The above graph shows results over 2 years (6 total sites in Oklahoma) where corn forage N uptake can be predicted from growth stages ranging from V8 to V10.  However, it should be noted that this was from by-plant data (NDVI and N uptake determined by-plant).

  Results from Iowa on larger plots showed that by the V12 growth stage in corn, 90 kg N /ha was accumulated in the plant, which is over 1/2 the total amount found by VT (point of maximum N accumulation).  Thus, because forage N uptake can be predicted (graph above), the use of this information for projecting N rates based on predicted yields should have merit.  Similar data from Oklahoma (graph directly below), show the same result, whereby more than 50% of the total N accumulated had taken place by V10.

Reeves, D.W., and J.T. Touchton. 1989. Nitrogen uptake by corn in a winter legume conservation-tillage system. USDA-ARS. National Soil Dynamics Laboratory. Auburn University, AL.

Nutrient uptake and partitioning in corn and potatoes in Manitoba.  2004. Manitoba Agric. Food and Rural Initiatives.

  Wright, David, Jim Marois, Jim Rich, and Richard Sprenkel. 2002. Field corn production
       guide. University of Florida, IFAS Extension, Gainesville, FL.

• 1.2 to 1.3 lbs of N required per bushel.
• 20-25 % of N needs applied at Planting.
• Remaining N needs should be applied side dress.
• No yield increases have been found from N applications after silking.
• Corn takes up 15 lbs N/ac by the time it is 15 inches tall.
• It will grow to 3 feet tall in the next two weeks and take up about 80 lbs N/ac during those 2 weeks, followed by another 50 lbs/acre in the next two weeks prior to tassel emergence.  Therefore, at least 130 lbs N/ac will be needed in the four weeks after corn reaches the 15 inch height.