Effect of ZnO nanoparticles on the productivity, Zn biofortification, and nutritional quality of rice in a life cycle study

Zinc oxide nanoparticles (ZnO NPs), have been commonly used in agriculture, and have attracted more attention for researchers. In this study, a 2-year experiment was conducted involving two Zn types (ZnO NPs and ZnSO4), two concentrations of Zn (25 and 100 mg kg(-1)), and three Zn application stages (basal stage, tillering stage, and panicle stage). This study comprehensively evaluated the effects of ZnO NPs on rice yield, nutrient uptake, Zn biofortification and grain nutritional quality. Our results showed that both ZnO NPs and Zn salt increased grain yield, NPK uptake, and grain Zn concentration. ZnO NPs application enhanced NPK content in rice, with subsequence increasing panicle number (3.8-10.3%), spikelet number per panicle (2.2-4.7%), and total biomass (6.8-7.6%), thereby promoting the rice yield. Compared with conventional fertilization, ZnO NPs enhanced Zn concentration of brown rice by 13.5-39.4%, this had no negative impact on human health. ZnO NPs application at panicle stage have a higher effectiveness in improving Zn concentration of brown rice than at basal and tillering stage. Furthermore, the application of ZnO NPs at panicle stage was more efficient in increasing Zn concentration of brown rice than for Zn salt. ZnO NPs application slightly altered the amino acids content of rice grains, but had no significant impact on total amino acids content. This study highlights that ZnO NPs could be used as a high performance and safe Zn fertilizer in rice production ecosystem.