Optimizing Zinc Biofortification in Basmati Rice Through Soil Application of Size-Varied Zinc Oxide Nanoparticles (ZnO-NPs)

Zinc (Zn) deficiency poses a significant global health concern, particularly in regions where rice is a staple food. Biofortification, the process of enhancing the nutrient content of crops, offers a sustainable solution. This study investigates the potential of soil applied zinc oxide nanoparticles (ZnO-NPs) of different sizes (30, 40, and 95 nm) as an alternative to enhance Zn uptake, growth, and grain quality in two popular basmati rice cultivars (Pusa Basmati-1121 and Pusa Basmati-1509). Results showed that ZnO-NPs treatments performed significantly but among the various sizes, the 30 nm ZnO-NPs performed the best and increased the photosynthetic rate by 21.5–23.4%, stomatal conductance by 35.7–38.5%, chlorophyll a, b, and total content by 21.7–47%, and carotenoids by 38.2–46.2% compared to the control. Similarly, the performance of ZnO-NPs was significantly higher for antioxidant enzyme activities, including protein, proline, superoxide dismutase (SOD), and catalase (CAT), but 30 nm ZnO-NPs increased the most by 18.1–36% compared to the control, with the. Soil amendment with ZnO-NPs significantly (p < 0.05) improved root length, surface area, volume, and average root diameter compared to the control. Additionally, ZnO-NP treatment increased tillers per hill, productive tillers per hill, panicle length, grain weight per panicle, and yield per hill by 20-47.3% over the control, with the 30 nm ZnO-NPs performing the best among the three sizes. Other sizes of NPs (40 and 95nm) also showed a significant improvement in crop yield attributes. ZnO-NP soil amendment significantly increased Zn density in roots and grains, with the 30 nm nanoparticles resulting in the highest increase (~ 57%) in grain Zn content in both cultivars. Furthermore, soil treated with ZnO-NPs significantly (p < 0.05) reduced phytic acid content in the grains of both rice cultivars. These findings demonstrate that ZnO-NPs, especially in smaller sizes (30 nm), can serve as an effective nano-biofortification strategy, addressing zinc deficiency in both crops and human diets while also supporting climate-resilient agriculture.