Mark,

 I recall I think it was Hay Wilson that calculated the actual amount of N in a bushel of dry corn is 0.6-0.7 pounds.

It seems logical, even ignoring any naturally occurring N generation from worm activity etc that anything over .6-.7 lb per bu is not used, is probably lost migrates down into the water table. Midwest Universities have, until recently, been recommending 1.1-1.2 or higher lb of N per bu. We also have many corn areas with high nitrates in well water which is not good for children. Maybe there is a correlation here? 

You could probably do similar calculations for the actual P & K in a bu of corn and I would bet that the actual removal is a lot less than we have been applying.

P & K are not immediately available to the plant but they are still there in some form. If you carefully apply the amount removed in a way where it is not wasted and in a location readily accessible to the plant when it needs it, over time the rates needed will be much less than many past application recommendations.

I am not against placing fertilizer deep occasionally. In strip till, P & K can be knifed in below the strip maybe every 3-5 years. But you don't need to do it every year, just like fertilizing the beans ahead of corn. jmho.

Jim at Dawn