting rice productivity and mitigating oxidative stress in zinc-deficient soils.