Efficacy of Nitrogen and Zinc Application at Different Growth Stages on Yield, Grain Zinc, and Nitrogen Concentration in Rice

Zinc (Zn) is an essential element involved in human metabolism, which can be supplied by an appropriate diet. Enhancing Zn enrichment in rice grains through agronomic biofortification is advocated as an immediate and effective approach to combat micronutrient malnutrition in hu-man. It has been well-documented that high grain Zn accumulation in rice can be achieved by Zn fertilizers management. This study evaluated the effects of foliar nitrogen (N) and Zn applied at the flowering and milky stages of brown rice plants with and without soil Zn application. A glasshouse pot experiment was conducted using a completely randomized design with four replicates. Soil Zn in the form of ZnSO₄ was applied at 0 and 50 kg ha⁻¹. Foliar fertilizer of 1% urea along with 0.5% ZnSO₄ was applied and assigned as (1) nil foliar N and Zn (N0Zn0), (2) foliar N with nil Zn (N+Zn0), (3) nil foliar N with foliar Zn (N0Zn+), and (4) foliar N and Zn (N+Zn+) at flowering and milky stages. Foliar application of N and Zn increased grain yield and yield components in both soil Zn conditions. Grain Zn concentration in brown rice was the highest when foliar N and Zn were applied under nil soil Zn conditions; however, grain N concentration decreased by 13.1–28.5% with foliar application at flowering and 18.8–28.5% with application at the milky stage. The grain Zn content was increased by foliar application of N0Zn+ and N+Zn+ at flowering and milky stages. Applying foliar N and Zn at flowering or milky stages tended to increase the grain N content when Zn was applied to the soil, while nil soil Zn decreased the N content by 26.8% at flowering and milky stages under N0Zn+. The results suggest that the milky stage is the most suitable for foliar application of Zn for increasing (i) grain yield and (ii) N and Zn concentrations in brown rice without having a dilution effect.