I am not an agronomist. I also believe the number is different iin different soil types.

I do know the University of MN gives two different P&K application rates on their soil test results, one for broadcast and one lower one for banded application systems. There is probably no one simple correct answer to your question.

I believe the banded rate is generally about 1/3 less than the broadcast rate. That recommendation is also probably not real popular with fertilizer dealers.

Dr George Rehm has done a lot of work in this area. Here is a link to an interesting paper on banded fertilizer.

The "replacement rate" argument is sure to fill a page here.

One issue touched on by poster below in this thread is the location-specific nature of P & K. They just don't move very far or very fast. Banding does insure the P & K is where the plant needs it. There is the other issue of tie-up in various soils.

One further advantage to banding rather than broadcast is that the concentration of fertilizer in the immediate area of the band is high so that even if a portion gets tied up by the soil there is an "excess" concentrationin the band area to be there and available to the crop plant roots near by.

Jim at Dawn