Nitrogen (N) is an inherent part of our production systems, influencing both crop productivity and environmental sustainability. Enhancing N utilization efficiency (NUE) through breeding is essential for sustainable corn production amidst changing climate conditions. It has been asserted that corn growth and total nitrogen (N) uptake post-R2 is essential for increasing crop yields, particularly when N fertilizers is applied judiciously according to crop demand. However, little is known about the evolution of corn traits in regards to N utilization efficiency associated with typical N fertilization practices at planting. The objectives of this research were to assess the genetic gain (GG) in yield and grain N content, and to identify key physiological process post- R2 that influence the overall improved gain in Bayer Crop Science hybrids. We studied 38 hybrids of similar maturity released commercially from 1983 to 2020. The experiments were conducted across 5 sites within the US Corn Belt under low- (40 kg N ha-1) and high-N rate (220 kg N ha-1) conditions from 2020 to 2022, achieving 8-site-years x N rates. Our preliminary results reveled significant increases in yield and yield components such as kernel number and kernel weight over time; however, this trend showed a tradeoff with nitrogen concentrations. Traits related to growth also increased over time, particularly biomass gain post-silking and partitioning to yield, attributed to enhanced stem N remobilization and retention of leaf N during the reproductive growth. Our evolutionary assessment suggested that modern hybrids are more efficient at taking up new N and utilizing it for growth than older maize hybrids, thereby resulting in greater yields. Future breeding strategies should focus on enhancing NUE by optimizing growth and partitioning with later-season N uptake.
