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| Pardon me for being cynical but isn’t the VRT of fall applied nitrogen a bit of an oxymoron? The biggest issues in nitrogen “requirement” are loss of nitrogen as nitrate through the water table and volatilization of nitrogen as NOx or N2 into the atmosphere. The magnitude of these losses generally far exceeds any possible fine tuning benefits.
If the goal is to learn how to best manage nitrogen on your farm, I suggest that you set up a series of strip trials (Fall application at x rate; Spring application at x rate and, Spring application at (x rate minus 50 pounds). Before harvest, go into the field and systematically harvest corn stalks for late season stalk nitrate testing. This sampling protocol should not be random but the stalk sampling sites should be specifically selected to cover the best and worst areas within the field with observations paired across strips whenever possible. This is followed up with yield monitor data. Now you have some data to make decisions on.
If fall stalk nitrogen is high, even with 50#’s less, then you know where to start. If a 50# reduction shows variability in comparative yields to the x rate (or drives stalk nitrate levels to low levels), you can start looking at maps to try to identify the issues relevant on your farm (soil type, elevation (knolls, mid-slopes and valleys), soil test data, drainage, etc.).
With GPS, setting these trials up is quick and easy.
To learn even more, you can split your planter and plant two hybrids; or plant the same hybrid at two different dates.
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Variable rate N
