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.

• 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 sidedress
• 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