Organ-Specific N Dynamics for Maize Plants at Varying N Stress in the Critical Period.

Previous research shows that up to 36% % of the N needed for the developing ears in maize originates from N accumulated during the post-silking period, making remobilization from the stems and leaves an important N source for the plant during the reproductive stages. The objective of this study was to determine the impact of N rate and timing of N application on the accumulation of N and dry matter in the earshoots, stems, and leaves of maize during the critical period (the two weeks before and after silking) in order to understand the differing sensitivity to N stress in these three plant organs. To test this, a two-year experiment was conducted using 6 to 8 N rates where N was either applied in a single early sidedress application or split with the last 45 kg delayed until V12. The N rate treatments included 0, 110, 110+45 (155S), 155, 155+45 (200S), 200, 200+45 (245S), and 245 kg N ha^-1. Preliminary data suggest that earshoot N concentration during the critical period is highly conserved, even under severe to moderate N stress. Ear growth rate was maintained across all but the 0 N rate. Ear N accumulation rate peaked during the week after R1 when the 200S, 245, and 245S treatments continued to accumulate N at a higher rate than the other N treatments. The leaves continued to accumulate both N and dry matter throughout the critical period. The stems, however, continued to gain dry matter but decreased in N content after R1 indicating that N remobilization was already occurring. Our findings indicate that, during the critical period, the stem is most sensitive to plant N status and is the primary source of N remobilization during the critical period.