Grain Mineral Accumulation Changes in Chinese Maize Cultivars Released in Different Decades and the Responses to Nitrogen Fertilizer

Evaluating changes in the accumulation of grain minerals, including nitrogen (N), copper (Cu), iron (Fe), potassium (K), magnesium (Mg), manganese (Mn), phosphorus (P), and zinc (Zn), across different genotypes can provide valuable information for the development of nutrient-enriched maize varieties. Meanwhile, N rates can affect maize yield and quality, but their effects on element accumulation remain to be elucidated. Here, field experiments were conducted at two locations in China over 2 years (2010 and 2011). Under a normal N application rate (240 kg N ha(-1)), 24 maize cultivars that had been bred and released between 1930 and 2010 were evaluated for the elemental concentrations in the grains. Cultivars Yedan 13 and Zhengdan 958, representing old- and new-era cultivars respectively, were selected to investigate grain element accumulation in response to different levels of N (0, 60, 120, 180, and 240 kg N ha(-1)). The results showed that element concentrations were significantly affected by year, genotype (G), N rates, and N x G interaction. Grain yield tended to increase with the year of cultivar released, while the concentrations of N, Cu, Mn, and Zn in the grain significantly declined in the new-era. The element concentrations of grains were mainly influenced by N rate or N x G interactions. As N levels increased, N, Cu, Fe, Mg, and Mn concentrations rose, while K, P, and Zn concentrations decreased. Compared with old-era cultivars, new-era cultivars showed an increase in grain yield of 25.39%; however, they demonstrated decreases in N, Cu, Fe, K, Mg, P, and Zn concentrations. In the new-era varieties, the reduction in Cu, Fe, K, and P concentrations were significantly exacerbated by high N rates, but this was not the case in the old-era varieties. The concentration of grain Cu, K, Mg, P, and Zn were higher under N-limited condition (N0), but grain yield was also lower. However, the optimal N rate (120-180 kg N ha(-1)) could increase N, Fe, Mg, and Mn concentrations without affecting grain yield in new-era varieties. It is concluded that maize breeding processes have improved grain yield, but reduced grain nutrient element concentrations. Enhanced concentrations of certain elements in maize grain could be achieved with optimal rates of N fertilizer being applied.