Dloc,

I question your numbers there.  I suspect when you talk about <1000 ppm N in your cornstalks at the end of the year, you are actually talking about Nitrate-N, which is what the Late-Season Stalk N Test measures.  My understanding is that the Nitrate-N would be the amount of available N in the stalk which could be utilized by the plant - either to produce more stalk or more ear.  However, you are not taking into account Total N, which would be the amount of N already tied up in the structural parts of the stalk.

If you take a look at this chart,  it shows the amount of nitrogen in corn stalks at 0.6-0.8% of D.M.  Using 5 tons per acre of corn stalks, and using these percentages, there would be 60-80 lb N in those corn stalks. At least, those are the numbers I see. 

If you have a better set of numbers, I wouldn't mind seeing them. 

FYI, I've been crunching the number of total amount of N in corn silage, figuring 8-9% crude protein, and subtracting out the total N in the grain, to arrive at the amount of N in the corn stalks, and, to me, the numbers don't jive.  At the end of the day, that 0.6-0.8% sounds reasonable.