Impact of Older Versus Newer Hybrid at Multiple Densities on Post-Flowering N Uptake.

Higher post-flowering N uptake (PostN) is common in newer maize hybrids and it typically results in increased grain N content (GrainN) at maturity. However, PostN is not a conservative trait; the relative amounts and proportions of PostN are strongly affected by genotype, environment, and management interactions. A 2-year and 2-location study with multiple N rates, plant densities, and hybrids was conducted in Indiana. Commercial hybrids ranged from 1970s to 2000s in 2012 and from 1960s to 2000s in 2013. Plant density treatments averaged 54,000, 79,000 and 104,000 plants ha^-1.  Maize genotype improvement was reflected in an average 31% (2012) and 32% (2013) higher PostN in newer hybrids compared to older hybrids. Similarly, the proportion of PostN relative to final GrainN was 10% higher in newer hybrids in 2012 and 5% higher in 2013. In terms of management, high N rate (220 kg N ha^-1) significantly increased PostN by 145% in 2012 (drought year) and 32% in 2013 compared to low N rate (55 kg N ha^-1). Low plant density treatments, averaged across hybrids, increased PostN by 24% and 28% compared to medium and high density, respectively, in 2013. Despite the consistent improvement in PostN with newer hybrids compared to older hybrids, relative PostN accumulations varied widely with weather, plant density and N rates.