Multi-decadal maize yield gains at varying nitrogen rates have lowered grain-specific nutrient concentrations but improved nutrient harvest indices

Decades of maize ( Zea mays L.) improvement have steadily increased plant productivity across varying nitrogen (N) regimes, yet how these gains have influenced grain and stover macro- and micronutrient stoichiometry remains poorly understood. We evaluated 38 elite Bayer commercial hybrids released between 1983 and 2020 in four field experiments conducted in Illinois and Indiana, USA, during 2021–2022 under contrasting N supply. Best linear unbiased predictors (BLUPs) of grain yield regressed against year of hybrid release estimated annual yield genetic gains (GG) of 77 and 86 kg ha −1 yr −1 under Low-N (45 kg N ha −1 ) and High-N (202 or 246 kg N ha −1 ) conditions, respectively. Under Low-N, grain N concentration declined more than stover N concentration from the oldest to the newest hybrids (11.3% vs. 2.6%), whereas both declined by comparable magnitudes under High-N (7.0% and 7.8%, respectively). Ratios of macro- and micronutrients to grain N increased with year of release under Low-N, particularly in modern hybrids, suggesting shifts in grain nutrient stoichiometry associated with long-term selection. Yield gains were accompanied by concurrent shifts in grain composition, including increased starch, reduced N, and stable oil concentrations. Increased starch concentration was associated with lower grain K and S concentrations but higher concentrations of Ca and some micronutrients (e.g., Cu). The relationship between nitrogen harvest Index (NHI) and nutrient harvest indices (NutHI) was positive for all nutrients studied, with stronger gains under Low-N than High-N, and showed no statistical evidence of plateauing. These results suggest that, within the range of hybrids evaluated, nutrient partitioning into grain has not yet approached a physiological ceiling, particularly under limited-N conditions, and that long-term maize improvement has been associated with changes in whole-plant uptake and grain allocation of multiple macro- and micronutrients.