Physiological Strategies for Yield Preservation Despite Delayed Nitrogen Availability in Modern Maize Hybrids.

A recent literature review found that, when under N stress at the onset of the reproductive stages, maize hybrids released after 1990 were better able to compensate by accumulating more post-silking N compared to hybrids released before 1990. In order to determine potential causal mechanisms, an experiment was initiated using seven Pioneer hybrids representing each decade from the 1940’s to the present (with the exception of the 1980’s). These hybrids were treated with the same total N rate of 220 kg N ha^-1 using a common N source (urea ammonium nitrate; UAN). At V5, either 220, 165, 55, or 0 kg N ha^-1 was applied with the balance applied as UAN at R1, in addition to a 0N control. These N rates resulted in a range of N stress present at R1. Surprisingly, the treatment with only 55 kg N applied prior to R1 did not result in significantly lower grain yields than those treatments receiving 220 or 165 kg N at V5. This maintenance of grain yield appears to be driven by the conservation of ear N content at R1 despite stem and leaf N content being only 50 and 80%, respectively, of the levels realized in treatments receiving 220 or 165 kg N at V5. Post-silking N accumulation was significantly higher in the 55 kg N treatment compared to N treatments with all (220) or most (165) N applied at V5. This was especially true for hybrids released after 1995. This preliminary data demonstrates the ability of modern hybrids to accelerate new N uptake after silking and maintain grain yield even when N stress is present at R1 if additional mineral N is supplied during the reproductive stages.