Characterization of Maize Genetic Improvement in Response to Plant Density and Nitrogen Stress.

Modeling efforts attempting to predict current and future maize yield, for example to future climate change would be improved if they incorporated accurate responses of modern maize hybrids. The objective of this study was to characterize the response of maize hybrids of different eras to stress as simulated through plant density and nitrogen treatments.  Hybrid era and technology trait variables were tested at three plant densities and two N rates in a two year (2012, 2013) study at two field sites in Indiana. Yield of recent (2005) commercial hybrids averaged 23% higher than a hybrid from 1975, and new hybrids displayed delayed leaf senescence during grain fill. Total N uptake was 11% higher new hybrids, with a higher kernel numbers but lower mean kernel weight. Shorter ASI is also observed in new hybrids. The improved stress tolerance of new hybrids that was evident in shorter ASI, delayed leaf senescence and better kernel formation contributed to yield gains in new hybrids. The implications of these alternate genotype x environment x management interactions on model improvement will be discussed.