Nitrogen fertilizer increases grain zinc along with yield in high yield rice varieties initially low in grain zinc concentration

Background and aims Nitrogen (N), commonly applied to increase rice yield, can influence grain quality by its effect on grain zinc (Zn) concentration. This study evaluated the effects of N fertilizer as applied to the soil and as foliar N on the yield and grain Zn and N concentrations. Methods Two rice varieties with low grain Zn and high yield potential (CNT1 and RD21), one variety with medium grain Zn and moderate yield potential (KDML105), and two with high grain Zn and low yield potential (KPK and NR) varieties were used in this study. Soil N fertilizer was applied at 50-300 kg ha(-1), and foliar N was applied at 0-2.5% N. Results Soil N fertilizer increased grain Zn concentration in all five rice varieties, but with different effects on grain yield. Increased grain Zn was associated with increases in grain yield in the high yield varieties with low Zn, while there were positive to no effects on grain yield in the varieties with moderate yield potential and moderate Zn. The largest increases in grain Zn from application of soil N were associated with yield depression in the high grain Zn and low yield potential varieties, while foliar N had little effect on grain yield. Positive associations between grain N and Zn were observed in both concentration and contents. Conclusions This study suggests that N and Zn act synergistically in their effects on the accumulation of grain Zn in rice, irrespective of initial grain Zn and yield potential of rice varieties.