How Much Nitrogen Credit Should be Taken.

You are planning on Corn on corn for next year and you are trying to figure out how much N credit to take from this year's crop.  Today I read one recommendation to subtract 1 pound for each bushel of corn from what you applied this year.  Cut the remainder in half and that should get you close.  This sounds like a SWAG to me.  What about cover crops?  The main thing that cover crops will do is stabilize the nitrogen in a complex form so they can start to decompose in spring and release nitrogen.  No-Till Farmer quotes  Dr. Fernandez of University of Illinois and he has some other mathematical gyrations to go through.  The big surprise is that he says that this would be a good year to do some spring nitrate testing.  He says to run tests to a depth of 2 feet.  The thought is that some of the nitrogen is in the subsoil.  Another thing to look at might be to do green strips in the spring and come back with a green-seeker to apply variable rate N.  My preference would be a spring test.  we usually start testing when corn is 4 to 5 leaf, but the test can be run when the ground is over 60 degrees Fahrenheit.  Spring testing takes the guess work out of it.  It also will take into account how weather affects the nitrogen in the soil between now and when it is needed.