Optimizing ZnO nanoparticles basal application for enhancing rice yield, quality, and zinc enrichment

Abstract

Zinc (Zn) oxide nanoparticles (ZnO NPs) have been increasingly utilized in agriculture as an innovative Zn fertilizer, prompting numerous studies to assess their impact on plant growth. However, research on the optimal application methods and dosages of ZnO NPs on rice remains limited. In this study, varied basal application dosages (0, 3.75, 7.5, 15, 30 and 60 kg hm-2) of ZnO NPs on rice yield, quality, and grain Zn content and distribution were investigated using field experiment in 2022 and 2023. Control experiments were also conducted including treatments without Zn application and those ZnSO4 applied at the same Zn dosage. Results showed that ZnO NPs and ZnSO4 application led to increases in rice grain yield of 0.34-0.50 t hm-2 and 0.06-0.40 t hm-2, respectively, over the two-year experiment compared to the treatment without Zn application. Furthermore, ZnO NPs improved rice quality by enhancing the head rice rate, reducing chalky grain percentage, and improving taste value and rice breakdown. The application of ZnO NPs significantly elevated Zn content in both milled and brown rice compared to the control. In 2022, Zn content in milled rice increased by 20.79%-41.67% and in brown rice by 25.20%-47.31%. In 2023, the increases were 12.18%-32.18% in milled rice and 17.68%-38.66% in brown rice. However, the utilization efficiency of ZnO NPs decreased from 7.02% to 1.26% as the application dosage increased from 3.75 kg hm-2 to 60 kg hm-2. Despite this decrease, the efficiency remained higher than that of ZnSO4 at the same Zn dosages. Considering yield, rice quality, Zn fertilizer utilization, and Zn accumulation, a basal application of 7.5-30 kg hm-2 ZnO NPs is optimal for improving rice yield, quality, and Zn accumulation. This study effectively demonstrated that ZnO NPs could serve as a highly efficient fertilizer for synergistically enhancing rice yield, quality, and Zn content in the edible grain fraction.