Temporal dynamics of post-silking nitrogen fluxes and their effects on grain yield in maize under low to high nitrogen inputs.

Post-silking nitrogen (N) fluxes from vegetative tissues to developing kernels affect both N use efficiency (NUE) and grain yield in maize, while the impacts of various N applications at and especially after silking on temporal dynamics of post-silking N uptake and remobilization are poorly understood. Field experiments were conducted with N regimes ranging from low to high N levels. Nitrogen applications above optimal rates at and after silking neither increased late-season N uptake and leaf photosynthesis, nor reduced leaf N export during grain filling compared to the optimal N input, and thus significantly reduced the NUE. In most experiments, reductions in leaf N concentrations were observed around 15 days after silking (DAS). A 15 N labeling study revealed that remobilization of N taken up prior to silking from vegetative tissues during the entire grain-filling phase was 58%–60%, which contributed 53%–61% of the total grain N at maturity, and more than 60% of it was remobilized during the 0–30 DAS. N remobilization initially occurred preferentially from stems relative to leaves, while significant amounts of N were remobilized from leaves during late grain filling and deposited in the stem, particularly in high N treatments. No matter whether 15 N was applied before or at silking, a greater proportion of 15 N taken up was allocated to leaves under N deficient than under N sufficient conditions. At maturity, 70%–76% of the N taken up after silking was allocated to grain. Under N deficiency, direct N allocation to grains originating from post-silking uptake was 45%, 56%, 70% and 96% at 0–15, 15–30, 30–46 and 46–60 DAS, respectively, while these values were relatively lower and constant in N-sufficient plants (43%–50%). Overall, results indicated a strong developmental control over post-silking N fluxes with limited differences observed between N deficient and N sufficient maize, but no impact of high N applications to N-sufficient plants at or after silking. [ABSTRACT FROM AUTHOR]